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J Feyen

Publications and source records attributed to J Feyen.

16 recordsLinked to original sources
PubMed2001

Numerical analysis of the transport and fate of nitrate in the soil and nitrate leaching to drains.

In this study, the transport and fate of nitrate within the soil profile and nitrate leaching to drains were analyzed by comparing historic field data with the simulation results of the DRAINMOD model. The nitrogen version of DRAINMOD was used to simulate the performance of the nitrogen transport and transformation of the Hooibeekhoeve experiment, situated in the sandy region of the Kempen (Belgium) and conducted for a 30-year (1969-1998) period. In the analysis, a continuous cropping with maize was assumed. Comparisons between experimentally measured and simulated state variables indicate that the nitrate concentrations in the soil and nitrate leaching to drains are controlled by the fertilizer practice, the initial conditions, and the rainfall depth and distribution. Furthermore, the study reveals that the model used gives a fair description of the nitrogen dynamics in the soil and subsurface drainage at field scale. From the comparative analysis between experimental data and simulation results it can also be concluded that the model after calibration is a useful tool to optimize as a function of the combination "climate-crop-soil-bottom boundary condition" the nitrogen application strategy resulting in an acceptable level of nitrate leaching for the environment.

Agriculture↗
PubMed2001

Modeling of nitrogen in river water using a detailed and a simplified model.

To model catchment surface water quantity and quality, different model types are available. They vary from detailed physically based models to simplified conceptual and empirical models. The most appropriate model type for a certain application depends on the project objectives and the data availability. The detailed models are very useful for short-term simulations of representative events. They cannot be used for long-term statistical information or as a management tool. For those purposes, more simplified (conceptual or meta-) models must be used. In this study, nitrogen dynamics are modeled in a river in Flanders. Nitrogen sources from agricultural leaching and domestic point sources are considered. Based on this input, concentrations of ammonium (NH4-N) and nitrate (NO3-N) in the river water are modeled in MIKE 11 by taking into consideration advection and dispersion and the most important biological and chemical processes. Model calibration was done on the basis of available measured water quality data. To this detailed model, a more simplified model was calibrated with the objective to more easily yield long-term simulation results that can be used in a statistical analysis. The results show that the conceptual simplified model is 1800 times faster than the MIKE 11 model. Moreover the two models have almost the same accuracy. The detailed models are recommended for short-term simulations unless there are enough data for model input and model parameters. The conceptual simplified model is recommended for long-term simulations.

Agriculture↗
PubMed1999

A novel inhibitor of the tyrosine kinase Src suppresses phosphorylation of its major cellular substrates and reduces bone resorption in vitro and in rodent models in vivo.

The tyrosine kinase Src has been implicated in the process of osteoclast-mediated bone resorption. Here, we describe a novel class of Src inhibitors, substituted 5,7-diphenyl-pyrrolo[2,3-d]pyrimidines, and characterize one of them, CGP77675, in vitro and in models of bone resorption in vivo. In vitro, CGP77675 inhibited phosphorylation of peptide substrates and autophosphorylation of purified Src (concentration producing half-maximal inhibition [IC50] values 5-20 and 40 nmol/L, respectively). The compound was selective toward other protein kinases: the Src IC50 value was lower than those for Cdc2 (>500-fold), epidermal growth factor (EGF) receptor (7.5-fold), and vascular endothelial growth factor receptor (>50-fold), and for v-Abl (15-fold) and focal adhesion kinase (Fak) (>25-fold). The Src kinase family members Lck and Yes were inhibited with IC50 values 20-fold higher than or equal to Src. To measure the inhibition of cellular Src activity, we identified the major tyrosine-phosphorylated proteins in an Src-overexpressing cell line IC8.1 as Src, Fak, and paxillin. CGP77675 potently inhibited tyrosine phosphorylation of the Src substrates Fak and paxillin, but had much less effect on Src (IC50 values 0.3, 0.5, and 5.7 micromol/L). The phosphorylation of Src in IC8.1 cells reflected phosphorylation of the negative regulatory tyrosine 527 (Y527); thus, the inhibitor was selective against the Y527 C-terminal Src kinase Csk. In osteoblastic MC3T3-E1 cells, CGP77675 inhibited signaling induced by PDGF at the receptor level, but not signaling by EGF, basic fibroblast growth factor, insulin-like growth factor-1, and phorbol 12-myristate 13-acetate. The effect of CGP77675 on bone resorption was evaluated in vitro and in vivo. The parathyroid hormone-induced bone resorption in rat fetal long bone cultures was inhibited with an IC50 of 0.8 micromol/L. CGP77675 dose-dependently reduced the hypercalcemia induced in mice by interleukin-1beta and partly prevented bone loss and microarchitectural changes in young ovariectomized rats, showing that the protective effect on bone was exerted via the inhibition of bone resorption. Thus, specific Src family kinase inhibitors may be useful for the treatment of diseases associated with elevated bone loss.

