Microstructural and Mechanical Characteristics of Porous Irons Produced with Small Particle Size Corn Starch

Powder Metallurgy and Metal Ceramics - The space holder technique was widely used in manufacturing high melting-point porous metals. Corn powders with a smaller size (11.4 μm on average) than...     

轧制工艺对VN微合金化厚钢板截面不均匀性的影响

在厚板轧制过程中,由于板厚所引起的由表面到心部变形不均匀,将导致组织与力学性能沿厚度方向上有较大差异,最终影响钢板的整体质量.因此合理选择控轧工艺对于厚板生产至关重要.该研究采用有限元方式模拟了50 mm厚板的轧制过程,得出了不同轧制条件下的厚板截面不同位置的变形情况.同时结合Gleeble热模拟实验,研究了不同控轧工艺对VN微合金化50 mm厚钢板截面效应的影响.结果表明,对于VN微合金化厚板,870 ℃终轧并保温可得到最佳的截面均匀性.     

手持式激光测距仪"测距标准偏差综合评定"的扩展不确定度

在确定的函数关系(数学模型)中,因变量(输出量)随自变量(输入量)的变化规律完全由数学逻辑所确定,自变量到因变量的传递系数(灵敏系数)也可由因变量的标准差和自变量的标准差之比所决定,而与自变量的来历(测量的或者给定的)没有关系[1].本文根据这一基本原理,采用模拟自变量随机变化的方法,成功计算了手持式激光测距仪的测距固定偏差和比例偏差系数的测量不确定度,从而计算出测距标准差综合评定的扩展不确定度,同时解决了复杂的数学模型中多个输入量到输出量的灵敏系数和输出量的不确定度的计算问题.     

Comparison of the Antimicrobial and Sanitizer Resistance of Salmonella Isolates from Chicken Slaughter Processes in Korea

Salmonella is a foodborne pathogen worldwide. Outbreaks of Salmonella are commonly associated with consumption of contaminated foods such as poultry products. Therefore, the objective of this study was to determine the occurrence, biofilm formation, antibiotic resistance, and sanitizer resistance of Salmonella enterica isolated from chicken carcasses. A total of 318 samples were collected from 15 chicken slaughterhouses in 8 provinces of Korea. They were then examined for Salmonella contamination. S. enterica isolates were tested for their susceptibilities to 15 antimicrobials by broth microdilution method. Their biofilm formation ability and resistance to sanitizers were also evaluated. Eighty‐two isolates of S. enterica were obtained from the 318 samples. There were 14 serotypes and 2 untypable isolates. Fifty‐seven (69.5%) isolates were resistant to at least one antibiotic while 30 (36.6%) isolates were resistant to 5 or more antibiotics. Two S. Senftenberg and 3 S. Montevideo isolates exhibited considerable biofilm formation ability (A₆₀₀>0.2) following incubation in Luria‐Bertani (LB) broth for 48 h. Biofilm cell survival and recovery growth assay after sanitization showed that most isolates were highly susceptible to 2.5% lactic acid and 0.1% cetylpyridinium chloride. Therefore, lactic acid and cetylpyridinium chloride might be alternatively or additionally used in addition to chlorine‐based sanitizers that are frequently used to reduce Salmonella contamination of chicken carcasses. Our results provide basic information on the distribution of Salmonella serotypes in chicken slaughterhouses. This study also highlights the necessity to improve farming practices and use antimicrobial agents cautiously. This study also suggests that sanitization during the slaughtering process might be necessary to reduce Salmonella contamination of chicken carcasses.     

快速气相色谱法测定烟草中有机氯农药残留

建立了一种同时测定烟草中17种有机氯农药残留量的毛细管气相色谱分析方法。样品在索格利特萃取器中用正己烷和弗罗里硅土一步提取和净化,采用SE-54弹性毛细管柱,GC-ECD(Ni63)检测,外标法定量。试验表明,样品的加标回收率在75.14%~106.93%,相对标准偏差(RSD)为1,52%~16,99%,并对3个不同产地的烟叶样品进行了实际有机氯农药残留量的测定。      

甘蔗渣纤维表面Zeta电位变化特性及其对酶水解效果的影响

将纤维素原料降解为可发酵糖是木质纤维素生物质生物转化乙醇过程中的重要环节,通过对原料的预处理可以提高纤维素酶的催化效率.本文通过改变甘蔗渣纤维的尺寸、添加多聚磷酸盐等方法,发现均能改变蔗渣纤维的表面Zeta电位.初步研究了其Zeta电位变化规律及Zeta电位的变化对纤维素酶水解效果的影响,并对Zeta电位的变化影响纤维...     

