Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate

Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion Lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it

Yield variability in organic versus conventional systems : a meta-analysis for horticultural systems. PS-8.1-02

Organic agriculture has the potential to reduce the impacts of agriculture on humans and ecosystems but its productivity compared to conventional agriculture remains a contentious issue. Previous meta-analyses have shown that yields in organic systems are 10 to 25 % lower compared with conventional systems. However, those metaanalysis estimated the average yield gap of organic versus conventional farming systems but did not consider yields spatio-temporal variability. Although it is a major concern for farmers and food chains, only few studies analysed the relative variability of organic systems compared to conventional ones. Two contrary hypotheses exist in the literature. On the one hand, because of its reliance on biological and ecological processes, organic production can be assumed to be more vulnerable to pests and diseases outbreaks. On the other hand, organic farming systems are known to have a greater structural diversity and to optimize nutrient cycling and biological pest regulation, which may hence induce a higher resilience of the system and yields. Here we focus on horticulture crops (fruits and vegetables) and make progress by estimating the variability of organic to conventional yield ratio across experiments and across years for a series of horticultural species from a meta-analysis of published field experiments. We define horticulture as production systems based on vegetables and/or fruit production, both in fields, market gardens or orchards. We analyse a dataset including the results of 52 papers reporting yield data for 37 horticultural species in 17 countries. We find that yields in organic horticulture are on average 10 to 32 % lower than those in conventional horticulture. The variance of yields was not significantly different between organic and conventional systems, hence we find no evidence of a larger inter annual variability in organic versus conventional horticulture. However, the coefficient of variation is significantly higher for organic yields vs. conventional ones reflecting the yield gap between these systems. We find no significant effect on yield ratios of type of crop, type of product nor type of climate. However, data on tropical zones were scarce. As a conclusion, despite lower yields, productivity of organic systems is not more instable that productivity of conventional ones, an important result for farmers and future development of organic horticulture

User Profile and Workload Analysis for Local Area Networks

Performance analysis tools for computer networks need accurate and comprehensive estimates of user workload. An approach is presented that estimates network impact for a wide variety of end user types and applications that are typical on local area networks. Fourteen user types and nine generic application types are defined, and data is collected to determine the average network bandwidth needed to accommodate the output of individual and aggregate user/application combinations. Workload is estimated using a combination of data obtained from live test experiments, and data collected from the literature. Finally, the implementation of this data in a highly interactive network modeling tool (NetMod) is illustrated with screen images generated during tool execution.http://deepblue.lib.umich.edu/bitstream/2027.42/107870/1/citi-tr-90-3.pd

Evaluation de la performance de l'agriculture naturelle dans la région du Centre au Cameroun par la méthode d'élicitation du jugement d'experts

De nombreux agriculteurs Camerounais pratiquent l'agriculture naturelle, un type d'agriculture potentiellement qualifiable de " biologique ". Pourtant, peu de références expérimentales sont disponibles sur sa capacité à contribuer aux enjeux de la sécurité alimentaire au Cameroun. De ce fait, la question de sa performance par rapport à l'agriculture conventionnelle reste crutiale pour sa renconnaissance institutionnelle. L'objectif est d'identifier des situations (régions et espèces cultivées) où les performances de l'agriculture naturelle sont proches ou supérieures à celle de l'agriculture conventionnelle. Pour atteindre cet objectif, nous avons mobilisé l'élicitation probabiliste des jugements d'experts. Cette méthode est appliquée auprès de 56 experts dans la région du Centre Cameroun. Les résultats montrent que les rendements en agriculture naturelle sont inférieurs de 26% à ceux conventionnelle tandis que pour les prix bord champ des spéculations en agriculture naturelle sont sensiblement identiques de celles en conventionnelle. De plus, le temps de travail exprimé en nombre d'heure/jour est élevé dans le système naturel par rapport au système conventionnel. Par ailleur, la quantité de travail exprimé en nombre d'homme/jour est plus faible en système naturel

Facing up to the paradigm of ecological intensification in agronomy: Revisiting methods, concepts and knowledge

International audienceAgriculture is facing up to an increasing number of challenges, including the need to ensure various ecosystem services and to resolve apparent conflicts between them. One of the ways forward for agriculture currently being debated is a set of principles grouped together under the umbrella term “ecological intensification”. In published studies, ecological intensification has generally been considered to be based essentially on the use of biological regulation to manage agroecosystems, at field, farm and landscape scales. We propose here five additional avenues that agronomic research could follow to strengthen the ecological intensification of current farming systems. We begin by assuming that progress in plant sciences over the last two decades provides new insight of potential use to agronomists. Potentially useful new developments in plant science include advances in the fields of energy conversion by plants, nitrogen use efficiency and defence mechanisms against pests. We then suggest that natural ecosystems may also provide sources of inspiration for cropping system design, in terms of their structure and function on the one hand, and farmers’ knowledge on the other. Natural ecosystems display a number of interesting properties that could be incorporated into agroecosystems. We discuss the value and limitations of attempting to 'mimic' their structure and function, while considering the differences in objectives and constraints between these two types of system. Farmers develop extensive knowledge of the systems they manage. We discuss ways in which this knowledge could be combined with, or fed into scientific knowledge and innovation, and the extent to which this is likely to be possible. The two remaining avenues concern methods. We suggest that agronomists make more use of meta-analysis and comparative system studies, these two types of methods being commonly used in other disciplines but barely used in agronomy. Meta-analysis would make it possible to quantify variations of cropping system performances in interaction with soil and climate conditions more accurately across environments and socio-economic contexts. Comparative analysis would help to identify the structural characteristics of cropping and farming systems underlying properties of interest. Such analysis can be performed with sets of performance indicators and methods borrowed from ecology for analyses of the structure and organisation of these systems. These five approaches should make it possible to deepen our knowledge of agroecosystems for action

