Reliability assessment of foundations for offshore mooring systems under extreme environments

textMooring systems for floating facilities that are used offshore to produce oil and gas, consisting of individual mooring lines and foundations, are currently designed on the basis of individual components and on a case-by-case basis. The most heavily loaded line and anchor are checked under extreme loading conditions (hurricane and loop current) with the system of lines intact and with one line removed. However, the performance of the entire mooring system depends more directly on the performance of the system of lines and foundations rather than on the performance of a single component. In this study, a floating production system design originally developed by the industry consortium, DeepStar, was chosen for study. The mooring system was designed for three different nominal water depths: 1000, 2000 and 3000 m. It is a classic spar with steel mooring lines in 1000 m of water and polyester mooring lines in deeper depths. Based on simulated results of loads on mooring lines and foundations using a numerical model, reliability analyses were conducted using representative probabilistic descriptions of the extreme met-ocean conditions, hurricanes and loop currents, in the Gulf of Mexico. The probability of failure of individual mooring line components during a 20-year design life is calculated first, followed by that of a complete mooring line which consists of top and bottom chains, a steel cable or polyester rope at the middle and a suction caisson foundation, and finally that of the mooring system. It is found that foundations have failure probabilities that are more than an order of magnitude smaller than those for lines under extreme loading. Mooring systems exhibit redundancy in that the failure of the most heavily loaded component during an extreme event does not necessarily lead to failure of the system. The system reliability and redundancy are greater for the taut versus semi-taut systems and is greater for designs governed by loop current versus hurricane events. Although this study concerns about the mooring systems of a classical spar, the methodology of the reliability analysis and the conclusions made in this study may have important implications to the other deepwater mooring systemsCivil, Architectural, and Environmental Engineerin

Display screens with variable refresh rate

Device displays of a mobile device such as a smartphone or tablet have capabilities to support different refresh rates. For optimal operation, the refresh rate of the screen of a mobile device can be refreshed based on the image or frame of video being displayed and on certain other conditions. This disclosure describes low-complexity, low-latency techniques to seamlessly transition between different screen refresh rates with minimal-to-zero changes in display settings

Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer

Magnetic skyrmions have fast evolved from a novelty, as a realization of topologically protected structure with particle-like character, into a promising platform for new types of magnetic storage. Significant engineering progress was achieved with the synthesis of compounds hosting room-temperature skyrmions in magnetic heterostructures, with the interfacial Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation. Here we report findings of ultrathin skyrmion formation in a few layers of SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer. Measurement of the topological Hall effect (THE) reveals a robust stability of skyrmions in this platform, judging from the high value of the critical field 1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film proves the rumpling of the Ru-O plane to be the source of inversion symmetry breaking and DMI. First-principles calculations based on the structure obtained from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the main source of skyrmion robustness. These features promise a few-layer SRO to be an important new platform for skyrmionics, without the necessity of introducing the capping layer to boost the spin-orbit coupling strength artificially.Comment: Supplementary Information available upon reques

Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer

Magnetic skyrmions have fast evolved from a novelty, as a realization of topologically protected structure with particle-like character, into a promising platform for new types of magnetic storage. Significant engineering progress was achieved with the synthesis of compounds hosting room-temperature skyrmions in magnetic heterostructures, with the interfacial Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation. Here we report findings of ultrathin skyrmion formation in a few layers of SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer. Measurement of the topological Hall effect (THE) reveals a robust stability of skyrmions in this platform, judging from the high value of the critical field 1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film proves the rumpling of the Ru-O plane to be the source of inversion symmetry breaking and DMI. First-principles calculations based on the structure obtained from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the main source of skyrmion robustness. These features promise a few-layer SRO to be an important new platform for skyrmionics, without the necessity of introducing the capping layer to boost the spin-orbit coupling strength artificially.Comment: Supplementary Information available upon reques

Divergent Selection and Primary Gene Flow Shape Incipient Speciation of a Riparian Tree on Hawaii Island

A long-standing goal of evolutionary biology is to understand the mechanisms underlying the formation of species. Of particular interest is whether or not speciation can occur in the presence of gene flow and without a period of physical isolation. Here, we investigated this process within Hawaiian Metrosideros, a hypervariable and highly dispersible woody species complex that dominates the Hawaiian Islands in continuous stands. Specifically, we investigated the origin of Metrosideros polymorpha var. newellii (newellii), a riparian ecotype endemic to Hawaii Island that is purportedly derived from the archipelago-wide M. polymorpha var. glaberrima (glaberrima). Disruptive selection across a sharp forestriparian ecotone contributes to the isolation of these varieties and is a likely driver of newellii’s origin. We examined genome-wide variation of 42 trees from Hawaii Island and older islands. Results revealed a split between glaberrima and newellii within the past 0.3–1.2 My. Admixture was extensive between lineages within Hawaii Island and between islands, but introgression from populations on older islands (i.e., secondary gene flow) did not appear to contribute to the emergence of newellii. In contrast, recurrent gene flow (i.e., primary gene flow) between glaberrima and newellii contributed to the formation of genomic islands of elevated absolute and relative divergence. These regions were enriched for genes with regulatory functions as well as for signals of positive selection, especially in newellii, consistent with divergent selection underlying their formation. In sum, our results support riparian newellii as a rare case of incipient ecological speciation with primary gene flow in trees