含WB烧结硬质合金的组织结构和性能研究

将不同含量的WB粉末添加到传统成分的WC-Co粉末中,利用低压烧结技术制备了系列含WB的WC-Co型硬质合金,并对其物相组成、组织结构和力学性能进行了系统表征分析。研究发现,在低压烧结过程中WB与Co发生反应,生成了具有超高硬度的WCoB相,由此降低了粘结相Co对WC晶粒的隔离,增加了WC晶粒间的接触度,引起合金韧性下降。添加WB制备的硬质合金材料其摩擦系数更低,随WB添加量的增加,硬度和耐磨性明显提高,当WB添加量为30%(质量分数)时,制备的硬质合金材料的硬度达到19 000 MPa,其磨损速率仅为传统WC-Co硬质合金1/10。然而,添加WB的WC-Co合金的断裂韧性约为传统WC-Co硬质合金的83%~91%。     

Comparative study of colorectal health related compounds in different types of bread: Analysis of bread samples pre and post digestion in a batch fermentation model of the human intestine

Seven different types of wheat and rye bread were analysed for colorectal health related compounds, pre and post digestion, in batch fermentation model of the human intestine. Pre digestion, higher amounts of colorectal health-related dietary fibre compounds (soluble/insoluble/total dietary fibre, arabinoxylans, β-glucans) and phytochemicals (mono-/di-phenolic acids, phytic acid, hydroxymethylfurfural) were detected in wholemeal than in refined flour types of bread, as well as in rye flour types than in wheat flour types of bread. Post digestion, faecal bacterial metabolites of colorectal health promoting (acetate/propionate/butyrate, lactate, free mono-/di-phenolic acids) and impairing (amino metabolites, bile acid metabolites) activities were found in fermentation supernatants of bread samples. All types of bread positively affected faecal bacterial metabolism; among the different types of bread, the highest stimulation of organic acid production (acetate/propionate/butyrate, lactate) and the lowest detrimental bacterial enzyme activities (β-glucuronidase, urease) were detected for wheat flour bread, whereas the strongest retardation of bacterial bile acid degradation and the strongest stimulation of phenolic acid metabolite release (phenylpropionic/phenylpropenoic acid derivatives) were induced by wholemeal rye bread. This study for the first time presents a qualitative and quantitative overview over the broad spectrum of colorectal health related compounds in high- and low-fibre types of bread, pre and post in vitro digestion, and highlights the significance of bread for the preventive nutritional intervention of colorectal cancer.     

Thermal Stability of WB2 and W-B-N Films Deposited by Magnetron Sputtering

The work is mainly to study the thermal stability including the phase stability, microstructure and tribo-mechanical properties of the AlB₂-type WB₂ and W-B-N (5.6 at.% N) films annealed in vacuum at various temperatures, which are deposited on Si and GY8 substrates by magnetron sputtering. For the WB₂ and W-B-N films deposited on Si wafers, as the annealing temperature increases from 700 to 1000 °C, a-WB (700 °C) and Mo₂B₅-type WB₂ (1000 °C) are successively observed in the AlB₂-type WB₂ films, which show many cracks at the temperature ≥?800 °C resulting in the performance failure; by contrast, only slight α-WB is observed at 1000 °C in the W-B-N films due to the stabilization effect of a-BN phase, and the hardness increases to 34.1 GPa first due to the improved crystallinity and then decreases to 31.5 GPa ascribed to the formation of α-WB. For the WB₂ and the W-B-N films deposited on WC-Co substrates, both the WB₂ and W-B-N films react with the YG8 (WC-Co) substrates leading to the formation of CoWB, CoW₂B₂ and CoW₃B₃ with the annealing temperature increasing to 900 °C; a large number of linear cracks occur on the surface of these two films annealed at ≥?800 °C leading to the film failure; after vacuum annealing at 700 °C, the friction performance of the W-B-N films is higher than that of the deposited W-B-N films, while the wear resistance of the WB₂ films shows a slight decrease compared with that of the deposited WB₂ films.     

WB智能电量传感器与S7-PLC的通讯

WB智能电量传感器与S7-PLC采用异步串行通讯,通过S7-200通讯口引脚及WB传感器RS485口端子排分配,以WB传感器通讯协议及S7-200 CPU编程实现通讯.S7-200 CPU编程包括初始化、读数据命令、向WB智能传感器发送命令、中断8端口0字符接受程序、读端口返回数据及处理.该通讯已在空调参数测试系统中应用.     

