Showing papers by "Wageningen University and Research Centre published in 1991"

Body Fat Distribution in Relation to Physical Activity and Smoking Habits in 38-year-old European Men The European Fat Distribution Study

Abstract: The authors studied 512 European men all born in 1950 from six different towns in the period October 1988 to May 1989. Anthropometric measurements were taken, including weight, height, and circumferences (waist, hip, thigh). Educational level, activity scores and information on smoking habits were obtained from a questionnaire. Higher educational level was associated with lower body mass index, waist/hip ratio, and waist/thigh ratio. The sports activity score was negatively related to waist/hip ratio (beta +/- standard error of the mean (SEM): -0.009 +/- 0.003) and waist/thigh ratio (-0.041 +/- 0.007), and this could be attributed to a negative relation with waist circumference and a positive relation to thigh circumference. Smoking habits were not related to body mass index but heavy smokers had larger waist circumferences (difference +/- SEM: 1.4 +/- 0.5 cm) as well as higher waist/hip ratios (difference +/- SEM: 0.014 +/- 0.005) and waist/thigh ratios (0.043 +/- 0.013) compared with men who never smoked. These associations between activity scores and smoking habits and fat distribution remained after adjustment for each other and for body mass index and educational level. The authors conclude that physical activity and smoking are independently related to indicators of fat distribution and may be potential confounders in the relations between fat distribution, risk factors, and disease.

A Clusterwise Regression Method for Simultaneous Fuzzy Market Structuring and Benefit Segmentation

Abstract: A generalized algorithm for fuzzy clusterwise regression (GFCR) is proposed that incorporates both benefit segmentation and market structuring within the framework of preference analysis. The metho...

The effect of aromatic structure on the inhibition of acetoclastic methanogenesis in granular sludge.

Abstract: Benzene derivatives are important constituents of certain effluents discharged by pulp and paper, petrochemical and chemical industries. The anaerobic treatment of these waste-waters can be limited due to methanogenic inhibition exerted by aromatic compounds. The objective of this study was to evaluate the effect of aromatic structure on acetoclastic methanogenic inhibition. The toxicity to acetoclastic methanogens was assayed in serum flasks utilizing granular sludge as inoculum. Among the monosubstituted benzenes, chlorobenzene, methoxybenzene and benzaldehyde were the most toxic with 50% inhibition occurring at concentrations of 3.4, 4.2 and 5.2 mm, respectively. In contrast, benzoate was the least inhibitory: concentrations up to 57.3 mm were non-toxic. In general, the toxicity of aromatic compounds increased with increasing length of aliphatic side-chains, increasing the number of alkyl or chlorine groups. The logarithm of the partition coefficient octanol/water (log P), an indicator of hydrophobicity, was observed to be positively correlated with the methanogenic inhibition. The results indicate that hydrophobicity is an important factor contributing to the high toxicity of the most inhibitory aromatic compounds.

Semiquantitative Estimates of Exposure to Methylene Chloride and Styrene: The Influence of Quantitative Exposure Data

Abstract: Nine occupational hygienists semiquantitatively estimated the exposure to methylene chloride and styrene in a small polyester factory. They ranked the jobs from low to high exposure, and subsequently classified them into three exposure categories (0–1/2TLV, 1/2TLV-TLV, and > TLV). The influence of quantitative exposure data on the results of the estimations was studied. Therefore, three estimations were performed. The first estimation was made after a visit to the workplace; the second and third were made after limited exposure data were presented. The results showed that presenting quantitative exposure data hardly improved the ranking of jobs from low to high exposure. The ranking of styrene exposure was, in general, poor compared to the ranking of methylene chloride exposure. Physical properties such as perception of smell, application in the process, and level of exposure might be the reasons for this striking difference. Classification of exposure into quantitative exposure categories was po...

Discharge by aphids of soluble secretions into dietary sources

Abstract: Substances secreted by aphids into diets through a rubber-wax membrane can be detected by their absorption of low wavelength ultraviolet light. Their detection can be simplified by presenting water as diet. Of the substances secreted into water by non-crowded aphids within 24 h, ca 35–55% of the absorbance at 200 nm can be accounted for by reactions with protein reagents and/or electrophoresis. Macrosiphum euphorbiae secreted over 30 ng of salivary protein in bovine serum albumin equivalents per mg fresh body weight. SDS-PAGE revealed that the proteins initially secreted had subunits mostly of > 100,000 Daltons. When dead or dying aphids were present on the membrane, however, e.g. due to crowding or prolonged confinement in the feeding chamber, additional subunits of < 30,000 Daltons also appeared in the water. When feeding continued for more than 24 h, proteins separable by electrophoresis began to disappear, possibly as a result of leakage of lyzing enzymes into the water from aphids that had died with their mouth parts still inserted through the membrane. The initial secretions possessed oxidase activity. Invertase was not detected but the secretion caused non-enzymatic reduction of a copper reagent used for detection of reducing sugars. Marked contrasts were noted between the electrophoretic protein patterns of the saliva of different species of aphids. The saliva of Macrosiphum euphorbiae and Myzus persicae contained over twice as much catechol oxidase activity per unit of salivary protein as that of Nasonovia ribisnigri and Aphis fabae. The significance of these findings in relation to use of artificial diets for colony maintenance and feeding experiments and for studies of aphid-plant interactions is discussed.

