Highly porous Germanium surfaces with uniformly distributed columnar nanovoid structures are fabricated over a large area (wafer scale) by large fluence Sn
irradiation through a thin silicon nitride ...layer. The latter represents a one-step highly reproducible approach with no material loss to strongly increase photon harvesting into a semiconductor active layer by exploiting the moth-eye antireflection effect. The ion implantation through the nitride cap layer allows fabricating porous nanostructures with high aspect ratio, which can be tailored by varying ion fluence. By comparing the reflectivity of nanoporous Ge films with a flat reference we demonstrate a strong and omnidirectional reduction in the optical reflectivity by a factor of 96% in the selected spectral regions around 960 nm and by a factor of 67.1% averaged over the broad spectral range from 350 to 1800 nm. Such highly anti-reflective nanostructured Ge films prepared over large-areas with a self-organized maskless approach have the potential to impact real world applications aiming at energy harvesting.
This review highlights the important role of the depth‐averaged sediment concentration (DASC) to understand the formation of a number of coastal morphodynamic features that have an alongshore ...rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and shoreface‐connected sand ridges. We present a formulation and methodology, based on the knowledge of the DASC (which equals the sediment load divided by the water depth), that has been successfully used to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and other disciplines, are located in different parts of the coastal zone and are characterized by different spatial and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur in the presence of depth‐averaged currents, the sediment transport approximately equals a sediment load times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and the current increases this mobilization and advects the sediment. In such conditions, knowing the spatial distribution of the DASC and the depth‐averaged currents induced by the forcing (waves, wind, and pressure gradients) over the patterns allows inferring the convergence/divergence of sediment transport. Deposition (erosion) occurs where the current flows from areas of high to low (low to high) values of DASC. The formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features, but the physical mechanisms for their migration, their finite‐amplitude behavior and their decay can also be explored.
Key Points
A methodology to examine interactions between flow and morphology is presented
It is applied to beach cusps, crescentic/transverse bars and inner shelf ridges
The depth‐averaged sediment concentration is crucial in the feedback mechanisms
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Circling in on Convective Organization Haerter, Jan O.; Böing, Steven J.; Henneberg, Olga ...
Geophysical research letters,
28 June 2019, Volume:
46, Issue:
12
Journal Article
Peer reviewed
Open access
Cold pools (CPs) contribute to convective organization. However, it is unclear by which mechanisms organization occurs. By using a particle method to track CP gust fronts in large eddy simulations, ...we characterize the basic collision modes between CPs. Our results show that CP interactions, where three expanding gust fronts force an updraft, are key at triggering new convection. Using this, we conceptualize CP dynamics into a parameter‐free mathematical model: circles expand from initially random points in space. Where two expanding circles collide, a stationary front is formed. However, where three expanding circles enclose a single point, a new expanding circle is seeded. This simple model supports three fundamental features of CP dynamics: precipitation cells constitute a spatially interacting system, CPs come in generations, and scales steadily increase throughout the diurnal cycle. Finally, this model provides a framework for how CPs act to cause convective self‐organization, clustering, and extremes.
Plain Language Summary
Cold pool (CP) dynamics constitutes a crucial organizing mechanism for midlatitude and tropical clouds—they play a key role in the lead‐up to extreme events and may influence how such events behave in a changing climate. CPs are dense air masses that form under precipitating thunderstorm clouds. Under gravity, CPs spread along the surface and stimulate new precipitation events when they collide with other CPs. We show that CP interaction can be captured by a simple model, where circles grow in space and form new circles when three of them collide. Generalizing to thousands of initial circle centers, the dynamics of these circles gives a steady scale increase over time, similar to the one found in high‐resolution atmospheric simulations. In summary, we introduce a cloud‐organizing mechanism that forms the basis for extreme convective precipitation events, such as those implicated in flash floods.
Key Points
Convection is often initiated by the collision of three cold pools
A model based on expanding and colliding circles captures the convective scale increase
This simple model can produce clustering of precipitation cells
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Synthetic multicellular systems hold promise as models for understanding natural development of biofilms and higher organisms and as tools for engineering complex multi-component metabolic pathways ...and materials. However, such efforts require tools to adhere cells into defined morphologies and patterns, and these tools are currently lacking. Here, we report a 100% genetically encoded synthetic platform for modular cell-cell adhesion in Escherichia coli, which provides control over multicellular self-assembly. Adhesive selectivity is provided by a library of outer membrane-displayed nanobodies and antigens with orthogonal intra-library specificities, while affinity is controlled by intrinsic adhesin affinity, competitive inhibition, and inducible expression. We demonstrate the resulting capabilities for quantitative rational design of well-defined morphologies and patterns through homophilic and heterophilic interactions, lattice-like self-assembly, phase separation, differential adhesion, and sequential layering. Compatible with synthetic biology standards, this adhesion toolbox will enable construction of high-level multicellular designs and shed light on the evolutionary transition to multicellularity.
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•Orthogonal, composable adhesin library allows control over specificity and affinity•Adhesion is maintained during cell growth and division•Cultures form lattice-like, phase separation, and differential adhesion patterns•Compatibility with synthetic biology standards allows complex multicellular designs
The development of a genetically encoded toolkit of surface-bound nanobodies and antigens in E. coli allows for precise manipulation of cell-cell adhesion and rational design of diverse self-assembled multicellular patterns and morphologies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Life as we know it Friston, Karl
Journal of the Royal Society interface,
09/2013, Volume:
10, Issue:
86
Journal Article
Peer reviewed
Open access
This paper presents a heuristic proof (and simulations of a primordial soup) suggesting that life—or biological self-organization—is an inevitable and emergent property of any (ergodic) random ...dynamical system that possesses a Markov blanket. This conclusion is based on the following arguments: if the coupling among an ensemble of dynamical systems is mediated by short-range forces, then the states of remote systems must be conditionally independent. These independencies induce a Markov blanket that separates internal and external states in a statistical sense. The existence of a Markov blanket means that internal states will appear to minimize a free energy functional of the states of their Markov blanket. Crucially, this is the same quantity that is optimized in Bayesian inference. Therefore, the internal states (and their blanket) will appear to engage in active Bayesian inference. In other words, they will appear to model—and act on—their world to preserve their functional and structural integrity, leading to homoeostasis and a simple form of autopoiesis.
