238 research outputs found

    Data Driven Forecast for Fire

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    Being able to forecast the evolution of a fire is essential for fire safety design and fire response strategies. Despite advances in understanding fire dynamics and improvements in computational capability, the ability to predict the evolution of a fire remains limited due to large uncertainties associated to multiple scales and the non-linearities. The data-driven approach provides a viable technique from models corrected by observations. However, the complicated coupling between gaseous and condensed phases has, in the past, limited proper prediction with a positive leading time. This work proposes and investigates a series of approaches to data-driven hybrid modelling that integrate analytical and numerical descriptions to address the coupling effects. The data-driven hybrid model is developed for different scenarios covering various complexity and scales. Different approaches are evaluated to reflect the dominant physics; nevertheless, they are structured by differentiating the condensed and gas phases. The initial scenario corresponds to one-dimensional convective-diffusive droplet combustion in micro and normal gravity. Then, concurrent flame spread in micro and normal gravity where a two-dimensional boundary layer combustion approach is implemented. Finally, the Malveira fire test represents a large-scale, three-dimensional, travelling fire. Coefficients assimilated with their experimental observations are used to alter analytical formulations describing the gas and condensed phases. By separating the phases, the data-driven hybrid model can forecast various types of variables while reducing processing resources. Convergence of the assimilated coefficients is used as an indicator for an appropriate representation of the model and therefore is suitable for predictions. The proposed methodology still requires ongoing research, however. This work provides evidence for specific approaches and of areas where additional attention is necessary. It has become apparent that to adequately predict real-scale fire, it is necessary for more sophisticated explanations of heat and mass transfer and descriptions of the interactions between fire and its environment

    Dark Purple Woods

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    Ground State Degeneracy of Infinite-Component Chern-Simons-Maxwell Theories

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    Infinite-component Chern-Simons-Maxwell theories with a periodic KK matrix provide abundant examples of gapped and gapless, foliated and non-foliated fracton orders. In this paper, we study the ground state degeneracy of these theories. We show that the ground state degeneracy exhibit various patterns as a function of the linear system size -- the size of the KK matrix. It can grow exponentially or polynomially, cycle over finitely many values, or fluctuate erratically inside an exponential envelope. We relate these different patterns of the ground state degeneracy with the roots of the ``determinant polynomial'', a Laurent polynomial, associated to the periodic KK matrix. These roots also determine whether the theory is gapped or gapless. Based on the ground state degeneracy, we formulate a necessary condition for a gapped theory to be a foliated fracton order.Comment: 15 pages, 1 figure; the authors are ordered alphabeticall

    Rising grain prices in response to phased climatic change during 1736-1850 in the North China Plain

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    Grain price volatility during historical periods is regarded as an important indicator of the impact of climate change on economic system, as well as a key link to adjust food security and social stability. The present study used the wheat prices in Baoding Prefecture, China, during 1736-1850 to explore connections between climatic transition and grain price anomalies in the North China Plain. The main findings were as follows: (1) The grain price change showed an apparent correspondence with climatic transition. The period 1781-1820 was a transition phase, with more extremes and decreased precipitations when the climate shifted from a warm phase to a cold one. Corresponding with the climatic transition, the grain price during 1781-1820 was characterized by that the mean of the original grain price series was significantly higher (lower) than the previous (later) phase, and the variance and anomaly amplitude of the detrended grain price series was the highest during 1736-1850. (2) The correspondence between grain price extremes and drought events occurred in phases. Five grain price extremes occurred following drought events during 1781-1810, while extreme droughts were the direct cause of the grain price spike during 1811-1820. (3) Social stability affected by climate change also played an important role in the grain price spike between 1811 and 1820. Paralleling the pathway of "precipitation-grain production-grain price", climate change could have an impact on grain price via the pathway of "precipitation-grain production-grain price-famine-uprising-grain price", as shown during the Tianli Uprising in 1813. These findings could contribute to an improved understanding of the interaction between climate change and human society during the historical period.Peer reviewe

    Detection of the dispersion and residence of volcanic SO2⁠ and sulfate aerosol from Nabro in 2011

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    Continuous detection of dispersion and residence of volcanic plumes in troposphere and lower stratosphere is vitally important for improving the understanding on the role of volcano eruptions in climate change. We report a 3-month continuous detection of dispersion and residence of volcanic plumes in the troposphere and stratosphere generated from the volcanic SO2 erupted by Nabro in Eritrea on June 12th, 2011 observed by the OMI sensor. The background SO2 concentration of 3 different height layers in troposphere and lower stratosphere were estimated by the 3-year-average daily concentration of monthly SO2 in 2005, 2007 and 2013, when there were no large explosive volcanic eruptions occurring. We also traced the diffusion path and the concentration of volcanic SO2 for the first 3 months after Nabro's eruption, and detected the appearance and dissipation of sulfate aerosols, which is a product converted from volcanic SO2. The results show that after Nabro erupted on June 12th, the volcanic plumes spread to middle latitudes (30 degrees N -60 degrees N) of Northern Hemisphere and loading by westerly jet. The volcanic SO2 in middle troposphere layer (TRM) and lower troposphere layer (TRL) stopped eastward spreading, and dissipated over the western Pacific Ocean on June 23rd. On June 26th, the volcanic SO2 in upper troposphere and lower stratosphere (STL) reached Mexico in Central America, and almost encircled the low latitudes and parts of middle latitudes. On June 28th, the volcanic SO2 plume showed an even distribution in STL. 37 days after the eruption, the volcanic SO2 in STL encircled the Northern Hemisphere evenly, sulfate aerosols in STL largely covered the low and middle latitudes and the daily concentration of SO2 was still higher than the background value. One month after the eruption, the global mean daily concentration of SO2 dropped to the normal value, but the daily concentration of SO2 and sulfate aerosols in low latitudes remained high, and dissipated not earlier than 3 months after the eruption of Nabro.Peer reviewe

    4D trajectory optimization of commercial flight for green civil aviation

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    For the current development of green civil aviation, this study aims to optimize the green four-dimensional (4D) trajectory of commercial flight by taking into account conventional cost and environmental cost. Some fundamental models, efficient processing methodologies, and conventional objectives are proposed to construct the framework of trajectory optimization. Based on the environmental cost including greenhouse gas cost and harmful gas cost, green objective functions are presented. The A* algorithm and the trapezoidal collocation method are employed to optimize the lateral path and vertical profile for 4D optimization trajectory generation. A case study for the A320 from Barcelona Airport to Frankfurt Airport yields the results that the optimal costs can be obtained under different objectives and the total cost can be more optimized by adjusting the weights of environmental cost and conventional cost. The study builds an aided tool for 4D trajectory optimization and demonstrates that environmental factors and conventional factors should be taken into comprehensive consideration when constructing the flight trajectory in the future, as well as it can underpin the green and sustainable development of the air transport industry

    Ground state degeneracy of the Ising cage-net model

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    The Ising cage-net model, first proposed in Phys. Rev. X 9, 021010 (2019), is a representative type I fracton model with nontrivial non-abelian features. In this paper, we calculate the ground state degeneracy of this model and find that, even though it follows a similar coupled layer structure as the X-cube model, the Ising cage-net model cannot be "foliated" in the same sense as X-cube as defined in Phys. Rev. X 8, 031051 (2018). A more generalized notion of "foliation'' is hence needed to understand the renormalization group transformation of the Ising cage-net model. The calculation is done using an operator algebra approach that we develop in this paper, and we demonstrate its validity through a series of examples
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