Comparing Two Methods for Measuring Soil Bulk Density and Moisture Content

Soil bulk density and moisture content are dynamic properties that vary with changes in soil and field conditions and have many agricultural, hydrological and environmental implications. The main objective of this study was to compare between a soil core sampling method (core) and the CPN MC-3 EliteTM nuclear gauge method (radiation) for measuring bulk density (ρB) and volumetric moisture content (θv) in a clay loam soil. Soil ρB and θv measurements were determined using the core and radiation methods at 0 - 10 and 10 - 20 cm soil depths. The mean values of soil ρB obtained using the core method (1.454, 1.492 g·cm−3) were greater than those obtained using the radiation method (1.343, 1.476 g·cm−3) at the 0 - 10 and 10 - 20 cm depths, respectively. Mean ρB and θv values averaged across both depths (referred to as the 0 - 20 cm depth) measured by the core method were 4.47% and 22.74% greater, respectively, than those obtained by the radiation method. The coefficients of variation (CV) of soil ρB values measured by the core method were lower than the CV values of those measured by the radiation method at both depths;however, the CV’s of ρB values for both methods were larger at the 0 - 10 cm depth than those measured at the 10 - 20 cm depth. Similarly, the CV values of soil θv values measured by the core method were lower than the CV values of those measured by the radiation method at both depths. There were significant differences between two methods in terms of ρB and θv, with the core method generating greater values than the radiation method at the 0 - 20 cm depth. These discrepancies between the two methods could have resulted from soil compaction and soil disturbance caused by the core and radiation techniques, respectively, as well as by other sources of error. Nevertheless, the core sampling method is considered the most common one for measuring ρB for many agricultural, hydrological and environmental studies in most soils.

Bulk MgB2 superconductor with high critical current density synthesized by self-propagating high-temperature synthesis method

Pure MgB2 bulk samples are successfully synthesized by self-propagatlng hlgh-temperature synthesis （SHS） method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepared MgB2 reach 1.5×10^6A/cm^2 （10K, 0.5T） and 1.7×10^6A/cm^2 （20K, 0T）, and the MgB2 particle sizes range from 2 to 5μm. The advantages of this method are that it is simple, economical and suitable for the manufacture of bulk MgB2 materials on industrial scale.

Bulk Flow方法分析孔型密封转子动力特性的有效性

基于Kleynhans和Childs的两控制容积等温BF(Bulk Flow)模型,通过增加能量方程和理想气体状态方程,建立了理想气体BF方法的数学模型,来预测和分析孔型密封转子在偏心状态下的静力学和动力学特性.由于转子在密封中心附近做微小涡动,故可通过采用摄动方法使得NS方程的求解过程得到较大的简化,再通过迭代求解简化后的零阶和一阶摄动方程组,就可以求出孔型密封的流场和动力特性系数.以此为依据发展了相关程序,计算出了不同工况条件下孔型密封的转子动力特性系数与激振频率的关系,通过与已有的实验数据和等温BF模型的计算结果进行对比,验证了理想气体BF模型及相关求解方法的有效性.结果表明:理想气体BF模型的预测结果与实验数据吻合良好,且优于等温BF模型的计算结果,证明了该理想气体BF模型的正确性和计算方法的可靠性.该方法可用于孔型密封动力特性的预测.

Air-sea carbon-dioxide flux estimated by eddy covariance method from a buoy observation

Precise measurements of the CO2 gas transfer across the air-sea interface provide a better under- standing of the global carbon cycle. The air-sea CO2 fluxes are obtained by the eddy covariance method and the bulk method from a buoy observation in the northern Huanghai sea. The effects of buoy motion on flux calculated by the eddy covariance method are demonstrated. The research shows that a motion correction can improve the correlation coefficient between the C02 fluxes esti- mated from two different levels. Without the CO2-H20 cross-correlation correction which is termed as PKT correction, the air-sea CO2 fluxes estimated by eddy covariance method using the motion corrected data are nearly an order of magnitude larger than those estimated by the bulk method. After the CO2-H20 cross-correlation correction, some eddy covariance CO2 fluxes indeed become closer to the bulk CO2 flux, whereas some are overcorrected which are in response to small water vapor flux.

First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides

A first principles study of the electronic properties and bulk modulus （B0） of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.

