Radial Variation in Sap Flux Density as a Function of Sapwood Thickness in Two Eucalyptus ( Eucalyptus urophylla ) Plantations

Radial variation in sap flux density (SFD) as a function of sapwood thickness is of importance in accurately estimating sap flux through sapwood area which, in turn, decides the precision of heat pulse application. However, until now, only a few studies have evaluated the magnitude and significance of sampling errors associated with radial gradients in SFD, which were based on the small monitoring measurement data from a few trees. Based on one year of heat pulse observation of two 3 - 4 years old Eucalyptus urophylla S. T.,P Blake plantations in Leizhou Peninsula, Guangdong Province, China, a way of data processing was developed to treat with the lots of SFD data measured from 39 trees. It was found that the radial variation in SFD as a function of sapwood thickness in the two eucalyptus plantation sites could be expressed as y = 3. 667 5x(3) - 7.295 5x(2) + 3.682 6x + 0. 567 4 (R-2 = 0. 939 1, n = 80, P = 0.01), where y is the ratio of SFD of a sensor to the average of four data in different depths, x is the ratio of a sensor depth to tire radial sapwood thickness. It was the same (as in the following equation) in Jijia site, y = 5.006 2x(3) - 9.116 1x(2) + 4. 454 4x + 0.463 4 (R-2 = 0. 806 9, n = 72, P = 0.01) in Hetou site. From cambium to heartwood, SFD showed some increases at first and then decreases continuously. However, because die trees were very young, the maximum SFD was only 0. 33 - 0. 36 times more than the minimum.

Variation in photosynthetic photon flux density within a tropical seasonal rain forest of Xishuangbanna, south-western China

The effects of canopy development, solar angle, and weather conditions on temporal variation in photosynthetic photon flux density（PPFD） at three heights within a tropical rain forest canopy in Xishuangbanna, China, were examined. PPFD was measured every second and stored as 10-min averages from 1 December 2002 to 30 November 2003. PPFD variability was examined at three different temporal scales. Specific days in March, September, and December with clear and overcast sky conditions were selected to separate the effects of leaf area index（LAI） and solar angle on diurnal variability. On both clear and overcast days, mean daily average PPFD was significantly different between March and September at all heights, except 10 m on clear days, suggesting that LAI directly influences PPFD. In contrast, the differences in daily average PPFD among three heights between September and December were likely due to variation in solar angle. In addition, daily average PPFD at all locations were significantly lower under overcast than clear sky conditions in March, September and December. Over the year-long study, the mean daily total PPFD at 2! m, 10 m and 4 m was 2.8, 2.7 and 0.7 mol/（m^2·d）, which accounted for 9.7%, 9.4% and 2.4% of the daily PPFD above the canopy, respectively. Significant differences in mean daily total PPFD occurred at the same heights among different seasons, and diurnal, day-to-day and seasonal PPFD varied at different heights within the canopy. The possible effects of light variability on physiological and morphological responses of plants are discussed.

A Re-examination of Density Effects in Eddy Covariance Measurements of CO_2 Fluxes

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and perturbation of the density of dry air, leading to a number of approaches to correct density effects. In this study, we re-examine physical processes related to different assumptions that are made to formulate the density effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist air flux in the surface layer, used for treating density variations, and their implications for correcting density effects. It is found that physical processes in relation to the assumption of a zero dry air flux account for the influence of dry air expansion/compression on density variations. Meanwhile, physical processes in relation to the assumption of a zero moist air flux account for the influence of moist air expansion/compression on density variations. In this study, we also re-examine mixing ratio issues. Our results indicate that the assumption of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the assumption of a zero moist air flux favors the use of the mixing ratio relative to the total moist air. Additionally, we compare different formula for the mean vertical velocity, generated by air-parcel expansion/compression, and for density effect corrections using eddy covariance data measured over three boreal ecosystems.

