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• A new DDES-Tr, based on the three-equation k-ω-γ transition/turbulence integrated model, was proposed through the similar way with the typical DDES. • A modification of the length scale was introduced to ensure the models worked in their own interest regions. • DDES-Tr model can not only resolve the massive separation on the leeward side, but also model the transition on the windward side. The hypersonic flow at high angle of attack past the Orion capsule was predicted by a delayed detached eddy simulation (DDES), based on a three-equation k-ω-γ transition/turbulence integrated model (Tr). The computational results of the mean and instantaneous heat rates by DDES-Tr are compared with the available measurements and DDES-FT (full turbulence). As expected, the massive separation on the leeward side can be well predicted by both DDES models, but DDES-FT cannot model the transition and over-predicts the heat flux on the windward side. Fortunately, the DDES-Tr model can not only resolve the massive separation on the leeward side, but also model the transition on the windward side. Furthermore, the contributions of the first, second, and crossflow modes on the transition are quantitatively explored. Although the freestream is hypersonic, the second Mack mode is very weak owing to the low supersonic speed after the strong bow shock wave. The transition is mainly dominated by the first and rarely by the crossflow mode. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel phthalonitrile copoly-oligomers were synthesized by an improved method. • Oligomers exhibited good processability for prepreg and hot-press manufacture. • Glass transition temperatures of cured polymers were higher than 450 °C. • Bending strength reached 942 MPa, capable as structural composite matrices. Abstract A novel series of phthalonitrile terminated fluorene based copoly-oligomers (BPNs) were designed and synthesized by an improved method and could be cured in the presence of bis[4-(4-aminophenoxy)phenyl]sulfone. The structure of oligomers was characterized, while their curing behavior was systematically studied. The oligomers exhibited good solubility, which facilitated the preparation of prepregs. Later quartz fiber reinforced composites were prepared by hot-pressing process, and their thermal and mechanical properties were characterized. The glass transition temperatures of the composites were higher than 450 °C, and the bending strength reached 942 MPa. The combination of excellent thermal and mechanical performance indicated BPNs could be potentially applied in high performance composites or as universal modifiers for heat resistant resins. [ABSTRACT FROM AUTHOR]

Abstract The global navigation satellite system (GNSS) is presently a powerful tool for sensing the Earth's ionosphere. For this purpose, the ionospheric measurements (IMs), which are by definition slant total electron content biased by satellite and receiver differential code biases (DCBs), need to be first extracted from GNSS data and then used as inputs for further ionospheric representations such as tomography. By using the customary phase-to-code leveling procedure, this research comparatively evaluates the calibration errors on experimental IMs obtained from three GNSS, namely the US Global Positioning System (GPS), the Chinese BeiDou Navigation Satellite System (BDS), and the European Galileo. On the basis of ten days of dual-frequency, triple-GNSS observations collected from eight co-located ground receivers that independently form short-baselines and zero-baselines, the IMs are determined for each receiver for all tracked satellites and then for each satellite differenced for each baseline to evaluate their calibration errors. As first derived from the short-baseline analysis, the effects of calibration errors on IMs range, in total electron content units, from 1.58 to 2.16, 0.70 to 1.87, and 1.13 to 1.56 for GPS, Galileo, and BDS, respectively. Additionally, for short-baseline experiment, it is shown that the code multipath effect accounts for their main budget. Sidereal periodicity is found in single-differenced (SD) IMs for GPS and BDS geostationary satellites, and the correlation of SD IMs over two consecutive days achieves the maximum value when the time tag is around 4 min. Moreover, as byproducts of zero-baseline analysis, daily between-receiver DCBs for GPS are subject to more significant intra-day variations than those for BDS and Galileo. [ABSTRACT FROM AUTHOR]

After considering the local effects of nose bluntness on the transition, a modification for the timescale of the second mode in the three-equation k-ω-γ transition model has been proposed to improve the hypersonic transition past cones. The ratio of local unit Reynolds number over freestream unit Reynolds number ( Re local / Re ∞ ) is introduced to delay and reduce the development of second mode instability, according to the results of linear stability theory. The hypersonic transitions past a cone with three nose radii at the angle of attack of 0° were simulated to calibrate the new model and its constants. Then, the improved model is extended to predict the hypersonic transitions past the cones with larger radius and at non-zero angles of attack. Despite the original model can reflect the transition trend, the improved model performs much better than the original one when comparing with the available measurements. [ABSTRACT FROM AUTHOR]

