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Showing papers by "Wageningen University and Research Centre published in 1996"


Journal ArticleDOI
TL;DR: In this paper, simple diagnostic tests based on OLS residuals were proposed for spatial error autocorrelation in the presence of a spatially lagged dependent variable and for spatial lag dependence.

1,681 citations


Book ChapterDOI
TL;DR: In this paper, the authors present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to North Atlantic.
Abstract: We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr-1 out of a total for the entire North Atlantic region of 13.1 Tg yr-1. On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S., all of which have riverine nitrogen fluxes greater than 1,000 kg N km-2 yr-1.

1,614 citations


Journal ArticleDOI
TL;DR: In this paper, the authors consider two types of commitment that may characterize interfirm relationships: affective commitment and calculative commitment, which measures the degree to which channel members experience the need to maintain a relationship with specific partners.

1,131 citations


Journal ArticleDOI
TL;DR: In this article, a two-factor conceptualization of exploratory consumer buying behavior is proposed, in which exploratory acquisition of products is distinguished from exploratory information seeking, and a scale for measuring individual differences in consumers' tendencies to engage in exploratory buying behaviors is developed based on this conceptualization, and the instrument is related to several other constructs and actual exploratory behaviors.

562 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a global atmospheric circulation model to estimate the sulfur species DMS, SO2 and sulfate in clouds, and found that about 2 3 of the sulfate is produced within clouds, with H2O2 being the most efficient pathway.

347 citations


Book ChapterDOI
TL;DR: In this paper, atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx), and mineral dust to the North Atlantic Ocean (NAO).
Abstract: Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx) and mineral dust to the North Atlantic Ocean (NAO). The estimated deposition of NOy to the NAO (excluding the coastal ocean) and the Caribbean is 360 × 109 Moles-N m-2 yr-1 (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NHx, 258 Moles-N m-2 yr-1 (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen.

339 citations


Journal ArticleDOI
TL;DR: Findings indicate that laccases may have a role in the oxidation of polycyclic aromatic hydrocarbons by white rot fungi.
Abstract: The in vitro oxidation of the two polycyclic aromatic hydrocarbons anthracene and benzo[a]pyrene, which have ionization potentials of <=7.45 eV, is catalyzed by laccases from Trametes versicolor. Crude laccase preparations were able to oxidize both anthracene and the potent carcinogen benzo[a]pyrene. Oxidation of benzo[a]pyrene was enhanced by the addition of the cooxidant 2,2(prm1)-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), while an increased anthracene oxidizing ability was observed in the presence of the low-molecular-weight culture fluid ultrafiltrate. Two purified laccase isozymes from T. versicolor were found to have similar oxidative activities towards anthracene and benzo[a]pyrene. Oxidation of anthracene by the purified isozymes was enhanced in the presence of ABTS, while ABTS was essential for the oxidation of benzo[a]pyrene. In all cases anthraquinone was identified as the major end product of anthracene oxidation. These findings indicate that laccases may have a role in the oxidation of polycyclic aromatic hydrocarbons by white rot fungi.

313 citations


Journal ArticleDOI
01 Apr 1996-Ecology
TL;DR: A plant-herbivore model where grazing becomes less efficient in dense vegetation is examined, and the behavior of this model along a gradient of primary productivity does not predict "top-down" control in productive environments.
Abstract: According to classical exploitation theory, an increase of primary produc- tivity should result in increased herbivore grazing pressure, thus maintaining a low plant standing crop. However, field data obtained from a salt marsh revealed a maximal grazing pressure by hares, rabbits, and geese at intermediate levels of plant standing crop. Grazing pressure was relatively low in the more productive parts. We argue that this pattern is due to a low foraging efficiency of these herbivores in dense vegetation. In order to investigate this hypothesis, we examine a plant-herbivore model where grazing becomes less efficient in dense vegetation, and analyze the behavior of this model along a gradient of primary productivity. In systems of intermediate productivity, the model predicts that a plant- herbivore system may have two stable states. In one state, the herbivore maintains a low standing crop. The other state is dominated by a dense vegetation unsuitable for herbivore grazing. In systems of high productivity, the herbivore is unable to keep plant growth in check and a dense vegetation develops. Thus, in line with our field data but in contrast to classical exploitation theory, our model does not predict "top-down" control in productive environments.

