89 research outputs found

    Aan de slag met niet kerende grondbewerking

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    Glooiende hellingen leveren een prachtig landschap op, maar jammer genoeg gaat dit vaak gepaard met bodemerosie. Zowel voor landbouwers als burgers is erosie ongewenst. Uit verschillende onderzoeken blijkt dat nietkerende grondbewerking en groenbedekking opvallend effectief zijn in de strijd tegen erosie. Toch blijkt het toepassen van niet-kerende grondbewerking niet zo evident. Hoe ga je aan de slag met niet-kerende grondbewerking? Met deze brochure trachten we om jou op weg te helpen naar een duurzaam bodemgebruik

    Careers in ecstasy use: do ecstasy users cease of their own accord? Implications for intervention development

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    <p>Abstract</p> <p>Background</p> <p>Ecstasy (MDMA, 3, 4-methylenodioxymethamphetamine) use is widespread in the Netherlands, with a lifetime prevalence of 4.3%, and two-thirds of dance party visitors being ecstasy users. However, research into Dutch ecstasy use patterns is lacking. In addition, recent studies suggest that ecstasy users cease their use automatically, which implies that interventions would do better to better focus on the promotion of harm reduction strategies than on inducing cessation. The current study addresses this process of ecstasy cessation.</p> <p>Methods</p> <p>32 participants from the Dutch dance scene were interviewed, and the results were systematically analysed using NVivo.</p> <p>Results</p> <p>Most ecstasy users had started to use out of curiosity. During use, users applied a host of harm reduction strategies, albeit inconsistently and sometimes incorrectly. Most users appeared to cease ecstasy use automatically because of loss of interest or changing life circumstances (e.g. a new job or relationship).</p> <p>Conclusion</p> <p>It appears that cessation of ecstasy use is largely determined by environmental variables and not by health concerns. This supports the idea that health promotion resources are better spent in trying to promote consistent and correct application of harm reduction practices than in trying to induce cessation.</p

    Two-way communication with neural networks in vivo using focused light

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    Neuronal networks process information in a distributed, spatially heterogeneous manner that transcends the layout of electrodes. In contrast, directed and steerable light offers the potential to engage specific cells on demand. We present a unified framework for adapting microscopes to use light for simultaneous in vivo stimulation and recording of cells at fine spatiotemporal resolutions. We use straightforward optics to lock onto networks in vivo, to steer light to activate circuit elements and to simultaneously record from other cells. We then actualize this 'free' augmentation on both an 'open' two-photon microscope and a leading commercial one. By following this protocol, setup of the system takes a few days, and the result is a noninvasive interface to brain dynamics based on directed light, at a network resolution that was not previously possible and which will further improve with the rapid advance in development of optical reporters and effectors. This protocol is for physiologists who are competent with computers and wish to extend hardware and software to interface more fluidly with neuronal networks.National Institutes of Health (U.S.) (Postdoctoral Fellowship)Simons Foundation (Postdoctoral Fellowship)National Institutes of Health (U.S.) (Predoctoral Fellowship)National Institutes of Health (U.S.)Simons Foundatio

    Characterization of callase (β-1,3-d-glucanase) activity during microsporogenesis in the sterile anthers of Allium sativum L. and the fertile anthers of A. atropurpureum

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    We examined callase activity in anthers of sterile Allium sativum (garlic) and fertile Allium atropurpureum. In A. sativum, a species that produces sterile pollen and propagates only vegetatively, callase was extracted from the thick walls of A. sativum microspore tetrads exhibited maximum activity at pH 4.8, and the corresponding in vivo values ranged from 4.5 to 5.0. Once microspores were released, in vitro callase activity peaked at three distinct pH values, reflecting the presence of three callase isoforms. One isoform, which was previously identified in the tetrad stage, displayed maximum activity at pH 4.8, and the remaining two isoforms, which were novel, were most active at pH 6.0 and 7.3. The corresponding in vivo values ranged from pH 4.75 to 6.0. In contrast, in A. atropurpureum, a sexually propagating species, three callase isoforms, active at pH 4.8–5.2, 6.1, and 7.3, were identified in samples of microsporangia that had released their microspores. The corresponding in vivo value for this plant was 5.9. The callose wall persists around A. sativum meiotic cells, whereas only one callase isoform, with an optimum activity of pH 4.8, is active in the acidic environment of the microsporangium. However, this isoform is degraded when the pH rises to 6.0 and two other callase isoforms, maximally active at pH 6.0 and 7.3, appear. Thus, factors that alter the pH of the microsporangium may indirectly affect the male gametophyte development by modulating the activity of callase and thereby regulating the degradation of the callose wall

    Effective Stimuli for Constructing Reliable Neuron Models

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    The rich dynamical nature of neurons poses major conceptual and technical challenges for unraveling their nonlinear membrane properties. Traditionally, various current waveforms have been injected at the soma to probe neuron dynamics, but the rationale for selecting specific stimuli has never been rigorously justified. The present experimental and theoretical study proposes a novel framework, inspired by learning theory, for objectively selecting the stimuli that best unravel the neuron's dynamics. The efficacy of stimuli is assessed in terms of their ability to constrain the parameter space of biophysically detailed conductance-based models that faithfully replicate the neuron's dynamics as attested by their ability to generalize well to the neuron's response to novel experimental stimuli. We used this framework to evaluate a variety of stimuli in different types of cortical neurons, ages and animals. Despite their simplicity, a set of stimuli consisting of step and ramp current pulses outperforms synaptic-like noisy stimuli in revealing the dynamics of these neurons. The general framework that we propose paves a new way for defining, evaluating and standardizing effective electrical probing of neurons and will thus lay the foundation for a much deeper understanding of the electrical nature of these highly sophisticated and non-linear devices and of the neuronal networks that they compose

    Illustrating and homology modeling the proteins of the Zika virus

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    The Zika virus (ZIKV) is a flavivirus of the family Flaviviridae, which is similar to dengue virus, yellow fever and West Nile virus. Recent outbreaks in South America, Latin America, the Caribbean and in particular Brazil have led to concern for the spread of the disease and potential to cause Guillain-Barré syndrome and microcephaly. Although ZIKV has been known of for over 60 years there is very little in the way of knowledge of the virus with few publications and no crystal structures. No antivirals have been tested against it either in vitro or in vivo. ZIKV therefore epitomizes a neglected disease. Several suggested steps have been proposed which could be taken to initiate ZIKV antiviral drug discovery using both high throughput screens as well as structure-based design based on homology models for the key proteins. We now describe preliminary homology models created for NS5, FtsJ, NS4B, NS4A, HELICc, DEXDc, peptidase S7, NS2B, NS2A, NS1, E stem, glycoprotein M, propeptide, capsid and glycoprotein E using SWISS-MODEL. Eleven out of 15 models pass our model quality criteria for their further use. While a ZIKV glycoprotein E homology model was initially described in the immature conformation as a trimer, we now describe the mature dimer conformer which allowed the construction of an illustration of the complete virion. By comparing illustrations of ZIKV based on this new homology model and the dengue virus crystal structure we propose potential differences that could be exploited for antiviral and vaccine design. The prediction of sites for glycosylation on this protein may also be useful in this regard. While we await a cryo-EM structure of ZIKV and eventual crystal structures of the individual proteins, these homology models provide the community with a starting point for structure-based design of drugs and vaccines as well as a for computational virtual screening
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