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Applying a coastal-geoarchaeological approach, we synthesize stratigraphic, sedimentological, mollusk-zooarchaeological, and radiometric datasets from recent excavations and sediment coring at Harbor Key (8MA15)—a shell-terraformed Native mound complex within Tampa Bay, on the central peninsular Gulf Coast of Florida. We significantly revise the chronological understanding of the site and place it among the relatively few early civic-ceremonial centers in the region. Analyses of submound contexts revealed that the early first millennium mound center was constructed atop a platform of sand and ex situ cultural shell deposits that were reworked during ancient storm landfalls around 2000 BP. We situate Harbor Key within a seascape-scale stratigraphic and paleoenvironmental framework and show that the shellworks comprise an artificial barrier protecting the leeward estuary basin (and productive inshore wetlands) from high-energy conditions of the open bay and swells from the Gulf of Mexico. The sedimentary and archaeological records attest to the long-term history of morphodynamic interaction between coastal processes and Indigenous shell terraforming in the region and suggest that early first millennium mound building in Tampa Bay was tied to the recognition and reuse of antecedent shellworks and the persistent management of encompassing cultural seascapes.
This paper introduces a novel 6-DOF parallel manipulator, which is composed of two 3-RUS parallel manipulators that share a common three-dimensional moving platform. Semi-analytical form solutions are easily obtained to solve the forward displacement analysis of the robot using the non-planar geometry of the moving platform, whereas the velocity, acceleration, and singularity analyses are performed using screw theory. A case study is included to show the application of the kinematic model, which is verified with the aid of a commercially available software. Simple kinematic analysis and reduced singular regions are the main benefits of the proposed parallel manipulator.
We will present a simplified approximate model showing how even small changes in the dielectric response result in substantial variations in the Hamaker coefficient of the van der Waals interactions. Since all the terms in the Matsubara summation depends on the variation of the dielectric response spectra at one particular frequency, the total change in the Hamaker coefficient depends on the spectral changes not only at that frequency but also at the rest of the spectrum properly weighted. The Matsubara terms most affected by the addition of a single peak are not those close to the position of the added peak, but are distributed over the entire range of frequencies. We comment on the possibility of eliminating van der Waals interactions and/or drastically reducing them by spectral variation in a narrow regime of frequencies.
Advances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusión Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline α-Fe samples have been irradiated with 150 keV Fe- ions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.
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