Dynamique multi-contact d'un système de solides tridimensionnels rigidesMulti-contact dynamics of a set of three-dimensional rigid bodies

This study is in keeping with the general pattern of dynamical simulations of a set of rigid three-dimensional bodies submitted to unilateral contact constraints with dry friction. An exact formulation (respecting the contact and friction laws) of the problem of predicting the system accelerations and the contact status, in further evolution is proposed. A numerical treatment of this kind of nonlinear problem is presented. This approach is applied to a simple multi-contact example, and yields results in agreement with those of analytical and numerical type, known for this example. To cite this article: C. Le Saux et al., C. R. Mecanique 331 (2003).     

Direct modeling of flow of FENE fluids

Direct simulations of macromolecular fluids are carried out for flows between parallel plates and in expanding and contracting channels. The macromolecules are modeled as FENE dumbbells with soft disks or Lennard-Jones dumbbell-dumbbell interactions. The results are presented in terms of profiles and contour plots of velocity, pressure, temperature, density, and flow fields. In addition the data for potential energy, shear stress, and the normal components of the stress tensor are collected. In general, an excellent agreement is found between the simulated profiles and the well-known flow structures, such as flow separation and formation of viscous eddies, indicating that micro-hydrodynamics is a viable tool in linking macroscopic phenomena with the underlying physical mechanisms. The simulations are performed in the Newtonian regime, for medium-size systems comprising up to 3888 dumbbells. This number is sufficiently large to control boundary and particle number effects. The flow is induced by gravity. The traditional stochastic (thermal) and periodic boundary conditions are employed. Also, diffusive boundary conditions, which could include a stagnant fluid layer and repulsive potential walls, are developed. The scaling problems, which are related to the application of a large external force in a microscopic system (of the size of the order 100 Å), result in extreme pressure and temperature gradients. In addition, the viscosity and thermal conductivity coefficients obtained from velocity and temperature profiles of the channel flow are presented. These results are confirmed independently from modeling of Couette flow by the SLLOD equations of motion and from the Evans algorithm for thermal conductivity.     

Tributylammonium Halochromates/silica Gel:Simple Reagents for Oxidative Coupling of Thiols to Symmetrical Disulfides

New orange solid tributylammonium halochromates, (C₄H₉)₃N⁺CrO₃X^?, TBAXC (X=F, Cl) are easily synthesized by the reaction of tributylammonium fluoride and chloride with CrO₃ in a 1:1 molar ratio in the presence of HF and HCl. Tributylammonium halochromates(VI) are versatile reagent for the effective and selective oxidation of organic substrates. Silica gel supported TBAFC and TBACC are versatile reagents for the effective and selective oxidation of organic substrates, in particular, thiols, under mild conditions. Considerable improvements are observed in the presence of the absorbent, making the work‐up much more convenient.     

(SrTiO_3)_(1-x)(SrTaO_2N)_x固溶体的制备及光催化性能研究(英文)

通过高温固相反应合成了N掺杂的SrTiO3和(SrTiO3)1-x(SrTaO2N)x固溶体,对其进行了X射线衍射,紫外可见吸收光谱,X射线光电子能谱分析和比表面积的表征。随x由0增大至0.4,固溶体带隙变窄,由3.2eV降至2.3eV,吸收光谱由紫外光区扩展到可见光区。在甲醇溶液(50mLCH3OH+220mLH2O)中进行了光催化分解水产生氢气的反应,在硝酸银溶液(270mL,0.01mol·L-1)中进行了光催化分解水产生氧气的反应,在可见光(λ420nm)照射下,实现了可见光响应的光催化分解水。     

铈锆固溶体的合成及其在CH_4和CO催化燃烧反应中的应用

分别利用固态反应和共沉淀法制备了铈锆固溶体,并以其为载体制备了车用三效催化剂,考察其在CH4和CO催化燃烧反应中的作用.研究发现固态反应法所得固溶体孔分布较宽,热稳定性较差,但表面较多的缺陷位贡献于其较高的储氧性能.而共沉淀法所得样品拥有较高的热稳定性和催化活性.固溶体的还原性质可以通过铈锆比调控.关联催化剂对CH4和CO的催化氧化性能发现,具有较大比表面积、集中孔径分布和较高储氧能力的固溶体显示了较低的催化剂起燃温度和较高的催化活性.     

