A Model for Cortical Rewiring Following Deafferentation and Focal Stroke

It is still unclear to what extent structural plasticity in terms of synaptic rewiring is the cause for cortical remapping after a lesion. Recent two-photon laser imaging studies demonstrate that synaptic rewiring is persistent in the adult brain and is dramatically increased following brain lesions or after a loss of sensory input (cortical deafferentation). We use a recurrent neural network model to study the time course of synaptic rewiring following a peripheral lesion. For this, we represent axonal and dendritic elements of cortical neurons to model synapse formation, pruning and synaptic rewiring. Neurons increase and decrease the number of axonal and dendritic elements in an activity-dependent fashion in order to maintain their activity in a homeostatic equilibrium. In this study we demonstrate that synaptic rewiring contributes to neuronal homeostasis during normal development as well as following lesions. We show that networks in homeostasis, which can therefore be considered as adult networks, are much less able to compensate for a loss of input. Interestingly, we found that paused stimulation of the networks are much more effective promoting reorganization than continuous stimulation. This can be explained as neurons quickly adapt to this stimulation whereas pauses prevents a saturation of the positive stimulation effect. These findings may suggest strategies for improving therapies in neurologic rehabilitation

Integrated Al2O3:Er3+ zero-loss optical amplifier and power splitter with 40 nm bandwidth

A combined planar lossless optical amplifier and 1x2 power splitter device has been realized in Al2O3:Er3+ on silicon. Net internal gain was measured over a wavelength range of 40 nm across the complete telecom -band (1525–1565 nm). Calculations predict net gain in a combined amplifier and 1x4 power splitter device over the same wavelength range for a total injected pump power as low as 30 mW

Homeostatic structural plasticity increases the efficiency of small-world networks

In networks with small-world topology, which are characterized by a high clustering coefficient and a short characteristic path length, information can be transmitted efficiently and at relatively low costs. The brain is composed of small-world networks, and evolution may have optimized brain connectivity for efficient information processing. Despite many studies on the impact of topology on information processing in neuronal networks, little is known about the development of network topology and the emergence of efficient small-world networks. We investigated how a simple growth process that favors short-range connections over long-range connections in combination with a synapse formation rule that generates homeostasis in post-synaptic firing rates shapes neuronal network topology. Interestingly, we found that small-world networks benefited from homeostasis by an increase in efficiency, defined as the averaged inverse of the shortest paths through the network. Efficiency particularly increased as small-world networks approached the desired level of electrical activity. Ultimately, homeostatic small-world networks became almost as efficient as random networks. The increase in efficiency was caused by the emergent property of the homeostatic growth process that neurons started forming more long-range connections, albeit at a low rate, when their electrical activity was close to the homeostatic set-point. Although global network topology continued to change when neuronal activities were around the homeostatic equilibrium, the small-world property of the network was maintained over the entire course of development. Our results may help understand how complex systems such as the brain could set up an efficient network topology in a self-organizing manner. Insights from our work may also lead to novel techniques for constructing large-scale neuronal networks by self-organization

Sustainability, Efficiency and Equitability of Water Consumption and Pollution in Latin America and the Caribbean

This paper assesses the sustainability, efficiency and equity of water use in Latin America and the Caribbean (LAC) by means of a geographic Water Footprint Assessment (WFA). It aims to provide understanding of water use from both a production and consumption point of view. The study identifies priority basins and areas from the perspectives of blue water scarcity, water pollution and deforestation. Wheat, fodder crops and sugarcane are identified as priority products related to blue water scarcity. The domestic sector is the priority sector regarding water pollution from nitrogen. Soybean and pasture are priority products related to deforestation. We estimate that consumptive water use in crop production could be reduced by 37% and nitrogen-related water pollution by 44% if water footprints were reduced to certain specified benchmark levels. The average WF per consumer in the region is 28% larger than the global average and varies greatly, from 912 m3 /year per capita in Nicaragua to 3468 m3 /year in Bolivia. Ironically, the LAC region shows significant levels of undernourishment, although there is abundant water and food production in the region and substantial use of land and water for producing export crops like soybean

Spontaneous Charging and Crystallization of Water Droplets in Oil

We study the spontaneous charging and the crystallization of spherical micron-sized water-droplets dispersed in oil by numerically solving, within a Poisson-Boltzmann theory in the geometry of a spherical cell, for the density profiles of the cations and anions in the system. We take into account screening, ionic Born self-energy differences between oil and water, and partitioning of ions over the two media. We find that the surface charge density of the droplet as induced by the ion partitioning is significantly affected by the droplet curvature and by the finite density of the droplets. We also find that the salt concentration and the dielectric constant regime in which crystallization of the water droplets is predicted is enhanced substantially compared to results based on the planar oil-water interface, thereby improving quantitative agreement with recent experiments.Comment: 10 pages, 7 figures, submitted for publicatio

Sustainability, Efficiency and Equitability of Water Consumption and Pollution in Latin America and the Caribbean

This paper assesses the sustainability, efficiency and equity of water use in Latin America and the Caribbean (LAC) by means of a geographic Water Footprint Assessment (WFA). It aims to provide understanding of water use from both a production and consumption point of view. The study identifies priority basins and areas from the perspectives of blue water scarcity, water pollution and deforestation. Wheat, fodder crops and sugarcane are identified as priority products related to blue water scarcity. The domestic sector is the priority sector regarding water pollution from nitrogen. Soybean and pasture are priority products related to deforestation. We estimate that consumptive water use in crop production could be reduced by 37% and nitrogen-related water pollution by 44% if water footprints were reduced to certain specified benchmark levels. The average WF per consumer in the region is 28% larger than the global average and varies greatly, from 912 m3/year per capita in Nicaragua to 3468 m3/year in Bolivia. Ironically, the LAC region shows significant levels of undernourishment, although there is abundant water and food production in the region and substantial use of land and water for producing export crops like soybean

Fleshy red algae mats act as temporary reservoirs for sessile invertebrate biodiversity

Comparative analyses of fleshy red algae mats and seagrass meadows highlight their value in fostering sessile invertebrate biodiversity. Many coastal ecosystems, such as coral reefs and seagrass meadows, currently experience overgrowth by fleshy algae due to the interplay of local and global stressors. This is usually accompanied by strong decreases in habitat complexity and biodiversity. Recently, persistent, mat-forming fleshy red algae, previously described for the Black Sea and several Atlantic locations, have also been observed in the Mediterranean. These several centimetre high mats may displace seagrass meadows and invertebrate communities, potentially causing a substantial loss of associated biodiversity. We show that the sessile invertebrate biodiversity in these red algae mats is high and exceeds that of neighbouring seagrass meadows. Comparative biodiversity indices were similar to or higher than those recently described for calcifying green algae habitats and biodiversity hotspots like coral reefs or mangrove forests. Our findings suggest that fleshy red algae mats can act as alternative habitats and temporary sessile invertebrate biodiversity reservoirs in times of environmental change.Peer reviewe