华北平原大孔隙优先流对农田氮素淋溶的影响

优先流是土壤水分入渗的一个重要途径,大孔隙是产生优先流的关键因素。研究优先流对于土壤水分和溶质运移研究及生态环境保护、制定合理的田间管理措施等具有重要意义。本研究将田间亮蓝染色示踪试验和WHCNS(soilwaterheatcarbonnitrogensimulator)模型模拟相结合,研究了华北平原冬小麦-夏玉米轮作体系存在大孔隙下,强降雨和不同施肥、灌溉情景下土壤水氮运移的情况,以此探讨大孔隙优先流对于土体中水分和硝态氮运移的影响。结果表明:明显含有虫洞的免耕土壤入渗深度和染色面积均高于旋耕土壤;免耕土壤的染色面积和稳定入渗速率的Pearson相关性不显著,染色示踪不能定量化土壤稳定入渗速率。同时WHCNS模拟的0～100cm土层硝态氮淋洗量结果显示:一方面,相较于无大孔隙情景,大孔隙存在会显著增加硝态氮的淋洗量;另一方面,大孔隙存在下优化施肥模式的硝态氮淋洗量比传统施肥模式减少46.0%。常规灌溉量下喷灌比漫灌处理的硝态氮淋洗量减少15.6%;强降雨导致硝态氮淋洗量增加119.4%。本研究为华北平原地区大孔隙存在条件下的农田水肥优化管理措施提供了理论指导。     

紫色土坡耕地土壤大孔隙流的定量评价

为阐明大孔隙丰富且孔径呈两极分化的紫色土坡耕地土壤大孔隙流的运移规律,通过室内土柱试验获取耕作层0~20 cm、非耕作层20~40 cm原状土柱和填装土柱的穿透曲线,分析饱和条件下土壤大孔隙流发生规律,并采用解析法CXTFIT软件拟合了水分优先运移参数,PFSP指标(大孔隙流引起的穿透曲线延展量与水动力弥散作用及两区作用引起的延展量的比值)定量评价土壤大孔隙流的贡献率。研究结果表明:1)以填装土柱水流为平衡基质流计算,耕作层0~20 cm原状土柱中大孔隙流的导水贡献率为66.2%~68.5%,而Br-累积淋出量占总淋出量的62.3%~66.1%。对于非耕作层20~40 cm,土壤大孔隙流导水贡献率为0.2%~1.7%,而Br-随大孔隙流运移的比例却达14.5%~20.5%。说明耕作层土壤中大孔隙流现象远比在非耕作层土壤中更为显著;2)PFSP值结果表明大孔隙流作用对穿透曲线延展量的贡献率最大,两区交换运移作用次之,水动力弥散作用的最小。即PFSP值越大,大孔隙流对总水流通量的贡献率越大。     

Near‐surface macropore flow and saturated hydraulic conductivity in drained and restored blanket peatlands

The impacts of blanket peatland management on water tables, near‐surface macropore flow and saturated hydraulic conductivity were investigated using automated dipwells and mini‐disc tension infiltrometers. Three neighbouring hillslopes which were undisturbed, drained and restored by drain blocking were studied. Mean water table depths at the undisturbed sites were slightly shallower than at the restored site and water tables at both sites were significantly shallower relative to the drained treatment. Through time, however, the water table at the restored treatment behaved in a markedly different way to that at the undisturbed site. Water tables reached the peat surface for only 2% of the time for the drained and restored treatments compared to 18% for the undisturbed treatment. The proportion of runoff flowing through macropores in the near‐surface layers of the peat was found to be large (≥60%) across all three treatments, yet functional macroporosity was found to be significantly greater in the undisturbed peat relative to the two other treatments. Meanwhile, saturated hydraulic conductivity was found to be significantly higher at the restored treatment relative to the two other treatments, with mean conductivities ca. 1.5 times greater, suggesting a form of heightened soil–water interaction. Combined, the results indicate that although restoration by ditch blocking may result in a relatively successful water table recovery, there may not be the full reinstatement of peatland hydrological processes.     

