Elemental analysis of cemented carbides by calibration-free portable laser-induced breakdown spectroscopy

The process of cemented carbides manufacturing requires rapid and field elemental analytical techniques to control and evaluate the properties of products. Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is such a potential elemental analytical technique. In this work, a portable LIBS instrument combined with a CF method was developed for the analysis of cemented carbides. Three batches of cemented compact carbides without reference samples were analyzed. Qualitative and quantitative analysis of the samples were achieved by using the portable LIBS instrument combined with CF method. To validate the analysis results, X-ray fluorescence spectrometry (XRF) was used to analyze the samples as well. The results of CF-LIBS agreed well with the results of XRF, with relative errors between ?29.53 and 24.70%. The results demonstrated that the portable LIBS instrument combined with CF method was capable for direct and rapid analysis without any need of standard measurements. Notably, with the portable LIBS instrument combined with CF method, acceptable accuracy could be obtained, which is promising for practical field applications.     

卡尔费休法测定液态氯乙烯中水含量的研究

采用卡尔费休法测定了液态氯乙烯单体中的水含量。试验确定了采样工具、样品的预处理方式及选用溶剂的最优方案,并进行了精密度与准确度的验证。结果表明卡尔费休法测定液态氯乙烯单体中的水含量准确、快速,可以用来准确、及时地指导生产。     

Studies on spinel cobaltites,MCo2O4 (M = Mn,Zn, Fe,Ni and Co) and their functional properties

Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo₂O₄ (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 °C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 °C, 550 °C and 750 °C; whereas FeCo₂O₄ and NiCo₂O₄ contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo₂O₄ and ZnCo₂O₄, submicron sized particles of FeCo₂O₄ and agglomerated submicron particle of NiCo₂O₄ are observed. Galvanostatic cycling has been conducted in the voltage range 0.005–3.0 V vs. Li at a current density of 60 mA g^?1 up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo₂O₄ – 365 mA h g^?1 (750 °C); ZnCo₂O₄ – 516 mA h g^?1 (550 °C); FeCo₂O₄ – 480 mA h g^?1 (550 °C); NiCo₂O₄ – 384 mA h g^?1 (750 °C); and Co₃O₄ – 675 mA h g^?1 (350 °C). The Co₃O₄ showed the highest reversible capacity of 675 mA h g^?1; the NiO present in NiCo₂O₄ acts as a buffer layer that results in improved cycling stability; the ZnCo₂O₄ with long needle-like shows good cycling stability.     

高效可撤销的身份基在线离线加密方案

身份基加密（IBE）需要提供一种有效的成员撤销机制，然而，现有可撤销成员的IBE方案存在密钥更新和加密运算量过大的问题，可能使执行该操作的设备成为系统的瓶颈。将完全子树方法和在线离线技术相结合，通过修改指数逆类型IBE的密钥生成和加密算法，提出了一种高效可撤销的身份基在线离线加密方案。方案利用完全子树方法生成更新钥，使得撤销用户无法获得更新钥，进而失去解密能力；利用在线离线技术，将大部分加密运算在离线阶段进行预处理，使得在线阶段仅执行少量简单计算即可生成密文。与相关知名方案相比，该方案不仅提高密钥生成中心的密钥更新的效率，而且极大减少了轻量级设备的在线加密工作量，适合于轻量级设备保护用户隐私信息。     

贝叶斯网络查询语义扩展的专家发现方法

专家发现是实体检索领域的一个研究热点，针对经典专家发现模型存在索引术语独立性假设与检索性能低的缺陷，提出一种基于贝叶斯网络模型的专家发现方法。该方法模型采用四层网络结构，能够实现图形化的概率推理，同时运用词向量技术能够实现查询术语的语义扩展。实验结果显示该模型在多个评价指标上均优于经典专家发现模型，能够有效实现查询术语语义扩展，提高专家检索性能。     

基于LBT-SA的LoRaWAN信道接入方法研究

标准LoRaWAN协议中定义的纯ALOHA信道接入方法在网络负载较大时会造成大量碰撞，使LoRa网络的可扩展性和可靠性受到极大挑战。为此提出了一种将先听后说与模拟退火相结合（Listen Before Talk combined with Simulated Annealing，LBT-SA）的LoRa信道接入方法。该方法通过在设备发送之前先监听信道，降低信道被同时接入的概率，并以成功传输所需退避时间为初始值，搜索更小的退避时间。仿真结果表明，LBT-SA和基于二元指数退避算法的先听后说（Listen Before Talk，LBT）方法在包成功传输率方面保持了高度的一致，并且LBT-SA在周期传输过程中逐渐减少了不必要的退避时间，从而减少了时延。在多达10 000个终端接入单个网关的场景中，该算法的平均退避时间至少降低了16.38%。     

Synthesizing a uniformly spaced array pattern using integral operator for removing progressive phase shift

In this article, an analytical technique is introduced to obtain the excitation coefficients of uniformly spaced linear antenna arrays in order to achieve a desired array factor. By integration of the prescribed array factor, the array factor dependency to the progressive phase shift is eliminated. A new system of linear equations is consequently obtained whose solution represents the excitation coefficients of the array. Some examples are presented to verify the accuracy of the introduced method. The performance of this strategy is compared with those obtained by the other well‐known techniques such as Woodward‐Lawson and Fourier transform. It is shown that the presented method estimates the desired array pattern with a very good precision.     

Perception‐aware autonomous mast motion planning for planetary exploration rovers

Highly accurate real‐time localization is of fundamental importance for the safety and efficiency of planetary rovers exploring the surface of Mars. Mars rover operations rely on vision‐based systems to avoid hazards as well as plan safe routes. However, vision‐based systems operate on the assumption that sufficient visual texture is visible in the scene. This poses a challenge for vision‐based navigation on Mars where regions lacking visual texture are prevalent. To overcome this, we make use of the ability of the rover to actively steer the visual sensor to improve fault tolerance and maximize the perception performance. This paper answers the question of where and when to look by presenting a method for predicting the sensor trajectory that maximizes the localization performance of the rover. This is accomplished by an online assessment of possible trajectories using synthetic, future camera views created from previous observations of the scene. The proposed trajectories are quantified and chosen based on the expected localization performance. In this study, we validate the proposed method in field experiments at the Jet Propulsion Laboratory (JPL) Mars Yard. Furthermore, multiple performance metrics are identified and evaluated for reducing the overall runtime of the algorithm. We show how actively steering the perception system increases the localization accuracy compared with traditional fixed‐sensor configurations.     

α径迹法用于分辨高浓铀和Pu微粒的方法研究

擦拭样品微粒分析技术是核保障环境样品分析的一种主要手段，从大量灰尘颗粒中识别并定位含高浓铀（HEU）或含Pu微粒是微粒分析首先需要解决的问题。本文以HEU和Pu微粒为研究对象，建立了用于微粒α径迹测量的样品制备方法，采用CR-39固体径迹探测器为α径迹探测器，测量了不同蚀刻时间2种微粒产生的α径迹星的径迹参数。结果表明：可通过测量径迹短轴与曲率直径并作图来分辨HEU和Pu微粒，该方法对于蚀刻时间大于10 h的微粒径迹星，均能明显分辨，对于径迹非常密集的径迹星，也能准确分辨。