Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.     

Ground-borne vibration due to static and dynamic axle loads of InterCity and high-speed trains

In predictions of railway-induced vibrations, a distinction is generally made between the quasi-static and dynamic excitation. The quasi-static excitation is related to the static component of the axle loads. The dynamic excitation is due to dynamic train–track interaction, which is generated by a large number of excitation mechanisms, such as the spatial variation of the support stiffness and the wheel and track unevenness. In the present paper, the quasi-static excitation and the dynamic excitation due to random track unevenness are evaluated by means of numerical predictions. A solution strategy is presented that allows for the evaluation of the second-order statistics of the response due to dynamic excitation based on the power spectral density function of the track unevenness. Due to the motion of the train, the second-order statistics of the response at a fixed point in the free field are non-stationary and an appropriate solution procedure is required. The quasi-static and dynamic contribution to the track and free-field response are analysed for the case of InterCity and high-speed trains running at a subcritical train speed. It is shown how the train speed affects the quasi-static and dynamic contribution. Finally, results of numerical predictions for different train speeds are compared with field measurements that have been performed at a site along the high-speed line L2 Brussels–Köln within the frame of homologation tests.     

Furanocoumarins in celery and parsnips: method and multiyear Canadian survey

The natural occurrence of biologically active furanocoumarins in common vegetables is an area of increasing interest with respect to human health. In this study, an efficient, rugged, and sensitive liquid chromatographic method with ultraviolet photodiode array detection was developed for the estimation of 5 biologically active furanocoumarins (psoralen, bergapten, xanthotoxin, trioxsalen, and angelicin) in celery and parsnips. When authentic samples were spiked with a mixture of furanocoumarins at individual levels of 2 to 10 microg/g, the method produced overall recoveries of 77 and 75% of all furanocoumarins from celery and parsnips, respectively. The method was applied in 2 laboratories to a multiyear survey of more than 200 samples. Of 110 parsnips samples, 109 (99%) contained quantitatable levels of furanocoumarins. The mean level of total furanocoumarins in the positive parsnip samples was 15.1 microg/g; the maximum level detected was 145 microg/g. Of 114 celery samples, 88 (77%) contained quantitatable levels of furanocoumarins. The mean level of total furanocoumarins in the positive celery samples was 1.9 microg/g; the maximum level detected was 15.2 microg/g. Xanthotoxin and bergapten were the most commonly detected furanocoumarins in both celery (68 and 63%) and parsnips (97 and 96%). Xanthotoxin had the highest mean level of positives in both celery (1.3 microg/g) and parsnips (8.5 microg/g). Little year-to-year variation in either total furanocoumarin levels or incidence was noted.     

ICP-AES法测定内蒙古地区六种沙生木本植物中金属元素

采用ICP-AES法分别对内蒙古地区梭梭、小叶锦鸡儿、沙冬青、红柳、沙枣和沙柳等六种沙生木本植物中金属元素进行了测定和分析。该方法的加标回收率为94.98％～120.25％,RSD＜3.4％,具有良好的准确度和精密度。结果表明,常量元素Ca,K,Mg,Na,Al及植物生命活动所必需的微量元素Fe,Mn,Cu,Zn在六种沙生木本植物中表现为不同的含量顺序,且Fe,Mn,Cu,Zn四种元素的含量均低于陆生高等植物的平均含量。该测定结果为改善西部地区生态环境,选择优良防风固沙树种提供可靠的数据和理论依据。     

Verification of an empirical prediction method for railway induced vibrations by means of numerical simulations

Vibrations induced by the passage of trains are a major environmental concern in urban areas. In practice, vibrations are often predicted using empirical methods such as the detailed vibration assessment procedure of the Federal Railroad Administration (FRA) of the U.S. Department of Transportation. This procedure allows predicting ground surface vibrations and re-radiated noise in buildings. Ground vibrations are calculated based on force densities, measured when a vehicle is running over a track, and line source transfer mobilities, measured on site to account for the effect of the local geology on wave propagation. Compared to parametric models, the advantage of this approach is that it inherently takes into account all important parameters. It can only be used, however, when an appropriate estimation of the force density is available. In this paper, analytical expressions are derived for the force density and the line source transfer mobility of the FRA procedure. The derivation of these expressions is verified using a coupled finite element-boundary element method.     

Determination continue du carbone-14 et du soufre-35 en milieu aqueux par un dispositif a scintillation: Application aux effluents chromatographiques

A recording apparatus is described for determining soft radiations (¹⁴C,³⁵S) in aqueous medium, especially adapted for continuous analysis of Chromatographie effluents It is based upon the spreading of the liquid in a thin layer in contact with a plastic scintillator coupled to a coincidence circuit The efficiency is comparable to that of a thin end-window GM counter in the absence of auto-absorption.     

Nondestructive Analysis of Metallic Elements in Diesel Soot Collected on Filter: Benefits of Laser Induced Breakdown Spectroscopy

The main methods of identification and quantification of metallic species in diesel soot require to render metallic species soluble by destruction of solid sample with all the difficulties associated to this analysis such as rate of solubility, destruction of sample, risk of sample pollution during preparation step. Furthermore, a few milligrams of sample are used, then lost and another analysis is not permitted. This article describes a new direct analysis of metals presents in exhaust particles and collected on a filter by using the TRELIBS (Time Resolved Laser Induced Breakdown Spectroscopy), which avoids the complete destruction of the sample. In a few a milliseconds, it is possible to obtain a qualitative and semi-quantitative composition of a complex matrix as diesel particulates: Fe, Mg, Ca, Cu, and Zn appear as the major metallic species. TRELIBS results are compared to SEM/EDS. After a presentation of the properties required by the filter for TRELIBS analysis, the identification of the metallic species collected in the exhaust gas of a diesel engine is presented and compared with another technique (SEM/EDS). The evolutions of the metallic concentrations in diesel particles for different air/fuel ratio are also presented.     

雾化角对液体火箭发动机燃烧室压力振荡的影响

针对液氧/煤油火箭发动机模型燃烧室实现了三维非稳态两相燃烧过程的数值模拟,得到的燃烧室截面平均压力和平均速度与实验吻合。在初边值条件不施加任何扰动的情况下,得到了燃烧室压力自激振荡过程,并研究了液氧和煤油喷嘴雾化角对燃烧室压力振荡的影响。计算结果表明:当雾化角为40°或120°时,由于燃料与氧化剂喷雾锥重叠区域较小或较大,导致了推进剂混合很差或很好,不易在燃烧室头部出现局部爆炸性的可燃混气团,致使燃烧室压力振荡强度较弱;而当雾化角为中间值65°时,易于出现爆炸性的可燃气团并导致剧烈的压力振荡,使燃烧室中出现燃烧不稳定性。因此,雾化角的合理设计是抑制燃烧不稳定性的一种途径。