708 research outputs found

    Development and application of a sensitive, high precision weighing lysimeter for use in greenhouses

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    A high precision weighing lysimeter for measuring evapotranspiration in greenhouses was developed. The instrument has a measurement of sensitivity of one part in 106, that is one order of magnitude better than any other so far described in the literature. With it, evaporation rates in a greenhouse, even at night, can be measured on a one minute time scale. Development and construction of the instrument are described and measurements of the transpiration of a tomato crop in a greenhouse are used to demonstrate its capabilities

    Towards a computational model for stimulation of the Pedunculopontine nucleus

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    The pedunculopontine nucleus (PPN) has recently been suggested as a new therapeutic target for deep brain stimulation (DBS) in patients suffering from Parkinson's disease, particularly those with severe gait and postural impairment [1]. Stimulation at this site is typically delivered at low frequencies in contrast to the high frequency stimulation required for therapeutic benefit in the subthalamic nucleus (STN) [1]. Despite real therapeutic successes, the fundamental physiological mechanisms underlying the effect of DBS are still not understood. A hypothesis is that DBS masks the pathological synchronized firing patterns of the basal ganglia that characterize the Parkinsonian state with a regularized firing pattern. It remains unclear why stimulation of PPN should be applied with low frequency in contrast to the high frequency stimulation of STN. To get a better understanding of PPN stimulation we construct a computational model for the PPN Type I neurons in a network

    Why Would Anyone Like To Share His Knowledge?

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    Why do workers within organizations, or organizations in a network share information and knowledge? This question reverses the logic in some of the knowledge management literature, which addresses impediments and problems in information and knowledge sharing. According to property rights theory, information sharing can be explained in terms of self-interest, maximizing behavior, indispensability of groups and complementarity of assets. Based on this line of reasoning and on empirical evidence presented in this paper, we conclude that the ownership structure of information and knowledge systems matters. In building knowledge management systems, developers should take into account that the intuitive wisdom, indicating that central control is better control, should be interpreted with great caution

    Rechters en de democratie

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    Control of proteolysis in perifused rat hepatocytes

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    AbstractThe mechanism by means of which amino acids inhibit intrahepatic protein degradation has been studied in perifused rat hepatocytes. Proteolysis was extremely sensitive to inhibition by low concentrations of amino acids. A mixture of 0.5 mM leucine and 1ā€“2 mM alanine, concentrations found in the portal vein of the rat after feeding, inhibited proteolysis to the same extent as a complete physiological mixture of amino acids. Inhibition by these two amino acids was accompanied by a rise in the intracellular concentrations of glutamate and aspartate, and was largely prevented by addition of glucagon, by addition of the transaminase inhibitor aminooxyacetate, or by omission of K+. Acceleration of proteolysis by K+ depletion was accompanied by a fall in intracellular glutamate caused by an increased rate of transport of this amino acid to the extracellular fluid. It is concluded that intracellular leucine, glutamate and aspartate are important elements in the control of hepatic protein degradation
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