Modelling of mode-I stable crack growth under hydrogen assisted stress corrosion cracking

The paper presents a new strategy based on combined analytical and finite element (FE) solution to hydrogen assisted stress corrosion crack growth. The diffusion process is solved analytically through both one-and two-dimensional modelling. These solutions are adopted with two-dimensional FE based cohesive zone model of crack extension study. The results fit well with published experimental data and show improvement over the predictions by full FE approach. The new solution approach helps to reduce time required for simulation/computation. The study has produced a relationship between concentration dependent reduction in cohesive strength and plastic strain rate.     

Pooled versus separate measurements of tree-ring stable isotopes

δ¹³C and δ¹⁸O of tree rings contain time integrated information about the environmental conditions weighted by seasonal growth dynamics and are well established as sources of palaeoclimatic and ecophysiological data. Annually resolved isotope chronologies are frequently produced by pooling dated growth rings from several trees prior to the isotopic analyses. This procedure has the advantage of saving time and resources, but precludes from defining the isotopic error or statistical uncertainty related to the inter-tree variability. Up to now only a few studies have compared isotope series from pooled tree rings with isotopic measurements from individual trees. We tested whether or not the δ¹³C and the δ¹⁸O chronologies derived from pooled and from individual tree rings display significant differences at two locations from the Iberian Peninsula to assess advantages and constraints of both methodologies. The comparisons along the period 1900-2003 reveal a good agreement between pooled chronologies and the two mean master series which were created by averaging raw individual values (Mean) or by generating a mass calibrated mean (MassC). In most of the cases, pooled chronologies show high synchronicity with averaged individual samples at interannual scale but some differences also show up especially when comparing δ¹⁸O decadal to multi-decadal variations. Moreover, differences in the first order autocorrelation among individuals may be obscured by pooling strategies. The lack of replication of pooled chronologies prevents detection of a bias due to a higher mass contribution of one sample but uncertainties associated with the analytical process itself, as sample inhomogeneity, seems to account for the observed differences.     

Comparison of plume rise models against water tank experimental data for neutral and stable crossflows

The evaluation of the trajectories of plumes rising into a crossflow is relevant for the correct modelling of pollutant dispersal in the atmosphere. Plume rise models are therefore an important part of several dispersion models. There is a general consensus on the formulation of plume rise through solution of equations describing the conservation of energy and momentum in the plume closed with an empirical formulation of the entrainment rate of fresh air into the developing plume. However, there are differences in the entrainment coefficients found in different studies. In this work the trajectories of sixty plumes, simulated at small scale in a towing water tank, have been analysed in order to test the performance of widely used dispersion codes and to find statistically the best entrainment coefficients for the different models. The plumes simulated cover a wide range of scenarios from pure jets to buoyant plumes developing in both neutral and linearly stable stratified crossflows. A new analytical model for stable crossflows, representing an extension of an existing model, has been presented and tested. Results show that the entrainment coefficients are different for neutral and stable crossflows, especially for approximate analytical codes. In contrast, the coefficients of the integral model seem to be less sensitive to the stability of the crossflow. The entrainment coefficients found by the fitting of the analytical models are significantly lower than the measured spread rate of the plumes. In neutral crossflows the generalised Briggs model and the integral model give statistically similar performances. In stable crossflows the new analytical model as well as the integral model are able to predict the oscillation of the plumes around their equilibrium height; however, there is an underestimation of both the oscillation frequency and the downwind position of the maximum height. The use of an added mass coefficient allows, with almost the same entrainment coefficients, improved prediction of the oscillation frequency and of the maximum rise position. Measured plume height oscillations are more strongly damped than predicted ones.     

Flexible top-emitting warm-white organic light-emitting diodes with highly luminous performances and extremely stable chromaticity

The flexible top-emitting white organic light-emitting diode (FTEWOLED) with a very high efficiency but a significant color alteration is achieved with a blue/red/blue sandwiched tri-emission-layer. The voltage-dependent recombination region alternation and the emission mechanism are systematically investigated through a delta-doping method and the time-resolved transient photoluminescence lifetime measurement. By locating the main exciton recombination region at the 4,4′,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) and 9,9-spirobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1) interface, replacing the carrier-trapping red dopant guest with an orange guest that utilizes energy transfer mechanism, and using a P–I–N structure together with the FIrpic blue guest dopant to balance the electron and hole carriers, an extremely color stable and a very high efficient FTEWOLED is fabricated, with the resulting high current and power efficiencies of 22.7 cd/A and 14.27 lm/W, and a warm white illumination with a small chromaticity variation of (−0.0087, +0.0015) over a broad luminance range of more than four orders of magnitude. In addition, the performances can be further improved to 23,340 cd/m², 24.49 cd/A and 15.39 lm/W with a slight concentration alteration of the orange emitter.     

