242 research outputs found

    Testing fluvial erosion models using the transient response of bedrock rivers to tectonic forcing in the Apennines, Italy

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    The transient response of bedrock rivers to a drop in base level can be used to discriminate between competing fluvial erosion models. However, some recent studies of bedrock erosion conclude that transient river long profiles can be approximately characterized by a transport‐limited erosion model, while other authors suggest that a detachment‐limited model best explains their field data. The difference is thought to be due to the relative volume of sediment being fluxed through the fluvial system. Using a pragmatic approach, we address this debate by testing the ability of end‐member fluvial erosion models to reproduce the well‐documented evolution of three catchments in the central Apennines (Italy) which have been perturbed to various extents by an independently constrained increase in relative uplift rate. The transport‐limited model is unable to account for the catchments’response to the increase in uplift rate, consistent with the observed low rates of sediment supply to the channels. Instead, a detachment‐limited model with a threshold corresponding to the field‐derived median grain size of the sediment plus a slope‐dependent channel width satisfactorily reproduces the overall convex long profiles along the studied rivers. Importantly, we find that the prefactor in the hydraulic scaling relationship is uplift dependent, leading to landscapes responding faster the higher the uplift rate, consistent with field observations. We conclude that a slope‐ dependent channel width and an entrainment/erosion threshold are necessary ingredients when modeling landscape evolution or mapping the distribution of fluvial erosion rates in areas where the rate of sediment supply to channels is low

    Gravity Currents in Aquatic Canopies

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    A lock exchange experiment is used to investigate the propagation of gravity currents through a random array of rigid, emergent cylinders which represents a canopy of aquatic plants. As canopy drag increases, the propagating front varies from the classic profile of an unobstructed gravity current to a triangular profile. Unlike the unobstructed lock exchange, the gravity current in the canopy decelerates with time as the front lengthens. Two drag-dominated regimes associated with linear and nonlinear drag laws are identified. The theoretical expression for toe velocity is supported by observed values. Empirical criteria are developed to predict the current regime from the cylinder Reynolds number and the array density.National Science Foundation (U.S.) (grant EAR0309188)National Science Foundation (U.S.) (grant EAR0509658)Massachusetts Institute of Technology (Presidential Graduate Fellowship

    One Health epidemic preparedness: Biosafety quality improvement training in Nigeria

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    Background and Aim: One of the key components of the O ne Health approach to epidemic preparedness is raising awareness and increasing the knowledge of emerging infectious diseases, prevention, and risk reduction. However, related research can involve significant risks to biosafety and biosecurity. For this purpose, we organized a multidisciplinary biosafety hands-on workshop to inform and increase the knowledge of infectious diseases and risk mitigation. This study aimed to describe the process and outcome of a hands-on biosafety training program using a One Health a pproach across a multidisciplinary and multi-specialty group in Nigeria. Materials and Methods: A face-to-face hands-on training for 48 participants was organized by the West African Center for Emerging Infectious Diseases (WAC-EID) at the Jos University Teaching Hospital, serving as a lead institution for the Nigeria project site. Topics covered included (1) an overview of the WAC-EID research; (2) overview of infection prevention and control; (3) safety in animal handling and restraint, sample collection, and processing; (4) safety in field studies including rodent, bird and bat handling; (5) safety practices in the collection of mosquito and other arthropod vectors; (6) personal protective equipment training (disinfection, donning and doffing); and (7) safety in sample collection, labeling, and transportation. The program was executed using a mixed method of slide presentations, practical hands-on sessions, and video demonstrations. Pre- and post-course evaluation assessments and evaluation measures were used to assess training. Results: A total of 48 trainees participated in this training, with 12 (25%), 16 (33.3%), 14 (29.2%), 6 (12.5%) categorized as ornithology, entomology, mammalogy, and clinical interest groups, respectively. The pass rate for the pre-test was 29.4%, while for the post-test, it was 57.1%, or a 28% improvement. 88.6% of the trainees rated the training as relevant to them. Conclusion: Didactic and hands-on biosafety training is relevant in this era of zoonotic epidemics and pandemic preparedness. During this training program, there was a clear demonstration of knowledge transfer that can change the current practices of participants and improve the safety of infectious diseases research

    White book on physical and rehabilitation medicine (PRM) in Europe. Chapter 10. Science and research in PRM: Specificities and challenges

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    In the context of the White Book of Physical and Rehabilitation Medicine (PRM), this paper deals with Research, the future of PRM. PRM students and specialists are mainly involved in biomedical research, investigating the biological processes, the causes of diseases, their medical diagnosis, the evaluation of their consequences on functioning, disability and health and the effects of health interventions at an individual and a societal level. Most of the current PRM research, often interdisciplinary, originates from applied research which, using existing knowledge, is directed towards specific goals. Translational medical research, research and development, implementation research and clinical impact research are in this field. PRM physicians, mainly master or PhD students, are nowadays increasing their participation in basic research and in pre-clinical trials. PRM physicians are involved in primary research, which is an original first hand research, but also in secondary research, which is the analysis and interpretation of primary research publications in a field, with a specific methodology. Secondary research remains an important activity of the UEMS PRM section and it will be the field of the new created Cochrane Rehabilitation. Secondary research with interest for persons with disabilities, will be developed world wide on the basis of evidence based medicine, with the participation of PRM physicians and of all other health and social professionals involved in rehabilitation. The development of research activities with interest for PRM in Europe is a challenge for the future, which has to be faced now. The European PRM schools, the European master and PhD program with their supporting research and clinical facilities, the European PRM organizations with their websites, the PRM scientific journals and European congresses are a strong basis to develop research activities, together with the development of Cochrane Rehabilitation field and of our cooperation with European high level research facilities, European and international scientific societies in different fields. PRM will be a leader in this field of research

    Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves

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    This work was supported by the grants by the Region Aquitaine (to E.M.B) and PEPS (Initial Support for Exploratory Projects to E.M.B) and National Agency for Research (Grant ANR-14-CE19-0006-01 to E.M.B).Plasmodesmata are remarkable cellular machines responsible for the controlled exchange of proteins, small RNAs and signalling molecules between cells. They are lined by the plasma membrane (PM), contain a strand of tubular endoplasmic reticulum (ER), and the space between these two membranes is thought to control plasmodesmata permeability. Here, we have reconstructed plasmodesmata three-dimensional (3D) ultrastructure with an unprecedented level of 3D information using electron tomography. We show that within plasmodesmata, ER-PM contact sites undergo substantial remodelling events during cell differentiation. Instead of being open pores, post-cytokinesis plasmodesmata present such intimate ER-PM contact along the entire length of the pores that no intermembrane gap is visible. Later on, during cell expansion, the plasmodesmata pore widens and the two membranes separate, leaving a cytosolic sleeve spanned by tethers whose presence correlates with the appearance of the intermembrane gap. Surprisingly, the post-cytokinesis plasmodesmata allow diffusion of macromolecules despite the apparent lack of an open cytoplasmic sleeve, forcing the reassessment of the mechanisms that control plant cell-cell communication.PostprintPeer reviewe

    Nanoscale surface topography reshapes neuronal growth in culture

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    International audienceNeurons are sensitive to topographical cues provided either by in vivo or in vitro environments on the micrometric scale. We have explored the role of randomly distributed silicon nanopillars on primary hippocampal neurite elongation and axonal differentiation. We observed that neurons adhere on the upper part of nanopillars with a typical distance between adhesion points of about 500 nm. These neurons produce fewer neurites, elongate faster, and differentiate an axon earlier than those grown on flat silicon surfaces. Moreover, when confronted with a differential surface topography, neurons specify an axon preferentially on nanopillars. As a whole, these results highlight the influence of the physical environment in many aspects of neuronal growth

    How Morphological Constraints Affect Axonal Polarity in Mouse Neurons

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    Neuronal differentiation is under the tight control of both biochemical and physical information arising from neighboring cells and micro-environment. Here we wished to assay how external geometrical constraints applied to the cell body and/or the neurites of hippocampal neurons may modulate axonal polarization in vitro. Through the use of a panel of non-specific poly-L-lysine micropatterns, we manipulated the neuronal shape. By applying geometrical constraints on the cell body we provided evidence that centrosome location was not predictive of axonal polarization but rather follows axonal fate. When the geometrical constraints were applied to the neurites trajectories we demonstrated that axonal specification was inhibited by curved lines. Altogether these results indicated that intrinsic mechanical tensions occur during neuritic growth and that maximal tension was developed by the axon and expressed on straight trajectories. The strong inhibitory effect of curved lines on axon specification was further demonstrated by their ability to prevent formation of multiple axons normally induced by cytochalasin or taxol treatments. Finally we provided evidence that microtubules were involved in the tension-mediated axonal polarization, acting as curvature sensors during neuronal differentiation. Thus, biomechanics coupled to physical constraints might be the first level of regulation during neuronal development, primary to biochemical and guidance regulations

    Interaction between sugar and abscisic acid signalling during early seedling development in Arabidopsis

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    Sugars regulate important processes and affect the expression of many genes in plants. Characterization of Arabidopsis (Arabidopsis thaliana) mutants with altered sugar sensitivity revealed the function of abscisic acid (ABA) signalling in sugar responses. However, the exact interaction between sugar signalling and ABA is obscure. Therefore ABA deficient plants with constitutive ABI4 expression (aba2-1/35S::ABI4) were generated. Enhanced ABI4 expression did not rescue the glucose insensitive (gin) phenotype of aba2 seedlings indicating that other ABA regulated factors are essential as well. Interestingly, both glucose and ABA treatment of Arabidopsis seeds trigger a post-germination seedling developmental arrest. The glucose-arrested seedlings had a drought tolerant phenotype and showed glucose-induced expression of ABSCISIC ACID INSENSITIVE3 (ABI3), ABI5 and LATE EMBRYOGENESIS ABUNDANT (LEA) genes reminiscent of ABA signalling during early seedling development. ABI3 is a key regulator of the ABA-induced arrest and it is shown here that ABI3 functions in glucose signalling as well. Multiple abi3 alleles have a glucose insensitive (gin) phenotype comparable to that of other known gin mutants. Importantly, glucose-regulated gene expression is disturbed in the abi3 background. Moreover, abi3 was insensitive to sugars during germination and showed sugar insensitive (sis) and sucrose uncoupled (sun) phenotypes. Mutant analysis further identified the ABA response pathway genes ENHANCED RESPONSE TO ABA1 (ERA1) and ABI2 as intermediates in glucose signalling. Hence, three previously unidentified sugar signalling genes have been identified, showing that ABA and glucose signalling overlap to a larger extend than originally thought
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