Electron cotunneling transport in gold nanocrystal arrays

We describe current-voltage characteristics I(V) of alkyl-ligated gold nanocrystals $\sim 5 nm$ arrays in long screening length limit. Arrays with different alkyl ligand lengths have been prepared to tune the electronic tunnel coupling between the nanocrystals. For long ligands, electronic diffusion occurs through sequential tunneling and follows activated laws, as function of temperature $\sigma \propto e^{-T_0/T}$ and as function of electric field $I \propto e^{-\mathcal{E}_0/\mathcal{E}}$. For better conducting arrays, i.e. with small ligands, the transport properties crossover to the cotunneling regime and follows Efros-Shklovskii laws as function of temperature $\sigma \propto e^{-(T_{ES}/T)^{1/2}}$ and as function of electric field $I \propto e^{-(\mathcal{E}_{ES}/\mathcal{E})^{1/2}}$. The data shows that electronic transport in nanocrystal arrays can be tuned from the sequential tunneling to the cotunneling regime by increasing the tunnel barrier transparency

Review article: assessing the costs of natural hazards - state of the art and knowledge gaps

Efficiently reducing natural hazard risks requires a thorough understanding of the costs of natural hazards. Current methods to assess these costs employ a variety of terminologies and approaches for different types of natural hazards and different impacted sectors. This may impede efforts to ascertain comprehensive and comparable cost figures. In order to strengthen the role of cost assessments in the development of integrated natural hazard management, a review of existing cost assessment approaches was undertaken. This review considers droughts, floods, coastal and Alpine hazards, and examines different cost types, namely direct tangible damages, losses due to business interruption, indirect damages, intangible effects, and the costs of risk mitigation. This paper provides an overview of the state-of-the-art cost assessment approaches and discusses key knowledge gaps. It shows that the application of cost assessments in practice is often incomplete and biased, as direct costs receive a relatively large amount of attention, while intangible and indirect effects are rarely considered. Furthermore, all parts of cost assessment entail considerable uncertainties due to insufficient or highly aggregated data sources, along with a lack of knowledge about the processes leading to damage and thus the appropriate models required. Recommendations are provided on how to reduce or handle these uncertainties by improving data sources and cost assessment methods. Further recommendations address how risk dynamics due to climate and socio-economic change can be better considered, how costs are distributed and risks transferred, and in what ways cost assessment can function as part of decision support

Star Formation from Galaxies to Globules

The empirical laws of star formation suggest that galactic-scale gravity is involved, but they do not identify the actual triggering mechanisms for clusters in the final stages. Many other triggering processes satisfy the empirical laws too, including turbulence compression and expanding shell collapse. The self-similar nature of the gas and associated young stars suggests that turbulence is more directly involved, but the small scale morphology of gas around most embedded clusters does not look like a random turbulent flow. Most clusters look triggered by other nearby stars. Such a prominent local influence makes it difficult to understand the universality of the Kennicutt and Schmidt laws on galactic scales. A unified view of multi-scale star formation avoids most of these problems. Ambient self-gravity produces spiral arms and drives much of the turbulence that leads to self-similar structures, while localized energy input from existing clusters and field supernovae triggers new clusters in pre-existing clouds. The hierarchical structure in the gas made by turbulence ensures that the triggering time scales with size, giving the Schmidt law over a wide range of scales and the size-duration correlation for young star fields. The efficiency of star formation is determined by the fraction of the gas above a critical density of around 10^5 m(H2)/cc. Star formation is saturated to its largest possible value given the fractal nature of the interstellar medium.Comment: accepted for ApJ, 42 pages, Dannie Heineman prize lecture, January 200

Effects of Heavy Metals and Arbuscular Mycorrhiza on the Leaf Proteome of a Selected Poplar Clone: A Time Course Analysis

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with the roots of most plant species. While receiving photosynthates, they improve the mineral nutrition of the plant and can also increase its tolerance towards some pollutants, like heavy metals. Although the fungal symbionts exclusively colonize the plant roots, some plant responses can be systemic. Therefore, in this work a clone of Populus alba L., previously selected for its tolerance to copper and zinc, was used to investigate the effects of the symbiosis with the AM fungus Glomus intraradices on the leaf protein expression. Poplar leaf samples were collected from plants maintained in a glasshouse on polluted (copper and zinc contaminated) or unpolluted soil, after four, six and sixteen months of growth. For each harvest, about 450 proteins were reproducibly separated on 2DE maps. At the first harvest the most relevant effect on protein modulation was exerted by the AM fungi, at the second one by the metals, and at the last one by both treatments. This work demonstrates how importantly the time of sampling affects the proteome responses in perennial plants. In addition, it underlines the ability of a proteomic approach, targeted on protein identification, to depict changes in a specific pattern of protein expression, while being still far from elucidating the biological function of each protein

