Onderzoek naar ‘Lissers’ bij hyacint van start

Het verschijnsel ‘Lissers’ veroorzaakt al enkele jaren achtereen schade in de broei bij hyacint. Oorzaak is een fytoplasma, dat vroeger slechts incidenteel voor kwam. Hierdoor is nog weinig bekend over beschermende maatregelen. PPO start daarom onderzoek naar de bestrijding van de overbrenger (dwergcicade) en bestrijding van het fytoplasma, dat de schade veroorzaakt. Daarbij speelt ook de vraag wanneer de planten besmet worden en wanneer en in welke teeltgebieden van hyacint de cicade aanwezig is

Drinking water temperature modelling in domestic systems

Domestic water supply systems are the final stage of the transport process to deliver potable water to the customers' tap. Under the influence of temperature, residence time and pipe materials the drinking water quality can change while the water passes the domestic drinking water system. According to the Dutch Drinking Water Act the drinking water temperature may not exceed the 25°C threshold at point-of-use level. This paper provides a mathematical approach to model the heating of drinking water within the domestic water supply system. It appears that residence time influences the drinking water temperature more than the ambient temperature itself.</p

Low absorption InP/InGaAs-MQW phase shifters for optical switching

InP/InGaAs-MQW phase shifters with low absorption loss and low electroabsorption loss have been realized. Phase shift efficiency for TE-polarized light at lambda =1.55 mu m was 6.8 degrees V/sup -1/ mm/sup -1/ with negligible absorption loss and at lambda =1.51 mu m the efficiency was 8.9 degrees V/sup -1/ mm/sup -1/ with 5 dB/cm absorption los

Importance of demand modelling in network water quality models: a review

Today, there is a growing interest in network water quality modelling. The water quality issues of interest relate to both dissolved and particulate substances. For dissolved substances the main interest is in residual chlorine and (microbiological) contaminant propagation; for particulate substances it is in sediment leading to discolouration. There is a strong influence of flows and velocities on transport, mixing, production and decay of these substances in the network. This imposes a different approach to demand modelling which is reviewed in this article. &lt;br&gt;&lt;br&gt; For the large diameter lines that comprise the transport portion of a typical municipal pipe system, a skeletonised network model with a top-down approach of demand pattern allocation, a hydraulic time step of 1 h, and a pure advection-reaction water quality model will usually suffice. For the smaller diameter lines that comprise the distribution portion of a municipal pipe system, an all-pipes network model with a bottom-up approach of demand pattern allocation, a hydraulic time step of 1 min or less, and a water quality model that considers dispersion and transients may be needed. &lt;br&gt;&lt;br&gt; Demand models that provide stochastic residential demands per individual home and on a one-second time scale are available. A stochastic demands based network water quality model needs to be developed and validated with field measurements. Such a model will be probabilistic in nature and will offer a new perspective for assessing water quality in the drinking water distribution system

Can interaction specificity in the fungus-farming termite symbiosis be explained by nutritional requirements of the fungal crop?

<p>Fungus-growing termites are associated with genus-specific fungal symbionts, which they acquire via horizontal transmission. Selection of specific symbionts may be explained by the provisioning of specific, optimal cultivar growth substrates by termite farmers. We tested whether differences in in vitro performance of Termitomyces cultivars from nests of three termite species on various substrates are correlated with the interaction specificity of their hosts. We performed single-factor growth assays (varying carbon sources), and a two-factor geometric framework experiment (simultaneously varying carbohydrate and protein availability). Although we did not find qualitative differences between Termitomyces strains in carbon-source use, there were quantitative differences, which we analysed using principal component analysis. This showed that growth of Termitomyces on different carbon sources was correlated with termite host genus, rather than host species, while growth on different ratios and concentrations of protein and carbohydrate was correlated with termite host species. Our findings corroborate the interaction specificity between fungus-growing termites and Termitomyces cultivars and indicate that specificity between termite hosts and fungi is reflected both nutritionally and physiologically. However, it remains to be demonstrated whether those differences contribute to selection of specific fungal cultivars by termites at the onset of colony foundation.</p

Haalbaarheidstudie: regenwater opvangen en benutten op luchthaven Schiphol

Voor een effectieve bescherming van beschikbare (zoet)waterbronnen is het opvangen en benutten van regenwater op regionale schaal noodzakelijk, evenals het vergroten van de regionale zelfvoorzienendheid. Deze studie op het terrein van luchthaven Schiphol laat zien dat regenwateropvang van verschillende oppervlakten haalbaar is, maar dat voor volledige dekking een vrij grote berging noodzakelijk is

Asexual and sexual reproduction are two separate developmental pathways in a <i>Termitomyces</i> species

Although mutualistic symbioses per definition are beneficial for interacting species, conflict may arise if partners reproduce independently. We address how this reproductive conflict is regulated in the obligate mutualistic symbiosis between fungus-growing termites and Termitomyces fungi. Even though the termites and their fungal symbiont disperse independently to establish new colonies, dispersal is correlated in time. The fungal symbiont typically forms mushrooms a few weeks after the colony has produced dispersing alates. It is thought that this timing is due to a trade-off between alate and worker production; alate production reduces resources available for worker production. As workers consume the fungus, reduced numbers of workers will allow mushrooms to 'escape' from the host colony. Here, we test a specific version of this hypothesis: the typical asexual structures found in all species of Termitomyces-nodules-are immature stages of mushrooms that are normally harvested by the termites at a primordial stage. We refute this hypothesis by showing that nodules and mushroom primordia are macro- and microscopically different structures and by showing that in the absence of workers, primordia do, and nodules do not grow out into mushrooms. It remains to be tested whether termite control of primordia formation or of primordia outgrowth mitigates the reproductive conflict.</p

Loss of HR6B ubiquitin-conjugating activity results in damaged synaptonemal complex structure and increased crossing-over frequency during the male meiotic prophase.

The ubiquitin-conjugating enzymes HR6A and HR6B are the two mammalian homologs of Saccharomyces cerevisiae RAD6. In yeast, RAD6 plays an important role in postreplication DNA repair and in sporulation. HR6B knockout mice are viable, but spermatogenesis is markedly affected during postmeiotic steps, leading to male infertility. In the present study, increased apoptosis of HR6B knockout primary spermatocytes was detected during the first wave of spermatogenesis, indicating that HR6B performs a primary role during the meiotic prophase. Detailed analysis of HR6B knockout pachytene nuclei showed major changes in the synaptonemal complexes. These complexes were found to be longer. In addition, we often found depletion of synaptonemal complex proteins from near telomeric regions in the HR6B knockout pachytene nuclei. Finally, we detected an increased number of foci containing the mismatc