1,721,136 research outputs found
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
Seasonal pattern of gross assimilation and net herbage production under continuous stocking.
No full textProductivity of grasslands under continuous and rotational grazing
No full textIn the Netherlands, rotational grazing, with grazing periods of 2 to 5 days, is the most common grazing system at present. In contrast with other countries of North-western Europe, the continuous grazing system is used here only to a limited extent. However, the results of numerous comparative trials at high nitrogen fertilization levels and high stocking rates, carried out in the 1970's, suggest that there is no significant difference in animal production between the two grazing systems.Experiments were carried out to determine the physiological and environmental limits to herbage production under continuous and rotational grazing. This was done by measuring the seasonal patterns and seasonal totals of sward CO 2 assimilation and animal production. The experiments were carried out on heavy clay soils at two nitrogen fertilization levels (125 and about 450 kg N ha -1yr -1). With 450 kg N ha -1yr -1cumulative gross assimilation over the grazing season was 9% higher with rotational than with continuous grazing, but there was no difference in animal production. The higher efficiency of utilization of gross assimilation products under continuous grazing was due to lower topping losses and lower costs of above-ground maintenance respiration. Under both grazing systems, gross CO 2 assimilation per unit leaf area was not depressed at all at 125 kg N ha -1yr -1. but there was a marked reduction of the rate of leaf area development in the second half of the grazing season. The absence of any effect in the first half of the grazing season was due probably to a residual effect of previously applied nitrogen. This effect can be considerable on heavy clay soils.The herbage intake under rotational grazing is often estimated using Linehan's formula, which takes into account the herbage production during grazing. This formula was evaluated by means of dynamic simulation, with measured assimilation-light response curves as the main input. It emerged that in some practical situations of rotational grazing, the herbage production during the grazing period is significantly underestimated using Linehan's formula. This is mainly because Linehan's formula assumes exponential growth of the sward at all stages of growth. Since this is not correct for a sward in the absence of grazing, a new comprehensive formula is derived, using the assumption that the sward is in the linear growth phase at the start of grazing. Comparisons with the simulation output show that this new formula for estimating herbage intake is valid for all situations of rotational grazing.To manage the continuous grazing system successfully, information is needed about the seasonal changes in production capacity with this grazing system. An experiment with dairy cows revealed that throughout the grazing season a constant proportion (equal to 0.25 at the high nitrogen level) of the carbohydrate pool, derived from gross assimilation minus above-ground maintenance respiration, was ingested by the grazing cattle. This observation formed the basis for a dynamic model to compute the net herbage production under continuous grazing throughout the grazing season, using data on radiation and temperature. It appears that, although there is a gradual decline from spring to autumn, the highest production rates occur in June. The average seasonal pattern of net herbage production, predicted by the model using average weather data, can be used for management purposes of the continuous grazing system. It is then possible to adjust stocking density during the grazing season, to achieve the maximum pasture output without adversely affecting the botanical composition and tiller density of the sward. Although the limited time available for this study made it impossible to examine effects of rotational and continuous grazing on the long term, there are good indications that continuous grazing is preferable in this respect. Moreover, the continuous grazing system seems better able to withstand periods with low rainfall, owing to the higher tiller density. During prolonged periods of water stress, however, the mean sward height must be lowered to about 6 cm, instead of the normal optimum level of 7 to 8 cm. It was observed on the clay soils that there is then actually no need for irrigation to achieve high pasture outputs. This is due partly to the unchanged carbon allocation pattern during periods of water stress.The simulated production rates under continuous grazing were compared with measured production rates of grass swards with an initial herbage mass close to the recommended grazing stage for rotational grazing (1700 kg DM haha -1above 4 cm), in order to develop a simple method for estimating the undisturbed herbage production rate at the onset of a rotational grazing period. The herbage production of a sward in the grazing stage for rotational grazing was, on average, 2 or 2.5 times the production level under continuous grazing. The higher value was found for the period early May-early June and was a result of stem elongation. This observation may serve as a simple method for estimation of the undisturbed production rate.A new procedure was developed to deal with grazing losses. Here, the utilization efficiency is calculated by comparing the total amount of harvested dry matter (herbage intake plus silage grass) with the total production under a certain cutting regime. This approach is applicable in any grassland management situation.The CO 2 assimilation of a leaf canopy is strongly dependent on the ratio between diffuse and direct radiation. This produces much of the scattering often observed in field measurements on the assimilation-light response of crop surfaces. It is shown that the crop production models PHOTON and BACROS, developed at the Department of Theoretical Production Ecology of the Wageningen Agricultural University, treat the distribution of diffuse and direct radiation over the leaves of a canopy correctly, but that the proportion of the diffuse component is significantly underestimated over a wide range of radiation levels. Radiation measurements were used to improve the section in these models describing the separation between diffuse and direct radiation. Literature survey showed that the leaf assimilation-light response in field-grown grass swards can be best calculated using a Blackman curve, rather than the frequently used asymptotic exponential curve. With these improvements, the relation between daily total radiation and daily total gross assimilation (and dry matter production) is shown to approximate to a Blackman curve, with the intersection at 60% of the maximum radiation total on that day, i.e. that under a perfectly clear sky
CO2 assimilation, herbage production and animal production under continuous and rotational grazing at two nitrogen levels
No full textBij doorlopend als wel bij afwisselend weidegebruik met overheersend Engels raaigras zijn studies verricht betreffende CO2-assimilatie, grasproduktie en rundveeproduktie, terwijl een laag (125 kg per ha per jaar) en een hoog (ongeveer 450 kg per ha per jaar) stikstofbemestingsniveau is toegepast. Bij een hoog stikstofniveau bleek de totale cumulatieve assimilatie over het graasseizoen 9 % hoger te liggen bij afwisselend weidegebruik dan bij doorlopend grazen, terwijl er geen verschil in dierproduktie was. Een kleine verandering in de koolstofbalans ten gevolge van de stikstoftoestand van het gras bleek een grote invloed op de weideopbrengst te hebbe
Wellicht meer melk met tetraploid Engels raaigras.
No full textOm meer informatie te verkrijgen over de geschiktheid van tetraploide weidetypen van Engels raaigras voor blijvend grasland werd door de vakgroep Landbouwplantenteelt en Graslandkunde van de Landbouwuniversiteit Wageningen een onderzoek opgezet. Hieruit kwam naar voren dat bij een te verwachten hogere opname van tetraploid gras door melkkoeien theoretisch de melkproduktie met een kg per koe per dag zal toenemen. Proefopzet en berekeningswijze zijn uiteengeze
Simulation of herbage production and herbage intake during a rotational grazing period
No full textDe reguliere bepalingsmethode van de grasopname gedurende omweiding is herzien door middel van simulatie van de grasproduktie tijdens beweiding. De berekening vindt plaats op basis van de geregistreerde assimilatie/licht-reactie van de graszode, met of zonder beweidin
- …
