The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Pengfei Yang - One of the best experts on this subject based on the ideXlab platform.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin JiangAbstract:Abstract Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M0 near a critical value. Below the critical M0,cr, oscillations of the initiation structure are observed and become severe with further decrease of M0. For low M0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by kR, the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M0 = 10 cases but varies for M0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M0 decreases. The instability parameter χ is introduced to quantify the numerical results. Although χ cannot reveal the detailed mechanism of the Structural Shift, a linear relation between χ and kR exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin Jiang, Hoi Dick NgAbstract:Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M-0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M-0 near a critical value. Below the critical M-0,M-cr, oscillations of the initiation structure are observed and become severe with further decrease of M-0. For low M-0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by k(R), the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M-0 = 10 cases but varies for M-0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M-0 decreases. The instability parameter chi is introduced to quantify the numerical results. Although chi cannot reveal the detailed mechanism of the Structural Shift, a linear relation between chi and k(R) exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Honghui Teng - One of the best experts on this subject based on the ideXlab platform.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin JiangAbstract:Abstract Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M0 near a critical value. Below the critical M0,cr, oscillations of the initiation structure are observed and become severe with further decrease of M0. For low M0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by kR, the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M0 = 10 cases but varies for M0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M0 decreases. The instability parameter χ is introduced to quantify the numerical results. Although χ cannot reveal the detailed mechanism of the Structural Shift, a linear relation between χ and kR exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin Jiang, Hoi Dick NgAbstract:Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M-0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M-0 near a critical value. Below the critical M-0,M-cr, oscillations of the initiation structure are observed and become severe with further decrease of M-0. For low M-0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by k(R), the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M-0 = 10 cases but varies for M-0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M-0 decreases. The instability parameter chi is introduced to quantify the numerical results. Although chi cannot reveal the detailed mechanism of the Structural Shift, a linear relation between chi and k(R) exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Go Shimada - One of the best experts on this subject based on the ideXlab platform.
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a quantitative study of social capital in the tertiary sector of kobe has social capital promoted economic reconstruction since the great hanshin awaji earthquake
International journal of disaster risk reduction, 2017Co-Authors: Go ShimadaAbstract:Abstract After a huge natural disaster, what are the factors that make recovery of the society possible? This paper examines how social capital has worked in the process of recovery and reconstruction in Kobe, Japan, since the Great Hanshin Awaji Earthquake in 1995. After ten years, the population of Kobe returned to its pre-earthquake level. It looks as though the city has recovered well. However, if we look closer, ward by ward data gives a different picture. Even if each ward suffered a similar level of damage, some have recovered faster than others. For this reason, this paper looks further into the factors that caused this difference. To analyze these factors, this paper focuses on the tertiary sector within Kobe because there has been a Structural Shift away from the secondary sector due to the damage caused by the earthquake. Additionally, the tertiary sector accounted for 80% of employment, the most important factor for reconstruction over the mid- and long-term. The paper uses panel data from 1995 to 2010, and employs social capital proxies, such as households where three generations live together and crime rates, to examine the factors of recovery. The empirical analysis found that social capital is the factor that generates more jobs in the tertiary sector, thus, the factor that created the differences in the pattern of recovery among wards. The findings indicate the ways a recovery can be made faster after future natural disasters so as to create resilient societies.
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a quantitative study of social capital in the tertiary sector of kobe has social capital promoted economic reconstruction since the great hanshin awaji earthquake
Research Papers in Economics, 2014Co-Authors: Go ShimadaAbstract:Social capital is thought to have both positive and negative aspects. This paper examines how social capital has worked in the process of recovery and reconstruction in Kobe since the Great Hanshin Awaji Earthquake. The paper focuses on the tertiary sector of Kobe because since the earthquake there has been a Structural Shift from the secondary sector due to the damage caused by the earthquake, and because the sector accounted for 80% of employment, the most important factor for reconstruction in the mid- and long-term. The paper proves that both bonding and bridging social capital are important factors for employment. This finding provides empirical evidence for the on-going debate on how to rebuild Tohoku.