The Improvement of Bulk-Heterojunction Order in Polymer Photovoltaic Device

The blend morphology and vertical arrangement are critical to the performance of organic bulk-heterojunction photovoltaic devices.In the present paper,the authors proposed a new annealing method that controls the blend morphology and vertical arrangement of two materials by means of simultaneously applying external electrical field and violet irradiation on the active layer of poly(3-hexylthiophene) (P3HT) and -phenyl C61-butyric acid methyl ester(PCBM) during annealing process.By using this annealing method,the power conversion efficiency increased by 36%,which was caused by vertical phased-separated blend of crystalline P3HT and PCBM and better charge extraction of electrodes.X-ray photoelectron spectroscopy(XPS) was measured to prove more fullerene derivatives at the organic/cathode interfaces by using this annealing method.The X-ray diffraction(XRD) analysis and UV-Vis absorption spectrum analysis also revealed more ordered polymer crystallization.

Preparation and Characterization of Copper-Nickel Bulk Nanocrystals

Copper-nickel nanoparticle was directly prepared by flow-levitation method （FL） and sintered by vacuum sintering of powder （VSP） method. Several characterizations, such as transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, differential thermal analysis （DTA）, and energy-dispersive X-ray spectroscopy （EDX） were used to investigate the prepared nanostructures. The results of the study show that FL method could prepare high purity Cu-Ni nanocrystals of uniform spheres with size distribution between 20 and 90 nm. After sintering the bulk nanocrystalline copper-nickel has obvious thermal stability and the surface Webster hardness increases with the rising sintering temperature. At the temperature of 900 ℃, the specimen shows higher surface Webster hardness, which is about two times of traditional materials. When the sintering temperature arrives at 1 000 ℃ the relative density of bulk nanocrystals can reach 97.86 percent. In this paper, the variation tendency of porosity, phase and particles size of bulk along with the changing of sintering temperature have been studied.

Preparation and thermal stability of Pd_(40.5)Ni_(40.5)Si_xP_(19-x) bulk metallic glasses

With the addition of Si to replace some P,Pd40.5Ni40.5SixP19-x（x=0,2.5,5,9.5,14,and 19 in atomic number fraction） bulk glassy samples with the diameter of about 5 mm were successfully prepared by use of flux treatment and water quenching technology.With the increase of Si content,the glass forming ability of Pd40.5Ni40.5Si-xP19-x increases first for low Si content and then decreases for high Si content （Si≥9.5at%）.The Pd40.50Ni40.5Si5P14 glassy alloy possesses the largest supercooled liquid region△T of 119 K,the largest reduced glass transition temperature of 0.621,and the largestγparameter of 0.460,indicating that this glassy alloy possesses very large glass forming ability and very high thermal stability.

Crystallization Kinetics and Magnetic Properties of Fe₄₀Ni₄₀B₂₀Bulk Metallic Glass

Fe-based bulk metallic glasses (BMGs) have been extensively studied due to their potential technological applications and their interesting physical properties such as a low modulus of elasticity, high yielding stress and good magnetic properties. In the present work, the bulk metallic glass (BMG) formation of Fe40Ni40B20 (numbers indicate at %) with a ribbon form was fabricated by the single roller melt-spinning method. Rapid solidification leads to a fully amorphous structure for all compositions. The thermal properties associated with crystallization temperature of the glassy samples were measured using differential scanning calorimetry (DSC) at a heating rate of 10℃/mn. The microstructure and constituent phase of the alloy composite have been analyzed by using X-ray diffractometry (XRD). The effect of high temperature on the isothermal crystallization of Fe40Ni40B20 ribbon was investigated by HTX-ray diffraction. In addition, these ribbon glasses also exhibit good soft magnetic properties with M-H curvature measured under the magnetic fields between –1 kOe and 1 kOe.

急倾斜薄矿体采场围岩及假底应力分布规律研究

急倾斜极薄矿脉是有色、黄金矿山常见的矿体形态,多采用人工假底的留矿法或削壁充填法回采,研究采动过程中围岩和人工假底的受力分布对于设计假底参数和安全开采具有重要意义。以某金矿削壁充填采场为工程背景,模拟研究了人工假底及围岩采动过程中应力变化规律。上、下盘围岩采动后最大主应力和最小主应力减小,回采区域顶板应力集中。假底中心处垂直压力最小,越靠近上、下盘边壁垂直压力增加,随着采高增加,假底各部位的垂直压力增加,最后呈收敛趋势。人工假底主要是剪应力破坏,假底破坏主要是上、下盘高水平应力未作用在同一轴线而产生的剪应力造成的。根据散体侧压力和采动应力变化规律,提出在采场内每隔10m利用混凝土铺底,增加人工假底中混凝土强度及垂直方向的配筋,提高假底抗剪强度,从而提高深部采场回采的安全性和人工假底的稳固性。

