1,041 research outputs found

    Ontwikkeling en implementatie van geïntegreerde bestrijding in zomerbloemen : toepassing van beschikbare producten en ontwikkeling van nieuwe natuurlijke vijanden

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    In 2008 en 2009 werden loslatingen verricht van de roofmijten Neoseiulus cucumeris en Amblyseius andersoni, soms aangevuld met Phytoseiulus persimilis, in de zomerbloemen rozenbottel, chrysant, Veronica, Alchemilla en Delphinium. Hierbij bleek dat roofmijten zich niet in alle gewassen in gelijke mate vestigen. In Alchemilla en Delphinium bleek al spontaan Neoseiulus cucumeris voor te kunnen komen. Als in deze gewassen nog geen roofmijten voorkomen, zal introductie van N. cucumeris zeker slagen, mits er geen breedwerkende middelen worden toegepast. Vooral Alchemilla bleek een goede roofmijtenplant te zijn. Behalve Neoseiulus cucumeris werden ook andere soorten gevonden. Roofmijten die in de handel zijn tegen spint, Phytoseiulus persimilis en Neoseiulus californicus, vestigen zich eveneens goed in dit gewas, in tegenstelling tot Amblyseius andersoni. Verder kunnen spontaan andere natuurlijke vijanden van plagen voorkomen: roofwantsen, gaasvliegen en galmuggen. Trips nam in beide jaren af gedurende de teelt of bleef op een laag niveau. Neoseiulus alpinus is een roofmijt, die eerder is verzameld van Alchemilla en in kweek genomen. Een loslating van deze roofmijt in Alchemilla slaagde in 2008 niet, maar in 2009 wel. In Delphinium was in 2008 vanaf het begin van de waarnemingen Neoseiulus cucumeris in het gewas aanwezig. Na introductie van Amblyseius andersoni werd ook deze soort teruggevonden. Spint kwam in 2008 niet tot ontwikkeling. Buiten de proef kwam plaatselijk cyclamenmijt voor. In 2009 werd in Delphinium zwavel verdampt tegen echte meeldauw. Er was geen goede vestiging van roofmijten in het gewas, ook niet van de roofmijt Phytoseiulus persimilis, waardoor chemische bestrijding van spint noodzakelijk was. In Veronica, chrysant en rozenbottel kwamen in vergelijking met Alchemilla en Delphinium minder roofmijten voor. Trips en spint waren in 2008 en 2009 geen probleem in Veronica, chrysant en rozenbottel. Op rozenbottel kwam zonder introductie Neoseiulus cucumeris voor. Andere soorten roofmijten, die soms spontaan optraden waren Neoseiulus reductus in Delphinium, Amblyseius graminis in Alchemilla en chrysant, en roofmijten die tot een andere groep (Bdelloidea) behoren, met name op chrysant en Veronica

    The Life History of Desmotrichum undulatum (Phaeophyceae) and its Regulation by Temperature and Light Conditions

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    Plurizoids of Desmotrichum undulatum (J. Ag.) Reinke, grow into microthalli bearing macrothalli under a wide range of temperature (4 "-30 "C) and light conditions: short day (SD) 1000, 2000, 4000 Lux; long day (LD) 500, 1000, 2000 Lux. At 35 "C microthalli die. It is mainly the temperature which modifies the n~orphological expression of the macrothallus: (1) Higher temperatures (ca 20 "-30 "C) support the development of uniseriate macrothalli; lower temperatures (ca 4 "-16 "C) of pluriseriate ribbon-like thalli; and intermediate temperatures (ca 16 "-20 "C) of proximally pluriseriate and distally umseriate macrothalli. These morphological expressions form a graded series. (2) Higher temperatures promote the growth rate of macrotalli; the rapid growth is soon overtaken by intense zoidogeneses which ends the vegetative growth of very small microthalli. (3) Temperature influences the time span before the onset of zoidogenesis; the time span varies from ca 1 week at 20 "C to ca 13 weeks at 4 "C. The result is that at lower temperatures (4 "-12 "C) the final macrothalli size is much larger than at higher temperatures, not withstanding a lower growth rate. Under short-day conditions the onset of zoidogenesis IS advanced, particularly so at lower temperatures. Therefore, the largest macrothalli are formed at lower temperatures and under long-day conditions; this corresponds to late spring in nature. Maximum microthalli length in culture (at 8 "C) was ca 60 cm Such macrothalli conform to the description of Punctaria latifolia also in other respects. Therefore D, undulatum (including D. balticum and D scopulorum) is thought to be synonymous with P. latifolia. The seasonal occurrence of macrothalli (winter-spring) and the geographic distribution are in accordance with results obtained in culture

    Damped Lyman alpha Absorbing Galaxies At Low Redshifts z<1 From Hierarchical Galaxy Formation Models