Zonglin Jiang - One of the best experts on this subject based on the ideXlab platform.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin JiangAbstract:Abstract Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M0 near a critical value. Below the critical M0,cr, oscillations of the initiation structure are observed and become severe with further decrease of M0. For low M0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by kR, the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M0 = 10 cases but varies for M0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M0 decreases. The instability parameter χ is introduced to quantify the numerical results. Although χ cannot reveal the detailed mechanism of the Structural Shift, a linear relation between χ and kR exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure.
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effects of inflow mach number on oblique detonation initiation with a two step induction reaction kinetic model
Combustion and Flame, 2018Co-Authors: Pengfei Yang, Honghui Teng, Zonglin Jiang, Hoi Dick NgAbstract:Oblique detonations induced by two-dimensional, semi-infinite wedges are simulated by solving numerically the reactive Euler equations with a two-step induction-reaction kinetic model. Previous results obtained with other models have demonstrated that for the low inflow Mach number M-0 regime past a critical value, the wave in the shocked gas changes from an oblique reactive wave front into a secondary oblique detonation wave (ODW). The present numerical results not only confirm the existence of such critical phenomenon, but also indicate that the Structural Shift is induced by the variation of the main ODW front which becomes sensitive to M-0 near a critical value. Below the critical M-0,M-cr, oscillations of the initiation structure are observed and become severe with further decrease of M-0. For low M-0 cases, the non-decaying oscillation of the initiation structure exists after a sufficiently long-time computation, suggesting the quasi-steady balance of initiation wave systems. By varying the heat release rate controlled by k(R), the pre-exponential factor of the second reaction step, the morphology of initiation structures does not vary for M-0 = 10 cases but varies for M-0 = 9 cases, demonstrating that the effects of heat release rate become more prominent when M-0 decreases. The instability parameter chi is introduced to quantify the numerical results. Although chi cannot reveal the detailed mechanism of the Structural Shift, a linear relation between chi and k(R) exists at the critical condition, providing an empirical criterion to predict the Structural variation of the initiation structure. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Erle C Ellis - One of the best experts on this subject based on the ideXlab platform.
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high spatial resolution three dimensional mapping of vegetation spectral dynamics using computer vision
Remote Sensing of Environment, 2013Co-Authors: Jonathan P Dandois, Erle C EllisAbstract:High spatial resolution three-dimensional (3D) measurements of vegetation by remote sensing are advancing ecological research and environmental management. However, substantial economic and logistical costs limit this application, especially for observing phenological dynamics in ecosystem structure and spectral traits. Here we demonstrate a new aerial remote sensing system enabling routine and inexpensive aerial 3D measurements of canopy structure and spectral attributes, with properties similar to those of LIDAR, but with RGB (red-green-blue) spectral attributes for each point, enabling high frequency observations within a single growing season. This “Ecosynth” methodology applies photogrammetric “Structure from Motion” computer vision algorithms to large sets of highly overlapping low altitude (< 130 m) aerial photographs acquired using off-the-shelf digital cameras mounted on an inexpensive (< USD$4000), lightweight (< 2 kg), hobbyist-grade unmanned aerial system (UAS). Ecosynth 3D point clouds with densities of 30–67 points m− 2 were produced using commercial computer vision software from digital photographs acquired repeatedly by UAS over three 6.25 ha (250 m × 250 m) Temperate Deciduous forest sites in Maryland USA. Ecosynth point clouds were georeferenced with a precision of 1.2–4.1 m horizontal radial root mean square error (RMSE) and 0.4–1.2 m vertical RMSE. Understory digital terrain models (DTMs) and canopy height models (CHMs) were generated from leaf-on and leaf-off point clouds using procedures commonly applied to LIDAR point clouds. At two sites, Ecosynth CHMs were strong predictors of field-measured tree heights (R2 0.63 to 0.84) and were highly correlated with a LIDAR CHM (R 0.87) acquired 4 days earlier, though Ecosynth-based estimates of aboveground biomass and carbon densities included significant errors (31–36% of field-based estimates). Repeated scanning of a 50 m × 50 m forested area at six different times across a 16 month period revealed ecologically significant dynamics in canopy color at different heights and a Structural Shift upward in canopy density, as demonstrated by changes in vertical height profiles of point density and relative RGB brightness. Changes in canopy relative greenness were highly correlated (R2 = 0.87) with MODIS NDVI time series for the same area and vertical differences in canopy color revealed the early green up of the dominant canopy species, Liriodendron tulipifera, strong evidence that Ecosynth time series measurements can capture vegetation Structural and spectral phenological dynamics at the spatial scale of individual trees. The ability to observe canopy phenology in 3D at high temporal resolutions represents a breakthrough in forest ecology. Inexpensive user-deployed technologies for multispectral 3D scanning of vegetation at landscape scales (< 1 km2) heralds a new era of participatory remote sensing by field ecologists, community foresters and the interested public.
