Multiplug filtration clean‐up with multiwalled carbon nanotubes in the analysis of pesticide residues using LC–ESI‐MS/MS

A novel design for a rapid clean‐up method was developed for the analysis of pesticide residues in fruit and vegetables followed by LC–ESI‐MS/MS. The acetonitrile‐based sample extraction technique was used to obtain the extracts, and further clean‐up was carried out by applying the streamlined procedure on a multiplug filtration clean‐up column coupled with a syringe. The sorbent used for clean‐up in this research is multiwalled carbon nanotubes, which was mixed with anhydrous magnesium sulfate to remove water from the extracts. This method was validated on 40 representative pesticides and apple, cabbage, and potato sample matrices spiked at two concentration levels of 10 and 100 μg/kg. It exhibited recoveries between 71 and 117% for most pesticides with RSDs < 15%. Matrix‐matched calibrations were performed with the coefficients of determination >0.995 for most studied pesticides between concentration levels of 10–500 μg/L. The LOQs for 40 pesticides ranged from 2 to 50 μg/kg. The developed method was successfully applied to the determination of pesticide residues in market fruit and vegetable samples.     

结构化学课件的开发与应用

阐述了多媒体用于结构化学教学的意义与必要性,介绍了用Authorware6.0组装制作的结构化学多媒体教学课件的逻辑结构和特点。探讨了采用计算机三维动画和多媒体技术描述结构化学中部分抽象问题的方法。     

高温下编织复合材料热相关参数识别方法研究

为了获取高温下编织复合材料的准确弹性参数与热膨胀系数,提出一种基于均匀化理论的热相关参数识别方法. 首先,在编织复合材料单胞有限元模型基础上,基于均匀化理论和热弹性理论,施加周期性位移边界条件和温度边界条件,预测编织复合材 料的热弹性相关参数. 然后,考虑到等效过程中编织复合材料应力分布不均匀等因素引起的误差,将复合材料精细模型的热模态数据作为补 充信息,识别编织复合材料热相关参数,对预测的材料参数进行校准. 本文在二维编织结构单胞模型基础上,开展等效预测和识别方法研 究,验证所提出方法的有效性和准确性. 对比等效和识别后热模态的误差,结果表明:本文提出的基于等效预测的参数识别方法,能够 准确识别高温下编织复合材料宏观热相关参数.      

有关实正定方阵行列式的几个不等式

本文得到实正定方阵行列式的几个不等式，改进了近期研究的一些结果．     

Maximum Kirkman Signal Sets for Synchronous Uni-Polar Multi-UserCommunication Systems

A unipolar signalingsystem transmits using intensity or amplitude in multiple dimensions.Typical examples arise in optical transmission or radio communicationusing MT-MFSK as both the signaling and the modulation technique.There are dimensions which represent pulses ortones. Each codeword consists of a selection of kof these tones with unit intensity. Each user is assigned mof these binary codewords. In a synchronous multi-user environment,two codewords assigned to a single user have distance 2k,while two codewords assigned to different users have distanceat least 2k-2. Such an assignment of codewords tousers is called a Kirkman signal set when the number of usersaccommodated is the maximum. In this paper, the existence ofKirkman signal sets with k=3 and mas large as possible is settled for all values of .     

Simultaneous determination of aflatoxin B1, B2, G1, and G2 in corn powder,edible oil,peanut butter,and soy sauce by liquid chromatography with tandem mass spectrometry utilizing turbulent flow chromatography

A novel fully automated method based on dual column switching using turbulent flow chromatography followed by liquid chromatography with tandem mass spectrometry was developed for the determination of aflatoxin B₁, B₂, G₁, and G₂ in corn powder, edible oil, peanut butter, and soy sauce samples. After ultrasound‐assisted extraction, samples were directly injected to the chromatographic system and the analytes were concentrated into the clean‐up loading column. Through purge switching, the analytes were transferred to the analytical column for subsequent detection by mass spectrometry. Different types of TurboFlow^TM columns, transfer flow rate, transfer time were optimized. The limits of detection and quantification of this method ranged between 0.2–2.0 and 0.5–4.0 μg/kg for aflatoxins in different matrixes, respectively. Recoveries of aflatoxins were in range of 83–108.1% for all samples, matrix effects were in range of 34.1–104.7%. The developed method has been successfully applied in the analysis of aflatoxin B₁, B₂, G₁, and G₂ in real samples.     

Privacy-Protection Scheme of a Credit-Investigation System Based on Blockchain

In response to the rapid growth of credit-investigation data, data redundancy among credit-investigation agencies, privacy leakages of credit-investigation data subjects, and data security risks have been reported. This study proposes a privacy-protection scheme for a credit-investigation system based on blockchain technology, which realizes the secure sharing of credit-investigation data among multiple entities such as credit-investigation users, credit-investigation agencies, and cloud service providers. This scheme is based on blockchain technology to solve the problem of islanding of credit-investigation data and is based on zero-knowledge-proof technology, which works by submitting a proof to the smart contract to achieve anonymous identity authentication, ensuring that the identity privacy of credit-investigation users is not disclosed; this scheme is also based on searchable-symmetric-encryption technology to realize the retrieval of the ciphertext of the credit-investigation data. A security analysis showed that this scheme guarantees the confidentiality, the availability, the tamper-proofability, and the ciphertext searchability of credit-investigation data, as well as the fairness and anonymity of identity authentication in the credit-investigation data query. An efficiency analysis showed that, compared with similar identity-authentication schemes, the proof key of this scheme is smaller, and the verification time is shorter. Compared with similar ciphertext-retrieval schemes, the time for this scheme to generate indexes and trapdoors and return search results is significantly shorter.     

铂锡铥和铂锡镱催剂上的烷烃芳构化反应的研究

用浸渍法制备了铂锡铥和铂锡镜催化剂。在脉冲微型反应器一色谱仪联合装置上,考察了环已烷、甲基环戊烷和正庚烷在上述催化剂上的芳构化反应。结果表明:稀土铥或镜改变了负载型铂锡催化剂的催化性能,其改性作用不尽相同,即使同一稀土元素也随其含量不同而异。