Soil loss is commonly predicted using the revised universal soil loss equation consisting of rainfall–runoff erosivity, soil erodibility, slope steepness and length, cover management, and support practice factors. Because of the multiple factors, their interactions, and spatial and temporal variability, soil erosion varies considerably over space and time. For these reasons, modeling soil loss is very complicated. Decision-makers need local and regional estimates of soil loss as well as their corresponding uncertainties. Neglecting the local and detailed information may lead to improper decision-making. This paper demonstrates a strategy based on a sample data set and a geostatistical method called sequential Gaussian simulation to derive local estimates and their uncertainties for the input factors of a soil erosion system. This strategy models the spatial and temporal variability of the factors and derives their estimates and variances at any unknown location and time. This strategy was applied to a case study at which the rainfall–runoff erosivity R factor was spatially and temporally estimated using a data set of rainfall. The results showed that the correlation between the observations and estimates by the strategy ranged from 0.89 to 0.97, and most of the mean estimates fell into their confidence intervals at a probability of 95%. Comparing the estimates of the R factor using a traditional isoerodent map to the observed values suggested that the R factor might have increased and a new map may be needed. The method developed in this study may also be useful for modeling other complex ecological systems. [Copyright &y& Elsevier]

To predict complex flow, including transition on the windward side and massive separation on the leeward side, a Reynolds averaged Navier Stokes-Large Eddy Simulation (RANS-LES) hybrid model based on the three-equation k - ω - γ transition model (RANS-LES-Tr) was developed. Then, it was applied to simulate the following three cases, such as the low-speed flow past a cylinder only with the first transition mode, the low-speed prolate spheroid flow at a high angle of attack (AoA) with both the first and crossflow modes; and hypersonic flow past the "Orion" capsule with the first, second and crossflow modes. RANS-LES-Tr shows much better agreements with available measurements, such as skin friction and heat flux on the windward side, than RANS-LES based on the full turbulence model. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Low melting dual-functional phthalonitrile monomers were synthesized. • Prepolymers exhibited processability capable for RTM manufacture. • Glass transition temperatures of cured polymers were higher than 470 °C. • Impact strength reached 13.63 kJ m−2, capable as structural composite matrices. Abstract Low melting phthalonitrile monomers containing allyl and/or methoxyl groups were designed, synthesized and characterized. In order to evaluate their potential application in phthalonitrile resins, these monomers were blended with 1,3-bis(3,4-dicyanophenoxy)benzene and 4-(4-aminophenoxy)phthalonitrile, then cured into polymers. Curing mechanisms of different prepolymers were proposed and compared, and processability, thermal and mechanical properties were characterized. The introduction of methoxyl units was found to postpone the curing, and thermal properties were slightly compromised. On the contrary, the usage of allyl was beneficial to both processability and thermal properties. More importantly, the impact strength for allyl-containing polymers could be as high as 13.63 kJ m−2, indicating such resin could be applied as high temperature structural composite matrices. [ABSTRACT FROM AUTHOR]

The degradation of permafrost in the Earth's cold regions due to climate warming and human activities is of increasing concern because of its impact on ecosystems and land management, thus, monitoring the degradation becomes critical. This study aimed to demonstrate a method in which Sentinel-1 DInSAR and MODIS data were combined to estimate and map seasonal and long-term land surface deformation (subsidence/uplifting) and permafrost active layer thickness (ALT) in Donnelly Training Area (DTA) in Alaska. The coherence (similarity) between the paired SAR images was analyzed for their applicability. A sensitivity analysis and accuracy assessment of the estimates were conducted to account for their quality. Results showed that the estimated seasonal subsidence mainly occurring in June and July was in the range of 0 to −0.43 m, while the estimated uplifting mainly happening from September to May of next year was as great as +0.34 m. Moreover, the estimated long-term (2015 to 2018) subsidence and uplifting were mostly distributed in the southern and northern parts of DTA, respectively. The spatially variable time delays led to the ALT estimates greater along the east river and in the west and south parts, and smaller in the north parts. At the significance level of 0.05, the coherence estimates of the paired images were significantly different from zero and compared with the referenced predictions from a widely used annual prediction model, the average residual of the ALT estimates did not significantly differ from zero at the significance level of 0.05. The spatial distributions of the uncertainties for the seasonal surface deformation estimates were similar to those of the input uncertainties from the estimates of model coefficients, the phase change, the modelling error, and the image pairs. Thus, the DInSAR image based method coupled with MODIS data offered the potential of mapping and monitoring the dynamics of permafrost environment for the cold regions such as DTA in which collecting field observations is difficult and costly. This study also enhanced understanding spatiotemporal variability of permafrost deformation in DTA and provided guidelines for developing a near real-time monitoring system of the permafrost environment. • Permafrost degradation due to climate warming and human activity is of great concern. • Land surface deformation of an installation in Alaska is mapped by SAR&MODIS images. • A quality assessment of the land surface deformation estimates is conducted. • The accuracy of the estimates is compatible with that from a widely used model. • This study provides guidelines for developing a near real-time monitoring system. [ABSTRACT FROM AUTHOR]