A Hydrodynamic-Based Robust Numerical Model for Debris Hazard and Risk Assessment

Debris flow simulations are important in practical engineering. In this study, a graphics processing unit (GPU)-based numerical model that couples hydrodynamic and morphological processes was developed to simulate debris flow, transport, and morphological changes. To accurately predict the debris flow sediment transport and sediment scouring processes, a GPU-based parallel computing technique was used to accelerate the calculation. This model was created in the framework of a Godunov-type finite volume scheme and discretized into algebraic equations by the finite volume method. The mass and momentum fluxes were computed using the Harten, Lax, and van Leer Contact (HLLC) approximate Riemann solver, and the friction source terms were calculated using the proposed splitting point-implicit method. These values were evaluated using a novel 2D edge-based MUSCL scheme. The code was programmed using C++ and CUDA, which can run on GPUs to substantially accelerate the computation. After verification, the model was applied to the simulation of the debris flow process of an idealized example. The results of the new scheme better reflect the characteristics of the discontinuity of its movement and the actual law of the evolution of erosion and deposition over time. The research results provide guidance and a reference for the in-depth study of debris flow processes and disaster prevention and mitigation

Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert

The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel

Comparison of surface wind speed and wind speed profiles in the Taklimakan Desert

Near-surface (10 m) wind speed (NWS) plays a crucial role in many areas, including the hydrological cycle, wind energy production, and the dispersion of air pollution. Based on wind speed data from Tazhong and the northern margins of the Taklimakan Desert in Xiaotang in spring, summer, autumn, and winter of 2014 and 2015, statistical methods were applied to determine the characteristics of the diurnal changes in wind speed near the ground and the differences in the wind speed profiles between the two sites. The average wind speed on a sunny day increased slowly with height during the day and rapidly at night. At heights below 4 m the wind speed during the day was higher than at night, whereas at 10 m the wind speed was lower during the day than at night. The semi-empirical theory and Monin–Obukhov (M–O) similarity theory were used to fit the NWS profile in the hinterland of the Tazhong Desert. A logarithmic law was applied to the neutral stratification wind speed profile, and an exponential fitting correlation was used for non-neutral stratification. The more unstable the stratification, the smaller the n. Using M–O similarity theory, the “linear to tens of” law was applied to the near-neutral stratification. According to the measured data, the distribution of φM with stability was obtained. The γm was obtained when the near-surface stratum was stable in the hinterland of Tazhong Desert and the βm was obtained when it was unstable. In summer, γm and βm were 5.84 and 15.1, respectively, while in winter, γm and βm were 1.9 and 27.1, respectively

Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert

The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel

A GPU-Accelerated Hydrodynamic Model for Urban Rainstorm Inundation Simulation: A Case Study in China

Frequent urban rainstorm inundations can cause serious damages to human life and social economy. Reliable simulation of urban rainstorm inundation is an effective approach for performing flood risk analysis to reduce losses. In this work, a full 2D high-performance hydrodynamic model for urban rainstorm inundation simulation based on Graphic Processing Unit (GPU) was developed. The idealized V-shape catchment and sponge city district of Fengxi New City were selected as the study areas to assess performance of the model. The model was validated against analytical benchmark results of the idealized V-catchment test which show good agreement between the modelled flow and analytical solutions. The model was then applied to simulate actual urban rainstorm inundation process under measured rainfall. The results indicated that the model can be applied to high-resolution urban region simulations. Specifically, the validation results indicated that the proposed model had a good performance, with an accepted error of less than 15%. When applied to compute the Fengxi New city under design rainstorms with different annual return periods of 1, 5, 10, 20, 50, and 100 years, it was found that the model effectively evaluated the temporal and spatial variation process of urban inundation, and quantitatively investigated flood risks according to the water depth change. The model has been substantially accelerated on GPU to quickly predict urban inundation. The accuracy and rapid simulation speed of the model were verified based on the actual study area. Therefore, the proposed model can help to predict the dynamic processes of urban flood inundation and thus reduce flood inundation disasters. This is essential for future optimal sponge urban construction planning in China

Elevated Midtrimester Triglycerides as a Biomarker for Postpartum Hyperglycemia in Gestational Diabetes

