课程文献中心 更多>>

关键词： 表面光散射   表面张力   黏度   密度   正十六烷  

摘要： 为拓展高温下流体黏度和表面张力的测量,改进了原有的表面光散射实验系统,将实验的温度区间拓展至570K,改进后的系统在整个温区内测量黏度和表面张力的扩展不确定度分别为2%和1%(k=2)。利用新的实验系统研究了正十六烷在353~547 K温度范围内的黏度和表面张力,并利用实验数据分别拟合了温度倒数多项式和van der Waals方程,在全温度范围内实验值与方程的偏差均在1%之内。在较宽的温度范围内获得的正十六烷的高精度黏度和表面张力数据和方程,可以作为参考数据和方程,用于相关仪器的标定和检验。

关键词： 复合土工膜   渗流性态   测压管水位   统计模型   参数反演  

摘要： 基于王甫洲水利工程近20a的渗流监测资料,对复合土工膜的防渗工作性态进行反馈分析。首先对围堤土石坝整体渗流性态进行定性分析;然后选取典型断面建立测压管水位统计模型进行定量分析;接着采用正交设计–神经网络-数值计算相结合的方法,反演复合土工膜的渗透系数;最后对复合土工膜工作性态进行综合分析。研究表明,测压管实测水位仅在蓄水运行初期出现较大变幅,目前变化较平稳;典型GY5断面中3支测压管的实测水位和分离出的时效分量均呈逐渐减小的趋势;基于实测水位反演获得的复合土工膜渗透系数为1.11×10^(-10)cm/s;综合分析认为王甫洲水利工程复合土工膜经过约20 a的服役,防渗效果依然良好且没有明显的老化趋势。

关键词： Solar energy   Desalination   Nanomaterials   Photothermal   Capillary flow   Water quality  

摘要： Solar energy is a sustainable energy source with many applications. Desalination of ocean/wastewater with solar energy has attracted considerable interest worldwide. However, solar desalination is a slow process with poor efficiency. In order to improve performance, highly efficient photothermal absorbers have been introduced. The main objective of the present work is to investigate capillary flow driven high broadband (full solar spectrum) absorptivity nanostructured absorbers for sea/wastewater treatment. The recent development in porous and selffloatable nanomaterial-enriched absorbers have improved the evaporation process through high broadband solar absorptivity (>95%) and porosity (>99%). One motivation of the research is to link the researchers of traditional absorbers to research on advanced materials, so the results of low-efficiency capillary materials are compared with the highly efficient materials. The ions in the seawater, including Na+, Mg2+, K+, Ca2+ and other contaminants before and after desalination, are investigated. Further, the effectiveness, best applicable material, challenges and future projections are described. The advanced nanostructured photothermal absorbers have the potential of being the most suitable candidates to be used in solar desalination systems. More improvements are needed in the absorbers stabilities, salt-blocking, scalability, lack of toxicity and affordability for commercialization.

摘要： We study flows on C*-algebras with the Rokhlin property. We show that every Kirchberg algebra carries a unique Rokhlin flow up to cocycle conjugacy, which confirms a long-standing conjecture of Kishimoto. We moreover present a classification theory for Rokhlin flows on C*-algebras satisfying certain technical properties, which hold for many C*-algebras covered by the Elliott program. As a consequence, we obtain the following further classification theorems for Rokhlin flows. Firstly, we extend the statement of Kishimoto's conjecture to the non-simple case: Up to cocycle conjugacy, a Rokhlin flow on a separable, nuclear, O-infinity-absorbing C*- algebra is uniquely determined by its induced action on the prime ideal space. Secondly, we give a complete classification of Rokhlin flows on simple classifiable KK-contractible C*-algebras: Two Rokhlin flows on such a C*-algebra are cocycle conjugate if and only if their induced actions on the cone of lower-semicontinuous traces are affinely conjugate.