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    We investigate Damped Ly-alpha absorbing galaxies (DLA galaxies) at low redshifts z<1 in the hierarchical structure formation scenario to clarify the nature of DLA galaxies because observational data of such galaxies mainly at low redshifts are currently available. We find that our model well reproduces distributions of fundamental properties of DLA galaxies such as luminosities, column densities, impact parameters obtained by optical and near-infrared imagings. Our results suggest that DLA systems primarily consist of low luminosity galaxies with small impact parameters (typical radius about 3 kpc, surface brightness from 22 to 27 mag arcsec^{-2}) similar to low surface brightness (LSB) galaxies. In addition, we investigate selection biases arising from the faintness and from the masking effect which prevents us from identifying a DLA galaxy hidden or contaminated by a point spread function of a background quasar. We find that the latter affects the distributions of DLA properties more seriously rather than the former, and that the observational data are well reproduced only when taking into account the masking effect. The missing rate of DLA galaxies by the masking effect attains 60-90 % in the sample at redshift 0<z<1 when an angular size limit is as small as 1 arcsec. Furthermore we find a tight correlation between HI mass and cross section of DLA galaxies, and also find that HI-rich galaxies with M(HI) \sim 10^{9} M_sun dominate DLA systems. These features are entirely consistent with those from the Arecibo Dual-Beam Survey which is a blind 21 cm survey. Finally we discuss star formation rates, and find that they are typically about 10^{-2} M_sun yr^{-1} as low as those in LSB galaxies.Comment: 21 pages, 13 figures, Accepted for publication in Astrophsical Journa

    Growth of children with Langerhans cell histiocytosis

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    Conclusion: GH deficiency is not a common manifestation of LCH in childhood and GH provocation tests are only indicated when there is a poor or decelerating growth rate. In our patients the number of organs involved and/or the treatment modality did not influence the growth in all but one. Diseases in childhood have an impact on growth. The influence of Langerhans cell histiocytosis (LCH) on growth has never been studied well. Recently a patient with LCH was treated with human growth hormone (GH) because of severe GH deficiency due to LCH involvement of both the hypothalamus and pituitary. This led us to review our charts from 1971 onward for evaluation of the growth patterns in patients with LCH. Here the long-term growth of 22 patients with LCH is reported, the median follow up being 7 years and 1 month. The height data were converted into standard deviation scores (SDS). At diagnosis the mean SDS of patients with isolated LCH at diagnosis was 0.04 and -0.37 in patients with disseminated LCH. Of the total group, 12 patients did not show any influence from the LCH or therapy on their growth. The remaining 10 patients reached, after a minimum of 3 years, a percentile clearly higher than that at diagnosis. However all the ten above mentioned patients, either isolated or disseminated LCH, had a lesion in the facial side of the skull

    Bestrijdingsadviezen herbiciden per computer

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    De keuze van het herbicide en de bepaling van de juiste dosering is heel belangrijk. Enerzijds om een goede effectiviteit tegen onkruiden te bereiken en anderzijds om gewasschade (zoveel mogelijk) te voorkomen. In een aantal gewassen zijn veel herbiciden beschikbaar en is de keuze van het optimale middel of middelencombinatie dan ook moeilijk. De laatste jaren is een aantal computerprogramma's beschikbaar gekomen die de teler ondersteunen bij het maken van deze keuze en bij het bepalen van de juiste dossering. Er wordt vanuit het praktijkonderzoek en andere organisaties gewerkt aan uitbreiding van het aantal programma's en aan verbetering erva

    Planetary Nebulae as Probes of Stellar Evolution and Populations

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    Planetary Nebulae (PNe) have been used satisfactory to test the effects of stellar evolution on the Galactic chemical environment. Moreover, a link exists between nebular morphology and stellar populations and evolution. We present the latest results on Galactic PN morphology, and an extension to a distance unbiased and homogeneous sample of Large Magellanic Cloud PNe. We show that PNe and their morphology may be successfully used as probes of stellar evolution and populations.Comment: to appear in: Chemical Evolution of the Milky Way: stars versus clusters, ed. F. Giovannelli and F. Matteucci, Kluwer (2000), in pres

    A search for Low Surface Brightness galaxies in the near-infrared I. Selection of the sample

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    A sample of about 3,800 Low Surface Brightness (LSB) galaxies was selected using the all-sky near-infrared (J, H and K_s-band) 2MASS survey. The selected objects have a mean central surface brightness within a 5 arcsec radius around their centre fainter than 18 mag/sq.arcsec in the K_s band, making them the lowest surface brightness galaxies detected by 2MASS. A description is given of the relevant properties of the 2MASS survey and the LSB galaxy selection procedure, as well as of basic photometric properties of the selected objects. The latter properties are compared to those of other samples of galaxies, of both LSBs and `classical' high surface brightness (HSB) objects, which were selected in the optical. The 2MASS LSBs have a (B_T_c)-(K_T) colour which is on average 0.9 mag bluer than that of HSBs from the NGC. The 2MASS sample does not appear to contain a significant population of red objects.Comment: accepted for publication in Astronomy and Astrophysics on 24/2/2003; 62 page
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