Many commuters still travel to work alone, in their private vehicle, causing negative externalities, including economic inefficiencies and environmental impacts. Nonprofit ridesharing is considered ...one of the sustainable modes to mitigate those effects. On multiple occasions, ad-hoc ridesharing-between-strangers has been shown to turn the expensive drive-alone commuting habit and achieve more sustainable results – by serving the demand of road users, while reducing the vehicle-miles travelled. Where organized ridesharing gains limited success, self-organized ridesharing (SORS) initiatives - which grow organically by reacting to strains and opportunities, had been shown in different contexts to draw substantial participation. However, the literature had treated these occurrences as anecdotal, un-replicable, context specific phenomena. Thus, limited theoretical and practical knowledge is offered, especially of the influential earlier stages. The presented research postulates SORS follows repeated emergence patterns, which can be externally and systematically influenced for better ridesharing solutions. Based on synthesis of existing literature, the research offers a descriptive framework for SORS analysis, which enables exploration and design of initiatives. The framework was validated through evaluation of seven case studies from around the world. The cases were explored using mixed methods approach, relying mainly on social-network data mining, supplemented by semi-structured interviews and observations. By merging knowledge areas of Sharing Economy, Grass-root Innovation and Practice Theory in Multi-Level-Perspective transition analysis, the framework allows explanation of different occurrences. Specifically, several repeated patterns are revealed: (a) activists and activist-less types; (b) the favourable commuting “line” structure which relies on choke-point transport geography, demand concentration and available public transport backup; (c) participants’ arena support; (d) emerging sense-of-community which provides additional resiliency; and (e) emergence process structure. The findings support improved policy decisions and recommendations for technology design. Through these enhancements, SORS techno-social processes can be stimulated, resulting in increase of ridesharing uptake.
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Efficient and stable catalysts for ammonia synthesis under mild conditions are required to meet the strong demand for NH3 as an important precursor chemical and hydrogen carrier. Here we report that ...during ammonia synthesis, flat-shaped Ru nanoparticles with a narrow distribution (2.1 ± 1.0 nm) and self-organized on Ca(NH2)2 exhibit high catalytic performance far exceeding alkali-promoted Ru-based catalysts in yield and turnover frequency (TOF). This catalyst enables continuous NH3 production, even at 473 K under ambient pressure. During ammonia synthesis, Ru nanoparticles are distinctly anchored on the surface of Ca(NH2)2 by strong Ru–N interaction, which leads to the epitaxial growth of Ru on the support surface. The high catalytic performance is due to the formation of high-density flat-shaped Ru nanoparticles and high electron donor ability at the Ru/Ca(NH2)2 interface. The catalytic stability is significantly improved by Ba-doping of Ca(NH2)2, and no degradation was observed after ca. 700 h of operation.
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Supramolecular nanofibers are formed from aqueous solutions of a bola‐ amphihile, containing two carboxylic end groups and a central π–π‐stacking moiety. The combined noncovalent interactions form ...the basis for the successful self‐assembly of the fibers. The obtained fibers (see figure), with widths on the nanometer scale and lengths of several micrometers or more, exhibit good thermal stability and interesting emittance properties.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Understanding the mechanisms of early embryonic patterning and the timely allocation of specific cells to embryonic regions and fates as well as their development into tissues and organs, is a ...fundamental problem in Developmental Biology. The classical explanation for this process had been built around the notion of positional information. Accordingly the programmed appearance of sources of Morphogens at localized positions within a field of cells directs their differentiation. Recently, the development of organs and tissues from unpatterned and initially identical stem cells (adult and embryonic) has challenged the need for positional information and even the integrity of the embryo, for pattern formation. Here we review the emerging area of organoid biology from the perspective of Developmental Biology. We argue that the events underlying the development of these systems are not purely linked to “self‐organization,” as often suggested, but rather to a process of genetically encoded self‐assembly where genetic programs encode and control the emergence of biological structures.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Complexity-thinking refers to a cluster of concepts popularized in several branches of science, primarily in the physical sciences but increasingly in the social sciences. There is reason to be ...cautious regarding how the concepts are used across disciplines and branches of science. This paper discusses self-organization in dynamic systems, tracing its roots in social science and critiquing current usage of the term with regard to systems involving consciousness - humans and groups of humans. A brief sketch of the levels of complexity sets the groundwork for understanding the critique of self-organization to follow. I argue that consciousness fundamentally changes the terms of discussion in self-organization by adding a self/selves that is not equivalent to the system as a whole, but which directly influences what is organized, how, and toward what end. Self-organization in complex adaptive systems involving consciousness should be distinguished as self-cultivating self-organization and self-presenting self-organization.
•Complexity concepts allegedly apply to all non-linear systems, even those studied by psychology.•Self-organization refers to something quite different in social rather than material sciences.•In a system with a conscious self, that self cultivates its own organization.•In non-conscious systems, organization is emergent.•Conscious systems involve self-cultivating self-organization.
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