Networks of coupled dynamical systems have been used to model biological oscillators, Josephson junction arrays, excitable media, neural networks, spatial games, genetic control networks and many other self-organizing systems. Ordinarily, the connection topology is assumed to be either completely regular or completely random. But many biological, technological and social networks lie somewhere between these two extremes. Here we explore simple models of networks that can be tuned through this middle ground: regular networks 'rewired' to introduce increasing amounts of disorder. We find that these systems can be highly clustered, like regular lattices, yet have small characteristic path lengths, like random graphs. We call them 'small-world' networks, by analogy with the small-world phenomenon (popularly known as six degrees of separation. The neural network of the worm Caenorhabditis elegans, the power grid of the western United States, and the collaboration graph of film actors are shown to be small-world networks. Models of dynamical systems with small-world coupling display enhanced signal-propagation speed, computational power, and synchronizability. In particular, infectious diseases spread more easily in small-world networks than in regular lattices.

/pdf/collective-dynamics-of-small-world-networks-205zhem3gm.pdf

Collective dynamics of small-world networks

In this review the theory and application of Smoothed particle hydrodynamics (SPH) since its inception in 1977 are discussed. Emphasis is placed on the strengths and weaknesses, the analogy with particle dynamics and the numerous areas where SPH has been successfully applied.

https://iopscience.iop.org/article/10.1088/0034-4885/68/8/R01/pdf

Smoothed particle hydrodynamics

One of the outstanding challenges in the field of porous materials is the design and synthesis of chemical structures with exceptionally high surface areas Such materials are of critical importance to many applications involving catalysis, separation and gas storage The claim for the highest surface area of a disordered structure is for carbon, at 2,030 m2 g(-1) (ref 2) Until recently, the largest surface area of an ordered structure was that of zeolite Y, recorded at 904 m2 g(-1) (ref 3) But with the introduction of metal-organic framework materials, this has been exceeded, with values up to 3,000 m2 g(-1) (refs 4-7) Despite this, no method of determining the upper limit in surface area for a material has yet been found Here we present a general strategy that has allowed us to realize a structure having by far the highest surface area reported to date We report the design, synthesis and properties of crystalline Zn4O(1,3,5-benzenetribenzoate)2, a new metal-organic framework with a surface area estimated at 4,500 m2 g(-1) This framework, which we name MOF-177, combines this exceptional level of surface area with an ordered structure that has extra-large pores capable of binding polycyclic organic guest molecules--attributes not previously combined in one material

/pdf/a-route-to-high-surface-area-porosity-and-inclusion-of-large-6gq9e8txip.pdf

A route to high surface area, porosity and inclusion of large molecules in crystals

Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Monthly Notices of the Royal Astronomical Society

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems1. Experiments to date have examined a multitude of molecules conducting in parallel2,3, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions4,5 or scanning probes6,7 as well as three-terminal single-molecule transistors made from carbon nanotubes8, C60 molecules9, and conjugated molecules diluted in a less-conducting molecular layer10. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.

Coulomb blockade and the Kondo effect in single-atom transistors

[1] We examine a narrow latitudinal band (60°N–70°N) on Mars to place constraints on the seasonally averaged velocity Q of boulder movements over patterned ground. These latitudes comprise a region of the northern lowlands where patterned ground covers nearly every surface. Here boulders meters in diameter are consistently found to be concentrated at or near the cracks that define the polygonal networks, indicating a mobilization process. Because impact craters are the source for many boulders, we can use craters and their degradation to estimate the time scales for boulder movement. We study and catalog 1018 degraded impact craters (100 m < D < 1 km) in 55 High Resolution Imaging Science Experiment (HiRISE) images. We find that crater degradation occurs on a time scale <∼1 Ma, which is too recent for melting-related mechanisms in a past, warmer epoch. Clustering of boulders occurs at a time scale of a few Ma or shorter, which means that boulders on 5–20 m diameter polygons move at seasonal velocities Q ∼1–10 μm/yr or faster.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JE003811

Boulder movement at high northern latitudes of Mars

Global scale impacts modify the physical or thermal state of a substantial fraction of a target asteroid. Specific effects include accretion, family formation, reshaping, mixing and layering, shock and frictional heating, fragmentation, material compaction, dilatation, stripping of mantle and crust, and seismic degradation. Deciphering the complicated record of global scale impacts, in asteroids and meteorites, will lead us to understand the original planet-forming process and its resultant populations, and their evolution in time as collisions became faster and fewer. We provide a brief overview of these ideas, and an introduction to models.

Global Scale Impacts

Possible mechanism of boulder clustering on Mars

Laboratory studies of igneously formed meteorites suggest that numerous meteorite parent bodies were melted to form metallic cores and silicate mantles. Studies by the Dawn spacecraft confirm that (4) Vesta melted in this way (McSween et al., 2013; see the chapter by Russell et al. in this volume). In principle, one would think the origin of iron and stonyiron meteorites and achondrites would be straightforward to investigate, but this is not the case. If disrupted Vesta-like differentiated bodies were once common in the main belt and they were the ultimate source of the differentiated meteorites, one might expect collisions to have created enormous numbers of V-type asteroids that were not derived from Vesta, as well as ample numbers of mantle and core fragments compared to the rest of the main-belt population. This is not observed. Instead, only limited examples of asteroids composed predominantly of core metallic Fe-Ni (possibly some M-type asteroids) or mantle olivine (some A-type asteroids) have been identified. Very few of these bodies are members of asteroid families, with those in families having orbits and sizes most consistent with being interlopers.

Erik Asphaug

Papers

Boulder movement at high northern latitudes of Mars

Global Scale Impacts

Possible mechanism of boulder clustering on Mars

Early Impact History and Dynamical Origin of Differentiated Meteorites and Asteroids

Constraining the thermal properties of planetary surfaces using machine learning: Application to airless bodies