Evaluation de la contribution de l'agriculture naturelle à la sécurité alimentaire au Cameroun par l'élicitation probabiliste du jugement d'experts

De nombreux agriculteurs Camerounais pratiquent l'agriculture naturelle, un type d'agriculture potentiellement qualifiable de " biologique ". Pourtant, peu de références expérimentales sont disponibles sur sa capacité à contribuer aux enjeux de la sécurité alimentaire au Cameroun. De ce fait, la question de sa performance par rapport à l'agriculture conventionnelle reste cruciale pour sa reconnaissance institutionnelle. L'objectif est d'identifier des situations (régions et espèces cultivées) où les performances de l'agriculture naturelle sont proches ou supérieures à celle de l'agriculture conventionnelle. Pour atteindre cet objectif, nous avons mobilisé l'élicitation probabiliste des jugements d'experts. Cette méthode est appliquée auprès de 56 experts dans la région du Centre Cameroun. Les résultats montrent que les rendements en agriculture naturelle sont inférieurs de 28% à ceux conventionnelle tandis que pour les prix bord champ des spéculations en agriculture naturelle sont sensiblement identiques de celles en conventionnelle. De plus, le temps de travail exprimé en nombre d'heures/jour est élevé dans le système naturel par rapport au système conventionnel. Par ailleurs, la quantité de travail exprimé en nombre d'hommes/jour est plus faible en système naturel

Contrast-Enhanced Magnetic Resonance Angiography Using a Novel Elastin-Specific Molecular Probe in an Experimental Animal Model

Objectives. The aim of this study was to test the potential of a new elastin-specific molecular agent for the performance of contrast-enhanced first-pass and 3D magnetic resonance angiography (MRA), compared to a clinically used extravascular contrast agent (gadobutrol) and based on clinical MR sequences. Materials and Methods. Eight C57BL/6J mice (BL6, male, aged 10 weeks) underwent a contrast-enhanced first-pass and 3D MR angiography (MRA) of the aorta and its main branches. All examinations were on a clinical 3 Tesla MR system (Siemens Healthcare, Erlangen, Germany). The clinical dose of 0.1 mmol/kg was administered in both probes. First, a time-resolved MRA (TWIST) was acquired during the first-pass to assess the arrival and washout of the contrast agent bolus. Subsequently, a high-resolution 3D MRA sequence (3D T1 FLASH) was acquired. Signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated for all sequences. Results. The elastin-specific MR probe and the extravascular imaging agent (gadobutrol) enable high-quality MR angiograms in all animals. During the first-pass, the probes demonstrated a comparable peak enhancement (300.6 +/- 32.9 vs. 288.5 +/- 33.1, p > 0.05). Following the bolus phase, both agents showed a comparable intravascular enhancement (SNR: 106.7 +/- 11 vs. 102.3 +/- 5.3; CNR 64.5 +/- 7.4 vs. 61.1 +/- 7.2, p > 0.05). Both agents resulted in a high image quality with no statistical difference (p > 0.05). Conclusion. The novel elastin-specific molecular probe enables the performance of first-pass and late 3D MR angiography with an intravascular contrast enhancement and image quality comparable to a clinically used extravascular contrast agent

An evolvable space telescope for future astronomical missions 2015 update

In 2014 we presented a concept for an Evolvable Space Telescope (EST) that was assembled on orbit in 3 stages, growing from a 4x12 meter telescope in Stage 1, to a 12-meter filled aperture in Stage 2, and then to a 20-meter filled aperture in Stage 3. Stage 1 is launched as a fully functional telescope and begins gathering science data immediately after checkout on orbit. This observatory is then periodically augmented in space with additional mirror segments, structures, and newer instruments to evolve the telescope over the years to a 20-meter space telescope. In this 2015 update of EST we focus upon three items: 1) a restructured Stage 1 EST with three mirror segments forming an off-axis telescope (half a 12-meter filled aperture); 2) more details on the value and architecture of the prime focus instrument accommodation; and 3) a more in depth discussion of the essential in-space infrastructure, early ground testing and a concept for an International Space Station testbed called MoDEST. In addition to the EST discussions we introduce a different alternative telescope architecture: a Rotating Synthetic Aperture (RSA). This is a rectangular primary mirror that can be rotated to fill the UV-plane. The original concept was developed by Raytheon Space and Airborne Systems for non-astronomical applications. In collaboration with Raytheon we have begun to explore the RSA approach as an astronomical space telescope and have initiated studies of science and cost performance