Experimental Evidence of Non-Linear Dissipation Using Acoustic Micro-Lapses

Non-linear material behaviour is observed experimentally in a laboratory using a new method called Acoustic Micro-Lapses (AML). In this approach, the shooting of two waves is synchronised in a way that the second wave (TW) is to sense the fluctuations in material stiffness induced by the first (PW). The tests include four samples; twenty trials are performed for each sample by increasing time-delays between the waves. The recorded waves are decoupled and compared to determine spectral differences by computing a quantity proportional to the energy difference as function of the increasing time delay (). For a tight sandstone and aluminium samples, the random behaviour of implies that TW finds the same equilibrium conditions as PW. The Lucite and the Berea sandstone depict distinct maxima, implying that TW sensed the transitory perturbations induced by PW. Therefore, it is inferred that PW and TW must propagate with different phase speeds. To assess the previous results, quasi-static modelling is performed using two time delayed step functions. The corresponding creep compliance shows a strong discontinuity when the second step is applied, implying the existence of two unrelaxed moduli. This supports the lab data in that the two waves must have different dispersion relations such that they propagate with different speeds

Scattering amplitude of a single fracture under uniaxial stress

Remotely sensing the properties of fractures has applications ranging from exploration geophysics to hazard monitoring. Newly developed capabilities to measure the in-plane component of dense laser-based ultrasound wave fields allow us to test the applicability of a linear slip model to describe fracture properties. In particular, we estimate the diameter, and the normal and tangential compliance of a fracture from the measured scattering amplitudes of P and S waves in the laboratory. Finally, we show that the normal compliance decreases linearly with increasing uniaxial static stress in the plane of the fracture, but that our measurements of the SV scattered field do not show significant changes in the tangential complianc

Het Beter Leven-kenmerk : de beleving van biologische consumenten

The aim of this qualitative study is to gain an insight into how and to what extent the Animal Protection Society’s Beter Leven (Better Life) mark contributes to the attractiveness of organic animal products in the opinion of light users. In order to investigate this, LEI conducted a qualitative study among 14 light users in 200

Workshop report: Farm-household modelling with a focus on food security, climate change adaptation, risk management and mitigation: a way forward

Related working paper at http://hdl.handle.net/10568/21112The workshop entitled: ‘Farm-household modelling with a focus on food security, climate change adaptation, risk management and mitigation: a way forward’ focused on identifying the current strengths and weaknesses of farm and household-level models, and laying out practical pathways to improve these models. This activity followed a recent review on farm household modelling commissioned by the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). The workshop took place in Amsterdam, The Netherlands on 23–25 April 2012. The most important conclusions of the workshop were: 1. It is possible to analyse household-level questions related to climate change in a reasonable short (6 months to 1 year) time span with existing tools and the expertise present in the group of participants. 2. Availability of component tools can be an issue; the tools are there but free usability of code and parameters is not always possible. 3. Activities to develop repositories of models and data are urgently needed to increase further development of household models and make better use of existing knowledge. A set of activities will be developed to move the work forward in three CCAFS target regions (West Africa, East Africa and South Asia). The expectation is that the workshop will serve as a springboard for a multi-year initiative that will eventually involve a wide range of participants both within and outside the CGIAR. The challenges associated with climate change, agriculture and food security are considerable, and household modelling has a key role to play in designing and evaluating adaptation, risk management and mitigation options that can help lead to the positive outcomes that CCAFS and research-for-development partners are seeking

Artificial neural networks for 3D cell shape recognition from confocal images

We present a dual-stage neural network architecture for analyzing fine shape details from microscopy recordings in 3D. The system, tested on red blood cells, uses training data from both healthy donors and patients with a congenital blood disease. Characteristic shape features are revealed from the spherical harmonics spectrum of each cell and are automatically processed to create a reproducible and unbiased shape recognition and classification for diagnostic and theragnostic use.Comment: 17 pages, 8 figure

Experimental harvesting of fish populations drives genetically based shifts in body size and maturation

Size-selective harvesting in commercial fisheries can induce rapid changes in biological traits. While experimental and wild harvested populations often exhibit clear shifts in body size and maturation associated with fishing pressure, the relative contributions of genetic and environmental factors to these shifts remain uncertain and have been much debated. To date, observations of so-called fisheries-induced evolution (FIE) have been based solely on phenotypic measures, such as size data. Genetic data are hitherto lacking. Here, we quantify genetic versus environmental change in response to size-selective harvesting for small and large body size in guppies (Poecilia reticulata) across three generations of selection. We document for the first time significant changes at individual genetic loci, some of which have previously been associated with body size. In contrast, variation at neutral microsatellite markers was unaffected by selection, providing direct genetic evidence for rapid evolution induced by size-selective harvesting. These findings demonstrate FIE in an experimental system, with major implications for the sustainability of harvested populations, as well as impacts on size-structured communities and ecosystem processes. These findings highlight the need for scientists and managers to reconsider the capacity of harvested stocks to adapt to, and recover from, harvesting and predation. © 2013 The Ecological Society of America

Granger causality revisited

This technical paper offers a critical re-evaluation of (spectral) Granger causality measures in the analysis of biological timeseries. Using realistic (neural mass) models of coupled neuronal dynamics, we evaluate the robustness of parametric and nonparametric Granger causality. Starting from a broad class of generative (state-space) models of neuronal dynamics, we show how their Volterra kernels prescribe the second-order statistics of their response to random fluctuations; characterised in terms of cross-spectral density, cross-covariance, autoregressive coefficients and directed transfer functions. These quantities in turn specify Granger causality - providing a direct (analytic) link between the parameters of a generative model and the expected Granger causality. We use this link to show that Granger causality measures based upon autoregressive models can become unreliable when the underlying dynamics is dominated by slow (unstable) modes - as quantified by the principal Lyapunov exponent. However, nonparametric measures based on causal spectral factors are robust to dynamical instability. We then demonstrate how both parametric and nonparametric spectral causality measures can become unreliable in the presence of measurement noise. Finally, we show that this problem can be finessed by deriving spectral causality measures from Volterra kernels, estimated using dynamic causal modelling

Dev Dyn

Ror2 is a receptor tyrosine kinase mutated in the human syndromes Brachydactyly type B (BDB) and recessive Robinow syndrome (RS). In this study, we used the chick as a model to investigate the role of Ror2 in skeletogenesis and to elucidate the functional consequences of Ror2 mutations. For this purpose, we cloned chicken Ror2 and analyzed its expression pattern at various embryonic stages by in situ hybridization and immunolabeling. We document expression of cRor2 in several organs, including mesonephros, heart, nervous system, intestine and cartilage. The high conservation of expression when compared with the mouse underlines the validity of the chick as a model system. Using replication-competent retroviral vector-mediated overexpression, we analyzed the functional consequences of truncating BDB and RS mutations in the developing chick limb. Overexpression of Ror2 mutants led to a disturbance of growth plate architecture and a severe block of chondrocyte differentiation, demonstrating the functional importance of Ror2 in skeletogenesis