Microstructure and Properties of WB2/Cr Multilayer Films with Different Bilayer Numbers Deposited by Magnetron Sputtering

The influence of the bilayer number on the microstructure, mechanical properties, adhesion strength and tribological behaviors of the WB₂/Cr multilayer films was systematically investigated in the present study. Five groups of WB₂/Cr films with the same modulation ratio were synthesized by magnetron sputtering technique. The crystalline structure of the films was determined by X-ray diffraction. The morphologies and the microstructure of the films were observed by scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Furthermore, Nano indenter, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. As bilayer numbers varied from 5 to 40, the hardness increased first and then decreased with the maximum hardness of 33.9 GPa when the bilayer number is 30. The H/E^* and H³/E^*2 values calculated to evaluate the fracture toughness showed the similar changing trend with hardness. The adhesion strength reached the maximum of 67 N when the bilayer number is 30. The surface roughness and friction coefficient decreased with increasing bilayer number. The wear mechanism was also investigated, and the results suggested that the multilayer film with bilayer number of 30 exhibited the best wear resistance (1.78 × 10^-7 mm³/Nm), benefiting from the contribution of high hardness, fracture toughness and adhesion strength.     

The influence of season on quality characteristics of hot-boned beef m. longissimus thoracis

Samples of m. longissimus thoracis (LT) muscle were randomly collected from 70 Omani beef cattle 1 h after slaughter between August 2001 and July 2002 in the Muscat Municipality central slaughterhouse to investigate the effect of seasonal parameters on meat quality during the hot and cool seasons of Oman. The collection period (12 months) was divided into two seasons according to ambient temperatures and relative humidity and termed: Cool Season (November–March with average temperature of 21.2±1.40 °C and 57.9±1.61% relative humidity) and Hot Season (April–October with average temperature of 34.3±1.67 °C and 48.8±7.57% relative humidity). The season had a significant effect on meat quality characteristics of the LT muscle. Muscles collected during the hot season had significantly (P<0.001) higher ultimate pH values (6.24) with significantly (P<0.001) lower Warner–Bratzler (WB) shear force values (10.12) than those collected during the cool season (5.54 and 15.58). In these hot-boned samples, there was a linear relationship between ultimate pH and WB shear values. Cooking loss was significantly (P<0.001) higher for cool season samples (26.01%) than from hot season samples (19.75%). Beef from the hot season group had significantly (P<0.001) darker meat than that of the cold season group, based on L* (31.45 vs 35.58), a* (18.53 vs 23.19) and b* (4.16 vs 6.40) colour measurements. There was a linear relationship between ultimate pH and cooking loss, L*, a* and b*. These results indicated that heat stress (>30 °C) lead to physiological stress in beef cattle, which in turn increased muscle ultimate pH and influenced related meat quality characteristics.     

WC-B-Al2O3作结合剂的聚晶立方氮化硼复合材料性能研究

以CBN、WC、B、Al₂O₃等高纯度粉末为原料,在高温高压下合成了聚晶立方氮化硼(PCBN)复合材料,研究了不同烧结温度合成的PCBN复合材料的微观形貌、物相和力学性能。结果显示,在超高压6 GPa、温度1200~1500 ℃、合成时间700 s条件下,合成的PCBN组织主要由BN、WB₂和WB相组成。1500 ℃烧结时,PCBN综合力学性能较好,气孔率1.05%、抗弯强度789 MPa、显微硬度36.5 GPa、磨耗比9810。     

An Embedded ACELP Speech Coding Based on the AMR‐WB Codec

This letter proposes a new embedded speech coding structure based on the Adaptive Multi‐Rate Wideband (AMR‐WB) standard codec. The proposed coding scheme consists of three different bitrates where the two lower bitrates are embedded into the highest one. The embedded bitstream was achieved by modifying the algebraic codebook search procedure adopted for the AMR‐WB codec. The proposed method provides the advantage of scalability due to the embedded bitstream, while it inevitably requires some additional computational complexity for obtaining two different code vectors of the higher bitrate modes. Compared to the AMR‐WB codec, the embedded coder shows improved speech qualities for two higher bitrate modes with a slightly increased bitrate caused by the decreased coding efficiency of the algebraic codebook.     

火力发电厂300MW机组4大管道管材优化选择

结合火力发电厂300WM机组工程实际,对4大管道的管材优化选择进行了全面的分析,提出了建设性的意见,以供工程参考.     

Experimental investigation and theoretical modelling of absolute convective drying of starch

Starch is a granular, hygroscopic, capillary-porous material with an intricate structure. It is known that drying starch till 0% moisture is a physical treatment that modifies starch properties. However, depending upon the heat and mass transfer mechanisms prevalent in the drying system, starch properties are modified in a unique manner. Therefore, the drying operation itself needs to be thoroughly understood. Potato starch was treated in an oven at three high-temperature levels (110, 130 and 140 °C) and for three sample thicknesses (2.8, 5.6 and 11.2 mm). It was observed that drying of starch with moisture content in the hygroscopic range occurred only in the 2nd falling rate period. Two existing theoretical, drying models, one based upon the Krischer Theory and the other based upon the Percolation Approach, were considered apt for modelling the oven drying. Both models describe the experimentally measured moisture profiles well. During drying, transition from one water sub-population to another was smooth. The effective diffusion coefficient decreased with moisture content and increased with temperature, but did not follow Arrhenius’ Law above 130 °C.