191 citations


Journal ArticleDOI
TL;DR: In this article, the general principles underlying the interaction between proteins and solid surfaces in an aqueous environment are discussed, illustrated by experimental results obtained with well-defined systems, mainly based on thermodynamic arguments.
Abstract: Under most conditions proteins show a strong tendency to adsorb at interfaces. The general principles underlying the interaction between proteins and solid surfaces in an aqueous environment are discussed. These principles are illustrated by experimental results obtained with well-defined systems. The approach is mainly based on thermodynamic arguments.

186 citations


Journal ArticleDOI
TL;DR: This extremely sensitive method enables, for the first time, determination of flavonols in body fluids after consumption of a normal diet.
Abstract: Flavonols are dietary antioxidants which may prevent coronary heart disease. To be able to study absorption of flavonols in humans, we developed a postcolumn derivatization with aluminum for HPLC with fluorescence detection. Variables governing postcolumn chelation, such as water content, buffer, organic modifier of the eluent, concentration of Al3+, presence of acetic acid in the postcolumn reagent, and temperature, were studied and optimized. Of the flavonoids, only flavonols that contain a free 3-hydroxyl and 4-keto oxygen binding site form fluorescent complexes with Al3+. The method has a detection limit of 0.15 ng/mL for quercetin, 0.05 ng/mL for kaempferol, 0.45 ng/mL for myricetin, and 0.05 mg/mL for isorhamnetin, thus improving detectability of quercetin 300-fold as compared to that possible with UV detection. The reproducibility relative standard deviation of the method is 1.4%. This extremely sensitive method enables, for the first time, determination of flavonols in body fluids after consumptio...

152 citations


Journal ArticleDOI
TL;DR: In this paper, an upflow anaerobic granular sludge bed reactor was used to study the influence of the superficial upward liquid velocity (vup), the influent composition and reactor pH on the competition between sulphate-reducing bacteria (SRB) and MPB for the available electron donors.

Journal ArticleDOI
TL;DR: G granular sludges are suggested as appropriate inocula for reactors treating lipids (fats, oils and greases) wastewaters, to decrease the toxic impact from their hydrolysis products-LCFA.

Journal ArticleDOI
TL;DR: In this article, the actual and potential benefits of anaerobic wastewater treatment when implemented at the core of a sustainable and non-vulnerable environmental protection program are described, focusing on the expansion granular sludge bed (EGSB) reactor.

Journal ArticleDOI
TL;DR: In this paper, the effect of temperature on the rate of volatile fatty acid (VFA) conversion by thermophilic methanogenic sludge, cultivated at 55°C, was studied using both batch activity tests and continuous flow experiments.

Journal ArticleDOI
TL;DR: In this paper, the competition of methanogenic and sulfidogenic bacteria was studied by assessing growth rates, activities and acetate and sulfate affinities at different pH levels and sulfide concentrations in batch reactors.

Journal ArticleDOI
TL;DR: The dendrogram for ITS1 revealed a close similarity for most species except F. beomiforme and F. polyphialidicum, and two UPGMA similarity dendrograms based on the sequences of the ITS1 and ITS2 regions were discordant with each other.
Abstract: Sequences of the internal transcribed spacers of the ribosomal DNA were used to compare 13 species from Fusarium sections Elegans, Liseola and Dlaminia. Two UPGMA similarity dendrograms based on the sequences ofthe ITS1 and ITS2 regions were discordant with each other. The dendrogram for ITS1 revealed a close similarity for most species except F. beomiforme and F. polyphialidicum. In con? trast, species groupings based on the ITS2 sequences formed two main clusters that did not coincide with