Physiological effects of long term exposure to low concentrations of SO2 and NH3 on poplar leaves.

Abstract: Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO2, NH3 or a mixture of SO2 and NH3 for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112-mu-g m-3 SO2 showed a small reduction in maximum CO2 assimilation rate (P(max)) and stomatal conductance (g(s)). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112-mu-g m-3 SO2 was more rapidly activated after transition from dark to light. An exposure to 64-mu-g m-3 NH3 had a positive effect on P(max), stomatal conductance and NH3 uptake of the leaves. This positive effect was counteracted by an SO2 concentration of 45-mu-g m-3. The exposure treatments appeared to have no effect on the relationship between net CO2-assimilation and g(s). Also, no injury of the leaf cuticle or of epidermal cells was observed. Resistance analysis showed that NH3 transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H2O transfer and NH3 concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH3 or to a mixture of NH3 and SO2. In contrast SO2 uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO2 and H2O molecules is proposed.

Higher education in the Third World: status symbol or instrument for development?

Abstract: Southern countries have invested rather heavily in higher education. Yet, their development is severely hampered by problems originating from both national policy conditions and institutional weaknesses. This paper presents an analysis of these problems through a critical analysis of the World Bank Report onEducation in Sub-Saharan Africa: Policies for Adjustment, Revitalization and Expansion. The paper further highlights the results of a recently published comparative study of higher agricultural education institutions in ten countries in Asia, Africa and Latin America. By carefully examining the concrete mandates, expectations and actual possibilities of higher education institutions, this paper tries to explore the academic and societal frontiers of higher education in the South. The paper ends by suggesting ways to improve higher education in the South by using the instrument of South-North university co-operation.

Polyunsaturated Fatty Acids in Adipose Tissue in European Men Aged 38 Years in Relation to Serum Lipids, Smoking Habits, and Fat Distribution

Abstract: Fat biopsies were taken from 327 men aged 38 years from five different European communities in 1988-1989. Linoleic acid content varied widely (F = 110.6, p less than 0.001) and was lowest in men from Poland (8.6%) and highest in men from Belgium (16.7%). Adipose tissue content of alpha-linolenic acid was subject to less variation (F = 13.9, p less than 0.001) and was lowest in men from Italy (0.5%) and highest in men from Sweden and the Netherlands (0.9%). In analysis combining information from all centers, linoleic acid was negatively correlated to low density lipoprotein cholesterol (r = -0.15, p less than 0.01) and total cholesterol (r = -0.17, p less than 0.01). alpha-Linolenic acid was negatively correlated to serum triglycerides only (r = -0.14, p less than 0.05). These fatty acids were not related to body mass index, waist/hip ratio, or smoking habits. The authors conclude that there are major differences in the fatty acid composition of adipose tissue in different European populations but that these do not explain the significant differences in serum high density lipoprotein cholesterol and serum triglycerides among the different populations.

Plenary paper 1:Dutch agriculture seeking for market leader strategies

Abstract: Dutch agriculture has benefited in the past 40 years from significant increases in production efficiency and the market opportunities of the Common Agricultural Policy (CAP). Marketing cooperatives, while often controlling significant market shares, have also concentrated on processing efficiency, encouraged to do so both by market conditions and members' expectations. During the 1980s operating conditions changed as the direction of the CAP came under pressure, the GATT round proceeded, and both processors and retailers responded to the possibilities of European integration. To meet these new challenges cooperatives will have to change both their funding methods and market strategies. Failures to do will lead to them becoming increasingly peripheralized in the market place. Copyright 1991 by Oxford University Press.

Polymer webs to prevent virus transmission by aphids in seed potatoes.

