超高压对大肠杆菌O157:H7细胞膜的损伤效应

本研究旨在揭示超高压对食源性致病微生物大肠杆菌O157:H7细胞膜的损伤。研究了200、400、500 MPa不同压力对大肠杆菌O157:H7的灭活作用,通过对菌体细胞核酸类物质、钾离子和镁离子泄漏量、碘化丙啶(propidium iodide,PI)摄入量、细胞膜Na+/K+-ATP酶和Ca~(2+)/Mg~(2+)-ATP酶活性变化的分析研究,评价不同超高压处理压力对大肠杆菌O157:H7膜损伤效应。结果表明,经200、400 MPa压力处理5 min后,大肠杆菌O157:H7菌落总数由初始8.8(lg(CFU/m L))分别下降至8.2(lg(CFU/m L))和6.3(lg(CFU/m L)),500 MPa压力处理后,大肠杆菌O157:H7全部死亡。压力升高,细菌细胞内核酸类物质、K+、Mg~(2+)离子泄漏量、PI摄入量均显著增加,细胞膜上Na+/K+-ATP酶和Ca~(2+)/Mg~(2+)-ATP酶活性显著降低。Ca~(2+)/Mg~(2+)-ATP酶对压力的敏感性更强,500 MPa处理组该酶活性几乎完全丧失。超高压处理引起大肠杆菌O157:H7细胞膜产生显著损伤,细胞膜上Ca~(2+)/Mg~(2+)-ATP酶的失活是导致大肠杆菌O157:H7死亡的主要原因。     

基于LogitBoost的误用检测技术

LogitBoost是直接优化二项对数损失的Adaboost算法。由于其解趋近于贝叶斯最优解,并且实现简单,成为机器学习中研究的热点。文章首次将LogitBoost的分类算法应用于网络误用检测中,实验结果表明,LogitBoost检测性能优于目前常用的模式匹配算法。     

Fabrication of graphitic carbon spheres and their application in Al2O3‐SiC‐C refractory castables

Graphitic carbon spheres (GCS) with an average diameter of about 0.8 μm were prepared via hydrothermal carbonization combined with catalytic graphitization using glucose and in situ formed Fe nanoparticles (NPs) as, respectively, a carbon precursor and catalyst. They were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis/differential scanning calorimetry (TG/DSC). The optimal content of Fe catalyst for graphitization of amorphous CS was found to be 1.0 wt%, and the optimal temperature and soaking time were, respectively, 1473 K and 3 hours. The transformation from CS to GCS was considered to be dominated by the “dissolution‐precipitation” mechanism. Using as‐prepared GCS instead of flake graphite (FG) as a carbon source, not only reduced water demand for casting Al₂O₃‐SiC‐C samples and decreased their final apparent porosity, but also enhanced their modulus of rupture and cold crushing strength. In addition, castable samples using GCS showed better oxidation resistance than those using FG.     

High-entropy rare earth titanates with low thermal conductivity designed by lattice distortion

High-entropy single-phase rare earth titanates (RE_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ could obtain the low thermal conductivity (1.51 W·m⁻¹·K⁻¹, 1500°C), high thermal expansion coefficient (average, 11.69×10⁻⁶ K⁻¹, RT ∼1500°C) and excellent high-temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A-site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y³⁺ and other RE³⁺ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high-entropy rare earth titanate (Y_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ has lower thermal conductivity, higher thermal expansion coefficient, and excellent high-temperature stability, which has great potential for application in the thermal protection field.     

三氧化二铝-碳化硅-碳浇注料防氧化技术研究进展

综述了三氧化二铝-碳化硅-碳浇注料防氧化技术的防氧化效果以及对材料性能、组成和结构的影响,根据含碳耐火材料的氧化损毁机理,主要分析了防氧化剂的两种作用形式即优先碳源氧化法和优化碳源法。防氧化剂法除了优先碳源氧化生成金属氧化物和碳化物阻止含碳材料的氧化外,还可以通过固相反应生成液相等物质堵塞材料内部气孔提升材料的致密度阻止氧气的进入来提高防氧化效果,优化碳源法则通过复合碳源以及在碳源的表面添加涂层达到一定的防氧化效果。详细阐述了3种方法的工艺特点以及目前存在的问题,并对其发展方向进行了展望,为开发新型三氧化二铝-碳化硅-碳浇注料防氧化技术提供参考。     