New Numerical Method to Calculate the True Optical Absorption of Hydrogenated Nanocrystalline Silicon Thin Films

The enhanced optical absorption measured by Constant Photocurrent Method (CPM) of hydrogenated nanocrystalline silicon thin films is due mainly to bulk and/or surface light scattering effects. A new numerical method is presented to calculate both true optical absorption and scattering coefficient from CPM absorption spectra of nanotextured nano-crystalline silicon films. Bulk and surface light scattering contributions can be unified through the correlation obtained between the scattering coefficient and surface roughness obtained using our method.

Probabilistic Modelling of Microstructural Evolution in Zr Based Bulk Metallic Glass Matrix Composites during Solidification in Additive Manufacturing

Bulk metallic glass and their composites (BMGMCs) are a new class of materials which possess superior mechanical properties as compared to existing conventional materials. Owing to this, they are potential candidates for tomorrow’s structural applications. However, they suffer from poor ductility and little or no toughness which render them brittle and they manifest catastrophic failure under applied force. Their behavior is dubious, unpredictable and requires extensive experimentation to arrive at conclusive results. In present study, an effort has been made to design bulk metallic glass matrix composites by the use of modeling and simulation. A probabilistic cellular automaton (CA) model is developed and described in present study by author which is used in conjunction with earlier developed deterministic model to predict microstructural evolution in Zr based BMGMCs in additive manufacturing liquid melt pool. It is elaborately described with an aim to arrive at quantitative relations which describe process and steps of operations. Results indicate that effect of incorporating all mass transfer and diffusion coefficients under transient conditions and precise determination of probability number play a vital role in refining the model and bringing it closer to a level that it could be compared to actual values. It is shown that proposed tailoring can account for microstructural evolution in metallic glasses.

变容积密集烤房的CFD分析与试验研究

为保障密集烤房装烟密度,降低烘烤的能源消耗,研发一套适用于密集烤房的变容积系统。在完成变容积装置的设计后,基于CFD方法模拟分析装置与烟叶的不同距离对烤房内部气体分布均匀性的影响。通过烘烤试验获取实际烘烤数据,对模拟值加以验证。试验结果表明:当隔板与烟叶距离为0 cm时,流速不均匀系数Kv为0.40,温度不均匀系数Kt为0.41,距离为10 cm时,Kv=0.41,Kt=0.43;距离为20 cm时,Kv=0.42,Kt=0.49。装烟区9个测量点的温度模拟值与实测值基本吻合,误差在6%以内。变容积烤房在装烟量为一半时,相比常规烤房的燃料消耗可节约13.4%。研究结果表明:当隔板与烟叶距离为0 cm时烤房内部的气体分布最均匀;CFD模型与数值模拟结果具有可靠性;变容积装置具有较好的保温效果,可保证装烟密度,降低烤烟能耗。

Ga-N熔体热力学性质及钠助熔剂法制备GaN单晶的研究进展

作为第三代半导体的关键材料之一,Ⅲ族氮化物在过去几十年中因其应用于光电子和微电子器件而得到了广泛的研究,如发光二极管(LED)、激光二极管(LD)和高电子迁移率晶体管(HEMT)。Na助熔剂法已成为生长高质量GaN晶体的重要技术之一。综述和讨论了Na助熔剂法GaN结晶的发展历程与最新技术,包括Ga-N的结晶热力学性质、熔体结构、助熔剂选择、单点籽晶技术、多点籽晶技术、孔隙与位错控制、形貌演化与生长条件优化等。最后,对比其他体GaN技术,展望了Na助熔剂法的挑战与机遇。

Server Workload in an M/M/1 Queue with Bulk Arrivals and Special Delays

We consider a variant of M/M/1 where customers arrive singly or in pairs. Each single and one member of each pair is called primary;the other member of each pair is called secondary. Each primary joins the queue upon arrival. Each secondary is delayed in a separate area, and joins the queue when “pushed” by the next arriving primary. Thus each secondary joins the queue followed immediately by the next primary. This arrival/delay mechanism appears to be new in queueing theory. Our goal is to obtain the steady-state probability density function (pdf) of the workload, and related quantities of interest. We utilize a typical sample path of the workload process as a physical guide, and simple level crossing theorems, to derive model equations for the steady-state pdf. A potential application is to the processing of electronic signals with error free components and components that require later confirmation before joining the queue. The confirmation is the arrival of the next signal.