EDTA配合法制备beta-Al_2O_3固体电解质

以金属硝酸盐和乙二胺四乙酸(EDTA)为原料,采用EDTA配合溶胶-凝胶法制备了beta-Al2O3前驱粉料,并利用X射线衍射分析(XRD)、红外光谱分析(FTIR)、热分析(TG/DSC)、交流阻抗谱(EIS)和扫描电镜(SEM)等测试技术对beta-Al2O3的合成工艺进行了详细的研究。结果表明:该法合成beta-Al2O3前驱粉料的温度为1150℃,比固相反应法低了150℃,平均粒径约为42nm,具有较好的成型和烧结性能。将素坯在1630℃保温烧结,得到的烧结体相对密度为96%以上,300℃时beta-Al2O3固体电解质的离子电导率为0.026S·cm-1。     

土壤与沉积物样品中多氯联苯总量的气相色谱-质谱法快速分析

建立了土壤和沉积物样品中多氯联苯总量的快速分析方法.样品经加速溶剂萃取,Bond ElutPCB SPE小柱净化后,采用气相色谱-质谱测定多氯联苯的总量,方法的平均回收率为84% ～106%,相对标准偏差为4.2% ～8.4%,多氯联苯总量的方法检出限为2.25 ng/g.该方法快速、灵敏、准确,适用于大部分土壤及沉积物样品中多氯联苯总量的快速筛查分析.     

活性炭纤维改性对ACF-SPME技术分析多环芳烃的影响

活性炭纤维经改性剂浸渍,水蒸气高温活化后,增大了其对水中多环芳烃的选择性和吸附量,提高了检出限。活性炭纤维活化的最佳条件:在45%磷酸中浸渍6 h,水蒸气中活化30 min,活化温度为500℃。与未改性炭纤维相比,改性后的炭纤维经固相微萃取技术与气相色谱联用测定16种多环芳烃(PAHs),检出限由0.5~50μg/L降至0.01~0.5μg/L,加标回收率由46%~112%增至74%~124%。方法的灵敏度和准确性得到明显的改善,提高了该技术的实际应用价值。     

UPLC-MS/MS对卷烟烟气中4种烟草特有亚硝胺的快速测定

建立了卷烟主流烟气中烟草特有亚硝胺的超高效液相色谱-电喷雾串联质谱(UPLC-MS/MS)测定方法。在标准吸烟条件下,采用剑桥滤片收集卷烟烟气粒相物,用醋酸铵缓冲液提取粒相物,经固相萃取净化后,以电喷雾正离子多反应监测方式,实现了烟气中N-亚硝基降烟碱、4-甲基亚硝基吡啶基丁酮、N-亚硝基新烟草碱和N-亚硝基假木贼碱的基线分离和快速测定。4种烟草特有亚硝胺在0~400μg/L范围内具有良好线性,相关系数大于0.998,定量下限为0.08~0.15μg/L,加标回收率为72%~104%,相对标准偏差为3.8%~9.7%。该方法灵敏、快速、准确,适用于卷烟烟气中烟草特有亚硝胺的测定。     

分散固相萃取-高效液相色谱-质谱联用法测定水稻秸秆、糙米、稻壳和土壤中戊唑醇残留

建立了分散固相萃取-液相色谱-质谱法测定水稻秸秆、糙米、稻壳及土壤中戊唑醇残留量。方法以乙腈为萃取溶剂,N-丙基-乙二胺(PSA)为吸附剂,实现样品快速制备;在Zorbax Eclipse XDB-C18色谱柱上,以甲醇-5 mmol乙酸铵缓冲溶液(70/30,V/V)为流动相,采用电喷雾质谱检测器,选择离子监测模式,以m/z308为定量检测离子,戊唑醇保留时间在9.5 min左右,在0.005~2 mg/L范围内浓度与峰面积呈良好的线性关系,相关系数为0.9999。在4种样本中添加不同浓度戊唑醇其平均回收率在73.6%~105.8%,相对标准偏差(n=5)小于15%,检出限(S/N=5)为2.5×10-11g。该方法简单、快速、灵敏、准确。