3T3 Cells↗
PubMed1996

Compartment syndrome associated with an osteocartilaginous exostosis.

The authors describe a compartment syndrome of the deep posterior flexor compartment due to perforation of the popliteal artery by an osteocartilaginous exostosis, in a healthy 13-year-old boy. The difficulties in making the diagnosis are discussed. In a review of the literature regarding this condition, the combination of compartment syndrome and exostoses could not be found.

Adolescent↗
PubMed1995

Regulation of parathyroid hormone/parathyroid hormone-related protein receptor expression by osteoblast-deposited extracellular matrix in a human osteoblast-like cell line.

Parathyroid hormone (PTH) receptors and the biological response to PTH in osteoblasts have been shown to be influenced by glucocorticoids, growth factors, cytokines or PTH itself. Furthermore, components of extracellular matrix (ECM) appear to regulate the response to PTH as well. We investigated the effects of osteoblast-deposited ECM on PTH-related protein (PTHrP)-stimulated cAMP production, PTHrP binding and PTH/PTHrP receptor mRNA in the human osteoblast-like cell line SaOS-2. ECM was laid down by the human osteoblastic cell line MG-63. At confluence, maximal cAMP stimulation induced by 100 nmol/l PTHrP (1-34) was decreased in SaOS-2 cells grown on ECM as compared with cultures on plastic dishes, without any change in PTHrP concentration producing half-maximal stimulation. In contrast, cAMP production stimulated by PGE2 was increased in cells on ECM. Saturable 125I-PTHrP binding (as evaluated by Scatchard plot analysis) was markedly diminished in cells grown on ECM (5,600 +/- 2,010 vs. 20,700 +/- 1,710 binding sites/cell, x +/- S.E.M., P < 0.01, n = 4 experiments), without any significant change in affinity (1.3 +/- 0.4 vs. 2.5 +/- 0.5 nmol/l (NS), in cells on ECM and plastic, respectively). This apparent decrease in membrane receptor density was associated with markedly lower steady state PTH/PTHrP receptor mRNA levels as assessed by Northern blot analysis (ECM/control: 0.4 +/- 0.1). A difference in PTH/PTHrP receptor mRNA levels between cells on ECM or on plastic dishes was detectable by 8 hours but not by 4 hours, after seeding the cells at high density. By 24 hours after plating, PTH/PTHrP receptor mRNA levels were maximally decreased in cells on ECM. These results in the human osteoblast-like cell line SaOS-2 indicate that PTH/PTHrP receptors are down-regulated by growth on ECM. Thus, attachment of bone cells to bone surface could influence differentiation and function of osteoblasts.

Down-Regulation↗
PubMed1994

Compartment syndrome after fracture of the distal radius.

A compartment syndrome of the forearm after a fracture of the distal radius is presented. This rare complication should be considered after high velocity trauma in young people. In this setting, we prefer general anesthesia for fracture reduction. Fracture fixation and avoidance of circular casts are recommended. Repeated evaluation allows early detection of compartment syndrome. Fasciotomy should be done if this syndrome occurs.

Adult↗
PubMed1984

The concept of an artificial tympanic membrane.

A review is given of the development of the concept of an artificial tympanic membrane. Starting with homologous tympanic membranes we compared biodegradable collagen materials (homologous and heterologous) and biodegradable synthetic materials, poly-glycolic acid, poly-lactic acid and poly-alpha-amino acids. As a non-degradable material microporous PTFE and bisphenol-A poly (carbonate) were investigated. It is concluded that either poly-alpha-amino acid or PTFE with poly-alpha-amino acid maybe a suitable material for an artificial tympanic membrane.

Animals↗
PubMed1983

Infection of the knee joint with Mycobacterium xenopi.

Mycobacterium xenopi infection of the knee joint occurred in a 71-year-old man. Owing to the failure to recognize the "contaminant" initially as a possible etiologic agent, the joint was destroyed and eventually treated by arthrodesis.

Aged↗