驯鹿足底非规则特征形貌数学模型构建及验证

为攻克常规防滑轮胎在冰面上通过性低的难题,以驯鹿足为仿生原型,对驯鹿足底特征形貌进行分析。该文通过逆向工程技术,将驯鹿足单个足底划分为内、外侧边缘曲线、脊线凹槽面和足跟凸冠面4个典型部位。运用1st Op软件和MATLAB软件对特征部位拟合并构建数学模型,利用X射线能谱仪对驯鹿足底特征部位进行元素分析。内、外侧边缘曲线方程的决定系数R~2分别为0.994、0.992;脊线凹槽面和足跟凸冠面曲面方程的R~2分别为0.96、0.98。通过模型验证发现,模型拟合值与实际值的相对误差均值在5%以下,实现了驯鹿足底特征形貌从生物模型到数学模型的转化。能谱分析结果表明驯鹿足底除含有大量的碳、氧及氮元素外,硫、硅、铁、铝、钙5种元素含量较高,并且不同部位的元素存在差别。该研究可为工程仿生技术应用于冰路面行驶车辆胎面设计提供新的研究方向和参考依据。     

Soil macropore dynamics affected by tillage and irrigation for a silty loam alluvial soil in southern Portugal

Soil tillage can have a significant effect on soil porosity and water infiltration. This study reports field measurements of near saturated hydraulic conductivity in an undisturbed soil under two tillage treatments, conventional tillage (CT) and minimum tillage (MT). The objective was to determine effective macro and mesoporosities, porosity dynamics during the irrigation season, and their contribution to water flow. Field observations were performed during the 1998 maize (Zea mays L.) cropping season in an Eutric Fluvisol with a silty loam texture, located in the Sorraia River Watershed in the south of Portugal. Infiltration measurements were done with a tension infiltrometer. At each location an infiltration sequence was performed corresponding to water tensions (φ) of 0, 3, 6 and 15 cm. Five sets of infiltration measurements were taken in both treatments in the top soil layer between May and September. One set of measurements was done at the depth of 30 cm at the bottom of the plowed layer in the CT plot. After 5 years of continuous tillage treatments the results show that regardless of the tillage treatment, saturated conductivity values K(φ₀) were several times larger than near saturation conductivity K(φ₃). This indicates that subsurface networks of water conducting soil pores can exist in both CT and MT maize production systems. In CT, the moldboard plow created macro and mesoporosity in the top soil layer while breaking pore continuity at 30 cm depth. This porosity was partially disrupted by the first irrigation, resulting in a significant decrease of 45% in the macropore contribution to flow. Later in the season, the irrigation effect was overlaid by the root development effect creating new channels or continuity between existing pores. In MT macroporosity contribution to flow did not show significant differences in time, representing 85% of the total flow. In both the treatments, macropores were the main contributing pores to the total flow, in spite of the very low macroporosity volumes.     

Container medium characterization by scanning electron microscopy and comparison with a Monte Carlo computer simulated medium

Abstract

A 1:1 by volume pine bark and sand containermedium was embedded with Spurr's epoxy resin and cross‐sectioned for SEM characterization of particle distribution. A Monte Carlo computer simulated medium was built with spheres of the same particle size distribution as the pine bark and sand grains used in the experiment. Cross‐sections from the simulated systems were compared with actual experimental data and good agreement was obtained. SEM makes it possible to analyze particle and pore distribution of container media. Computer simulation provides a good approximation of container medium structure and may prove useful in estimating properties of container medium mixtures.     

逆流式气-气换热器的设计与性能试验

介绍了一种逆流式气-气换热器的结构、设计及工作过程,并利用数值计算与现场试验的方法对该换热器进行了性能测试。该气-气换热器采用聚丙烯（PP）塑料材料作为换热片,流体方向为逆流式换热。数值方法计算结果表明,换热器换热量与风量呈正相关关系,换热效率随热端风量的增大而提高：热端风量为4 475 m3/h时,换热效率为0.55～0.75;热端风量为7 800 m3/h时,换热效率为0.6～0.8。性能测试的结果表明,该换热器的实际换热效率与数值计算的换热效率基本吻合：热端风量为4 475 m3/h时,实测值为0.45～0.7;热端风量为7 800 m3/h时,实测值为0.65～0.9。因此,该PP逆流式气-气换热器具有很好的换热性能。     

Isolation and biochemical characterization of a basic myrosinase from ripe Crambe abyssinica seeds,highly specific for epi-progoitrin