关键词： NetFlow   network traffic   intrusion detection   machine learning   features   CICIDS2017   cyber-attacks  

摘要： Cyber-attacks continue to grow, both in terms of volume and sophistication. This is aided by an increase in available computational power, expanding attack surfaces, and advancements in the human understanding of how to make attacks undetectable. Unsurprisingly, machine learning is utilised to defend against these attacks. In many applications, the choice of features is more important than the choice of model. A range of studies have, with varying degrees of success, attempted to discriminate between benign traffic and well-known cyber-attacks. The features used in these studies are broadly similar and have demonstrated their effectiveness in situations where cyber-attacks do not imitate benign behaviour. To overcome this barrier, in this manuscript, we introduce new features based on a higher level of abstraction of network traffic. Specifically, we perform flow aggregation by grouping flows with similarities. This additional level of feature abstraction benefits from cumulative information, thus qualifying the models to classify cyber-attacks that mimic benign traffic. The performance of the new features is evaluated using the benchmark CICIDS2017 dataset, and the results demonstrate their validity and effectiveness. This novel proposal will improve the detection accuracy of cyber-attacks and also build towards a new direction of feature extraction for complex ones.

关键词： Flow injection analysis   Electrochemical detection   Carbon nanotubes   Wine   Polyphenols   Discriminant analysis  

摘要： This paper proposes a simple electroanalytical methodology for classification of wine samples according to their grape variety (Verdejo, Airen, Albarino and Godello) employing flow injection analysis with electrochemical detection together with chemometric analysis. To this aim, a glassy carbon electrode (GCE) modified with carbon nanotubes (CNT) film was developed from optimized aqueous dispersions of this nanomaterial using polyvinylpyrrolidone (PVP) as dispersing agent. This CNT-based electrode was incorporated to a flow injection system, showing excellent electrochemical performance for the amperometric detection of polyphenols commonly present in wine. The adequate sensitivity and excellent signal stability allowed a high sample throughput analysis of white wines and the estimation of electrochemical indexes (EI) based on the applied detection potential, that are related to different polyphenol fractions in wines. The valuable information of these EI supplement that provided by other spectrophotometric methodologies developed for total polyphenol content. Finally, the hydrodynamic voltammograms of the analyzed samples were subjected to principal component analysis and discriminant analysis for classification purposes. It was demonstrated that these amperometric signals possessed some latent information that characterize the wine depending on its grape varietal. Indeed, the discriminant analysis model built using those signals obtained at +0.30, +0.40, +0.50, +0.60, +0.80 and +1.00 V was able to assign successfully the grape varietal of the analyzed samples, with a mean classification rate of 97.0% in random subsampling validation assays.

关键词： Biofilm   Oxygen mass transfer   Aeration rates   Microbial community  

摘要： A laboratory-scale aerobic fluidized bed biofilm reactor (AFBBR) was established to evaluate the oxygen mass transfer (OMT) process and its impact on municipal wastewater treatment performance. Aeration rates had different effects on the OMT of the wastewater and biofilm. In the wastewater, oxygenation performance, oxygen uptake rate (OUR), and volumetric OMT coefficient (k(L)a) improved under high aeration rates. However, within the biofilm, the OMT process under the aeration rate of 0.096 L/(min.L) were higher than under other conditions [0.064 L/(min.L) and 0.128 L/(min.L)]. The denitrifying bacteria (DNB) abundance under the aeration rate of 0.096 L/(min.L) were improved so that total nitrogen (TN, 66.98 +/- 4.23%) and ammonia nitrogen (NH4+-N, 74.70 +/- 2.30%) removal were higher than those under other aeration conditions. These results showed that suitable aeration could improve wastewater treatment efficiency through changing the OMT process and microbial community structure.