Abstract: Electrical registration and visual observation of penetration behaviour combined with ELISA-technique showed that laboratory-made webs of synthetic fibers were very promising to protect plants against virus infection by aphids. It was demonstrated that stylet penetration by aphids into potato leaves could be prevented by covering plants with these materials. The recent mass production of polypropylene sealed fiber fleeces and polyethylene nettings have made field experiments possible to determine their effect on aphid probing behaviour and virus transmission. Field experiments with potatoes showed that one particular fleece completely protected the plants against virus transmission (PVY and PLRV) and with a second fleece and a netting a small proportion of plants were infected. In uncovered plots up to 25% of plants became infected. A seed potato crop covered with polypropylene fleece which is inspected regularly for damage will be fully protected against virus transmission. Resume Utilisation de toiles de polymeres afin d'empecher la transmission de virus par les pucerons chez les pommes de terres semencieres Des enregistrements electriques et des observations visuelles du comportement de penetration, combines avec l'usage de la technique ELISA, ont montre que l'usage de toiles de fibres synthetiques elaborees au laboratoire etait tres prometteur pour la protection des plantes contre des infections virales transmises par des aphides. On a pu demontrer que la penetration du stylet dans des feuilles de pomme de terre pouvait etre empechee en couvrant les plantes avec ces materiaux. La production en masse recente de nappes en fibres de polypropylene soudees et de filets de polyethylene a rendu possibles des experiences de terrain pour determiner leur effet sur le comportement de sondage des pucerons et sur la transmission des virus. Des essais en plein champ avec des pommes de terre ont montre qu'un type de nappe en particulier protegeait completement les plantes contre la transmission de virus (PVY en PLRV) et qu'avec un second type de nappe et un filet une petite proportion de plantes etait infectee. Dans des parcelles non couvertes la proportion de plantes infectees sx'elevait jusqu'a 25%. Une recolte de pommes de terre semencieres couverte d'une nappe de polypropylene regulierement inspectee afin de remedier aux deteriorations eventuelles sera totalement protegee contre la transmission de virus.

Possible hazards to wild plants of growing transgenic plants. A contribution to risk analysis

Abstract: Genetic manipulation resulting in transgenic plants may cause hazards to the wild flora. Some of these hazards can be listed and a few quantified. To do this, all links in the chain of possible undesirable events have to be identified. The paper discusses some methodological issues. The methodology may lead us to predict some undesirable events and their probability but cannot help us to differentiate the undesirable from the acceptable. That decision must result from political consensus which should be based on informed opinion.

Use of the iterative diagnosis and design approach in the development of suitable agroforestry systems for a target area.

Abstract: The process of iterative diagnosis and design with the active participation of farmers and extension agents was found effective in identifying appropriate agroforestry systems for farmers in the Bugesera and Gisaka-Migongo (BGM) regions of Rwanda. Periodic re-evaluation of research assumptions and technology designs was based on feedback from farmers and extentionists through regular visits to station trials, early initiation of on-farm testing, and interaction with farmer cooperators through informal discussions and formal surveys focused on specific agroforestry technologies. Statistical analysis is valuable for comparison between regions or periods. However, valid conclusions can be drawn without statistics, by employing several farmer-participatory approaches and pooling and properly interpreting the data obtained from them.

Retrospective evaluation of occupational exposures in cancer epidemiology: a European concerted action of research.

Abstract: Assessing exposures in the investigation of occupational cancer is difficult because of the historical nature of exposures. Yet, misclassification of exposures can have a profound effect on the interpretation of risk. It is therefore important to reduce misclassification as much as possible. In an effort to improve our ability to assess exposures, the European Concerted Action of Research has identified three areas which will be given the attention of researchers: elaboration of job-exposure matrices (JEMs), methods to build ad hoc and general questionnaires, and statistical issues. JEMs should be developed for specific industries after evaluation of individual worksites; improved by using standardized coding systems and by identifying level, probability, calendar time, etc.; and evaluated by comparing their performance with other methods of assessment. Questionnaires for specific exposures, methods to code information obtained from questionnaires to allow better evaluation of exposures, and qual...

Enrichment of Soil with Sclerotia to Isolate Antagonists of Sclerotinia Sclerotiorum

Abstract: In order to select naturally occurring antagonists against Sclerotinia sclerotiorum , sclerotia were repeatedly added to soil (about 1% w/w), in order to enhance the antagonist population. This resulted in an accelerated breakdown of test sclerotia. The number of S. sclerotiorum colonies after two weeks incubation of test sclerotia in amended soil and subsequent plating on agar was frequently decreased by antagonists like Coniothyrium minitans and Trichoderma hamatum. Growth suppression of S. sclerotiorum from fresh sclerotia treated with these antagonists confirmed this result. These results correlated well with a reduction in apothecia production from similarly treated sclerotia buried in soil. The antagonists did not control white mould when applied as a spray on a flowering bean crop. However, their well-known effect on the viability of freshly produced sclerotia was confirmed. In addition, some of the antagonists proved to be effective in protecting root crops against storage rot.

The influence of water and temperature on the multiplication of Polymyxa betae, vector of beet necrotic yellow vein virus

Abstract: DE HEIJ, A. 1990. The influence of water and temperature on the multiplication of Polymyxa betae , vector of beet necrotic yellow vein virus. In order to obtain more knowledge about the population dynamics of Polymyxa betae , vector of beet necrotic yellow vein virus, it is important to know what influence water and soil temperature have on multiplication of the fungus. A method was developed to grow beets at a certain temperature at different pF-levels. Between pF-levels of below 2.00 and the multiplication rate of P. betae there is a negative linear relation at temperatures between 15° and 22.5°. Only primary infections were still observed at a temperature as low as 11.5° and also at a pF as high as 2.10. Water is essential for the multiplication of P. betae. The period with a pF of below 2.00, viz. the duration of precipitation, is more important for the multiplication of P. betae than the amount of precipitation.