Effects of catch crops on silage maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.): yield,nitrogen uptake efficiency and losses

Under the climatic conditions of north-western Europe, silage maize (Zea mays L.) production optimized with respect to nitrogen (N) fertilization and crop rotation is required to reduce N losses. Whether winter catch crops (CC) can serve as a beneficial biological tool in terms of N-loss abatement as well as maize yield also under optimized N management, is unclear. Therefore, a 2-year field experiment was conducted to study the short-term effects of a continuous maize-catch cropping system on maize yield performance, N₂O emission and N leaching, as affected by maize harvest/CC sowing date (10, 20, 30 September and 15 October, respectively, hd₁–hd₄) and CC species (rye, Secale cereale L. and Italian ryegrass, Lolium multiflorum Lam.). Treatments without CC served as control and N fertilization was applied as synthetic N to better adjust to maize N demand. The CC treatment (with or without) had no effect on maize dry matter and N yields, but the N uptake efficiency of maize responded significantly to the N accumulation (N_tot) of CC. Nitrate leaching mostly stayed below the critical load value for EU drinking water and rye significantly reduced nitrate leaching, given that environmental conditions allowed sufficiently high CC biomass accumulation. Annual nitrous oxide emission was unaffected by CC treatment. Restricted N fertilization of maize following CC led to N deficiency, since CC decomposition obviously was not synchronized with maize N demand. Under the given environmental conditions, rye may serve as beneficial CC in continuous maize cropping even in already optimized N management.     

微结构与收缩的关系

微结构的特性是非常复杂的,并且对其进行定量化的描述必然受到龄期和环境变化的限制.混凝土的整体性质和退化过程一般认为是干缩和碱集料反应及其他反应引起的体积变化有关.收缩和徐变是因干燥和加载、反复冻融所引起的长度变化.碱集料反应和硫酸盐侵蚀改变了局部体积并带来内部损伤.近来的研究表明,收缩引起的内部损伤是可以清楚定位的,但是,损伤的程度却很难量化评估.     

Bestandsaufnahme Grundwasser nach der EU-Wasserrahmenrichtlinie im Koordinierungsraum Mulde-Elbe-Schwarze Elster

Die Wasserrahmenrichtlinie regelt den Schutz von Grund- und Oberflächengewässern und fordert eine nachhaltige Wassernutzung. Sie legt einen Zeitplan fest, um bis zum Jahr 2015 für alle Gewässer einen guten Zustand zu erreichen. Der erste Schritt ist eine Bestandsaufnahme der Gewässer. Für das Grundwasser besteht diese aus einer erstmaligen Beschreibung, einer weitergehenden Beschreibung und der Prüfung der Auswirkungen menschlicher Tätigkeit auf das Grundwasser. Die Wasserrahmenrichtlinie wird unabhängig von administrativen Grenzen innerhalb von hydrologischen Einzugsgebieten umgesetzt. Im deutschen Teil des Flusseinzugsgebietes der Elbe wurden 5 Koordinierungsräume gegründet. Der Koordinierungsraum Mulde-Elbe-Schwarze Elster (MES) wird vorgestellt. Beispielhaft für die angewandten Methoden wird die Beurteilung diffuser Stoffeinträge in das Grundwasser bei der erstmaligen Beschreibung erläutert. Die Ergebnisse der Bestandsaufnahme Grundwasser im Koordinierungsraum MES werden präsentiert. Von 54 Grundwasserkörpern ist für 25 Körper aufgrund der Belastungen durch Punktquellen und diffuse Quellen, wegen des mengenmäßigen Zustands oder sonstiger anthropogener Einwirkungen die Zielerreichung nach der Wasserrahmenrichtlinie unklar/unwahrscheinlich.     

景观设计展望:国际性和中国特色

中国的当代景观设计仍然在传统的范例和国际的范例之间探寻其自己的风格。北京土人景观规划设计研究院所做的项目展示了当代的、同时又是自己的设计语言,彰显了全球化背景下当代中国人的身份。     

Experimental investigation on the avoidance of self-excited vibrations

Self-excited vibrations are observed in many technical applications. Frictional contacts are often involved in the mechanism which generates vibrations. Reasons for the excitation mechanisms are decreasing friction characteristics depending on the sliding velocity, fluctuating normal loads or different geometrical effects. First, the mechanisms are explained using simple examples. The practical relevance of self-excited, friction-induced vibrations is exemplified with three technical systems: a system with an axial seal; a tread block of a tyre; and a disc brake. The knowledge of the excitation mechanism is necessary to introduce successfully design countermeasures. These measures to avoid self-excited vibrations are important to solve practical problems. They are the main focus of this work. Further, additional passive and active subsystems are described and validated experimentally. Therefore, a large range of design, active and passive solutions are given.     

Influence of electron irradiation on the crystallisation,molecular weight and mechanical properties of poly-(<Emphasis Type="Italic">R</Emphasis>)-3-hydroxybutyrate

Biosynthetic poly[(R)-3-hydroxybutyrate] (PHB) undergoes a deleterious ageing process which has been attributed to progressive crystallisation. In this work an attempt has been made to arrest this crystallisation behaviour by an irradiation treatment which is known to induce cross-linking in many polymers. PHB films were irradiated with different doses of electrons and at different times after the initiation of crystallisation. The degree of crystallinity was subsequently determined as a function of time after irradiation using wide-angle X-ray scattering measurements. In addition, melting endotherms were obtained by differential scanning calorimetry (DSC) and molecular weights by gel permeation chromatography (GPC). Corresponding tensile stress–strain experiments were performed in order to obtain information on the mechanical properties of the sample films. The melting point and molecular weights were found to decrease linearly with radiation dose indicating that higher radiation doses cause degradation due to chain scission. However, lower doses applied to samples still in their amorphous state indicate a high degree of cross-linking, in which a network is formed and the ageing process can be prevented to some extent. The tensile modulus and breaking strain were influenced strongly by the point in time at which the material was irradiated during crystallisation.