Physical Processes in Star Formation

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00693-8.Star formation is a complex multi-scale phenomenon that is of significant importance for astrophysics in general. Stars and star formation are key pillars in observational astronomy from local star forming regions in the Milky Way up to high-redshift galaxies. From a theoretical perspective, star formation and feedback processes (radiation, winds, and supernovae) play a pivotal role in advancing our understanding of the physical processes at work, both individually and of their interactions. In this review we will give an overview of the main processes that are important for the understanding of star formation. We start with an observationally motivated view on star formation from a global perspective and outline the general paradigm of the life-cycle of molecular clouds, in which star formation is the key process to close the cycle. After that we focus on the thermal and chemical aspects in star forming regions, discuss turbulence and magnetic fields as well as gravitational forces. Finally, we review the most important stellar feedback mechanisms.Peer reviewedFinal Accepted Versio

Techniques d’évaluation des risques côtiers liés aux tempêtes

Le principal objectif du présent article est de décrire quelques techniques pour évaluer les risques côtiers induits par les tempêtes extrêmes et les surcotes marines. Nous examinons principalement les impacts physiques des tempêtes sur les systèmes littoraux. Le premier chapitre définit brièvement la notion de risque. Le second chapitre décrit quelques techniques appliquées pour évaluer la vulnérabilité côtière et les risques liés aux tempêtes. Le troisième chapitre décrit des moyens mis en œuvre afin de réduire les risques auxquels sont exposées les régions et les populations côtières. Enfin, la conclusion tente de synthétiser les principaux outils et les principales techniques utilisés pour évaluer ou réduire les risques côtiers

Review article : assessing the costs of natural hazards, state of the art and knowledge gaps

Efficiently reducing natural hazard risks requires a thorough understanding of the costs of natural hazards. Current methods to assess these costs employ a variety of terminologies and approaches for different types of natural hazards and different impacted sectors. This may impede efforts to ascertain comprehensive and comparable cost figures. In order to strengthen the role of cost assessments in the development of integrated natural hazard management, a review of existing cost assessment approaches was undertaken. This review considers droughts, floods, coastal and Alpine hazards, and examines different cost types, namely direct tangible damages, losses due to business interruption, indirect damages, intangible effects, and the costs of risk mitigation. This paper provides an overview of the state-of-the-art cost assessment approaches and discusses key knowledge gaps. It shows that the application of cost assessments in practice is often incomplete and biased, as direct costs receive a relatively large amount of attention, while intangible and indirect effects are rarely considered. Furthermore, all parts of cost assessment entail considerable uncertainties due to insufficient or highly aggregated data sources, along with a lack of knowledge about the processes leading to damage and thus the appropriate models required. Recommendations are provided on how to reduce or handle these uncertainties by improving data sources and cost assessment methods. Further recommendations address how risk dynamics due to climate and socio-economic change can be better considered, how costs are distributed and ris

Costs of Natural Hazards - A Synthesis

CONHAZ project final repor

Multi‐Level Switching and Reversible Current Driven Domain‐Wall Motion in Single CoFeB/MgO/CoFeB‐Based Perpendicular Magnetic Tunnel Junctions

One of the critical issues in spintronics-based technologies is to increase the data storage density. Current strategy is based on shrinking the devices size down to tens of nanometers, or several nanometers, which is reaching its limit. A new proposal is to use multi-level cells (MLCs) to store more than two bits in each cell. In this work, the multi-level switching is realized in CoFeB/MgO/CoFeB based nano-scale single perpendicular magnetic tunnel junctions (p-MTJs) with three or four stable resistance states. A large range of writing currents for each state is obtained, accompanying with a good repeatability of set-reset operations between different states. The developed multi-domain model perfectly matches the experimental results, reflecting the magnetic behaviors during multi-level switching. Furthermore, current-driven domain wall (DW) motion is revealed in the circular p-MTJs, where the DW position can be reversibly manipulated by applied current. To design high-performance multi-level p-MTJs, the parameter diagrams are calculated, suggesting various feasible strategies to improve the multi-level switching through materials optimization and devices geometry. In summary, the demonstration of multi-level switching in single p-MTJ shows the high potential of realizing the new generation of p-MTJ-based multi-level spintronic devices, such as multi-level memories and spin-neuron devices