一种基于节点状态预测机制的高稳定性路由设计

该文旨在为拓扑动态变化的无线自组织网络设计一种稳定性路由机制。首先建模分析了动态变化网络中节点间通信路径存在的条件,以及数据包在该路径上可靠传输的条件,基于以上分析提出了保证路径有效的关键指标：链路持续时间、拥塞可能性因子。接下来提出基于节点当前运动情况计算链路持续时间,以及基于缓冲区队列长度与队列长度变化率计算节点拥塞可能性因子的算法。结合链路持续时间与节点拥塞可能性等信息,该文提出了一种面向路径可靠性及稳定性综合指标的按需路由机制(ODRP-DR),并利用NS2仿真平台对该机制性能进行分析,仿真结果表明,在网络拓扑结构动态变化的情况下能有效减小数据包丢包概率,路由重建次数。     

RBFN输出层学习率的一种稳定算法

该文运用Lyapunov稳定性原理,针对RBF网络作为辨识器和控制器,分别推导出其输出权值学习率更新的稳定算法。然后以某转台位置跟踪系统为对象进行辨识器的仿真,结果显示辨识效果大大改善;对于作为控制器的情况,选用[4]中的仿真实例进行仿真验证,结果表明,该方法对控制性能有一定改进。     

无线移动网络节点发包概率的演化博弈模型

针对大规模无线移动网络中节点对信道资源的群体性随机博弈问题,在载波侦听多路访问/冲突避免(CSMA/CA)的机制下,建立一种节点发包概率的演化博弈模型。考虑节点成功发送数据包的收益、监听、退避和冲突等成本因素,给出并证明该模型的演化稳定策略(ESS),推导节点发包概率演化的复制动态方程。数值仿真结果表明,该模型能提供更强的ESS,保证在多个移动节点干扰时演化稳定点的鲁棒性。     

Subsoil <Superscript>15</Superscript>N-N<Subscript>2</Subscript>O Concentrations in a Sandy Soil Profile After Application of <Superscript>15</Superscript>N-fertilizer

Studies on emissions of nitrous oxide (N₂O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in the topsoil. However, in soils with shallow water tables, significant N₂O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N₂O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N₂O to the overall losses of N₂O to the environment. We applied ¹⁵N labeled fertilizer at a rate of 5.22 kg ¹⁵N ha⁻¹; 50% as Ca(NO₃)₂ and 50% as NH₄Cl, on a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.), and traced soil N₂O concentrations and fluxes over a one-year period. Throughout the year, total N₂O and the amount of ¹⁵N recovered in soil N₂O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m⁻³ and 24 μg ¹⁵N m⁻³, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of N₂O was 446 g N₂O-N ha⁻¹, the recovery of ¹⁵N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N₂O concentrations. During winter, no such relation was found. We concluded that the formation of N₂O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO₃⁻ concentration or temperature. Although high subsoil N₂O concentrations did not lead to high surface fluxes of N₂O in the winter, artificial draining may lead to high indirect N₂O emissions through supersaturated drainage water.     

Antibody-based computing: an application to the stable marriage problem

Antibodies, among other things, are important components of the immune system. This paper proposes using the specific recognition capability exhibited by antibodies for computation, in particular, for solving the stable marriage problem, which has been studied as a combinatorial computational problem. Antibody-based computation is proposed by integrating the recognition capabilities of antibodies. The computation is carried out on an array form that is suitable not only for expressing stable marriage problems, but also for further integration to antibody microarrays. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

RC—Y3／86型燃烧器熄火原因浅析

装置三合一炉选用RC-Y3/86型半预混式燃烧器,在2003年、2004年多次发生燃烧器熄火问题。从该燃烧器结构特点入手,分析RC-Y3/86型半预混式燃烧器熄火的原因,并提出一些解决方法。