Radial Non-uniformity Index Research on High-density,High-flux CFB Riser with Stratified Injection

A high-density, high-flux circulating fluidized bed （CFB） riser （100 mm in ID and 10.614 m in height） was ap- plied in a wide range of operating conditions （with solid fluxes up to 400 kg/m2s and superficial gas velocities up to 12 m/s） to examine its radial non-uniformity dynamics. The solids holdup was determined through the use of a fiber-optic probe at 11 axial levels. The results indicated that under all operating conditions, the high superficial gas velocity and low solid flux- es maintained a low radial non-uniformity index （RNI）. The high-density/flux CFB riser had several unique characteristics, so that the peak of the radial solids holdup profile occurred at a position with r/R=0.8. The RNI and solids holdup at the cross-sectional position had a good logarithmic relationship at the low-density condition （with a mean solids holdup of 〈0.2）, and the RNI decreased when the mean solids holdup exceeded 0.2. Investigation of the dynamics of stratified injec- tion revealed that the feed ratio had an important effect on G, and on solids holdup distribution. A novel ＂〈＂ shaped axial solids holdup profile was found. Gs decreased sharply when the up-flow feed ratio exceeded 0.5, and RNI was lowest when the up-flow feed ratio was 1.

Determining absolute value of thermal neutron flux density based on monocrystalline silicon in nuclear reactors

A new type of neutron detector based on monocrystalline Si is developed to measure the fluence and flux density of thermal and fast neutrons.The principle of this detector is based on the relationship between changes in electrical conductivity and neutron fluence during irradiation.Therefore,the absolute values of thermal neutron fluence and flux density are measured in a facile manner with high reliability.Compared with activation methods,our method not only possesses a similar accuracy,but also demonstrates superior application potential for the investigation of neutron fields in nuclear reactors owing to its suitable half-life.

Density Perturbation and Energy Flux of Internal Waves from Velocity Data

Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology for calculating density perturbation and energy flux of internal waves only using a velocity field that is based on linearized equations for internal waves. The method was tested by numerical simulations of internal waves generated by tidal flowing over a Gaussian topography in a stratified fluid. The density perturbations and energy fluxes determined using our method that only used velocity data agreed with density perturbations and energy fluxes determined by the equation of state based on temperature data. The mean relative error(MRE) and root mean square error(RMSE) between the two methods were lower than 5% and 10% respectively. In addition, an experiment was performed to exam our method using the velocity field measured by Particle Image Velocimetry(PIV), and the setup of the experiment is consistent with the numerical model. The results of the experiments calculated by the methods using PIV data were also generally equal to those of the numerical model.

DEVELOPMENT OF THE CONTROL METHODOLOGY OF THE GIANT MAGNETOSTRICTIVE ACTUATOR BASED ON MAGNETIC FLUX DENSITY

According to the principle of the magnetostriction generating mechanism, thecontrol model of giant magnetostriction material based on magnetic field and the control method withmagnetic flux density are developed. Furthermore, this control method is used to develop a giantmagnetostrictive micro-displacement actuator (GMA) and its driving system. Two control methods whosecontrol variables are current intensity and magnetic flux density are compared with each other byexperimental studies. Finally, effective methods on improving the linearity and control precision ofmicro-displacement actuator and reducing the hysteresis based on the controlling magnetic fluxdensity are obtained.

Distribution of Magnetic Flux Density in Soft-Contact EMCC Rectangular Mold

The distribution of the magnetic flux density in a soft-contact electromagnetic continuous casting （EMCC） rectangular mold was investigated. The experimental results show that with an increase in electric power, the magnetic flux density increases. The position where the maximum magnetic flux density appears will shift up when the coil moves to the top of the mold. At the same time, the maximum magnetic flux density will increase and the effective acting range of electromagnetic pressure will widen. As a result, in practice, the coil should be placed near the top part of the mold. The meniscus should be controlled near the top part of the coil, as this not only remarkably improves the billet surface quality but also saves energy. With the same electric power input, the higher the frequency, the lower the magnetic flux density.