关键词： Wind farms   Fault detection   Wind speed   Protective relaying   Circuit faults   Automatic voltage control   Distance relay   fault detection   fault classification   transient monitor index   unified power flow controller (UPFC)   wind farms  

摘要： In recent years, there is an increasing trend of integrating large capacity offshore wind farms into power grids through UPFC compensated TLs for accommodating large flow of power. The nonlinear fluctuations of output power due to unpredictable variation of wind speed and the different operating modes of the UPFC greatly affect the performance of the conventional distance relaying-based TL protection scheme. This article investigates the impact of such TLs on distance relay performance and proposes a two criteria-based new fault detection and classification scheme. The method utilizes the sign of the change in the magnitude of positive-sequence current at both ends of the line for fault detection and the transient monitor index derived from the locally measured three-phase current for fault classification. The performance of the proposed scheme is evaluated on different fault and nonfault transients generated on two standard test systems through EMTDC/PSCAD during different operating modes of UPFC and at different wind speed. The performance of the proposed scheme is further validated through dSPACE DS 1103-based real-time digital simulation platform. Finally, the comparative assessment results with some important existing methods justify the effectiveness of the proposed method.

关键词： Calcium looping   CO2 capture   Carbonator modelling   Fluidized bed hydrodynamics   CaO/Al2O3 composite  

摘要： This manuscript presents a general model for the fluidized bed carbonator reactor of the Calcium Looping (CaL) process based on bed hydrodynamics, kinetics and sorbent properties. The model proposed relies on the Kunii-Levenspiel theory for circulating fluidized beds in the fast fluidization regime and considers recent findings on the CO2 capture properties of CaO, including the effects of the diffusion-controlled carbonation stage and CaO modification by means of additives. By performing a sensitivity analysis, it is found that the solids inventory in the carbonator and superficial gas velocity are the main operational and hydrodynamic factors affecting the CO2 capture efficiency. Decay constant of the fraction of solids in the lean region and fraction of solids in the dense region are also identified as two important model parameters. Model predictions are shown to agree with experimental results retrieved from pilot-scale tests. The main novelty of the model is the consideration of a CaO/Al2O3 composite either as main CO2 sorbent used in the carbonator or as a make-up flow fed into the calciner. Using CaO/Al2O3 as the main CO2 sorbent leads to a 14.17% loss of capture efficiency after 100 cycles compared to 72.81% when using limestone derived CaO. It is demonstrated that feeding a very low ratio (similar to 0.1) of the CaO/Al2O3 composite or a rather high ratio (similar to 5) of limestone as makeup flow, leads to a significant improvement of the capture efficiency. The results obtained may be relevant for optimizing CaL operation conditions to be used in power plants.

关键词： 热流体   水化学   环境同位素   形成年龄   地热系统  

摘要： 利用大量的地热流体化学成分及环境同位素（δD、δ18O、14C）测试数据，深入分析了隆起山地 构造对流型、沉降盆地传导型地热流体的化学特征及分布规律，进而对地热流体的环境同位素分 布特征及形成年龄进行了梳理总结，得出了明确的结论。结果表明：隆起山地构造对流型地热田 地热流体主要以断裂上升泉的形式出露，分布于西秦岭-祁连造山带，补给来源为当地及周边大气 降水入渗，地热流体形成年龄一般小于 5 000 ~ 30 000 a，水质较好，属“开启型”的地热系统；热储层 岩性、断裂规模及水热循环方式和深度等明显控制着地热流体化学类型、环境同位素特征和形成 年龄。沉降盆地传导型地热田地热流体主要以管井开采的方式出露；热储埋藏深度小于 1 600 m 的 地热井，地热流体补给来源为当地及周边大气降水入渗，形成年龄一般小于 5 000 ~ 30 000 a，水质相对较好，属“半开启-半封闭型”的地热系统；热储埋藏深度介于 1 600 ~ 2 600 m 之间的地热开采 井，主要为地质历史时期逐步形成的“古水”，水化学类型复杂且水质较差，地热流体形成年龄介于30 000 ~ 50 000 a,属“封闭型”的地热系统；热储层岩性、埋藏深度、地下水在岩层中的滞留时间与循 环深度等明显控制着地热流体化学类型、环境同位素富集程度和形成年龄。