On the basis of previous studies on the mechanism-based inhibition, activation, and active site structure of myrosinase(s) isolated from Sinapis alba and other cruciferous seeds, crambe myrosinase shows uncommon properties and behavior. For this reason homogeneous crambe myrosinase was isolated and investigated to establish the most important physicochemical features, including kinetic properties determined with the epimers progoitrin (R) and epi-progoitrin (S) as substrates, with and without ascorbate as an activator. The results of this study demonstrate that crambe myrosinase is highly specific for epi-progoitrin due to a better stabilization of the enzyme-substrate complex. This stabilization is caused by additional hydrogen bonding that only epi-progoitrin can set up between its hydroxyl group and a suitable residue in the hydrophobic pocket where the "docking" of the glucosinolates side chain takes place.     

山羊蹄底部非规则曲面仿生形貌数学模型构建及验证

山羊蹄底部非规则曲面形貌是影响山羊在崎岖路面稳定行走的关键因素之一,研究山羊蹄底部曲面特征将有助于将其这一优越特征应用到仿山羊农业四足行走机器人上,以解决目前农业四足行走机器人在崎岖地面上行走稳定性差的难题。该研究选取6个月的雄性波尔山羊蹄,采用三维立体扫描仪获取山羊蹄点云数据,并导入Geomagic Studio软件中进行点云去噪声、采样、封装、表面处理,得出山羊蹄的精确曲面,进行曲面偏差分析,最后根据山羊蹄偶型结构把山羊蹄底部曲面划分为2部分,利用Catia软件中的Digitized Shape Editor模块,对2个曲面的密集点云进行过滤,保留曲面形貌的特征点,并导出2个区域特征点云三维坐标数据。运用Matlab软件中的cftool工具箱对特征曲面的点云三维坐标数据进行3次多项式拟合,分别得到2个曲面的拟合方程、残差平方(SSE)、均方差(RMSE)和决定系数R2,研究结果表明:山羊蹄曲面标准偏差为1.402 2 mm,山羊蹄底部左侧曲面拟合残差平方(SSE)是359,均方差(RMSE)是0.792 9,决定系数(R2)是0.988 9;山羊蹄底部右侧曲面拟合残差平方(SSE)是256.2,均方差(RMSE)是0.7253,决定系数(R2)是0.987 9。对构建的数学模型进行验证发现,模型的拟合值与实际值的相对误差最大值分别为8.63%和9.58%,相对误差均值分别为4.32%和4.73%,相对误差均值能满足工程设计允许的误差范围±5%,验证了模型的有效性,实现了山羊蹄底部非规则曲面由生物模型到数学模型的转化。该研究为将山羊蹄底部曲面形貌进行仿生学应用奠定了理论基础,并为利用仿生学技术研究农业四足行走机器人提供参考依据。     

Artificial neural network-based predictive model for bacterial growth in a simulated medium of modified-atmosphere-packed cooked meat products

The data of Devilieghere et al. (Int. J. Food Microbiol. 1999, 46, 57--70) on bacterial growth in a simulated medium of modified-atmosphere-packed cooked meat products was processed for estimating maximum specific growth rate mu(max) and lag phase lambda of Lactobacillus sake using artificial neural networks-based model (ANNM) computation. The comparison between ANNM and response surface methodology (RSM) model showed that the accuracy of ANNM prediction was higher than that of RSM. Two-dimensional and three-dimensional plots of the response surfaces revealed that the relationships of water activity a(w), temperature T, and dissolved CO(2) concentration with mu(max) and lambda were complicated, not just linear or second-order relations. Furthermore, it was possible to compute the sensitivity of the model outputs against each input parameter by using ANNM. The results showed that mu(max) was most sensitive to a(w), T, and dissolved CO(2) in this order; whereas lambda was sensitive to T the most, followed by a(w), and dissolved CO(2) concentrations.     

