The role of sea-ice albedo in the climate of slowly rotating aquaplanets

We investigate the influence of the rotation period (Prot) on the mean climate of an aquaplanet, with a focus on the role of sea-ice albedo. We perform aquaplanet simulations with the atmospheric general circulation model ECHAM6 for various rotation periods from one Earth-day to 365 Earth-days in which case the planet is synchronously rotating. The global-mean surface temperature decreases with increasing Prot and sea ice expands equatorwards. The cooling of the mean climate with increasing Prot is caused partly by the high surface albedo of sea ice on the dayside and partly by the high albedo of the deep convective clouds over the substellar region. The cooling caused by these deep convective clouds is weak for non-synchronous rotations compared to synchronous rotation. Sensitivity simulations with the sea-ice model switched off show that the global-mean surface temperature is up to 27 K higher than in our main simulations with sea ice and thus highlight the large influence of sea ice on the climate. We present the first estimates of the influence of the rotation period on the transition of an Earth-like climate to global glaciation. Our results suggest that global glaciation of planets with synchronous rotation occurs at substantially lower incoming solar irradiation than for planets with slow but non-synchronous rotation

Long-term transients in fluidization of oxide nanoparticle agglomerates

Nanopowders are frequently fluidized for research during the last two decades. Interestingly, it was believed for a long time that nanopowders cannot be fluidized since they are classified as group C, very cohesive powders, in the Geldart diagram. For these powders the acting adhesion forces are too strong to allow fluidization. However, many studies showed that nanoparticles can be fluidized as micron-sized fractal agglomerates with very low densities and very high porosities [1]. The high porosities of the agglomerates are very attractive because most of the particle surface is accessible for mass transfer and reaction. The formation of the agglomerates in the fluidized bed is a dynamic process which includes collision, unfolding, breaking, and reagglomeration. This makes it likely that the agglomerate size distribution will change over time. On the other hand, long-duration fluidization of nanopowders is required for possible industrial applications such as coating or catalysis. Therefore, a better understanding of, the influence of time on the properties of fluidized nanoparticle agglomerates is crucial. Here we present a detailed analysis of the agglomerate size distribution over time during long-time fluidization of oxide nanoparticles. A settling tube set-up is used to investigate the agglomerate size distributions (see Fig. 1) as well as X-ray tomography which suggest stratification of the bed during long time fluidization (see Fig. 2). Further, the influence of the acting contact forces on the arising agglomerate size distributions was investigated. The results show that microscopic properties such as agglomerate size distribution can directly be linked to macroscopic properties as the bed expansion and that the time is a very important factor for the fluidization of nanopowders, because the bed dynamics changes strongly over time. Please click Additional Files below to see the full abstract

Fluidization of graphene nanoplatelets for atomic layer deposition

Graphene is an ideal catalysis support: it has a high surface area, is chemically and thermodynamically inert, and has high carrier mobility. A special type of graphene nanoparticles are graphene nanoplatelets. They consist of small stacks of graphene giving them a thickness of 1 – 15 nm while their diameters can range up to a few micrometres. However, for catalysis these nanoplatelets have to be provided with catalyst materials such as platinum or titania. One very promising technique for such a modification is Atomic Layer Deposition of nanoparticles on the graphene, which can provide a fast, highly controlled and scalable process. However, to separate the carbon nanoplatelets and achieve free large accessible surfaces in the reactor nanoplatelets have to be fluidized. While fluidization of carbon nanotubes is already well established, fluidization of nanoplatelets is a completely new research topic and was, to the best of our knowledge, not investigated so far. Based on the size of the carbon nanoplatelets they are treated as very cohesive (Geldart group C) powders which are hard to fluidize. Nevertheless, homogenous fluidization could be achieved by using assistance methods such as mechanical vibration. Here we present a detailed analysis of the fluidization behaviour of carbon nanoplatelets for atomic layer deposition. We analysed the bed expansion behaviour of the nanoplatelets depending on the gas velocities. Since the Atomic Layer Deposition process can be run at different temperatures, depending on the used precursors, we further analysed the influence of the temperature on the fluidization behaviour. Finally, we investigated the reproducibility of our results by an statistical analysis of our results. Please click Additional Files below to see the full abstract