Journal ArticleDOI
TL;DR: In this article, the process stability of thermophilic anaerobic wastewater treatment systems is investigated and a relatively low sensitivity to temperature changes if high-rate reactors with immobilized biomass are used.
Abstract: Thermophilic anaerobic digestion offers an attractive alternative for the treatment of medium- and high-strength wastewaters. However, literature reports reveal that thermophilic wastewater treatment systems are often more sensitive to environmental changes than the well-defined high-rate reactors at the mesophilic temperature range. Also, in many cases a poorer effluent quality is experienced while the carry over of suspended solids in the effluent is relatively high. In this paper recent achievements are discussed regarding the process stability of thermophilic anaerobic wastewater treatment systems. Laboratory experiments reveal a relatively low sensitivity to temperature changes if high-rate reactors with immobilized biomass are used. Other results show that if a staged process is applied, thermophilic reactors can be operated for prolonged periods of time under extreme loading conditions (80-100 kg chemical oxygen demand.m-3.day-1), while the concentrations of volatile fatty acids in the effluent remain at a low level.

Journal ArticleDOI
TL;DR: In this article, the authors developed a series of hypotheses delineating the impact of arousal potential on arousal and of arousal on stimulus evaluation, and introduced the concept of need for stimulation (NST) as a key moderating variable which takes into account other sources of stimulation and individual differences in preferred level of stimulation.

Journal ArticleDOI
TL;DR: In aphids the olfactory receptor neurones are housed in placoid sensilla on the antennae, the so-called distal and proximal primary rhinaria on segments six and five, respectively, and, in winged aphids, the secondary rhinarius on segments three and four.
Abstract: In aphids the olfactory receptor neurones are housed in placoid sensilla on the antennae, the so-called distal and proximal primary rhinaria on segments six and five, respectively, and, in winged aphids, the secondary rhinaria on segments three and four (Shambaugh et al, 1978; Bromley et al., 1979). The overall responses of these receptors to plant odours can be studied by the electroantennogram (EAG) technique. In this way, it can be shown which plant volatiles are detected and, thus, are likely to play a role in the discrimination between the odour blends of host and non-host plant species during orientation and landing. EAGs in response to plant volatiles have been recorded in a number of aphid species, i.e., the English grain aphid Sitobion avenae (F.) and the rose-grain aphid Metopolophium dirhodum (Walk.) (Yan & Visser, 1982; Visser & Yan, 1995), the black bean aphid Aphis fabae Scop. (Hardie et al., 1995), and the vetch aphid Megoura viciae Buckton (Visser & Piron, 1994, 1995).

Journal ArticleDOI
TL;DR: The crystal structure of the cyclodextrin glycosyltransferase (CGTase) from the thermophilic microorganism Thermoanaerobacterium thermosulfurigenes EM1 has been elucidated at 2.3 Angstrom resolution and apparently some catalytic functionality of CGTase has been sacrificed for the sake of structural stability by modifying loop regions near the active site.

Journal ArticleDOI
TL;DR: This constitutes the first report demonstrating the anaerobic mineralization of 5-aminosalicylate, which indicates that at least some azo dye cleavage products can be degraded in methanogenic consortia.

Journal ArticleDOI
TL;DR: Biological sulfate reduction was studied in laboratory‐scale gas‐lift reactors and special attention was paid to the effect of CO addition on the sulfate conversion rate, aggregation, and aggregate composition.
Abstract: Biological sulfate reduction was studied in laboratory-scale gas-lift reactors. Synthesis gas (gas mixtures of H(2)/CO/CO(2)) was used as energy and carbon source. The required biomass retention was obtained by aggregation and immobilization on pumice particles. Special attention was paid to the effect of CO addition on the sulfate conversion rate, aggregation, and aggregate composition.Addition of 5% CO negatively affected the overall sulfate conversion rate; i.e., it dropped from 12-14 to 6-8 g SO(2-) (4)/L day. However, a further increase of CO to 10 and 20% did not further deteriorate the process. With external biomass recycling the sulfate conversion rate could be improved to 10 g SO(2-) (4)/L day. Therefore biomass retention clearly could be regarded as the rate-limiting step. Furthermore, CO affected the aggregate shape and diameter. Scanning electron microscopy (SEM) photographs showed that rough aggregates pregrown on H(2)/CO(2) changed into smooth aggregates upon addition of CO. Addition of CO also changed the aggregate Sauter mean diameter (d(32)) from 1.7 mm at 5% CO to 2.1 mm at 20% CO. After addition of CO, a layered biomass structure developed. Acetobacterium sp. were mainly located at the outside of the aggregates, whereas Desulfovibrio sp. were located inside the aggregates.

