1,720,993 research outputs found
LEDs for greenhouse lighting
No full textLight Emitting Diodes (LED's) are a promising technology for greenhouse lighting with their efficiency to activate plant photosynthesis potentially higher in red LEDs than in HPS lamps. Due to their particular light colour, LEDs can initiate special effects in plants or steer plant processes and plant balanc
Effects of CO2 concentration on photosynthesis, transpiration and production of greenhouse fruit vegetable crops
No full textThe effect of the C0 2 concentration of the greenhouse air (C) in the range 200 to 1100 μmol mol -1was investigated in tomato ( Lycopersicon esculentum Mill.), cucumber ( Cucumis sativus L.), sweet pepper ( Capsicum annuum L.) and eggplant ( Solanum melongena L.), grown in greenhouses.The effect of C on canopy net photosynthetic C0 2 assimilation rate (or photosynthesis, P) was expressed by a set of regression equations, relating P to PAR, C and LAI. A rule of thumb ('CO 2 -rule') was derived, approximating the relative increase of P caused by additional C0 2 at a certain C. This C0 2 -rule is: X = (1000/C) 2* 1.5 (X in % per 100 μmol mol -1, and C in μmol mol -1). Two models for canopy photosynthesis were examined by comparing them with the experimental photosynthesis data. No 'midday depression' in P was observed.The effects of C on leaf conductance ( g ) and on rate of crop transpiration ( E ) were investigated. An increase of 100 μmol mol -1in C reduced g by about 3-4% in sweet pepper, tomato and cucumber and by about 11 % in eggplant. The effect of C on E was analyzed by combining the regression equation for g with the Penman-Monteith equation for E . C had only a relatively small effect on E , owing to thermal and hydrological feedback effects. The decoupling of g and E was quantified. No timedependent variation or 'midday depression' in E was observed, and no significant effect of C on average leaf temperature was established.In five experiments, the effect of C on growth and production and on specific features were analyzed: light use efficiency was increased by about 10 to 15% per 100 μmol mol -1increase in C; fruit set of sweet pepper was greatly increased by high C; allocation of biomass to fruits was increased by high C in sweet pepper and cucumber; specific leaf area (SLA) was reduced by 15 to 20% at 150 to 250 μmol mol -1increase in C (except in cucumber); dry matter content (DMC) of vegetative organs slightly increased at high C (also not in cucumber); fruit production (dry weight) was most affected by C in sweet pepper; fresh weight fruit production per unit CO 2 was highest in cucumber; fruit quality was not influenced by C. High C promoted the 'short leaves syndrome' in tomato and 'leaf tip chlorosis' in eggplant, probably related to calcium and boron translocation, respectively. The observed effect of C on production was larger than expected on the basis of the CO 2 -rule. Intermittent CO 2 supply (ICS) could under normal ventilation accomplish only a limited increase in average C, and hence a limited increase in production. No physiological advantages of ICS were revealed
Led: Hoe meer onderzoek, hoe meer vragen (Elly Nederhoff tijdens workshop Energiek Event in Bleiswijk)
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Air humidity, stomata & transpiration
No full textThe plant's water status is the balance of water uptake and water loss. Transpiration (water loss) in influenced by sun, wind humidity, leaf area, and opening of stomatal pores in the leaves
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
Lichtmeetprotocol - Afspraken voor lichtmetingen in proef met LED en SON-T belichting in kassen bij WUR in Bleiswijk in 2009/2010
No full textVoor onderzoek aan belichting is het van het grootste belang dat de belichtingsintensiteit en de lichtverdeling goed afgesteld en goed bekend zijn. Dit vereist goede lichtmetingen. Er zijn protocollen voor lichtmetingen, maar deze zijn bedoeld voor metingen aan SON-T belichting in grote kassen in de praktijk. Dan wordt meestal gemeten in een klein representatief meetveldje dat afgestemd is op de verdeling van de SON-T lampen. Lichtmeten in kasafdelingen voor lichtonderzoek vraagt een heel andere benadering. Ten eerste worden daar vaak verschillende lamptypen gebruikt, zoals SON-T en LED en combinaties. Ten tweede wordt gewerkt met verschillende posities van (LED) lampen, bv boven en tussen het gewas, verticaal en horizontaal. Ten derde zijn de kasafdelingen relatief heel klein, met veel randeffecten. In dit meetprotocol komt niet aan de orde hoe het licht zich verspreidt in het gewas (bv het verschil tussen LED-tussenbelichting en bovenbelichting in dit opzicht). Daarvoor is een heel ander soort onderzoek nodig, en dit type lichtmetingen valt niet onder dit protocol. Dit rapport is een samenvatting van de belangrijkste zaken die nodig zijn om aan de slag te gaan met lichtmetingen aan belichtingsinstallaties in kleine kasafdelingen. Er bestaan echter nog veel meer aspecten, aanpakken en zienswijzen. Wellicht kan dit rapport een aanzet vormen voor verdere discussie met deskundigen en betrokkenen op dit gebied
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
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