The nonlinear heat release response of stratified lean-premixed flames to acoustic velocity oscillations

This paper analyzes the forced response of swirl-stabilized lean-premixed flames to high-amplitude acoustic forcing in a laboratory-scale stratified burner operated with CH4 and air at atmospheric pressure. The double-swirler, double-channel annular burner was specially designed to generate high-amplitude acoustic velocity oscillations and a radial equivalence ratio gradient at the inlet of the combustion chamber. Temporal oscillations of equivalence ratio along the axial direction are dissipated over a long distance, and therefore the effects of time-varying fuel/air ratio on the response are not considered in the present investigation. Simultaneous measurements of inlet velocity and heat release rate oscillations were made using a constant temperature anemometer and photomultiplier tubes with narrow-band OH*/CH* interference filters. Time-averaged and phase-synchronized CH* chemiluminescence intensities were measured using an intensified CCD camera. The measurements show that flame stabilization mechanisms vary depending on equivalence ratio gradients for a constant global equivalence ratio (φg=0.60). Under uniformly premixed conditions, an enveloped M-shaped flame is observed. In contrast, under stratified conditions, a dihedral V-flame and a toroidal detached flame develop in the outer stream and inner stream fuel enrichment cases, respectively. The modification of the stabilization mechanism has a significant impact on the nonlinear response of stratified flames to high-amplitude acoustic forcing (u'/U∼0.45 and f=60, 160Hz). Outer stream enrichment tends to improve the flame's stiffness with respect to incident acoustic/vortical disturbances, whereas inner stream stratification tends to enhance the nonlinear flame dynamics, as manifested by the complex interaction between the swirl flame and large-scale coherent vortices with different length scales and shedding points. It was found that the behavior of the measured flame describing functions (FDF), which depend on radial fuel stratification, are well correlated with previous measurements of the intensity of self-excited combustion instabilities in the stratified swirl burner. The results presented in this paper provide insight into the impact of nonuniform reactant stoichiometry on combustion instabilities, its effect on flame location and the interaction with unsteady flow structures. © 2011 The Combustion Institute.

Thermal-creep analysis of concrete bridges

The creep effects on sequentially built bridges are analysed by the theory of thermal creep. Two types of analysis are used: time dependent and steady state. The traditional uniform creep analysis is also introduced briefly. Both simplified and parabolic normalising creep-temperature functions are used in the analysis for comparison. Numerical examples are presented, calculated by a computer program based on the theory of thermal creep and using the displacement method. It is concluded that different assumptions within thermal creep can lead to very different results when compared with uniform creep analysis. The steady-state analysis of monolithically built structures can serve as a limit to evaluate total creep effects for both monolithically and sequentially built structures. The importance of the correct selection of the normalising creep-temperature function is demonstrated.

H5N2亚型禽流感病毒血凝素裂解位点碱性氨基酸对应mRNA核苷酸的二级结构分析

以H5N2亚型禽流感病毒毒株血凝素蛋白裂解位点碱性氨基酸为研究对象,对其密码子偏好性和对应mRNA序列的折叠二级结构特点进行研究和分析.旨在探讨裂解位点氨基酸对应mRNA核苷酸片段的二级结构与病毒致病力的关系,希望能对禽流感病毒的研究提供一些基础性信息.将mRNA样本按照序列等步长递增的方法,用RNAstructure 4.1程序预测这些样本的动态延伸折叠二级结构.序列和结构的分析结果:裂解位点的碱性氨基酸对富含腺嘌呤的密码子有强烈偏好;与碱性氨基酸对应的mRNA片段上的核苷酸主要位于折叠二级结构的单链环区,少数位于配对螺旋区.结果表明:裂解位点氨基酸对应的mRNA核苷酸形成发夹端环的大小与其碱性氨基酸的多少具有正相关性.

中国西南部三种湍蛙的核型与带型的比较研究

本文研究了中国西南部3种湍蛙的核型、C-带及Ag-NORs。就核型而言,除雄性棘皮湍蛙比较特殊,具有27条染色体外,3种湍蛙的核型基本形式都是2n=26（NF=52）,由5对大型染色体和8对小型染色体组成,与其他蛙科种类的核型相类似。但是染色体形态,如臂比值和次缢痕的位置和数目存在一定差异。C-带显示的结果表明,湍蛙类的染色体上结构异染色质区域比较多,尤其是居间区C-带比较多,这表明湍蛙类的核型是比较特化的。其中棘皮湍蛙的居间区和端部C-带最多。3种湍蛙的Ag-NORs都位于No.6的短臂上,与该染色体上的次缢痕位置相一致。比较3种之间的异同,认为棘皮湍蛙与金江湍蛙核型和带型的相似程度较大,而绿点湍蛙则比较特殊。 雄性棘皮湍蛙的二倍体染色体数是27, 即有一条染色体不能配对,经过对其形态、C-带等的研究,认为该染色体为性染色体,其相对长度介于No.6和No.7之间（RL=6.26）,臂比值为1.32（m）,C-带显示该染色体几乎完全异染色质化,表明该染色体为特化的Y染色体。在其余各对中未见异形现象。 金江湍蛙（A.jinjiansensis）被认为是凉山湍蛙（A.liangshanensis）的同物异名,...

湘鄂与闽粤猕猴颅骨的多变量分析

湘鄂与闽粤猕猴颅骨分析结果表明, 二者存在较大差异, 湖南-湖北种群的颅骨结构相对大于福建-广东 种群, 四者雌雄两性颅骨形态结构均有较大差异, 分属不同亚种。

Accelerated ageing of a stabilised/solidified contaminated soil at elevated temperatures

Despite the widespread use of stabilisation/solidification (S/S) techniques, the validation and the availability of predictive modelling of the behaviour of stabilised/solidified soils in the longer-term is very limited. The authors were involved in the assessment of the behaviour of a contaminated site in the UK treated with cement-based in-situ S/S over the first five years after treatment. In parallel, two experimental methods, namely elevated temperatures and combined elevated temperatures and accelerated carbonation, were used in the laboratory to model accelerated ageing of the site soil. A graphical technique, based on the Arrhenius equation, was then used to model the laboratory observations and the in-situ five-year behaviour. The paper presents the details of the two experimental methods used for the accelerated ageing of stabilised/solidified model site soil, the numerical predictive model and a comparison between the results of the two experimental techniques and with the site results. © 2005 Taylor & Francis Group.