Early Mesoamerican Cities

Urbanization is a phenomenon that brings into focus a range of topics of broad interest to scholars. It is one of the central, enduring interests of anthropological archaeology. Because urbanization is a transformational process, it changes the relationships between social and cultural variables such as demography, economy, politics, and ideology. As one of a handful of cases in the ancient world where cities developed independently, Mesoamerica should play a major role in the global, comparative analysis of first-generation cities and urbanism in general. Yet most research focuses on later manifestations of urbanism in Mesoamerica, thereby perpetuating the fallacy that Mesoamerican cities developed relatively late in comparison to urban centers in the rest of the world. This volume presents new data, case studies, and models for approaching the subject of early Mesoamerican cities. It demonstrates how the study of urbanism in Mesoamerica, and all ancient civilizations, is entering a new and dynamic phase of scholarship.

Spontaneous trail formation in populations of auto-chemotactic walkers

We study the formation of trails in populations of self-propelled agents that make oriented deposits of pheromones and also sense such deposits to which they then respond with gradual changes of their direction of motion. Based on extensive off-lattice computer simulations aiming at the scale of insects, e.g., ants, we identify a number of emerging stationary patterns and obtain qualitatively the non-equilibrium state diagram of the model, spanned by the strength of the agent–pheromone interaction and the number density of the population. In particular, we demonstrate the spontaneous formation of persistent, macroscopic trails, and highlight some behaviour that is consistent with a dynamic phase transition. This includes a characterisation of the mass of system-spanning trails as a potential order parameter. We also propose a dynamic model for a few macroscopic observables, including the sub-population size of trail-following agents, which captures the early phase of trail formation.

Using Zeolite-Zirconia-Copper Nanocomposites as a New Asphaltene Inhibitor for Improving Permeability Reduction during CO 2 Flooding

Using nanoparticles for adsorbing asphaltene was known as an efficient method among researchers for crude oil upgrading and in this study, Zeolite-zirconia-copper nanocomposites (NCs) has been synthesized and characterized with SEM, XRD, BET, and EDX for asphaltene precipitation inhibition in the static phase and solving asphaltene deposition problems of dynamic CO2 flooding in low permeability carbonate reservoir. CO2-oil IFT tests, isotherm models, natural depletion tests at static phase were performed in the presence of NCs and the results were compared with zeolite nanoparticles. Then, CO2 core flooding tests at dynamic phase were designed in the presence of NCs at obtained static conditions for surveying permeability/porosity reduction in porous media. After adding NCs and zeolite nanoparticles, the 2nd to 1st slope ratio in CO2-oil IFT tests increased from 19.697 % to 20.895 % and 29.851 %, respectively which shows NCs adsorbed more asphaltene in comparison to zeolite nanoparticles which confirmed UV-Vis results. NCs was decreased asphaltene precipitation more than zeolite at same points during natural depletion tests and it was selected for dynamic CO2 tests. After adding NCs, asphaltene depositions which occurs after CO2 injection was decreased and permeability/porosity reduction parameters were improved.

Nanostructured silica spin–orbit optics for modal vortex beam shaping

Modality is a generic concept of wave-optics at the basis of optical information and communications. One of the challenges of photonics technologies based on optical orbital angular momentum consists in the production of a modal content for both the azimuthal and radial degrees of freedom. This basically requires shaping the complex amplitude of an incident light beam, which is usually made up from adaptive spatial light modulators or bespoke devices. Here, we report on the experimental attempt of a recent theoretical proposal [Opt. Lett. 42, 1966 (2017)] toward the production of various optical vortex modes of the Laguerre–Gaussian type relying on the spin–orbit interaction of light. This is done in the visible domain from optical elements made out of silica glass. The idea consists in exploiting the combined effects of azimuthally-varying geometric phase with that of radially-varying propagation features. The proposed approach can be readily extended to any wavelength as well as to other families of optical modes, although some dynamic phase problems remain to be solved to make it a turnkey technology.

Plasmonic metasurfaces manipulating the two spin components from spin–orbit interactions of light with lattice field generations

Artificial nanostructures in metasurfaces induce strong spin–orbit interactions (SOIs), by which incident circularly polarized light can be transformed into two opposite spin components. The component with an opposite helicity to the incident light acquires a geometric phase and is used to realize the versatile functions of the metasurfaces; however, the other component, with an identical helicity, is often neglected as a diffused background. Here, by simultaneously manipulating the two spin components originating from the SOI in plasmonic metasurfaces, independent wavefields in the primary and converted spin channels are achieved; the wavefield in the primary channel is controlled by tailoring the dynamic phase, and that in the converted channel is regulated by designing the Pancharatnam–Berry phase in concurrence with the dynamic phase. The scheme is realized by generating optical lattice fields with different topologies in two spin channels, with the metasurfaces composed of metal nanoslits within six round-apertures mimicking the multi-beam interference. This study demonstrates independent optical fields in a dual-spin channel based on the SOI effect in the metasurface, which provides a higher polarization degree of freedom to modify optical properties at the subwavelength scale.

Full 360° Terahertz Dynamic Phase Modulation Based on Doubly Resonant Graphene–Metal Hybrid Metasurfaces

Dynamic phase modulation is vital for tuneable focusing, beaming, polarisation conversion and holography. However, it remains challenging to achieve full 360° dynamic phase modulation while maintaining high reflectance or transmittance based on metamaterials or metasurfaces in the terahertz regime. Here, we propose a doubly resonant graphene–metal hybrid metasurface to address this challenge. Simulation results show that by varying the graphene Fermi energy, the proposed metasurface with two shifting resonances is capable of providing dynamic phase modulation covering a range of 361° while maintaining relatively high reflectance above 20% at 1.05 THz. Based on the phase profile design, dynamically tuneable beam steering and focusing were numerically demonstrated. We expect that this work will advance the engineering of graphene metasurfaces for the dynamic manipulation of terahertz waves.