Effect of Distribution of Magnetic Flux Density on Purifying Liquid Metal by Travelling Magnetic Field

The distribution of the magnetic flux density in the magnetic field generator which provided travelling magnetic field was determined. The experiments using liquid gallium and aluminum silicon alloy to observe the turbulent flow or remove inclusions were performed to obtain the basic principles how the distribution of the magnetic flux density took effect on removing inclusions from molten metal by electromagnetic field. The suitable area in the field for purifying metal was suggested.

Reconstruction of conductivity distribution of brain tissue from two components magnetic flux density

In this paper the recent Magnetic resonance electrical impedance imaging (MREIT) technique is used to image non-invasively the three-dimensional continuous conductivity distribution of the head tissues. With the feasibility of the human head being rotated twice in the magnetic resonance imaging (MRI) system, a continuous conductivity reconstruction MREIT algorithm based on two components of the measured magnetic flux density is introduced. The reconstructed conductivity image could be obtained through solving iter- atively a non-linear matrix equation. According to the present algorithm of using two magnetic flux den- sity components, numerical simulations were per- formed on a concentric three-sphere and realistic human head model (consisting of the scalp, skull and brain) with the uniform and non-uniform isotropic target conductivity distributions. Based on the algorithm, the reconstruction of scalp and brain conductivity ratios could be figured out even under the condition that only one current is injected into the brain. The present results show that the three-dimensional continuous conductivity reconstruction method with two magnetic flux density components for the realistic head could get better results than the method with only one magnetic flux density component. Given the skull conductivity ratio, the relative errors of scalp and brain conductivity values were reduced to less than 1% with the uniform conductivity distribution and less than 6.5% with the non-uniform distribution for different noise levels. Furthermore, the algorithm also shows fast convergence and improved robustness against noise.

High Efficiency LSM with High Flux Density for Transportation

A new linear synchronous motor (LSM) with permanent magnet (PM) is proposed to develop a linear motor for transportation with high efficiency. The LSM has very high air-gap flux density beyond the remanent magnetization of rare earth PM, which is generated by a special field structure with rare earth PM. Two PMs are arranged to form a triangle over each pole to concentrate the flux of PMs. The maximum value of air-gap flux density is limited to the magnetic saturated value in the core of field and armature, respectively, which is about 2T. The configuration is insusceptible to armature reaction because of large equivalent magnetic resistance in the flux path. The characteristics are analyzed using a two-dimensional finite element method (FEM) considering the core material. For high air-gap flux density and small armature reaction, the very high thrust density beyond the conventional maximum value of 100kN/m2 can be obtained. Using normal thrust density with small magneto-motive force (mmf) of armature, this LSM has efficiency and power factor that are as high as or higher than a rotational motor.

The Effect of Photon Flux Density and Lighting Period on Growth,Flowering,Powdery Mildew and Water Relations of Miniature Roses

Miniature roses (Rosa sp.) were grown at 100 and 150 μmol m-2·s-1 photon flux densities (PFD) with 16, 20 and 24 h·day-1 lighting periods (LP) in a greenhouse compartment in midwinter at latitude 59° north. The study included 10 different treatments and six rose cultivars, altogether 900 plants. The 16 and 20 h LP were applied with or without a dark period of 8 and 4 h·day-1, respectively, by timing the LP in relation to daylight that lasted for 7 - 8 h. Number of days until flowering decreased with an increase in PFD and in LP up to 24 day-1 and was unaffected by the timing of the 16 and 20 h·day-1 LP. Number of flowers and plant dry weight increased 20% to 30% by increasing the PFD. Plant dry weight increased by increasing the LP from 16 to 20 h·day-1 (about 25%), but no effect was found with a further increase to 24 h·day-1. Mean growth rate until flowering increased 30% to 40% by increasing the PFD or by increasing the LP from 16 to 20 h day-1, while little effect was found by a further increase to 24 h·day-1. Increasing the photosynthetic active radiation (PAR) by increasing the LP from 16 to 20 h·day-1 increased the growth rate more than increasing the PFD did. Three of the cultivars were tested for water loss after the detachment of some leaves. Leaves that had developed without a dark period showed a considerably higher water loss than the treatments that included a dark period of 4 or 8 h·day-1. The keeping quality at indoor conditions, however, was unaffected by the treatment due to sufficient watering. Powdery mildew developed significantly more on plants grown with a dark period of 8 h as compared with the other treatments. It was concluded that 20 h·day-1 LP including a dark period of 4 h·day-1 and a PFD of at least 150 μmol·m-2·s-1 should be applied to miniature roses during the winter months in order to effectively produce miniature pot roses with a high quality.