彩色数字图像的小波变换和混沌序列加密

根据彩色数字图像的基本特点,运用数字图像加密和解密原理,将离散小波变换和离散混沌序列有机地结合起来,研究了彩色数字图像的小波变换和混沌序列的加密和解密方法;对原始图像进行加密实质是利用混沌序列对其低频小波系数进行加密,对加密图像进行解密实质是利用混沌序列对其低频小波系数进行解密;研究的彩色数字图像加解密方法,为彩色数字图像加密提供了一种有效可行的方法,不仅能够使加密彩色数字图像具有理想的加密效果,而且能够保证加密彩色数字图像足够的安全。     

Preparation of mono-dispersed carbonaceous spheres via a hydrothermal process

Mono-dispersed carbonaceous spheres (CS) with a narrow size distribution were synthesized via hydrothermal treatment of glucose. The effects of hydrothermal temperature and time, glucose concentration and pH value of solution were investigated in detail. Structures and surface properties of as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Induced coupled plasma emission spectroscopy (ICP), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), Nitrogen adsorption/desorption and Fourier transformed infrared spectroscopy (FTIR). The results showed that the production yield of CS increased from 2.1 to 32% with increasing the temperature from 160 to 180 °C, and the average size increased from 0.23 to 0.95 μm with extending the hydrothermal time from 8 to 16 h. pH value of the starting solution showed an evident effect on the morphology of CS via affecting the decomposition products of glucose. CS could be obtained when the pH value of starting solution was less than 12, but further increasing the pH value to 13–14 led to the formation of lumpy aggregations of carbon rather than spherical CS. The CS prepared under pH 6 and 9 showed good adsorption capacity for Methylene blue (MB), which was attributed to their relatively high specific surface area.     

面向领域实体关系联合抽取的标注方法

针对传统实体关系标注方法存在效率低下、错误传播、实体冗余等问题,对于某些领域语料中存在“一实体（主实体）同时与多个实体之间存在重叠关系”的特点,提出一种面向领域实体关系联合抽取的新标注方法。首先,将主实体标注为一个固定标签,将文本中与主实体存在关系的其他每个实体标注为对应实体对间的关系类型,这种对实体和关系进行同步标注的方式节省了至少一半的标注成本;然后,直接对三元组进行建模,而不是分别对实体和关系进行建模,通过标签匹配和映射即可获取三元组数据,从而缓解重叠关系抽取、实体冗余以及错误传播等问题;最后,以作物病虫害领域为例进行实验,测试了来自转换器的双向编码器表征量（BERT）-双向长短期记忆网络（BiLSTM）+条件随机场（CRF）端到端模型在1 619条作物病虫害文档的数据集上的性能。实验结果表明该模型的F1值比基于传统标注方式+BERT模型的流水线方法提高了47.83个百分点;与基于新标注方式+BiLSTM+CRF模型、卷积神经网络（CNN）+BiLSTM+CRF等经典模型的联合学习方法相比,该模型的F1值分别提高了9.55个百分点和10.22个百分点,验证了所提标注方法和模型的有效性。     

新型混合SVC模型及其基于人工免疫算法的控制策略

针对静止无功补偿器(SVC)在抑制电压闪变、滤除谐波方面效果不理想以及静止无功发生器(SVG)成本过高的问题,提出一种FC+TCR+SVG型混合SVC模型。成本低廉的大容量SVC(FC+TCR)完成初步粗补偿,小容量SVG负责微补偿、抑制电压闪变以及滤除谐波,两者优势互补,最大限度地兼顾成本与性能。通过分析不同的模块布局,确定可行的电路分布结构,最大限度地减少模块间的干扰。提出基于人工免疫算法的改进型动态PI控制器以及模块间的协调控制策略。PSCAD仿真结果表明,新型混合SVC比传统SVC响应速度更快,补偿效果更好,并对谐波有较好的抑制作用,其综合性能媲美SVG,且可以节省50%以上的成本。     

高密度表面肌电信号无线数据采集同步机制研究

高密度表面肌电信号研究需要获取高精度、高空间分辨率、高质量的肌电信号,同时也对采集系统的便捷性、响应性、续航能力等方面提出了更高要求.本文在考虑可穿戴性、实时性、高通量等基础上,对sEMG采集系统架构和传输网络设计进行了深入研究,设计了基于模块化分层架构、有线USB结合无线WIFI传输模式、异步采集和同步聚合方法、双缓存和时隙切换的高精度同步机制的实时肌电采集通信系统.为验证系统功能和算法机制,本文还构建了实验平台装置,实现了128通道1 kHz采样率16 bit精度sEMG信号的实时采集、处理和传输.通过测试,在采用通信周期为50 ms下,通道间同步误差小于320μs,刷新率可达20 Hz,系统的平均延时小于80 ms.