In this work, the effects of mould pre-heating temperatures and hot isostatic pressing （HIPping） process on the microstructural characteristics and mechanical properties, including static tensile and ...damage- tolerance properties of large thin-wall cylindrical Ti-6Al-4V casting, have been studied. The experimental results show that with the increasing mould pre-heating temperature from 673 to 873 K, the casting mi- crostructures change from a mixture of Widmanstatten and colony microstructure to a primary colony. The centre of the thick wall section has relatively coarse microstructure than the edge and thin section. Lower mould pre-heating temperature brings about more porosities. HIPping process, which not only reduces the casting pores effectively but also increases the prior β grain boundary cohesion and coars- ens the microstructure, is essential to improving the ductility of the casting. Due to the oxygen contamination and finer microstructure on the surface, micro-hardness profiles on the cross section present a decreas- ing tendency from the surface to inner. The thickness of the reaction layers for the different mould pre-heating temperatures is nearly the same （-450 μm）. On the whole, the tensile strength and micro- hardness decrease with increasing mould pre-heating temperature from 673 to 873 K. However, the fracture toughness and fatigue crack growth resistance of the castings increase with increasing mould pre- heating temperature.
A public bicycle system (PBS) is a promising countermeasure for the traffic issues induced by rapid urbanization, and it is widely acknowledged that the built environment has a significant impact on ...the use of a PBS. However, as the urban built-up area expands, different regions within a city can exhibit diverse characteristics. The spatial effects and differences among regions have been neglected by existing studies. To better understand how the urban built environment affects PBS ridership, this study conducts a quantitative analysis of the spatial relationship. It introduces a multi-scale geographically weighted regression (MGWR) to accomplish this task and conducts and evaluates a case study of the PBS in Nanjing, China. Six types of "D" variables (density, diversity, design, destination accessibility, distance to transit, and demand management) are involved in the analysis. The proposed method outperforms linear regression and standard geographically weighted regression (GWR) in terms of explanatory power. The modeling results demonstrate different influencing patterns between traditional downtown areas and newly built-up areas, especially for the density of population, road network, parking space, and various points of interest.
Background: The termination of pregnancy in patients with placenta accreta spectrum disorder (PASD) during the second trimester remains uncertain. In addition, interventional radiology techniques, ...such as arterial embolization and balloon placement, are potential options. We evaluated the outcomes of pregnancy termination in patients with PASD during the second trimester and the effectiveness of preoperative interventional radiology techniques.Methods: This retrospective study analyzed 48 PASD patients who underwent pregnancy termination during the second trimester between January 2016 and May 2021.Results: Of the 48 patients, 20 (41.67%) underwent transvaginal termination, whereas 28 (58.33%) underwent cesarean section. Notably, no significant differences were observed in success rates between the transvaginal termination and cesarean section groups (80.00% vs. 92.86%, P = 0.38). Furthermore, no statistically significant differences were observed in the success rates (94.12% vs 90.32%, P = 1.00) and blood loss (512.35 ± 727.00 ml vs 804.00 ± 838.98 ml, P = 0.23) between the artery embolization and non-embolization groups. In the vaginal termination group, statistically significant differences were observed in gestational weeks (16.70 ± 3.12 vs 22.67 ± 3.63, P < 0.01) and blood loss (165.00 ± 274.43 ml vs 483.64 ± 333.53 ml, P = 0.04) between the (artery embolization and non-embolization) subgroups. Conversely, in the cesarean section group, no significant differences were observed in gestational weeks (23.59 ± 3.14 vs 23.20 ± 4.37, P = 0.79) and blood loss (811.11 ± 879.55 ml vs 989.47 ± 986.52 ml, P = 0.76) between the subgroups.Conclusions: Further studies are needed to evaluate the efficacy of vaginal termination in PASD patients during the second trimester. Regarding cesarean termination, arterial embolization did not demonstrate increased effectiveness.
The high cost of laser powder bed fusion (LPBF) fabricated high-strength Sc containing aluminium alloy hinders its applications. To reduce the cost, we reported a LPBF fabricated strong and ductile ...Al–Mn–Mg–Sc–Zr alloy using large layer thicknesses to improve the fabrication efficiency on coarse powder particles. A high relative density exceeding 99.2% was achieved at layer thicknesses up to 120 μm. In post-process heat-treated specimens, the yield strength only had a slight 6% decrease from layer thickness of 30 to 120 μm; such a decrease in strength was attributed to the larger grain size resulted from the adopted larger layer thickness. The fabricated sample at layer thickness of 120 μm still exhibited high tensile yield strength of 472 MPa and fracture strain of ∼10%. This work showed a successful application of improving the LPBF fabrication efficiency of high-strength Al–Mn–Mg–Sc–Zr alloy using large layer thickness in LPBF process.
A compositionally graded material has been fabricated using direct laser fabrication (DFL). Two types of feedstock were fed simultaneously into the laser focal point, a burn resistant (BurTi) alloy ...Ti–25V–15Cr–2Al–0.2C powder and a Ti–6Al–4V wire. The local composition of the alloy was changed by altering the ratio of powder to wire by varying the feed rate of the powder whilst maintaining a fixed feed rate of wire-feed. For the range of compositions between about 20% and 100% BurTi only the beta phase was observed and the composition and lattice parameter varied monotonically. The grain size was found to be much finer in these functionally graded samples than in laser fabricated Ti64. Some samples were made using the wire-feed alone, where it was found that the microstructure is different from that found when using powder feed alone. The results are discussed in terms of the power requirements for laser fabrication of powder and wire samples.
With the escalating challenges of climate change and the imperative for carbon neutrality, evaluating the carbon footprint of regional power systems becomes crucial. To address this issue, a ...low-carbon evaluation framework for regional power systems is developed. First, this study identifies the fundamental requirements that the index system for the low-carbon power system should follow and specifies the general direction for the index system’s creation. Second, an evaluation model for carbon reduction ability is proposed by considering generation side, grid side and load side of the power system. Then, a comparative evaluation model for the carbon reduction capability of multi-regional power systems is proposed to spatiotemporally compare the carbon reduction capability of different power systems. Next, a quantification method for the weights of low-carbon evaluation indicators is established based on the power system simulation of multi-scenario scheduling and index sensitivity analysis method. Finally, a low-carbon comprehensive score for regional power systems is created by combining the evaluation results of the system’s carbon reduction capacity with index weights. The practical research results in a region of Zhejiang province in China demonstrate that the proposed model can provide a reasonable and feasible evaluation plan for the low-carbon construction of regional power systems.
Pastoral nomadism, as a successful economic and social system drawing on mobile herding, long-distance trade, and cavalry warfare, affected all polities of the Eurasian continent. The role that arid ...Inner Asia, particularly the areas of northwestern China, Kazakhstan, and Mongolia, played in the emergence of this phenomenon remains a fundamental and still challenging question in prehistoric archaeology of the Eurasian steppes. The cemetery of Liushiu (Xinjiang, China) reveals burial features, bronze bridle bits, weaponry, adornment, horse skulls, and sheep/goat bones, which, together with paleopathological changes in human skeletons, indicate the presence of mobile pastoralists and their flocks at summer pastures in the Kunlun Mountains, ∼2,850 m above sea level. Radiocarbon dates place the onset of the burial activity between 1108 and 893 B.C. (95% probability range) or most likely between 1017 and 926 B.C. (68%). These data from the Kunlun Mountains show a wider frontier within the diversity of mobile pastoral economies of Inner Asia and support the concept of multiregional transitions toward Iron Age complex pastoralism and mounted warfare.
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