Background. Whether elevated triglyceride (TG) levels during pregnancy were a biomarker for postpartum abnormal glucose metabolism (AGM) in women with previous gestational diabetes mellitus (GDM) remained unknown. The aim of this study was to investigate the association between TG levels during the second trimester and postpartum AGM in GDM women. Methods. This was a retrospective cohort study including 513 GDM women. A 75 g oral glucose tolerance test (OGTT) was performed, and lipid levels were determined during pregnancy and the postpartum period. GDM patients were categorized into tertiles according to their TG levels at 24–28 weeks of gestation (TG2.89 mmol/L). A logistic regression model was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs). Results. During pregnancy, women in the high TG tertile showed higher HbA1c levels (5.47±0.58% versus 5.28±0.49%, p=0.006), higher total cholesterol (TC) levels (5.85±1.23 mmol/L versus 5.15±0.97 mmol/L, p=0.026), and higher HOMA-IR (2.36 (1.62-3.45) versus 1.49 (0.97-2.33), p<0.001) than the participants in the low TG tertile. After delivery, the prevalence rates of AGM based on above tertiles of TG levels during pregnancy were 26.90%, 33.33%, and 43.27%, respectively (p=0.006). High TG tertile during the second trimester was associated with the presence of postpartum AGM (adjusted OR: 2.001, 95% CI: 1.054-3.800, p=0.034). Conclusions. The elevated midtrimester TG levels were not only accompanied by higher glucose and lipid levels and more severe insulin resistance at the time of the measurement but were a biomarker for postpartum AGM as well

Breaking the Transverse Magnetic-Polarized Light Extraction Bottleneck of Ultraviolet‑C Light-Emitting Diodes Using Nanopatterned Substrates and an Inclined Reflector

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (UV-C) spectral range (210–280 nm) exhibit extremely low external quantum efficiency, primarily due to the presence of large threading dislocations and extremely low transverse magnetic (TM) light extraction efficiency. Here, we have demonstrated that such critical issues can be potentially addressed by using AlGaN quantum-well heterostructures grown on a hexagonal nanopatterned sapphire substrate (NPSS) and a flip-chip-bonded inclined Al mirror. Our finite-difference time domain-based numerical analysis confirms that the maximum achievable efficiency is limited by the poor light extraction efficiency due to the extremely low TM-polarized emission. In our experiment, with the usage of a meticulously designed hexagonal NPSS and an inclined Al side wall mirror (>90% reflective in the UV-C wavelength), the AlGaN quantum-well UV-C LEDs showed nearly 20% improvement in the light output power and efficiency compared to the conventional flat flip-chip LEDs. The UV-C LEDs operating at ∼275 nm exhibit a maximum output power of ∼25 mW at 150 mA, a peak external quantum efficiency of ∼4.7%, and a wall plug efficiency of ∼3.25% at 15 mA under continuous wave (CW) conditions. The presented approach opens up new opportunities to increase the extraction of UV light in the challenging spectral range by using properly designed patterned substrates and an engineered Al reflector

Breaking the Transverse Magnetic-Polarized Light Extraction Bottleneck of Ultraviolet‑C Light-Emitting Diodes Using Nanopatterned Substrates and an Inclined Reflector

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (UV-C) spectral range (210–280 nm) exhibit extremely low external quantum efficiency, primarily due to the presence of large threading dislocations and extremely low transverse magnetic (TM) light extraction efficiency. Here, we have demonstrated that such critical issues can be potentially addressed by using AlGaN quantum-well heterostructures grown on a hexagonal nanopatterned sapphire substrate (NPSS) and a flip-chip-bonded inclined Al mirror. Our finite-difference time domain-based numerical analysis confirms that the maximum achievable efficiency is limited by the poor light extraction efficiency due to the extremely low TM-polarized emission. In our experiment, with the usage of a meticulously designed hexagonal NPSS and an inclined Al side wall mirror (>90% reflective in the UV-C wavelength), the AlGaN quantum-well UV-C LEDs showed nearly 20% improvement in the light output power and efficiency compared to the conventional flat flip-chip LEDs. The UV-C LEDs operating at ∼275 nm exhibit a maximum output power of ∼25 mW at 150 mA, a peak external quantum efficiency of ∼4.7%, and a wall plug efficiency of ∼3.25% at 15 mA under continuous wave (CW) conditions. The presented approach opens up new opportunities to increase the extraction of UV light in the challenging spectral range by using properly designed patterned substrates and an engineered Al reflector