The Effect of IMF-Bz and F10.7 Solar Flux on Neutral Molecule Density of Ionospheric E-Region

In this study, the relationship between the neutral components （N2 and 02） in the E-region of the ionosphere （at 110 km altitude） for the Singapore （01.23 N; 103.55 E） station in the equatorial region and the FI0.7 solar flux and z-component of Interplanetary Magnetic Field （IMF-Bz） was investigated. This relationship was determined by means of statistical multiple regression model. As a result, it was observed that the changes in F10.7 solar flux and IMF-Bz were inversely proportional to the changes in N2 and 02. 92% and 83% of changes in N2 and O2 were found to be explained by F10.7 solar flux and IMF-Bz, respectively. When the F10.7 solar flux is changed by 1 s.f.u., it causes a decrease of 2.61×10TM m-3 in N2 and 2.96×1014 m-3 in O2. Change of I nT in IMF-Bz causes a decrease of 9.95× 1015 m-3 in N2 and 1.69× 1015 m-3 in O2.

Optimization of Power Density for Axial-Flux Machinethrough Generalized Sizing Equations

With the cvolution of various high powerr-density machines, it beeomes important to optimize the power potential of machines of vastly different topologies with a variety of waveforms of back emf and current. The approach of tins paper is based oil the gencral-purpose sizing equations. which permit the optinlization method of machine power density to be applied to the axial-flux toroidal permanent-magnet (AFTPM) machine, and,furthermore, the power-production capabilities of the AFTPM machinc and the wen-known squirrel-cage indution machine are compared.

基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断研究

该文提出一种基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断方法。首先,建立电机的d轴等效磁路模型,分析均匀退磁故障后径向气隙磁密的变化规律;然后,获取电机的径向气隙磁密和定子电流信号,对各极下径向气隙磁密幅值进行归一化处理,并绘制雷达图,根据雷达图和比较相同定子电流幅值下健康电机和故障电机的各极下径向气隙磁密幅值的平均值,来诊断均匀退磁故障;利用空载各极下径向气隙磁密幅值的平均值计算故障程度。最后,仿真和实验结果均验证所提均匀退磁故障诊断方法的有效性。

双频DC-DC变换器的磁集成技术

双频Buck变换器由两个降压单元级联构成,具有动态响应快,开关损耗小等优势。然而不足的是磁件占据了整个系统的大部分体积与重量,降低了系统的功率密度。针对这一问题,提出一种三段式绕制磁集成技术,将磁件以解耦的方式集成在一副磁心中。该文首先建立集成磁件的磁路等效模型,通过抵消各绕组之间的耦合作用推导出解耦条件,并详细阐述了磁心的选取、匝数以及气隙的设计原则。其次,利用有限元仿真平台对所提集成磁件进行建模分析,与现有的集成方法相比,磁通密度分布更为均匀,磁心的利用率得到了有效提升。最后,搭建一台48 V/12 V、108 W的实验样机,体积和重量同分离磁件相比降低了31.2%和25.3%,提高了系统的功率密度,验证了该集成方法理论分析的正确性和可行性。