Formation and characterization of aerobic granules in a sequencing batch reactor treating soybean-processing wastewater

Aerobic granules were cultivated in a sequencing batch reactor (SBR) fed with soybean-processing wastewater at 25+/-1 degrees C and pH 7.0+/-0.1. The granulation process was described via measuring the increase of sludge size. The formation of granules was found to be a four-phase process, that is, acclimating, shaping, developing, and maturated. A modified Logistic model could well fit with the granule growth by diameter and could be employed to estimate the maximum diameter, lag time, and specific diameter growth rate effectively. Both normal and log-normal distributions proved to be applicable to model the diameter distribution of the granules. The granule-containing liquor was shear thinning, and their rheological characteristics could be described by using the Herschel-Buckley equation. The suspended solids concentration, pH, temperature, diameter, settling velocity, specific gravity, and sludge volume index all had an effect on the apparent viscosity of the mixed liquor of granules. The matured granules had fractal nature with a fractal dimension of 1.87+/-0.34. Moreover, 83% of matured granules were permeable with fluid collection efficiencies over 0.034. As compared to activated sludge flocs, the aerobic granules grown on the soybean-processing wastewater had better settling ability, mass transfer efficiency, and bioactivity.     

天然植物活性物质阿魏酸糖酯的研究进展

阿魏酸糖酯具有降血糖,抗氧化,改善肠道环境等多种生物活性,由此赋予其极高的开发价值和广阔的市场前景。本文对阿魏酸糖酯的分布、结构、营养价值、制备方法等方面的研究现状进行综述。     

Spatial distribution of hexachlorocyclohexanes in agricultural soils in Zhejiang province, China, and correlations with elevation and temperature

Large quantities of hexachlorocyclohexanes (HCHs) were historically applied to soils in Zhejiang, a hilly province of eastern China, yet very limited information is publicly available for the present levels and residue characteristics of HCHs in the region. In this work, concentrations of HCHs and enantiomeric fractions (EFs) of α-isomer were analyzed in 58 agricultural soil samples (0-20 cm) collected in Zhejiang province. On the basis of the ratio of α-HCH/β-HCH and the fact that HCHs were banned in 1983 for agricultural use in China, fresh application of technical HCHs in a large quantity was unlikely in this province. Significant correlation was found between soil concentrations and elevation (R = 0.52, P < 0.001) and temperature (R = -0.55, P < 0.0001), but not between soil concentrations and total technical usage (R = -0.24, P = 0.1), suggesting a typical secondary distribution pattern. The soil residue inventories of HCHs derived from the relationship between concentration and elevation indicated 14.2 tons of HCHs left in agricultural soils in plain areas with the average elevation less than 100 m, and 61.6 tons of HCHs left in mountain soils with the average elevation higher than 100 m. It was also found that EFs of α-HCH were significantly negatively correlated with carbon biomass (C(bio)) in soils. This implies that C(bio) might have important impact on orientation and extent of enantioselective degradation of α-HCH in the region, which is, according to our knowledge, the first report of this kind.     

Antibacterial activity of a chitooligosaccharide mixture prepared by cellulase digestion of shrimp chitosan and its application to milk preservation

The antibacterial activity of a chitooligosaccharide mixture prepared by digestion of shrimp chitosan with cellulase at 50 degrees C for 14 h was evaluated. Sugars with 1 to 8 degrees of polymer (DP) were found in this chitooligosaccharide mixture, and the weight percentage of sugars with DP > or = 6 was 44.3%. Minimal lethal concentrations of this mixture against Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, Shigella dysenteriae, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus in nutrient broth were 5 to 29 ppm, which were much lower than those of the chitosan reactant (50 to 1,000 ppm). The antibacterial activity of this mixture in the sterilized milk against E. coli O157, L. monocytogenes, Salmonella Typhimurium, and S. aureus was much stronger at 4 degrees C than at 37 degrees C. When raw milk was supplemented with either 0.24% or 0.48% (wt/vol) of this oligosaccharide mixture and stored at 4 degrees C for 12 days, its mesophilic and psychrotrophic counts were reduced by at least 3 log cycles, and there was very little change in pH. In addition, this mixture retarded the growth of Salmonella species and caused quicker reduction of Staphylococcus species in raw milk. Accordingly, the shelf life of raw milk at 4 degrees C was extended by at least 4 days.