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high spatial resolution three dimensional mapping of vegetation spectral dynamics using computer vision
Remote Sensing of Environment, 2013Co-Authors: Jonathan P Dandois, Erle C EllisAbstract:High spatial resolution three-dimensional (3D) measurements of vegetation by remote sensing are advancing ecological research and environmental management. However, substantial economic and logistical costs limit this application, especially for observing phenological dynamics in ecosystem structure and spectral traits. Here we demonstrate a new aerial remote sensing system enabling routine and inexpensive aerial 3D measurements of canopy structure and spectral attributes, with properties similar to those of LIDAR, but with RGB (red-green-blue) spectral attributes for each point, enabling high frequency observations within a single growing season. This “Ecosynth” methodology applies photogrammetric “Structure from Motion” computer vision algorithms to large sets of highly overlapping low altitude (< 130 m) aerial photographs acquired using off-the-shelf digital cameras mounted on an inexpensive (< USD$4000), lightweight (< 2 kg), hobbyist-grade unmanned aerial system (UAS). Ecosynth 3D point clouds with densities of 30–67 points m− 2 were produced using commercial computer vision software from digital photographs acquired repeatedly by UAS over three 6.25 ha (250 m × 250 m) Temperate Deciduous forest sites in Maryland USA. Ecosynth point clouds were georeferenced with a precision of 1.2–4.1 m horizontal radial root mean square error (RMSE) and 0.4–1.2 m vertical RMSE. Understory digital terrain models (DTMs) and canopy height models (CHMs) were generated from leaf-on and leaf-off point clouds using procedures commonly applied to LIDAR point clouds. At two sites, Ecosynth CHMs were strong predictors of field-measured tree heights (R2 0.63 to 0.84) and were highly correlated with a LIDAR CHM (R 0.87) acquired 4 days earlier, though Ecosynth-based estimates of aboveground biomass and carbon densities included significant errors (31–36% of field-based estimates). Repeated scanning of a 50 m × 50 m forested area at six different times across a 16 month period revealed ecologically significant dynamics in canopy color at different heights and a Structural Shift upward in canopy density, as demonstrated by changes in vertical height profiles of point density and relative RGB brightness. Changes in canopy relative greenness were highly correlated (R2 = 0.87) with MODIS NDVI time series for the same area and vertical differences in canopy color revealed the early green up of the dominant canopy species, Liriodendron tulipifera, strong evidence that Ecosynth time series measurements can capture vegetation Structural and spectral phenological dynamics at the spatial scale of individual trees. The ability to observe canopy phenology in 3D at high temporal resolutions represents a breakthrough in forest ecology. Inexpensive user-deployed technologies for multispectral 3D scanning of vegetation at landscape scales (< 1 km2) heralds a new era of participatory remote sensing by field ecologists, community foresters and the interested public.
