Methodological aspects of determining soil particle‐size distribution using the laser diffraction method

This paper presents the influence of selected methodological aspects on the results of particle‐size distribution (PSD) as measured by the laser diffraction method (LDM). The investigations were carried out using the Mastersizer 2000 with Hydro MU attachment (Malvern Ltd., UK). It was found that for the investigated soils: (1) optimal speed of pump and stirrer was 2500 rpm, (2) optimal measurement time was ≈ 1 min, (3) there are two, practically equivalent methods for soil‐sample dispersion: chemical (with the use of a solution of sodium hexametaphosphate) or physical (by means of ultrasound application for 4 min at a maximum power of 35W), (4) one must not use the chemical and physical dispersing methods simultaneously, because this can lead to aggregation (not dispersion) of soil particles, (5) the Fraunhofer theory (physical models) can be used to convert scattered‐light data to PSD. In the case of the Mie theory, the best results were obtained for a refractive index (RI) in the range of 1.5–1.6 and an absorption index (AI) of 1.0. It was also found that most of the discussed parameters depend on design of the measuring device and on the type and volume of the investigated suspensions. It is necessary, therefore, to explain how the data was obtained every time and to specify the details in the methodological part of the paper.     

Quantifying aggregate stability of a clay soil under annual forage crops

This study explored the influence of 10 annual forage legumes belonging to the Lathyrus and Vicia genera on wet aggregate stability (WAS) and dispersion ratio (DR) indices of a clay soil. Five Lathyrus and five Vicia species were sown in autumn. Seed‐to‐seed and row‐to‐row distance was maintained at 5 cm and 20 cm, respectively. The experiment was planned in a randomized block design with three replications. After 90 d following seed harvest, soil cores were collected from two depths (0–15, 15–30 cm) in each plot and WAS and DR were determined. Annual forage legumes increased WAS of the soil but decreased the DR index. The WAS and DR values were affected at level of p < 0.001 by genus, species, and soil depth. Values of WAS and DR of the control plots without plant on the average were found to be 44.5% and 9.3% for 0–15 cm, and 41.2% and 10.1% for 15–30 cm, respectively. For 0–15 cm depth, the highest WAS (77.7%) and the lowest DR (6.4%) values were found in L. sphaericus L. (wild) plots. For 15–30 cm depth, the highest WAS value (62.6%) was obtained in L. annuus L. (wild) plots and the lowest DR value (6.7%) was in L. sativus L. (Gurbuz‐2001) plots.     

静态混合原理在松脂熔解过程中的应用

松脂熔解过程实际上是一个传热、反应及萃取同时存在的综合过程。过程进行的好坏与各物料间的分散混合及其在熔解器中的停留时间密切相关。在连续熔解器中设置静态混合元件可以促进物料在熔解器径向的分散和混合,强化熔解过程;另一方面,混合元件可抑制物料在熔解器轴向的大幅度混合,从而使各部分松脂在熔解器中的实际停留时间均较接近所计算的表观停留时间,提高熔解过程的总体效果。     

应用有限单元法解恒定平面渗流

应用有限单元法解恒定平面渗流,首先是将连续的渗流区域离散化,即划分成若干个小单元,然后选取插值函数,建立单元特性方程,将偏微分方程式化为代数方程组,再结合边界条件组合成总体方程即线性代数方程组,解总体方程即可得到整个渗流区域的解。     

Effect of Addition of Al Hydroxides on Changes in Dispersibility and Charge Characteristics of Soils

Using a soil from a newly reclaimed area where high dispersibility of fine particles had led to poor physical properties in the field, changes in dispersibility and charge characteristics after artificial precipitation of Al hydroxides onto the soil were investigated. Al hydroxides were precipitated by neutralization with NaOH of an acidic A1C1₃ solution in which the soil samples were placed.

When the titration rates were changed, no significant differences in dispersibility were observed in the resultant soils. In the systems with the addition of 2 g kg^-1 or less of A1(OH)₃, dispersion ratios of clays were almost identical with those of blank samples although the specific surface areas were reduced. In the systems with 5 g kg^-1 or more of A1(OH)₃, considerable effects of Al hydroxides on reduction of clay dispersibility were recognized (e.g. 10 g kg^-1 addition yielded less than one-third of the original ratio of the clay dispersion). A slightly larger decrease in dispersion was observed by the addition of 15 g kg^-1 or more. As the amount of added Al increased, the amount of negative charges of the soil decreased while that of positive charges increased. The charge characteristics of the system with the addition of 20 g kg^-1 of A1(OH)₃ were closer to those of the adjacent forest soil which was characterized by a very low dispersibility. It was inferred that added Al hydroxides polymerized to form Al polycation species that were not readily exchangeable, neutralizing negative charges of clays, and acting as interparticle bonding between the clays. On the other hand, forest soils were considered to have acquired a physical stability against the dispersion of fine particles as free Al oxides had been accumulated in the process of natural weathering. It was concluded that charge characteristics primarily determined the dispersion and flocculation behavior of soils and that Al hydroxides were important modifiers of charge characteristics of soils.     

