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The present work shows that the order of events taking place in complex networks may dramatically alter the way diffusion occurs in them. The Internet, motorways and other transport systems as well as many social and biological systems are composed of nodes connected by edges, and can be represented as networks.

Scientists studying diffusion over such networks over time have now identified the temporal characteristics that affect their diffusion pathways. In this paper, the authors show that one key factor that can dramatically change a diffusion process is the order in which events take place in complex networks.

They developed an analytical model to better understand the properties of time-dependent networks that either accelerate or slow down diffusion. Their study focused on different classes of popular models for diffusion, namely random walks and epidemic spread models, and found the way in which the temporal ordering of events matters. They expect these results to help in building more appropriate metrics to understand real-world complex network data.

Metamaterials — artificially engineered structures with building blocks smaller than the wavelength of light — have delivered a new way to design and make materials with exotic electromagnetic properties. The current challenge is to make these metamaterials into meta-devices that convert the promising research into practical applications. Nanotechnology has made it possible to fabricate ultrathin metamaterials – less than a 15^th of the wavelength – shrinking conventional optical devices into planar form. In the coming years, research in metamaterials, plasmonics and nanofabrication will revolutionize device form and function throughout the electromagnetic spectrum.

This paper reports experimental demonstration of a planar ultrathin (50 nm) gold diffraction grating, mimicking the function of a bulk dielectric grating but tens of times thinner. It uses the resonant properties of individual sub-wavelength meta-atoms to change the phase of the light passing through it, in the same way as a blazed diffraction grating. It functions throughout the visible region of the spectrum (400 – 900 nm), with peak efficiency at 736 nm, and exhibits asymmetric diffraction, sending 25 times more light to the left than the right.

Fluid generation in rocks is a common phenomenon: generation of hydrocarbons (oil\gas) from source rocks during diagenesis, dehydration of sedimentary and metamorphic rocks during burial and partial melting of the Earth’s mantle. Fluid generation leads to local increase in fluid pressure. If the rate of fluid production is high compared to the rate at which fluids can escape by flow through the initial permeability, the fluid pressure increases and may cause fracturing and creation of new fluid transport pathways.

This paper presents the development of fracture networks in a simple quasi-2D system consisting of a confined layer of gelatine containing yeast that consumes sugar to produce CO₂. The topological properties of the emerging fracture networks were found to be intermediate between the tree-like structure of river networks and the fragmentation cracking patterns observed in drying muds, domain splitting during rock weathering and fracturing of cooling basalts. The ratio of the number of dead ends to the amount of nodes is ~0.4, between the ratio for rivers (=1) and fragmentation crack patterns (=0). Understanding of fluid drainage network topology is crucial for uncovering the mechanisms which lead to its formation.