Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere

Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, where tree growth is often limited by nutrient supply, in particular nitrogen. Here we present evidence that estimates of increases in carbon sequestration of forests, which is expected to partially compensate for increasing CO2 in the atmosphere, are unduly optimistic. In two forest experiments on maturing pines exposed to elevated atmospheric CO2, the CO2-induced biomass carbon increment without added nutrients was undetectable at a nutritionally poor site, and the stimulation at a nutritionally moderate site was transient, stabilizing at a marginal gain after three years. However, a large synergistic gain from higher CO2 and nutrients was detected with nutrients added. This gain was even larger at the poor site (threefold higher than the expected additive effect) than at the moderate site (twofold higher). Thus, fertility can restrain the response of wood carbon sequestration to increased atmospheric CO2. Assessment of future carbon sequestration should consider the limitations imposed by soil fertility, as well as interactions with nitrogen deposition.     

Removal of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> by radical injection

Removal of NOx(DeNOx, NOx is the total of NO and NO2) from flue gas by radical injection has been investigated .the discharge characteristics were examined and the steady streamer corona was acquired hy adjusting the nozzle gases properly. It was Found that an increase in the voltage resulted in a decrease in the NO concentration and the concentration of the NO2 increased at tow voltages but decreased as the voltage rose to a certain level. The DeNOx efficiency increased as the applied voltage rose and reached a maximum of 70% when the voltage approached the breakdown voltage. The hypothetical mechanism of NOx removal suggested that the radicals formed in the discharge process converted the NO and NO2 into acidic species. The Monte Carlo method was used to calculate the rate coefficients and the productivity of the radicals, and then the concentrations of both NO and NO2 and the DeNOx effielencies were calculated with chemical kinetics. The calculated DeNOx efficiencies were coalparable with the experimental DeNOx efficiencies at low voltages, but were lower at high voltages.     

自供式伺服变量泵节能液压系统的研究

在一套大型结构加载系统的节能改造中，采用一种新型的无须外加辅助油源的自供式伺服变量泵节能控制系统，并针对容积式控制方式中存在的问题，采用非线性变增益补偿法改善系统动态性能．实践表明，该系统具有良好的降低能耗、减少温升的作用；动态补偿方法效果显著     

射孔套管剩余抗挤能力分析

套管射孔后其抗挤能力将有所降低。建立了射孔段套管弹性抗挤性能分析控制的一般方程 ,并利用摄动理论给出了射孔套管弹性抗挤能力系数的一般计算公式。利用弹塑性有限元方法确定了孔口附近塑性区随射孔套管的外压增加的变化规律 ,并给出了确定射孔套管抗挤能力的计算方法。研究结果表明 ,孔眼附近的应力集中所引起的塑性区的存在 ,明显影响了射孔套管的抗挤强度。与弹性分析结果比较 ,弹塑性分析结果更接近实验值。孔眼的形状对射孔套管抗挤能力有直接影响。长轴在环向的椭圆形孔眼的套管抗挤能力降低得最少 ,方形孔眼的降低得最多。在孔眼形状相同的情况下 ,孔眼面积增大 ,射孔套管的抗挤能力降低。当射孔密度小于 2 0孔 /m时 ,无论采用何种布孔方式 ,除方形孔眼外 ,套管抗挤能力的降低均不会超过 4 % ;大于 2 0孔 /m时 ,射孔参数对套管抗挤能力的影响明显增加     

SiO_2含量对损耗型CoFeB-SiO_2颗粒膜电磁性能的影响

研究一种可应用于抗电磁干扰和微波吸收的磁性纳米颗粒膜,选用FeCoB作为磁性合金,SiO2为电介质材料,采用磁控溅射工艺制备纳米颗粒膜.重点研究电介质SiO2体积分数对颗粒膜微结构以及电磁性能的影响规律和作用机理.结果表明,适当的电介质体积分数可使颗粒膜保持微波高磁导率和高磁损耗并有效降低介电常数,2 GHz时,复磁导率的实部μ′=31,虚部μ″=45,复介电常数实部ε′=671,虚部ε″=593.     

Size-dependent optical properties of Au nanorods

In the fast evolving field of nanoscience and nanotechnology,where size and shape are crucial in deciding the optoelectronic properties of nanomaterials,the understanding of size and shape dependent behavior is of direct relevance to device applications.Present study reports the synthesis of Au nanorods with well controlled aspect ratios,and the influence of the aspect ratio on the surface enhanced Raman scattering(SERS) activity using crystal violet(CV) as the probe molecule.The influence of pH and the concentrations of reducing agent and Ag ions in controlling the aspect ratio of gold nanorods are also investigated.The structural and optical properties of the synthesized samples have been characterized by transmission electron microscopy(TEM) and UV-visible absorption spectroscopy.The nonlinear optical(NLO) transmission of the Au nanorods investigated using the open aperture Z-scan technique revealed the absorption saturation followed by an optical limiting behavior,which may find potential applications in optoelectronic nanodevices.     

基于嵌入式操作系统的应用软件设计

介绍了如何在嵌入式的实时多任务操作系统上设计应用软件，给出了实现多任务操作的具体步骤，并用该方法进行了热敏打印机应用软件的设计，从而提高了应用软件的实时性，增强了其可移植性，缩短了软件开发周期。     

大型轧机主传动系统在线监测研究

介绍了一套用于大型轧机主传动的在线监测系统，该系统对扭矩采用间接监测法，既达到了监测扭矩的目的，又避开了轧机恶劣的工作环境，其中的剩余寿命预测有助于实现基于状态的预测性维修，这对保证轧机运行的安全性和可靠性，避免灾难性事故发生，减少停机损失，具有指导作用。     

Sub-laser-cycle electron pulses for probing molecular dynamics

Experience shows that the ability to make measurements in any new time regime opens new areas of science. Currently, experimental probes for the attosecond time regime (10(-18) 10(-15) s) are being established. The leading approach is the generation of attosecond optical pulses by ionizing atoms with intense laser pulses. This nonlinear process leads to the production of high harmonics during collisions between electrons and the ionized atoms. The underlying mechanism implies control of energetic electrons with attosecond precision. We propose that the electrons themselves can be exploited for ultrafast measurements. We use a 'molecular clock', based on a vibrational wave packet in H(2)(+) to show that distinct bunches of electrons appear during electron ion collisions with high current densities, and durations of about 1 femtosecond (10(-15) s). Furthermore, we use the molecular clock to study the dynamics of non-sequential double ionization.     

汶川震区地震动三维地形效应的谱元法模拟

针对三维波动弹性动力方程推导了谱元法算法,并考虑三维真实地形及介质的衰减特性,基于并行计算环境采用谱元法和ASTER DEM模型对5.12汶川地震动的地形效应进行了模拟.模拟结果表明陡峻地形对地震波两个水平分量的影响要大于对竖向分量的.震中附近区域的PGA最大值为671 cm/s2,高PGA区多分布于山顶及山脊区域.与...