基于FLUENT的高含硫天然气管道泄漏扩散模拟

利用CFD软件FLUENT首次对高含硫天然气管道破裂泄漏扩散规律进行了数值模拟,得到了甲烷、硫化氢在一定风速、地形条件影响下的扩散规律,以及甲烷和硫化氢的浓度分布规律,为有效预测高含硫天然气泄漏扩散的影响范围提供了依据。研究结果对于认识高含硫天然气泄漏扩散规律以及相关安全事故的预警和救援具有指导意义。     

牛肌肉组织中苯并咪唑类药物的基质固相分散-高效液相色谱多残留分析法

将基质固相分散 ( MSPD)与酸碱萃取相结合 ,对组织中的残留物进行净化。反相高效液相色谱( HPLC)测定 ,流动相为乙腈 -0 .0 1 7mol/L磷酸 ( 7 3) ,检测波长 2 90 nm。建立了牛肌肉组织中 4种苯并咪唑类药物的基质固相分散 -高效液相色谱 ( MSPD-HPLC)多残留分析法。在 0 .0 5～ 0 .4 0 mg/kg添加范围内 ,4种苯并咪唑类药物的平均回收率为 ( 6 9.2± 1 2 .4 ) %。本方法检测限为 0 .0 1～ 0 .0 5mg /kg。     

土壤水流通量对饱水带溶质运移参数的影响

The transport processes of solutes in two soil columns filled with undistrubed soil material collected from an unsaturated sandy aquifer formation in Belgium subjected to a variable upper boundary condition were identified from breakthrough curves measured by means of time domain reflectometry(TDR),Solute breakthrough was measured with 3 TDR probes inserted into each soil column at three different depths at a 10 minutes time interval.In addition,soil water content and pressure head were measured at 3 different depths.Analyteical solute transport models were used to estimate the solute disperison coefficient and average pore-water velocity from the observed breakthrough curves,the results showed that the analytical solutions were suitable in fitting the observed solute transport,The dispersion coefficient was found to be a function of the soil depth and average proe-water velocity,imposed by the soil water flux.the mobile moistrue content on the other hand was not correlated with the average pore-water velocity and the dispersion coefficient.     

液液系统中荷电射流不稳定性

针对生物柴油液液静电雾化乳化过程,建立了色散方程并应用Matlab进行数值计算,分析了水射流速度、荷电电压、水与生物柴油各自的黏度、表面张力对生物柴油中水射流不稳定性的影响.研究结果表明,在水-生物柴油系统中,提高水射流的速度或荷电电压,均能使界面波最大增长率增大,对应的最优波数也随之增加.水的黏度阻碍水射流的破碎雾化,而生物柴油黏度对水射流的破碎雾化却起着促进作用.水-生物柴油的界面张力越小,对液液静电雾化乳化过程越有利.在水-生物柴油液液静电雾化乳化实际应用过程中,除提高水射流速度和荷电电压外,提高水的温度同时尽可能地降低生物柴油的温度,可以形成粒径细小均匀离散相液滴,获得优质的生物柴油乳化燃油.     

球磨-酶解法制备纳米竹纤维的结构表征

采用机械球磨对竹纤维进行预处理,再经纤维素酶水解制备纳米竹纤维。通过光学显微镜(OM)、透射电子显微镜(TEM)、傅立叶红外光谱仪(FTIR)和X射线衍射仪(XRD)对竹纤维的形貌、组成、光谱学性能以及晶体特性进行了表征。实验结果表明:球磨法和酶解法在一定程度上都可以细化竹纤维;球磨预处理有助于竹纤维的酶解过程,且球磨-酶解法制备的纳米竹纤维粒径在100 nm左右;所制备的纳米竹纤维仍然保持竹纤维的基本化学结构,但球磨处理破坏了纤维素的结晶结构,其结晶度由64.15%降低到了38.55%。