可变进气涡流系统气道入口流速的PIV测量

为了研究双进气道柴油机缸内涡流的调节原理及性能,在稳流气道试验台上测试了一种带涡流调节阀的新型气道组合的流通能力与调节涡流的性能.用PIV系统对各个工况下气道入口的流场进行测量,通过PIV系统输出的二维流场信息估算气道进气质量流量的变化及分配情况,同时利用AVL-FIRE对整个实验系统进行了CFD分析.结果表明,柴油机双进气道通过涡流控制阀调节直气道的进气质量流量及流速,引起总的质量流量的变化,进而改变了缸内涡流的大小.     

关于停时的一个注记

对任意停时T,定义A(T)={停时S:S≤T,在{T>O}上S相似文献   

基于稳定性考虑战斗机进气装置一体化设计分析

基于发动机稳定性考虑，回顾了超音速战斗机进气装置的发展历程，并阐述了高性能战斗机所面临的进气装置一体化设计问题，重点分析了国外先进战斗机进气装置在布局型式、结构、附面层控制等方面的一体化设计特点及其卓越性能，最后得出一些有益于解决我国在研新机以及老机的改进改型面临的推进系统稳定性问题的结论和启示。     

内燃机进气压力的频谱分析

提出了分析内燃机进气压力频谱特性的方法,研究了气缸数目不同的内燃机进气压力频谱特性,探讨了进气压力频谱特性与发动机充气特性之间的关系.结果表明:采用谐振型进气管能明显地改善发动机的充气特性.     

苯二氮草化合物提高鹅的摄食和增重的研究

本试验利用苯二氯簟化合物—F_(89)来提高鹅的摄食量,以加速动物的生长。经翅静脉血管瘘管注入 F_(89)(0.2mg/kg·B·W/d)、十二指肠瘘灌注 F_(89)(0.2mg/kg·B·W/d)和日粮中添加2ppmF_(89),分别提高成年母鹅每天平均摄食量8.1%(p<0.05)、29.1%(p<0.01)和23.9(p<0.01)。日粮中添加2ppmF_(89),连续饲喂55～85日龄的生长期鹅,日摄食量较对照组增加12.7%,增重提高21.7%(p<0.05),耗料比下降7.41%。血液代谢物分析表明:饲喂 F_(89)后,仔鹅血清中葡萄糖浓度下降,胰岛素水平上升。     

Exposure assessment to ochratoxin A from the consumption of Italian and Hungarian wines

A total of 267 wine samples including 19 dessert, 186 red, 11 rosé and 51 white produced mostly in the years 1997–2002 in Italian and Hungarian regions were analyzed for ochratoxin A (OTA) using inmunoaffinity column (IAC) clean-up and HPLC with fluorimetric detection. None of Hungarian wine samples were contaminated with this mycotoxin. For Italian red wines, 84% of the samples were positive for OTA ranged from 0.01 to 4.00 ng/mL. Furthermore, OTA was detected in 63% of dessert, in 56% of rosé and in 19% of white wine samples ranged from 0.01 to 1.64, from 0.01 to 1.04 and from 0.01 to 0.21 ng/mL, respectively. A study of OTA daily exposure assessment in Italian wines was also carried out outlining a quite low contribution to the overall daily intake.     

The need for reference materials when monitoring nitrate intake

Whether dietary exposure to nitrate metabolites is detrimental or beneficial to human health has long been a matter of controversy. In spite of no consistent epidemiological evidence, nitrate metabolites are associated with the formation of carcinogenic-nitrosamines and gastric cancer. Furthermore, recent studies demonstrate that ingested nitrate plays a role in host defence against gastrointestinal pathogenic bacteria. Analytical values of nitrate content in foods are essential for estimating nitrate intake. The analytical process is of paramount importance for assessing human nitrate exposure and for establishing a link between these exposures and the current and future observed health effects. Therefore, the quality assurance of the measurement process is crucial to obtaining reliability, comparability and traceability of results. Certified Reference Materials (CRM) should play a role in the consistency of the measurement process. However, the availability of nitrate CRMs is still poor. When food monitoring is demanded, an approach could be to use In House Reference Materials (IHRM), prepared at a high metrological level, and all preparation steps should be quality driven. IHRMs were prepared, and available CRMs were used to provide traceability of the process. The homogeneity of IHRM was evaluated using an appropriate statistical design. The stability was monitored using an isochronous method. The material shelf life and storage conditions are presented.HPLC was optimised for the determination of nitrates in four vegetable categories. When a suite of IHRMs were used, the response of the HPLC system was linear over the range 1 to 8 mg L^–1. The detection limit for these compounds was 0.2 g L^–1 and the determination limit 1.2 g L^–1.The relationship between measurement uncertainty and critical points of the analytical process is presented. The differences in observed relative uncertainty between food categories could reflect current limitations in the food matrix reference materials.     

