荒漠公益林中典型灌木树种光谱特征研究

应用地面高光谱仪测定古尔班通古特沙漠中梭梭和柽柳的冠层光谱,结合遥感影像分析比较了两种灌木树种的光谱响应曲线差异。结果表明:不论是沙土还是盐碱土,柽柳在近红外波段内反射率均高于梭梭,并根据这一规律性总结出了基于光谱特征的梭梭和柽柳的识别模型,最后对不同树种的光谱响应机制进行了探讨。     

垂直轴风力机塔柱结构的分析及优化

为了避免风力机系统的共振而导致的系统损坏和噪声污染,通过系统动力特性分析和动力学响应计算分析,得到了风力机塔柱的低阶固有频率和谐响应的数据,以及风轮和塔柱之间的动态关系与整个系统的动态特性,为结构动态设计以及优化提供科学依据.首先确定对风力机塔柱系统结构动态性能影响最大的模态频率,提取该阶模态频率作为动态优化的目标,最后分析塔柱结构与风轮之间的动态干扰.结果表明：原设计在风轮以设计额定转速160 r/min运行时,其产生的简谐荷载对风力机塔柱具有十分严重的破坏性,通过增加主轴钢管的壁厚并提高其刚度等优化工作,经计算证明,在激振力不变的情况下,第一阶固有频率得到提高,塔柱的各阶固有频率下的最大位移大幅减小,优化效果明显,达到结构动力设计的目的.     

Effects of arbuscular mycorrhizal fungi on zinc uptake, translocation and accumulation in winter wheat during whole plant growth stages

Although arbuscular mycorrhizal fungi (AMF) could play important roles in zinc (Zn) uptake in host plants, the effects of AMF on Zn uptake and transport in winter wheat during the whole growth stages remain unclear. A pot experiment was conducted to investigate the effects of Funneliformis mosseae (Fm) and Claroideoglomus etunicatum (Ce) on Zn absorption, transport, and accumulation in winter wheat growing in soils spiked with different Zn levels (0, 2.5, and 25 mg kg^-1). The results showed that there was a significant correlation between mycorrhizal colonization rate and Zn absorption efficiency in winter wheat roots during the post-anthesis period, but there was no significant correlation during the pre-anthesis period. Arbuscular mycorrhizal fungi significantly increased Zn concentrations (0.56-1.58 times) in wheat grains under 0 mg kg^-1 Zn level, but decreased Zn concentrations in wheat grains under 25 mg kg^-1 Zn level. Additionally, at the filling and maturity stages, AMF increased Zn absorption rate and the contribution of root Zn uptake to grain Zn by 3-14 and 0.36-0.64 times, respectively, under 0 mg kg^-1 Zn level and 0.21-1.02 and 0.27-0.37 times, respectively, under 2.5 mg kg^-1 Zn level. However, AMF decreased root Zn absorption rate (0.32-0.61 times) and increased the contribution of Zn remobilization in vegetative tissues to grain Zn (1.69-2.01 times) under 25 mg kg^-1 Zn level. This study would complement the mechanisms and effects of AMF on Zn absorption and transport in winter wheat and provide a potential method for the application of AMF to enrich wheat grain Zn.     

萃取蔗皮二十八烷醇工艺

以果蔗皮为试验原料,采用响应曲面分析法（RSM）优化超临界CO2萃取蔗皮二十八烷醇的工艺条件。在单因素试验的基础上,选取萃取压力、温度和时间为影响因子,应用Box-Behnken中心组合进行了3因素3水平的试验设计。验证了二次多项数学模型的有效性,并探讨了萃取压力、温度、时间对二十八烷醇萃取物产率的作用规律。统计分析表明压力、温度以及压力和时间的交互作用对二十八烷醇的提取量有显著影响。根据该模型进行了工艺参数的优选,试验所得二十八烷醇超临界CO2萃取的优化工艺条件为：压力31．2MPa,温度44．8℃,时间226．17min,该条件下提取量高达7．5855mg／g。     

Forest stand dynamics and sudden oak death: Mortality in mixed-evergreen forests dominated by coast live oak