Journal ArticleDOI
TL;DR: Fractal analysis of the structures shows nonuniversal fractal scaling for all systems, with lower bound ${\mathit{r}}_{0}$ and fractal dimensionality ${\ mathit{d}}_{\Mathit{f}}$.
Abstract: In this paper we simulate the aggregation of interacting particles using Brownian dynamics. The parameters varied are volume fraction and interaction potential well depth. At volume fractions above 0.07 percolated structures are observed; these are formed differently from cluster-cluster aggregation. Fractal analysis of the structures shows nonuniversal fractal scaling for all systems, with lower bound ${\mathit{r}}_{0}$ and fractal dimensionality ${\mathit{d}}_{\mathit{f}}$. Both of these properties depend on the simulation parameters and on time. Compactification in time leads to an increasing ${\mathit{r}}_{0}$ and a decreasing ${\mathit{d}}_{\mathit{f}}$, that is, structures with thick strands. This effect is most pronounced at large well depths. Due to compactification in time, percolated states can be transient. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: The results indicate that xenobiotic compound oxidation by white rot fungi cannot be improved by overproducing peroxidases without increasing the endogenous production of H(inf2)O(inf1) without affecting the oxidation of anthracene and the decolorization of Poly R-478.
Abstract: The overproduction of ligninolytic peroxidase by the N-deregulated white rot fungus Bjerkandera sp. strain BOS55 under nitrogen-sufficient conditions had no noteworthy effect on the oxidation of anthracene or the decolorization of the polymeric aromatic dye Poly R-478 in 6-day-old cultures. Only when the endogenous production of H(inf2)O(inf2) was increased by the addition of extra oxygen and glucose could a 2.5-fold increase in the anthracene oxidation rate and a 6-fold increase in the Poly R-478 decolorization rate be observed in high-N cultures with 10- to 35-fold higher peroxidase activities than N-limited cultures. Further increase of the H(inf2)O(inf2) generation rate in high-N cultures with glucose oxidase led to an additional 3.5-fold increase in the anthracene oxidation rate (350 mg liter(sup-1) day(sup-1)) and a 10-fold increase in the Poly R-478 decolorization rate. These results indicate that xenobiotic compound oxidation by white rot fungi cannot be improved by overproducing peroxidases without increasing the endogenous production of H(inf2)O(inf2). The absence of Mn, which decreased the manganese peroxidase titers and increased the lignin peroxidase titers, was associated with up to 95% improvements in the anthracene oxidation rate. The simultaneous presence of Mn and veratryl alcohol was observed to have a synergistic negative effect on the oxidation of anthracene and the decolorization of Poly R-478.