高海拔地区铁路隧道施工期围岩热流密度数值模拟

冷负荷预测是隧道施工的重要任务,目前传统隧道冷负荷预测方法无法满足高海拔铁路隧道施工环境。为高海拔铁路隧道的冷负荷预测提供准确方法,建立一个热湿耦合多孔介质模型,考虑围岩孔隙率和低压环境对隧道围岩热流密度的影响。建立高海拔铁路隧道围岩热流密度预测模型,分析渗流水和衬砌的存在对围岩热流密度的影响,对比不同环境参数对围岩热流密度的影响。结果表明,隧道的冷负荷取决于围岩的热流密度。预测模型可以准确计算隧道围岩热流密度,其均方根误差为0.573 W/m^(2)。围岩渗流水和衬砌对隧道热湿环境产生显著影响。压力对围岩热流密度的影响最小。围岩温度每升高10℃时,围岩初始热流密度增加了58.74 W/m^(2)。此外,每当隧道目标温度增加4℃或孔隙率增加0.1,分别导致围岩初始热流密度减少了23.5、0.14 W/m^(2)。研究结果可以为实际高海拔铁路隧道工程的冷负荷预测提供新的理论方法和参考依据。

气隙偏心对同步发电机定子绕组温升特性的影响

为了分析同步发电机气隙偏心对定子绕组的铜耗及温升的影响规律。首先理论推导了正常情况和偏心下的磁通密度及相应的铜耗,分析了绕组的温升特性;然后建立了CS-5型故障模拟发电机的三维有限元模型,计算得到了发电机在不同负载和不同故障程度下定子绕组的铜耗和温度变化规律;最后在CS-5型故障模拟发电机上对定子绕组温度进行了实测,所得实验结果和仿真数据与理论分析结论基本一致。研究发现:定子绕组直线段温度高于端部温度;定子绕组的铜耗和温度在气隙偏心工况下均高于正常情况,且随着偏心量和负载的增加呈现升高趋势;在静偏心下靠近小气隙一侧的绕组温度高于其他部位。

基于气隙磁密差信号峭度因子的永磁同步电机局部退磁故障诊断

该文提出一种新型基于气隙磁密信号差峭度因子的永磁同步电机局部退磁故障诊断方法。首先,建立永磁同步电机等效磁路模型,根据简化模型分析局部退磁故障后各极主磁路下径向气隙磁密的变化规律。然后,将预存健康电机空载状态下气隙磁密信号与测量的在线状态下气隙磁密信号作差并计算其峭度值,作为故障特征值。取健康电机空载状态下气隙磁密信号与不同工况下气隙磁密信号差峭度值的最大值作为参考值,根据故障特征值与参考值的大小诊断出局部退磁。最后,仿真和实验结果均验证提出的局部退磁故障诊断方法的有效性。

流体黏性对盐指型双扩散对流扩散通量影响的试验研究

为研究盐指型双扩散对流过程中流体黏性对通量的影响,使用中间有移动挡板的试验水箱形成初始为静止状态的糖-盐双层系统,并通过调整糖、盐组分质量分数设计了一系列密度稳定比相同而流体黏性不同的试验工况,进行了双扩散对流扩散通量变化规律的试验研究。试验结果表明:流体黏性对盐指型双扩散对流扩散通量的影响不可忽略,在双扩散对流强度相同的条件下,试验流体黏性越大,盐指型双扩散对流扩散通量越小;当试验流体的运动黏滞系数均小于1.15 mm2/s时,糖和盐这两种组分跨界面的双扩散对流扩散通量随流体黏性增大而减小的趋势相近,当两种组分的质量分数持续增大时,盐溶液的黏性仍缓慢增大,而糖溶液的黏性迅速变大,此时糖组分的跨界面双扩散对流扩散通量仍会随糖溶液黏性的增大而减小,但盐组分的跨界面双扩散对流扩散通量不再变化;Stern数与流体黏性呈负相关关系。