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Cylindrical Langmuir probe measurements in a low-pressure DC argon discharge are used to obtain the spatial evolution of ion, cold and hot electron parameters across the cathodic pre-sheath. The cathodic pre-sheath is formed by a stainless steel plate allowed to float negatively with respect to the plasma. The velocity distribution function of the hot electron population in the pre-sheath is shown to be matched by a drifting Maxwellian that thermalizes across it. The source of the hot electron population is hypothesized to arise from secondary electron emission from the plate. A Bayesian estimation routine is proposed to compare and validate different Langmuir probe models as well as calculating the relative uncertainty between models. The results are analyzed using existing pre-sheath theory for which experimental evidence of the spatial influence of energetic electrons is lacking. The data are shown to follow Riemann's pre-sheath model that the ion-neutral mean free path [Formula: see text] is proportional to the pre-sheath characteristic length l, and that the potential drop [Formula: see text] with distance x from the sheath/pre-sheath boundary x0 follows [Formula: see text].

Naturbasierte Lösungen – also Maßnahmen, die ökologische Prozesse zur Bewältigung gesellschaftlicher Herausforderungen nutzen – können bei der Erarbeitung integrierter Entwicklungskonzepte für Flusslandschaften eine zentrale Rolle einnehmen. Ziel dieses Beitrags ist, das Konzept der naturbasierten Lösungen am Beispiel von Flusslandschaften zu beleuchten. In Form von zehn Thesen werden das Konzept der naturbasierten Lösungen charakterisiert, damit einhergehende Vorteile thematisiert und Chancen für einen erfolgreichen Einsatz diskutiert. Die Thesen wurden vom Autorenteam gemeinsam mit Experten aus Politik und Praxis in einem angepassten Delphi-Verfahren entwickelt. Der Beitrag soll konzeptionelle Missverständnisse vermeiden helfen, die Dringlichkeit zur Umsetzung aufzeigen, und Praktiker motivieren, naturbasierte Lösungen stärker als bisher zu berücksichtigen. Wir hoffen, damit Transformationsprozesse zu einer zukunftsfähigen Entwicklung von Flusslandschaften für die Menschen und die Natur zu unterstützen. Nature-based solutions – understood here as actions that utilize ecological processes to address societal challenges – can play key roles in creating integrated development concepts for river landscapes. This contribution aims at elaborating the concept of nature-based solutions with a focus on river landscapes. We present ten propositions that characterize the concept of nature-based solutions, introduce the comparative advantages of applying such solutions, and discuss chances for successful deployment. We developed the propositions using an adapted Delphi method, together with experts from policy and practice. Our contribution should help avoiding conceptual misunderstandings, illustrate the urgency for implementation, and encourage practitioners to enhance the consideration of nature-based solutions. We hope the propositions thus help to support transformations towards a more sustainable development of river landscapes for people and nature.

Inertial electrostatic confinement (IEC) is a method of confining and heating a plasma at benchtop scales to sufficient energies for nuclear fusion to occur. Ion velocity and flow direction were measured in an IEC discharge using laser induced fluorescence (LIF) on argon ions. A cathode of two parallel rings, with a common axis of symmetry, resulted in predominant discharge beams, otherwise known as microchannels, along this axis. The device was operated in the abnormal glow discharge regime where both current and voltage increase monotonically, replicating a conventional high voltage IEC device. It was found that argon ions accelerated and flowed outward from the midpoint between the rings along the axis; we have labeled this ion motion as being divergent. The predominant direction of ion flow in the discharge is opposite to the conventional ion focus model, where the discharge at the cathode center is assumed to be the result of ion flow toward it from outside of the cathode. An ion sheath model is shown to produce a virtual anode at the axial midpoint between the rings. The model also shows that ions within the virtual anode are accelerated outward with a spatial velocity profile that replicates those measured using LIF.

This paper explores the benefits and the costs of strengthening infrastructure assets to make them more resilient, reducing the repair costs and infrastructure disruptions caused by natural hazards. Strengthening infrastructure assets in low- and middle-income countries would increase investment needs in power, transport, and water and sanitation by between $11 billion and $65 billion a year, i.e. 3 percent of baseline infrastructure investment needs. The uncertainty pertaining to the costs and benefits of infrastructure resilience makes it difficult to provide a single estimate for the benefit-cost ratio of strengthening exposed infrastructure assets. To manage this uncertainty, this paper explores the benefit-cost ratio in 3,000 scenarios, combining uncertainties in all parameters of the analysis. The benefit-cost ratio is higher than 1 in 96 percent of the scenarios, larger than 2 in 77 percent of them, and higher than 4 in half of them. The net present value of these investments over the lifetime of new infrastructure assets -- or, equivalently, the cost of inaction -- exceeds $2 trillion in 75 percent of the scenarios and $4.2 trillion in half of them. Moreover, climate change makes the strengthening of infrastructure assets even more important, doubling the median benefit-cost ratio.

The power sector is both highly vulnerable to natural hazards and a priority for any country'srecovery and reconstruction. After Hurricane Maria in Puerto Rico in 2017, most of the power gridwas down. One year and tens of billions of dollars later some customers were yet to be reconnected to the main grid. This type of long and widespread power outage has major consequences on people's health and well-being, for instance through lacking access to refrigeration for food and medicine, and on the ability of firms to produce and provide people with goods, services, jobs, and income. In most countries, the power system is designed to cope with high-frequency but relatively low impact events. Low-frequency, high-impact events – such as many natural disasters – are rarely considered fully, and the implementation of planned management measures is often patchy. Furthermore, the power system is a special kind of infrastructure due to the heterogeneity of the generation assets and its wide spatial distribution. The latter means that power systems are often exposed to natural hazards and sometimes to more than one hazard, leading to high repair costs when disasters strike. This paper, prepared as a sectoral note for the Lifelines report on infrastructure resilience, investigates the vulnerability of the power system to natural hazards and climate change, and provides recommendations to increase its resilience. It first describes how power outages are often the consequence of natural disasters and outlines the main vulnerabilities of the power sector. It then proposes a range of approaches and solutions for building a more resilient power sector – from increased robustness to greater flexibility – showing that the additional cost of resilience is not high if resources are well spent. Finally, it describes how emergency preparedness and disaster recovery encompass not only technical aspects, like asset strengthening or criticality analysis, but also "softer" skills, like governance, regulatory or capacity building, and education.

This paper explores the investments needed to achieve universal access to electricity in Sub-Saharan Africa by 2030, and the additional operation and maintenance costs these investments entail. It also explores the drivers of these costs, by exploring hundreds of scenarios that combine alternative assumptions on the level of service targeted, population growth, urbanization, industrial demand, and technology cost. The main driver of electrification costs is found to be the tier of service offered to newly connected households. The annual investment required to reach universal access varies between US$14.5 billion per year on average for the basic access scenarios (0.7 percent of the region's gross domestic product per year over the period) and US$22.7 billion on average for the high-quality scenarios (1 percent of gross domestic product). In the basic access scenario, costs depend mostly on industrial demand, which takes a large share of total demand. In the high-quality scenarios, costs depend on urbanization rates, as it is cheaper to connect urban households to the grid. Investment costs are not sufficient to provide reliable service, and when operations and maintenance are accounted for, total costs increase to US$39.7 billion on average for the basic scenarios and US$61.5 billion on average for the high-quality scenarios.