纵轴流联合收获机关键部件改进设计与试验

针对当前履带式纵轴流联合收获机中存在的工作状态无法在收获不同作物间快速转换,割台损失率较高、脱粒分离能力较差以及功耗高等不足,对割台、脱粒、清选、行走等主要工作部件进行了改进设计与试验研究。将割台设计为无级调速可伸缩式结构,脱粒装置改为纵轴同径差速滚筒脱粒装置,采用单HST(hydro static transmission)原地转向行走装置及防粘附清选装置,并经室内试验和田间试验表明:可伸缩割台能实现稻麦收割状态与油菜收割状态的快速转换,扩大了割台的使用功能,收获油菜损失显著减少,与常规相比较,油菜损失率降低2.8个百分点;差速轴流滚筒提高了脱粒效果和分离能力,与等长度单转速轴流滚筒相比,夹带与脱不净损失率分别减少了0.02个百分点与0.09个百分点,破碎率减少了0.017个百分点;原地转向行走机构减少了地表土壤的破坏并降低了转向功耗,以原地转向替代单边制动转向时,节约功耗37.0%;清选机构抖动板和清选筛面经不沾水处理,改善了潮湿谷物的清选性能,清选损失率降低0.9个百分点,含杂率降低0.4个百分点;这些联合收获机主要工作部件的改进设计提高了整机工作性能,以期为联合收获机主要工作部件改进,提高联合收获机工作性能提供参考。     

Isolation and characterization of a cDNA from Catharanthus roseus which is highly homologous with phosphate transporter

The PIT1 gene which is highly homologous with phosphate transporter was isolated from Catharanthus roseus and analyzed. The cBNA PIT1 contained an open reading frame of 542 amino acids and its sequence showed a 31, 30, and 34% identity with the phosphate transporter of Saccharomyces cerevisiae (PBO84), Neurospora crassa (PHO-5), and Glomus versiforme (GvPT), respectively. Furthermore, the cDNA PIT1 encoded a highly hydrophobic protein with 12 putative membrane-spanning regions and contained a conserved amino acid sequence reported in the human glucose transporter super-family* S. cerevisiae strain DpU (pho84 knockout strain) was unable to grow on low phosphate (55 μM) medium (LP medium). Expression of the PIT1 cDNA enabled DpU to grow on LP medium. Northern hybridization analysis revealed that the PIT1 gene was expressed in roots, stems, and young whole plant of C. roseus, but not in leaves.     

浓缩风能型风力发电机相似模型流场特性试验——车载法试验与分析

浓缩风能型风力发电机的流场具有特殊性,它的流场特性直接影响该类型风力发电机的性能。浓缩风能的目的是为了有效地提高风能品位、单机输出功率和风能资源利用率,降低风电度电成本。200W浓缩风能型风力发电机是由风洞测试后的浓缩风能型风力发电机整体试验模型简化改进的实用机型。采用车载法对200W浓缩风能型风力发电机相似模型的流场进行了测试,运用皮托管和数字压力计测试了各断面特征点的总压、静压,获取了流场流速分布等特性。试验表明：相似模型的中央圆筒叶轮安装处流速增至来流流速的1.31倍,风能增至来流风能的2.25倍。通过相似模型的车载法试验结果分析研究,找出了流场流速分布的规律性。     

In-canopy throughfall measurements in Norway spruce: Water flow and consequences for ion fluxes

Canopy throughfall was collected in funnels equipped with tipping buckets. The funnels were installed at 4 distances from the tree trunk and at 6 depths in the canopy of a Norway spruce forest at Klosterhede, Denmark. The throughfall water flux was registered during individual rain events. The smallest quantity of throughfall was sampled closest to the tree trunk, and the largest quantity of throughfall was sampled in the periphery of the canopy at all levels in the canopy. The quantity of throughfall was highest at the top of the tree and decreased down through the canopy. The intensity of the water flow decreased through the canopy which brought the throughfall water in contact with the foliage for longer periods in the lower canopy than in the upper canopy. The higher wettability caused a larger leaching of especially potassium in the lower canopy. Differences in rain intensity did not influence the distribution and the pattern of water flow in the canopy.     

拖拉机作业机组模糊综合控制模型及仿真试验

拖拉机作业机组是一个复杂的非线性且有惯性的控制系统，系统参数间存在耦合关系，建立精确数学模型进行综合控制比较困难，通过对拖拉机作业机组动态特性的研究，建立了基于发动机负荷率、驱动轮滑转率和作业阻力3参数的综合控制仿真模型，并应用模糊控制技术实现了机组的综合控制。试验结果表明，该仿真模型能够根据作业阻力的变化自动推理输出档位、油门位置或耕深控制信号，由下位机执行机构完成控制，实现了由计算机模拟驾驶员对机组进行综合自动控制。由计算机实现机组综合自动控制，能根据选定的控制策略使发动机按最低油耗曲线运行，获得了很好的动力性和经济性，而且计算机自动控制摆脱了人工经验控制，控制更精确，比人工控制效果好，且控制具可重复性和试验结果具可比性。因此，所设计的拖拉机作业机组模糊综合控制模型对拖拉机作业机组综合自动控制研究有一定的实用和参考价值。     

