Tetraiodoethylene: a supramolecular host for Lewis base donors

Tetraiodoethylene (TIE) forms charge transfer complexes with diazine donors through N···I interactions, in which the structure of the complex is very similar to that of TIE. In TIE, two unique molecules form distinct “layers”, and in the complexes the donor molecules take the place of TIE molecules in one of the layers. I···I interactions within the remaining layer of TIE maintain the structure of the layer and yet allow enough flexibility to accommodate a wide variety of donor molecules. Phenazine, quinoxaline, 1,4–dicyanobenzene, and 2,2′–bipyridine all form complexes with TIE which have very similar structures. Phenazine and 2,2′–bipyridine donors sit on the same inversion center as the TIE molecules they replace, and the donor·TIE chains run in the (1 1 0) direction. 1,4–Dcb·TIE has a very similar structure to that of the previously determined pyrazine·TIE complex, but the donor molecules span TIE acceptors in the (1 −2 1) direction rather than (1 1 1). The asymmetric environment of the donor sites in quinoxaline result in a very distorted layered structure, and the I···I interactions between neighboring TIE molecules are the weakest of those reported here. Decomposition of TIE in its reaction with 2,2′–bipyridine gave the side product, [2,2′–bipyridine(H)]I₃·TIE, in which I···I interactions link TIE molecules and I₃⁻ anions to form a pseudo–polyiodide layer.     

Plasticity in multiphase intermetallics

We have studied the mechanical behavior of model NiAl-based eutectic composites to gain insight on micromechanisms of plasticity in multiphase intermetallics. We show that in composites where the NiAl matrix and the reinforcing ductile second phase can deform compatibly due to easy slip transfer across interfaces, high room temperature tensile ductility and fracture toughness are obtained. In composites where interfaces are strong barriers to slip transfer and the metallic second phase has high strength and limited ductility, incompatible deformation of the two phases results in negligible tensile ductility and limited toughness enhancement. Factors that affect ease of slip transfer across interfaces are discussed. Calculations of dislocation pile-up stresses are used to predict whether slip is activated prior to cleavage or vice-versa for a given set of respective yield strengths and crystallographic orientation relationships between the two phases.     

High thermoelectric performance of (Bi1-xPrx)2(Te0.9Se0.1)3 alloys prepared by high-pressure sintering method

In this article, n-type (Bi_1-xPr_x)₂(Te_0.9Se_0.1)₃ (x = 0, .002, .004, .008) alloys were fabricated by high-pressure sintering (HPS) method together with annealing. The effect of high pressure and Pr contents on the microstructure and thermoelectric performance of samples were explored in detail. The results show that the HPS samples are composed of nanoparticles. Pr doping has significant impacts on the electrical and thermal transport properties of the Bi₂Te_2.7Se_0.3 alloys. The HPS sample with x = .004 shows the maximum ZT value of .31 at 473 K, which is enhanced by 41% to compare with the Pr-free sample. Annealing can improve the thermoelectric properties by increasing the electrical transport properties and decreasing the thermal conductivity simultaneously. As a result, the highest ZT value of 1.06 is achieved for the annealed sample with x = .004 at 373 K, which is beneficial to the thermoelectric power generation.     

美国食品安全惩罚性赔偿制度的指向与中国路径

通过观察和审视美国食品安全惩罚性赔偿制度,得出中国当前的食品安全惩罚性赔偿制度存在忽视对主观恶性的评价、惩罚性赔偿金额计算方式刻板僵化,以及赔偿的上限倍数过高等亟待解决的问题。对此,可以从构建以主观恶性为标准的惩罚性赔偿主体确定制度、建立基于损失补偿原则的弹性惩罚性赔偿金额计算制度和设置惩罚性赔偿的金额上限等方面,对中国的食品安全惩罚性赔偿制度进行优化与构建。     

