1,722,537 research outputs found
Competition and yield advantage in mixtures of pea (Pisum sativum L.) and oats (Avena sativa L.)
No full textIn field trials on a fertile fluvisol in 1995 and 1996 near Gottingen, Germany, pea (Pisum sativum; cv. Messire/conventional leafed, cv, Profi/semileafless) and oats (Avena sativa; cv. Alf) were grown as sole crops and in substitutive mixtures. The sole crops were established at 80 pea seeds m(-2) and 300 oat seeds m(-2). The mixtures consisted of 67% (pea) and 33% (oats) of the monoculture densities, respectively. Interactions of cv. Messire or cv. Profi and oats were similar in 1995 and 1996. The mixtures outyielded the monocultures with respect to total above ground dry matter (RYT = 1.15) and grain yield (RYT = 1.09). Grain yield of pea and oats averaged 4.9 t ha(-1) in monocultures and 5.5 t ha(-1) in mixtures. Oats was relatively the stronger of the two competitors. Decreasing number of pods per plant could be highlighted as the factor for a lower pea seed frequency in the yield of the mixtures. For oats the number of panicles per plant and kernels per panicle were higher in the mixtures compared with the oat monocultures. The average amount of the harvest index (HI) was 0.52 for pea and 0.46 for oats. Favourable growth conditions increased HI values however, prolific vegetative growth in the mixtures resulted in lower HI values. The predicted RYT-values estimate the maximum combined grain yield of 6.3 t ha(-1) in the mixture of 87% pea (70 seeds m(-2)) and 13% oats (39 kernels m(-2))
The performance of pea (Pisum sativum L.) and its role in determining yield advantages in mixed stands of pea and oat (Avena sativa L.)
No full textOn a brown warp soil (Fluventic Eutrochrept) near Goettingen, Germany, conventional leafed pea (Pisum sativum L. cvs Messire and Bohatyr) and semileafless types (cvs Profi. Juno and Azur) were grown in mixed stands together with oat (Avena sativa cvs Alf and Lutz) in substitutively designed experiments from 1995 to 1997. Oat was the dominant component. Crowding coefficients for oat averaged 7.4. No relationship could be detected between the crowding coefficient of oat and any yield advantage from the mixture. Crowding coefficients for pea varied substantially, between 0.1002 (Juno and Alf in 1996) and 0.2979 (Bohatyr and Alf in 1996). Crowding coefficients for semileafless pea cultivars were smaller than for conventional leafed types. The yield advantage of the mixture increased as the crowding coefficient of pea increased. The maximum yield increase for the mixture was achieved when the relative yield total (RYT) = 1.17 or + 11 dt grain DM ha(-1) for mixtures of the long-strawed conventional leafed cultivars Bohatyr and Alf (in 1996). The crowding coefficients of pea were positively correlated with the level of symbiotically fixed N(2) in the mixed stands. When N(2) fixation with mixed cropping was about 30 kg N ha(-1), RYT was unity. Increasing symbiotic N(2) in the mixtures resulted in increasing yield advantages in the mixture. Short-strawed pea cultivars seem unsuitable for mixing with oat. Plant height of pea appeared to be more important than plant leaf type. Accordingly, mixtures containing the long-strawed semileafless pea cultivars Profi and Alf were more successful. It is concluded that increased competitiveness of the pea component in the mixture with oat entails increasing the level of symbiotic N(2) fixation including resource complementarity and thus yield advantage in the mixed stands
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Application of fourier transform infrared spectroscopy to silica diagenesis: the opal-A to opal-CT transformation
No full textKinetic modelling of reactions for the synthesis of 2-methyl-5-ethyl pyridine
No full textThe kinetics of the acid catalyzed reactions of acetaldehyde ammonia trimer (AAT) and paraldehyde (para) to 2-methyl-5-ethyl pyridine (MEP) in the presence of an acid catalyst were investigated systematically. A reaction model has been developed based on experimental data. With full characterisation of side products it is possible to describe the reaction as a polymerisation and to understand the different reactivity of AAT and para, respectively. A kinetic model to describe the formation of MEP and the side products was developed using operando Raman spectroscopy. The model, involving four main reactions, is able to describe the formation of MEP and side products and incorporates the effects of reactant concentration, temperature and promoter concentration. This model is an important step that allows for further process intensification and evaluation of each of the two reaction routes. This journal i
Packed Periodic Open Cellular Structures – an Option for the Intensification of Non-Adiabatic Catalytic Processes
Full text linkConductive structured catalysts offer significant potential for the intensification of gas-solid catalytic processes owing to their enhanced heat transfer properties. A major drawback is the limited catalyst inventory. Recently, packed foams were proposed to overcome the catalyst inventory limitation. The effectiveness of this concept was proven at lab-scale for intensified reactors filled with small catalyst particles. When adopting commercial foams and industrial-scale catalyst pellets, however, poor packing efficiencies are expected, limiting the potential of this concept. Similarly to foams, Periodic Open Cellular Structures (POCS) grant high heat transfer rates thanks to substantial heat conduction in their solid matrix. Additively manufactured POCS additionally offer great design flexibility. This allows for using a wider range of pellet sizes. In this work, particle packed POCS are introduced and packing efficiencies are systematically studied. Pressure drop in packed POCS is also analyzed and a suitable correlation is proposed. The heat transfer associated with this innovative reactor solution is investigated by performing non-reactive heat transfer experiments. Based on these experiments, a predictive heat transfer model is established and successfully validated with experimental data. The enormous potential of packed POCS for process intensification is illustrated by a case study of a Sabatier pilot reactor
PH effects in the acetaldehyde-ammonia reaction
No full textThe pH dependency of the reaction of acetaldehyde and ammonia to form the acetaldehyde-ammonia trimer has been studied in detail. The acetaldehyde-ammonia trimer is a molecule of interest in organic synthesis, since it can be used as a substrate in many reactions involving acetaldehyde or ammonia. This trimer is well known in the literature but no references are present so far to describe its formation from ammonia sources other than ammonium hydroxide. The focus of this study is on describing the course of reaction after addition of acetaldehyde to solutions of ammonia and various acids. Products have been analysed by means of 1H-NMR and IR spectroscopy and the complete range of pH values has been covered. Depending on the pH, two reaction regimes can be distinguished. At high pH, only the trimer is formed. In contrast, at low pH, only low quantities of the trimer are produced and the nature of the applied acid has a distinct effect on the reaction outcome. Inorganic acids result in low trimer concentration and high quantity of unreacted ammonia. Polymer formation dominates with simple carboxylic acids. Complex organic acids, such as e.g. maleic or nicotinic acid, lead to comparable quantities of the trimer and acetaldehyde. Based on our results, we propose some adjustments to the traditional reaction scheme developed for acetaldehyde-ammonia trimer formation at high pH
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