Quantifying soil macropore networks in different forest communities using industrial computed tomography in a mountainous area of North China

Purpose

Macropores have important effects on the movement of soil water, air, and chemical substances. However, the quantitative relationship between complex 3D soil macropore networks and forest communities remains unclear in the northern mountainous area in China. The objectives of this study were to (1) use industrial computed tomography (CT) scanning and image analysis to quantitatively analyze macropore networks in intact soil columns and (2) identify characteristics of soil macropore networks in different forest communities.

Materials and methods

Intact soil columns (100-mm diameter, 300 mm long) were taken from six local forest communities with three replicates for a total of 18 samples. Industrial X-ray CT was used to scan soil samples; then, the scanned images were used to obtain the 3D images of rock fragments and macropore structures. Next, the macropore structure was quantified, including volume, diameter, surface area, length, angle, tortuosity, and number of macropores. This technique provided an accurate method to quantify the structure of macropores.

Results and discussion

The analysis and results revealed that different forest communities influence soil macropore 3D structure significantly and in different ways. Macropores in mixed Pinus tabulaeformis, Castanea mollissima, and Ulmus pumila forest had the largest diameter, surface area, network density, and length density of macropores as well as the smallest mean tortuosity of soil macropores. This is caused by the fact that mixed forest soils had more complex root systems, better soil structure, and more biotic activity. Within the soils of a single forest community, macropore porosity, network density, surface area density, and length of macropores decreased with increased soil depth, because more roots and more biological activity were present in the surface soil.

Conclusions

Advanced industrial CT technology can allow an accurate quantification of soil macropore structure. This is important because this type of structure has significant effects on soil water, air, and chemical transport. The results suggest that mixed forest is the best afforestation model in the northern mountainous area in China because of its ability to improve soil structure.

     

鱼糜凝胶脆性的力学性能表征与模型建立

为了用客观准确的方法评价鱼糜凝胶的脆性,以求为鱼糜凝胶的质构调控等相关研究奠定基础,该研究采用感官评价和单轴压缩、三点弯曲、穿刺等物性分析方法,对不同交联度的鱼糜凝胶感官脆性和力学指标进行测定,研究鱼糜凝胶感官脆性与交联度和力学指标的关系并建立鱼糜凝胶脆性的表征模型。结果表明,不同交联度的鱼糜凝胶表现出不同的口感,鱼糜凝胶的感官脆性评分随着交联度的增加而增大。当鱼糜凝胶的交联度小于30%时,咀嚼时鱼糜凝胶不具备脆性。当交联度超过30%后,鱼糜凝胶开始出现脆性,且随着交联度的增加其脆性显著增加。而当交联度超过75%时,感官脆性不再明显增加。在交联度30%~75.5%范围内,对鱼糜凝胶脆性进行力学表征并进行多元回归分析,建立了基于破断力、脆裂功、断裂应力、初始切割系数和压缩常数5个参数的鱼糜凝胶的脆性表征方程(R~2=0.981 9),可较好地表征鱼糜凝胶脆性。经验证,该模型预测值与实测值无差异(P0.05),具有较好的准确性和精确度,可客观表征鱼糜凝胶脆性,为开发不同口感鱼糜制品提供理论基础。     

Flavor encapsulation in yeasts: limonene used as a model system for characterization of the release mechanism

Empty yeast cells are used as a new delivery system for flavor encapsulation. The flavor release mechanism from yeast cells is characterized using a series of analytical techniques, and limonene is used as a model representing a hydrophobic flavor. Furthermore, the thermal stability of the capsules was assessed. The characterization of the cell wall structure gives rise to the development of an empirical model explaining water adsorption as well as the desorption singularities observed on drying. The study of the rate of flavor release as a function of temperature and water uptake in the cell wall clearly demonstrated a particular behavior of the yeast cell wall permeability. Below a water activity around 0.7, no flavor release is permitted whereas release occurs above it. Surface analysis on dry or wet cells using atomic force microscopy is discussed.