Occurrence of ochratoxin A in bread consumed in Morocco

One hundred samples of commercial bread purchased from January to October (2006) from retail bakeshops in five different cities (Rabat, Témara, Salé, Casablanca and Meknès) in Morocco were surveyed for the presence of ochratoxin A (OTA) using liquid chromatography coupled to fluorescence detection. The identification of OTA in positive bread samples was confirmed by methyl ester derivatization. Analytical results showed that forty eight (48%) samples were positive with OTA greater than the limit of quantification (LOQ = 0.051 ng/g). Levels of OTA in positive samples ranged between 0.14 and 149 ng/g. The average contamination of bread samples with OTA was 13 ± 1.5 ng/g. The highest frequency of positive samples (61.5%) and the most contaminated sample (149 ng/g) were found in bread commercialized in the Casablanca area. Twenty six of the positive samples exceeded the maximum level of 3 ng/g set by European regulations for OTA in cereals and derivatives. Based in the results presented in this study, the estimated daily intake of OTA from bread was 126 ng/kg bw/day. The present paper is the first ever drafted on the natural occurrence of OTA in bread consumed in Morocco. Data on the daily intake of OTA by the Moroccan population are also estimated for the first time.     

自优化剩余函数量子Monte Carlo方法

提出剩余函数量子Monte Carlo的一个新算法，这是一个自优化和自改善的过程.与以前的算法相比，本算法中的试探函数的优化是在剩余函数方法中同步进行的，而不是在变分Monte Carlo计算之前.为了优化试探函数，使用一种改进了的速降法，这是一个步长能够自动调节，超线性收敛的优化技术.在这个算法中,还使用了一种新的相关函数，它满足电子与电子以及电子与核奇点条件.此方法已被用于计算H2、LiH、Li2、H2O分子的基态以及CH2的X 3B1态、1 1A1态和2 1A1态的能量值.     

Determination of Toxic Pyrrolizidine Alkaloids in Traditional Chinese Herbal Medicines by UPLC-MS/MS and Accompanying Risk Assessment for Human Health

Pyrrolizidine alkaloids (PAs) are a class of natural toxins with hepatotoxicity, genotoxicity and carcinogenicity. They are endogenous and adulterated toxic components widely found in food and herbal products. In this study, a sensitive and efficient ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was used to detect the PAs in 386 kinds of Chinese herbal medicines recorded in the Chinese Pharmacopoeia (2020). The estimated daily intake (EDI) of 0.007 μg/kg body weight (bw)/day was adopted as the safety baseline. The margin of exposure (MOE) approach was applied to evaluate the chronic exposure risk for the genotoxic and carcinogenic potential of PAs. Results showed that PAs was detected in 271 out of 386 samples with a content of 0.1–25,567.4 μg/kg, and there were 20 samples with EDI values above the baseline, 0.007 μg/kg bw/day. Beyond that, the MOE values for 10 out of 271 positive samples were below 10,000. Considering the actual situation, Haber’s rule was used to assume two weeks exposure every year during lifetime, and still the MOE values for four out of 271 positive samples were under 10,000, indicating these products may have potential health risk. The developed method was successfully applied to detect the PAs-containing Chinese herbal medicines. This study provides convincing data that can support risk management actions in China and a meaningful reference for the rational and safe use of Chinese herbal medicines.