Size distribution prediction of nanoparticle agglomerates in a fluidized bed

Nanoparticles have acquired considerable attention from academia and industry due to their unique properties arising from the large surface area to volume ratio. A promising method to process these particles is fluidization. Furthermore, it is worth knowing that nanoparticles fluidize as clusters called agglomerates, formed by the relatively strong adhesion forces among the individual particles (1). These agglomerates are large, highly porous fractal structures; thus, easy to access but extremely fragile. During fluidization, agglomerates move, collide, break, reform, deform, and combine, which make them suitable for a wide range of applications. Nanopowders can fluidize with bubbles or uniformly, which show different dynamics that might affect the morphology of the fluidized agglomerates. In order to better understand the dynamic behaviour of the system, it is crucial to know the agglomerate size distribution within the fluidized bed. Therefore, we developed a model based on a simple force balance to predict the agglomerate size distribution, which enables the optimization of processing methods. Please click Additional Files below to see the full abstract

An architecture governance approach for Agile development by tailoring the Spotify model

The role of software architecture in large-scale Agile development is important because several teams need to work together to release a single software product while helping to maximise teams’ autonomy. Governing and aligning Agile architecture across autonomous squads (i.e., teams), when using the Spotify model, is a challenge because the Spotify model lacks practices for addressing Agile architecture governance. To explore how software architecture can be governed and aligned by scaling the Spotify model, we conducted a longitudinal embedded case study in a multinational FinTech organisation. Then, we developed and evaluated an approach for architectural governance by conducting an embedded case study. The collected data was analysed using Thematic Analysis and informed by selected Grounded Theory techniques such as memoing, open coding, constant comparison, and sorting. Our approach for architectural governance comprises an organisational structure change and an architecture change management process. The benefits reported by the practitioners include devolving architectural decision-making to the operational level (i.e., Architecture Owners), enhancing architectural knowledge sharing among squads, minimising wasted effort in architectural refactoring, and other benefits. The practitioners in our case study realised an improved squad autonomy by the ability to govern and align architectural decisions. We provide two key contributions in this paper. First, we present the characteristics of our proposed architectural governance approach, its evaluation, benefits, and challenges. Second, we present how the novel Heterogeneous Tailoring model was enhanced to accommodate our architectural governance approach

Domain walls at the spin density wave endpoint of the organic superconductor (TMTSF)2PF6 under pressure

We report the first comprehensive investigation of the organic superconductor (TMTSF)2PF6 in the vicinity of the endpoint of the spin density wave - metal phase transition where phase coexistence occurs. At low temperature, the transition of metallic domains towards superconductivity is used to reveal the various textures. In particular, we demonstrate experimentally the existence of 1D and 2D metallic domains with a cross-over from a filamentary superconductivity mostly along the c?-axis to a 2D superconductivity in the b?c-plane perpendicular to the most conducting direction. The formation of these domain walls may be related to the proposal of a soliton phase in the vicinity of the critical pressure of the (TMTSF)2PF6 phase diagram.Comment: 5 page

Adhesion mechanisms of the contact interface of TiO2 nanoparticles in films and aggregates

Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of few nanometers is impeded by the difficulties associated with direct measurements of contact forces at such a small size scale. Here we develop a strategy based on AFM force spectroscopy combined with all-atom molecular dynamics simulations to quantify and explain the nature of the contact forces between 10 nm small TiO2 nanoparticles. The method is based on the statistical analysis of the force peaks measured in repeated approaching/retracting loops of an AFM cantilever into a film of nanoparticle agglomerates and relies on the in-situ imaging of the film stretching behavior in an AFM/TEM setup. Sliding and rolling events first lead to local rearrangements in the film structure when subjected to tensile load, prior to its final rupture caused by the reversible detaching of individual nanoparticles. The associated contact force of about 2.5 nN is in quantitative agreement with the results of molecular dynamics simulations of the particle–particle detachment. We reveal that the contact forces are dominated by the structure of water layers adsorbed on the particles’ surfaces at ambient conditions. This leads to nonmonotonous force–displacement curves that can be explained only in part by classical capillary effects and highlights the importance of considering explicitly the molecular nature of the adsorbates