Ecological drivers of fish metacommunities: Environmental and spatial factors surpass predation in structuring metacommunities of intermittent rivers

Metacommunity theory is a new approach for explaining how local and regional processes contribute to community organisation and integrative studies are needed to fully characterise the processes underlying its structure and function. We analysed, through variation partitioning and distance decay relationships, how metacommunities of fish in pools of intermittent rivers are structured by environmental, species interaction and spatial factors. The results indicate that both species sorting and dispersal limitation (spatial factors) were important in shaping fish metacommunities. Species sorting was the most influential driver within fish metacommunities, but predation was much less relevant and did not show any pure effect in metacommunity structure. However, environmental factors were determinant among metacommunity patches.     

Automatic grading of sawlogs: A comparison between X-ray scanning,optical three-dimensional scanning and combinations of both methods

As sawmills become increasingly efficient, the importance of focusing on value recovery becomes obvious. To maximize value recovery, sawmills require the ability to sort logs according to quality. This study compares four different combinations of three-dimensional (3D) and X-ray scanning that can be used to grade logs automatically. The study was based on 135 Scots pine (Pinus sylvestris L.) logs that had been scanned with both a 3D scanner and an X-ray scanner with two X-ray sources. The percentage of boards with correct grade sawn from automatically graded logs varied from 57% when using only 3D scanning to 66% when using a combination of 3D scanning and X-ray scanning in two directions. The highest possible result, with ideal log grading, was 81%. The result also shows that the combination of a 3D scanner and one X-ray direction results in higher accuracy than a scanner based on two X-ray directions.     

湿地松种子分级育苗的研究

湿地松湿系种子筛分为大、中、小三个粒度级进行发芽和播种育苗，据此进行的两地点两年度的试验结果表明，分级改变了种子的大小和重量分布，影响种子的发芽速度，进而影响到苗木的早期生长。在芽苗时期和苗木生长早期，各粒度级种子所育苗木有差异，但在生长后期已基本消失，混系种子分级未能达到改进苗木质量和一致性的目的，在育苗时首先要考虑种批的遗传构成，其次才是按种子大小或重量分级。     

胡麻脱粒清选装置作业过程仿真与试验

针对分段收获后胡麻脱出物形状差异小、混杂程度大、清选困难等问题,设计了胡麻脱粒清选装置。为提高胡麻脱粒清选装置作业效率,探究胡麻脱粒物料气流式清选机理,以装置气流清选系统为研究对象,分别建立清选系统CFD模型和胡麻脱出物DEM模型。采用CFD-DEM耦合仿真技术,通过研究各组分脱出物料的运动轨迹与空间位置分布,得出清选系统内胡麻脱出物分离规律,并进行验证试验,校验仿真模型可靠性。仿真试验表明,胡麻脱粒物颗粒在清选系统内气流场的作用下表现出较好的分离清选效果,同时,通过分析模拟试验所得到的胡麻脱粒物颗粒数量和平均速度变化曲线,探明了胡麻脱粒物料在分离清选作业过程中运移的平均速度和数量的变化规律。验证试验表明,该装置在最佳工作状态下作业后胡麻籽粒的清选损失率为2.78%,含杂率为2.23%,与仿真模拟胡麻籽粒损失率（2.05%）、含杂率（1.56%）相比,二者试验结果分别仅相差0.73、0.67个百分点,实际试验结果与仿真模拟结果吻合度较高,验证了模型的可靠性。     

Development of a method for sorting picea abies pulp wood with respect to basic density

The basic density of pulp wood can be used to convert green volume to dry weight, and as an indicator of the fibre quality. Because the methods for measuring basic density are cumbersome, a practical, on‐line method for sorting Norway spruce pulp wood with respect to basic density was developed. The relationship between mean annual ring width and basic density was used to sort the pulp wood. Brief visual inspection could separate piles of logs with different mean annual ring widths from each other with an acceptable precision. The resulting classes had significantly different mean basic densities (380, 400 and 434 kg m^?3). Means of other properties, such as juvenile wood content, heartwood content, and dry matter content, also differed among classes.     

Heartwood diameter measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning

Abstract

Quality sorting of sawlogs based on three-dimensional (3D) or X-ray scanning or a multivariate combination of variables from both methods may be used to decrease the production of off-grade products carrying unwanted combinations of dimension and grade. There is, however, potential for further improving the sorting accuracy if 3D and X-ray raw data are combined at an early stage using path length compensation. From the measured 3D shape, a good estimate of the length of each X-ray path through the log can be made, enabling the calculation of a log density profile from the measured X-ray attenuation. The effect of this technique on heartwood diameter measurements of 423 Scots pine (Pinus sylvestris L.) logs was evaluated. By the addition of 3D data to the X-ray data it was possible to raise the predictability of the heartwood diameter from R ²=0.84 to 0.95 and to improve the root mean square error from 17 mm to 9.3 mm, primarily because of the enhanced contrast between heartwood and sapwood.     

网页中按任意字段对数据动态排序显示的算法设计

在动态网站中查看数据时,不同的用户希望能够方便地按照不同的字段排列数据并进行显示。设计了一个简洁通用的函数利用表单实现表头字段,将数据动态地按任意表头字段进行排序,并可以灵活地选择顺序与逆序的排序方式,用于动态网页中的数据显示。     

农村生活垃圾三化体系运行模式设想

分析了天津农村生活垃圾的主要特征,指出农村垃圾收集、处理存在的主要问题。讨论了近郊农村开展垃圾分类的利弊,并提出近郊农村垃圾实现垃圾减量化、无害化及资源化综合处理运行模式的设想。     

基于OHTA颜色空间的瓜果轮廓提取方法

提出了一种对彩色水果图像进行果实轮廓提取的算法.首先将图像转换为OHTA颜色空间中的灰度图像,用阈值法实现了图像分割;然后用BLOB算法滤去图像中的噪声;最后用插值的方法得到平滑的轮廓曲线.利用开发的智能瓜果精选分级试验样机,按照大小对温室西红柿进行分类,对算法的精度和实时性进行检验,结果表明算法的精度可达98%,分选速度达到3个/s,达到了实用化的目标.     

果蔬产品品质无损检测技术的研究进展

该文较为全面地介绍了国内外基于果蔬产品物理特性的无损检测技术的研究现状及方法,如电学特性检测技术、光学特性检测技术、声波振动特性检测技术、核磁共振(NMR)技术、电子鼻技术、撞击技术以及一些其他技术与方法,并对未来的发展方向予以了展望,认为综合应用多种高科技技术进行果蔬产品的无损检测与分选是未来发展的趋势。