聚乙烯与过渡金属介入对木质素热解过程中表面官能团演变的影响

木质素（LG）含氧量高，化学结构复杂，难于资源化利用。共混剂和催化剂的介入，能够强化LG分解，有效提高其利用效率，但具体机制尚待进一步剖析。本文基于原位红外手段，考察低密度聚乙烯（PE）和过渡金属（Ni、Fe、Mn）的添加对造纸黑液LG表面官能团演变的影响。研究结果显示，LG在200℃左右从C—C连接键开始逐渐分解（波数在2044 cm^-1处），而含氧表面官能团在500℃以后才开始减少（波数在1040~1645 cm^-1和3450~3600 cm^-1处的—OH、C—O、C—O—C和C\stackrel{}{̿}O等）。PE的介入，在400℃左右即能开始促进LG含氧表面官能团的脱除，在500℃左右即能实现大部分含氧表面官能团的脱除。而Ni的添加，能够强化LG与PE之间的相互作用，使得LG中大部分含氧表面官能团在PE快速分解阶段（460℃左右）即脱除。另外，工艺参数，包括过渡金属种类、过渡金属浓度、LG与PE混合比例、升温速率等均对混合体系中LG和PE的相互作用存在不同程度的影响。本文从表面官能团变化的角度为LG的资源化利用提供了重要技术指导。     

A parallel SP-DBSCAN algorithm on spark for waiting spot recommendation

Multimedia Tools and Applications - It is challenging for complex urban transportation networks to recommend taxi waiting spots for mobile passengers because the traditional centralized mining...     

A novel low-permittivity LiAl0.98(Zn0.5Si0.5)0.02O2-based microwave dielectric ceramics for LTCC application

Phase composition, morphology, and microwave dielectric properties of (1−x) LiAl_0.98(Zn_0.5Si_0.5)_0.02O₂ + x CaTiO₃ (0.05 ≤ x ≤ 0.20) materials synthesized via the solid state reaction method were investigated. All these densified materials were obtained at a sintering temperature of 1150°C. All compositions showed a major LiAlO₂ phase that was accompanied by a minor CaTiO₃ phase. The ε_r value increased gradually from 10.88 to 11.60, whereas the Q × f value remarkably decreased from 33 251 GHz to 13 511 GHz. The τ_f value changes from −85 ppm/°C to 212 ppm/°C, thereby indicating that CaTiO₃ could effectively adjust this value. HBO₃-doping was used to further decrease the sintering temperature to 900°C. The optimum value was obtained at 7 wt.% HBO₃ doped with microwave dielectric properties of ε_r = 9.39, Q × f = 10 224 GHz, and τ_f = −7.8 ppm/°C. This material also exhibited chemical compatibility with silver, making it a candidate for low temperature co-fired ceramics applications.     

关节型工业机器人扭转振动的伺服补偿技术研究

针对工业机器人用RV减速机传动误差所引起的动态失稳现象,在建立由驱动电机-RV减速机-负载所构成的机电耦合系统的基础上,同时考虑负载侧不宜安装传感器的限制条件,依据转矩波动引起转速波动的原理,将由状态观测器间接得到的能够反映转矩波动变化的状态变量——负载加速度变化率作为反馈控制量,对电磁转矩进行实时补偿。经系统的时频域性能分析证明,补偿后的电机转矩命令值抵消了转矩波动的影响,负载侧转速波动得到了很好的抑制,能够极大提高工业机器人在变工况下的动态工作精度。     

基于改进YOLOv3的电容器外观缺陷检测

针对部署于有限算力平台的YOLOv3(you only look once v3)算法对电容器外观缺陷存在检测速度较慢的问题, 提出了基于 YOLOv3算法改进的轻量化算法MQYOLOv3。首先采用轻量化网络MobileNet v2作为特征提取模 块,通 过利用深度可分离式卷积替换一般卷积操作,使得模型的参数量大幅度降低进而提高模型的 检测速度,同 时也带来了检测精度的降低;然后在网络结构中嵌入空间金字塔池化结构实现局部特征与全 局特征的融合、 引入距离交并比(distance intersection over union, DIoU)损失函数优化交并比(intersection over union, IoU)损失函数以及使用Mish激活函数优化Leaky ReLU激活函数来提高模型的检 测精度。本文采用自制的电容器外观缺陷 数据集进行实验,轻量化MQYOLOv3算法的平均精度均值(mean average precision,mAP)为87.96%, 较优化前降低了1.16%,检测速度从1.5 FPS提升 到7.7 FPS 。实验表明,本文设计的轻量化MQYOLOv3算法在保证检测精度的同时,提高了检测速度。     

浅谈图书馆馆藏结构资源的变化与发展

随着社会的发展,电子资源的兴起,促使人们的阅读方式发生改变。纸质文献与电子文件优势互补,图书馆应根据校情合理配置两者的经费比例,让二者协调发展。馆藏结构的变化也使图书馆服务读者的方式发生改变,服务水平得到提高。