Journal ArticleDOI
TL;DR: The results support the idea that there are multiple nongenotoxic mechanisms in carcinogenesis, and that working hypothesis-oriented approaches are encouraged rather than simple screening of chemicals in developing test systems for the detection of nonganotoxic carcinogens.
Abstract: While the accumulation of genetic changes in a somatic cell is considered essential for the genesis of a cancer, it has become clear that not all carcinogens are genotoxic, suggesting that some carcinogens indirectly participate in the generation of genetic changes during carcinogenesis. A European project funded by the European Community was thus conceived to study mechanisms of nongenotoxic aspects of carcinogenesis. Two main strategical approaches were adapted: (i) to study whether and how Syrian hamster embryo (SHE), Syrian hamster dermal (SHD) and BALB/c 3T3 cell transformation systems simulate in vivo carcinogenesis, and to examine whether they can detect nongenotoxic carcinogens; (ii) to study, refine and validate mechanisms-based end-points for detection of nongenotoxic carcinogens. For mechanisms-based research, the proposed end-points included gap junctional intercellular communication (GJIC) inhibition, altered expression of critical genes, immortalization and aberrant cell proliferation. We also selected model compounds commonly usable for various endpoints. Our major results can be summarized as follows: (1) SHE and BALB/c 3T3 transformation systems reflect both genotoxic and nongenotoxic carcinogenic events; they detect not only genotoxic but also many although not all, nongenotoxic carcinogens. This is further supported by the fact that both genotoxic and nongenotoxic carcinogens were able to immortalize SHD cells. (2) Many nongenotoxic carcinogens, although not all, inhibit GJIC in vitro as well as in vivo. Mechanistic studies suggest an important role of blocked GJIC in carcinogenesis and that different mechanisms are involved in inhibition of the communication by different agents used. However, inhibition of GJIC is not a prerequisite for the enhancement (or induction) of transformation of SHE or BALB/c 3T3 cells. (3) Among compounds examined, there was a good correlation between induction of micronuclei and cell transformation in SHE cells while no such correlation was found between the induction of cell transformation and ornithine decarboxylase activity. (4) Two transgenic mouse mutation assays (lacI and lacZ) were established and validated. The genotoxin dimethylnitrosamine was shown to be mutagenic to the liver in both assays. Ortho-anisidine, a bladder-specific carcinogen that was inactive in standard rodent genetic toxicity assays was uniquely mutagenic to the bladder of the transgenic mice. The peroxisome proliferator methyl clofenipate was established as nonmutagenic to the liver of both transgenic mice. That eliminated DNA damage as a cause of the liver tumours produced by this chemical and weakened the idea that induced cell division leads to mutation induction. (5) With an in vitro DNA replication model, it was found that DNA damage induced by genotoxic agents can be responsible for inhibition of DNA replication, while certain nongenotoxic agents such as phorbol esters increase DNA replication. (6) An attempt to use structure-activity relationship for subfamilies of nongenotoxic carcinogens, e.g., receptor-mediated carcinogens, has been initiated with some promising results. Our results support the idea that there are multiple nongenotoxic mechanisms in carcinogenesis, and that working hypothesis-oriented approaches are encouraged rather than simple screening of chemicals in developing test systems for the detection of nongenotoxic carcinogens.

Journal ArticleDOI
TL;DR: In this article, the effect of surface properties and the effects of several process conditions, e.g., loading rate, ionic strength and the presence of polymers, on the degree of aggregation of sulphur particles were studied.

Journal ArticleDOI
TL;DR: The MPN-PCR detection method is adequate to assess the impact of stress conditions affecting P. azotofixans in FSL and probably other soils, since it abolishes the need for culturing or specific markers and is direct and unambiguous due to its high specificity.

Journal ArticleDOI
TL;DR: In this paper, the authors present general guidelines for designing appropriate measurement strategies; how to obtain detailed data with an applicable measurement method, what sampling strategy should be applied, which frequency and duration of measurements are required, and how differences between workers, shifts and tasks are addressed.

Journal ArticleDOI
01 Jan 1996-Oikos
TL;DR: Two phylogenetically related cucoilid parasitoids, Leptopilina boulardi a host specialist, and L. heterotoma a generalist, were attracted to odours of adult hosts in windtunnel tests.
Abstract: Parasitoids foraging for larvae of Drosophila flies can use odours of adults of their hosts as well as odours of the food of their host larvae. Adult Drosophila deposit volatile aggregation pheromones into a substrate when mating and ovipositing. In this paper three species of parasitoids with different degrees of host specialization are compared in bioassays with regard to innate responses to aggregation pheromones of adult drosophilid hosts. Specialist parasitoids are assumed to use more specific information about their hosts than generalist parasitoids. Two phylogenetically related cucoilid parasitoids, Leptopilina boulardi a host specialist, and L. heterotoma a generalist, were attracted to odours of adult hosts in windtunnel tests. L. heterotoma responded to odours of all species within its host range and one non-host. The specialist L. boulardi was attracted to odours of adult hosts within its range but also to some non-host species. Production of similar pheromonal compounds by non-host and host Drosophila species can explain the reponses by L. heterotoma and L. boulardi to non- host species. A phylogenetically unrelated braconid host specialist Asobara tabida did not respond to any odours of adult hosts. However, when A. tabida females were given an oviposition experience in the presence of host pheromones, they became attracted to aggregation pheromones of their host. (Less)

Journal ArticleDOI
TL;DR: Single and population-mean cosinor analyses document a circadian rhythm in salivary cortisol of pigs (p < 0.001) and provides indispensable quantitive characteristics as reference standards for future basic or applied work.