Sudden oak death (SOD), caused by the recently discovered non-native invasive pathogen, Phytophthora ramorum, has already killed tens of thousands of native coast live oak and tanoak trees in California. Little is known of potential short and long term impacts of this novel plant–pathogen interaction on forest structure and composition. Coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica) form mixed-evergreen forests along the northern California coast. This study measured tree mortality over a gradient of disease in three time periods. Direct measurements of current mortality were taken during 2004, representing a point-in-time estimate of present and ongoing mortality. Past stand conditions, c. 1994, were estimated using a stand reconstruction technique. Future stand conditions, c. 2014, were calculated by assuming that, given a lack of host resistance, live trees showing signs of the disease in 2004 would die. Results indicate that coast live oaks died at a rate of 4.4–5.5% year⁻¹ between 1994 and 2004 in highly impacted sites, compared with a background rate of 0.49% year⁻¹, a ten-fold increase in mortality. From 2004 to 2014, mortality rates in the same sites were 0.8–2.6% year⁻¹. Over the entire period, in highly impacted sites, a 59–70% loss of coast live oak basal area was predicted, and coast live oak decreased from 60% to 40% of total stand basal area, while bay laurel increased from 22% to 37%. Future stand structures will likely have greater proportions of bay laurel relative to coast live oak.     

云南松与华山松人工混交林针叶光合速率对光及CO2浓度的响应特征

采用Licor-6400型便携式光合作用测定系统测定了人工混交林中云南松、华山松光合作用对光、CO2浓度的响应曲线,阐述了云南松、华山松光合作用对光和CO2浓度的响应特征.结果表明:云南松、华山松光合速率随光强或CO2浓度的提高而增大,均可用非直角双曲线拟合,并得出一些光合响应特征参数,两树种间差异显著(P＜0.05);云南松、华山松具有较高的光饱和点(LSP)和补偿点(LCP),表现为典型的喜阳性特点,具有较强的光能利用能力.在CO2饱和下,云南松、华山松最大净光合速率(Pmax)分别可达14.768、10.289 μmol·m-2·s-1,与光饱和下相比,最大净光合速率(Pmax)分别提高了56.9%和62.0%.与华山松及几个北方针叶树相比,云南松具有较高的光饱和点、最大净光合速率、RuBP羧化效率(CE)、光呼吸速率(却)、CO2饱和点(CSP),以及较低的暗呼吸速率(Rd)、光补偿点、CO2补偿点(CCP),云南松具有高光效和高CO2利用率等光合特性,属于高光能生产潜力的针叶树种.     

Routing protocol of the wireless sensor networks for bridge health monitoring

By analyzing the reason that why the existing routing protocols cannot be applied to the wireless sensor networks for bridge health monitoring, a new routing protocol is proposed. Since the locations of the collecting modules are fixed, the proposed protocol exchanges the routing information between the neighbor nodes by adjusting the exchange cycle according to reliability of the modules. For the low routing security requirement, while to increase the routing efficient, the middle nodes replying the routing requirements with variable thresholds is introduced. In order to make full use of information in route discovering procedure, the backup routes mechanism is adopted. The proposed protocol can efficiently forward data and is suitable for the bridge health monitoring.     

Analysis of the distorted scaling factor in wind tunnel modeling of power transmission line system

Because of the limitation of the model making and the existing wind tunnel’s size, it is difficult to keep the line and tower in the same scaling factor in developing the aeroelastic model of the power transmission lines system, and a distorted scaling factor is needed in span length of the lines. With the instance of a 1 000 kV two circuit power transmission lines, the finite element analysis under the along wind load in time history is conducted with keeping the tower in the same and the line scaling factor being 1, 0.5 and 0.25 respectively. The results show that the response of the power transmission lines systems keep in the same, and then the wind induced vibration of the distorted model in the wind tunnel test can actually reflect the response of the power transmission lines system under the wind load.     

Dynamic analysis and optimization of gear trains in a megawatt level wind turbine

Through coupling vibration analysis of the transmission system of a 1.5 MW wind turbine gearbox, a torsional vibration model of a gear drive system in wind turbines is established. The fourth order Runge Kutta integration method is applied to calculate the dynamic response of a gear system caused by wind loads, time varying meshing stiffness, and system damping. The harmonic balance method is used to find the analytic solution. Based on the solution, a mathematical model for optimum gear system design is established. The model aims at minimizing the vibration acceleration of the planet gear and the total mass of the gear transmission system. The optimization toolbox in MATLAB program is adopted to obtain the optimal solution. A calculated example shows that the primary natural frequency of the gear system has been raised, the dynamic properties of the gear train have been improved remarkably, and the total mass of the gear train has been decreased.     

响应面法优化超声波提取核桃油工艺的研究

应用超声波法辅助浸提核桃油,在单因素实验的基础上,通过Box-Benhnken中心组合实验,确定超声波辅助提取核桃油的最佳工艺条件为:正己烷作提取溶剂,液料比为7(mL∶g),提取温度53℃,超声时间48 min,超声波功率120 W,核桃油提取率达到61.91%。