砂土与EPS颗粒混合的轻质土(LSES)临界循环应力比的试验研究

循环荷载下,砂土与EPS颗粒混合的轻质土(LSES)存在临界循环应力比Sth,将割线弹性模量衰减系数δ与循环次数的关系曲线能保持平缓的最大循环应力比定义为Sth,它是结构稳定与破坏两种状态的界限指标,根据动三轴试验结果,认为影响Sth的主要因素有围压、水泥掺量和EPS颗粒含量。一般来说,水泥掺量的增加、围压和EPS颗粒含量的减小均会提高Sth,但由于高围压下的结构重塑,水泥掺量低且EPS颗粒含量高的试样的Sth表现出一些不同的性状。     

Total mercury in marine species from the French coast of the Eastern English Channel

Mercury (Hg) in fish can present a potential risk to wildlife and human consumers. Mercury levels were determined in 12 fish species and 2 invertebrate species from the French coast of the Eastern English Channel collected in June and November 2012. Total mercury concentrations in the muscle tissues ranged between 0.04 and 1.63 µg g^-1 (d.w.). Dab and sandeel displayed a significant positive correlation between Hg concentrations and fish length. Seasonal differences in Hg concentrations were observed for dab and shrimp. The lesser weever showed significantly higher concentrations of Hg (0.97 ± 0.34 µg g^-1 d. w.) than all other species. Gobies and sprat, which had the smallest size, showed significantly lower concentrations than herring, whiting, pout and sardine. Among the considered species, flatfish such as dab, flounder, plaice and sole displayed intermediate levels of Hg. In the present study, the fish age expressed as specimen length seems to be one of the major factors governing Hg contents in muscle tissues. Finally, mercury concentrations in commercial fish from the Eastern English Channel were below the levels fixed by the European Union for total mercury in edible parts of fish products.     

Biogenic cements from rice hull ash doped with aluminum and iron

This work describes the use of rice hull as starting material for the synthesis of cements doped with iron and aluminum. Rice hull contains about 10-20% of silica along with organic material. In many countries rice hull represents an environmental problem since this material is merely burned at rice fields, rendering suspended silica particles in the air. Dicalcium silicate (beta-Ca(2)SiO(4)) is the second most important component of Portland cement and presents many environmental advantages over commercial cement. It can be prepared at lower temperatures saving energy and raw-materials. In this work we describe the synthesis beta-Ca(2)SiO(4) using silica derived from rice hull ash. Silica was obtained from heating rice hull at 600 degrees C. Starting materials (silica, calcium oxide, barium chloride, iron or aluminum oxide) were weighed in stoichiometric proportions and aqueous dispersions having water:solid ratio of approximately 20:1 were prepared and treated in an ultrasonic bath for 60min. After this, an intermediate silicate and the excess of calcium hydroxide were obtained. Finally solids were dried, grounded and heated up to 800 degrees C. It was observed that beta-Ca(2)SiO(4) was obtained when dopant concentration was limited to 1%.     

Serum concentrations of selected organochlorine pesticides in a Lebanese population and their associations to sociodemographic,anthropometric and dietary factors: ENASB study

Organochlorine pesticides (OCPs) were banned by the Stockholm Convention many years ago; however, they are still detected in the environment due to their high persistence, their current illegal use, and their import from countries where they have not been banned. We evaluated the serum concentrations of selected OCPs (hexachlorobenzene (HCB), β-hexachlorocyclohexanes (β-HCH), p,p′-dichlorodiphenyltrichloroethane (DDT) and its metabolite p,p′-dichlorodiphenyldichloroethylene (DDE) in a sample of Lebanese adults using gas chromatography coupled to an ion trap mass spectrometer detector. The mean concentrations of HCB, β-HCH, DDT, and DDE were 7.1, 8.6, 2.1, and 18.9 ng/g of lipids, respectively, and the major contributor among the four OCPs was DDE. The OCP levels in the present study were in general lower than the values observed in several countries worldwide and their concentrations at the 95th percentile were lower than the biomonitoring equivalents (BEs) excluding any appreciable health risk. We observed an inverse association between HCB concentrations and body mass index (BMI) as well as HCB, β-HCH, and DDE levels, and smoking habits. Milk consumption however was positively associated with an increased serum level of β-HCH. This study, which was the first to investigate OCP serum levels in a Lebanese population, provides a baseline to which future measurements can be compared.     

The deployment of γ-irradiation for reducing polycyclic aromatic hydrocarbons and microbial load in wheat kernels

Food contamination may contribute to serious human health problems. In this work, the effect of γ-irradiation 0, 5, 10, and 15 kGy doses on the removal of polycyclic aromatic hydrocarbons from wheat kernels was investigated. Additionally, variations in the contents of 16 congeners on bacterial load and other chemical parameters were studied. Polycyclic aromatic hydrocarbons concentrations were determined by high-performance liquid chromatography followed by fluorescence detection. The effects of γ-irradiation on the concentrations varied for each congener, with the highest irradiation dose being the most effective. Benzo[a]pyrene was reduced by ～50%, and the total concentration of all congeners decreased dramatically from 154 to 21 µg.kg^?1 upon 15 kGy irradiation at a dose rate of 8.49 kGy h^?1. The total bacterial load was reduced from 2.4 to < 1 log₁₀ cfu g^?1, while wheat chemical properties were not affected.     

南通市长江堤防渗透性能数值模拟研究

结合南通长江堤防渗透试验数据,利用Plaxis岩土工程专用有限元软件对南通市长江堤防典型地段分别进行不同潮位及设计水位条件下的非稳定渗流数值模拟。模拟结果表明,在已监测江水位条件下堤体渗透基本不受外江水位变化的影响;设计水位条件下的各地段江堤稳定安全系数都在1.5以上;对各典型潮位下各监测断面水位的模拟结果与其实测结果具有良好的一致性。南通市长江堤防渗流稳定安全性能优良。应用实际表明,Plaxis软件具有良好的实用性能,适合用于堤防渗流稳定安全评估。