响应面法制备有机硅氧烷气凝胶的工艺优化及表征

为探究降低二氧化硅气凝胶体积密度的有效途径,以甲基三甲氧基硅烷(MTMS)和二甲基二乙氧基硅烷(DMDES)为硅源合成有机硅氧烷气凝胶,基于Box-Behnken Design响应面设计方法,分析MTMS/DMDES摩尔比、H_(2)O/Si摩尔比、氨水浓度这3个因素及其交互作用对气凝胶体积密度的影响机理与规律,得到最佳制备工艺条件。制备低密度有机硅氧烷气凝胶的最佳工艺条件为MTMS/DMDES摩尔比6/4,H_(2)O/Si摩尔比25,氨水浓度1mol/L。在此优化条件下,气凝胶体积密度为0.148g/cm^(3),与理论值基本吻合。研究结果表明:各因素对气凝胶体积密度的影响主次顺序为氨水浓度、MTMS/DMDES摩尔比、H_(2)O/Si摩尔比;气凝胶由球形粒子连接组成,粒径为3~4μm;平均孔径约为7.03μm;气凝胶具有良好的疏水性、抗压缩性和热稳定性,接触角高达146.2°,60%应变时应力为25.4kPa,热分解温度达到389.2℃,导热系数为0.0564W/(m·K)。

基于BIM的航站楼钢网架屋盖高空散装法施工模拟与力学仿真分析

以南充高坪机场改扩建施工为背景进行技术应用,结果表明:在场地不足的情况下,高空散装法是较优的安装方案;基于BIM的施工模拟,能够合理规划场地模型、提高施工效率;对施工全过程进行数值模拟力学分析,得出关键杆件与关键施工步,确保施工过程安全进行。

土壤类型和容重对离心机法测定土壤水分特征曲线的影响

本研究以杨凌塿土和嫩江黑土为研究对象,分别设置了4个土壤容重处理(1.0、1.1、1.2、1.3 g/cm^(3)),利用离心机法测定土壤失水过程,以压力膜仪法为标准,对比不同吸力下的含水量实测值和van Genuchten模型参数的差异。结果表明,随着土壤容重的增加,离心机法测定土壤水分特征曲线准确度逐渐增加,获取黑土和塿土的van Genuchten模型参数α的准确度增幅分别为38.46%~83.08%和56.38%~95.75%。离心机法测定土壤水分特征曲线的准确度在不同吸力段表现不同,近饱和段(0~10 kPa)离心机法测定值偏低,而高吸力段(10~1500 kPa)测定值偏高,且高吸力段离心机法测定准确度较低,与压力膜仪法测定值具有极显著差异(P<0.01)。综上所述,为了提高离心机法测定土壤水分特征曲线的准确度,优先考虑应用于大容重和高有机质含量的土壤。

基于双给体三元体异质结的高性能倍增型有机光电探测器

为了拓展光谱响应范围至近红外,采用双给体单受体的三元体异质结策略,基于溶液法制备了以ITO/PEDOT∶PSS/活性层/Al为基本结构的倍增型有机光电探测器,活性层由P3HT∶PTB7-Th∶IEICO-4F(100-x∶x∶1,wt/wt/wt)组成,研究了不同质量比的PTB7-Th对器件光电特性的影响。优化后的三元倍增型有机光电探测器以P3HT∶PTB7-Th∶IEICO-4F(60∶40∶1,wt/wt/wt)为活性层,在-15 V偏压下,在450、520、655和850 nm处的外量子效率分别为2 666.40%、1 752.11%、1 894.26%和938.22%,响应度分别为965.80、733.35、998.68和641.91 A/W,比探测率均超过10^(13)Jones,在850 nm处的响应度与比探测率分别是相同条件下二元器件P3HT∶IEICO-4F(100∶1,wt/wt)的2.23倍和7.08倍。结果表明,在二元体系P3HT∶IEICO-4F中掺入适量的PTB7-Th,不仅能拓展光谱响应范围至近红外,还能改变活性层中激子解离界面、电子陷阱类型和空穴注入势垒高度,优化器件的电学性能。