Search Results (97)

Using low-cost transition-metal chlorides and furfuryl alcohol as raw materials, the (TiZrHfNbTa)C precursor was prepared, and a three-dimensional braided carbon fiber preform (C/C) coated with pyrolytic carbon (PyC) was used as the reinforcing material. A C/C-(TiZrHfNbTa)C composite was successfully fabricated through the precursor impregnation pyrolysis (PIP) process. Under extreme oxyacetylene ablation conditions (2311 °C/60 s), this composite material demonstrated outstanding ablation resistance, with a mass ablation rate as low as 0.67 mg/s and a linear ablation rate of only 20 μm/s. This excellent performance can be attributed to the dense (HfZr)₆(TaNb)₂O₁₇ oxide layer formed during ablation. This oxide layer not only has an excellent anti-erosion capability but also effectively acts as an oxygen diffusion barrier, thereby significantly suppressing further ablation and oxidation within the matrix. This study provides an innovative strategy for the development of low-cost ultra-high-temperature ceramic precursors and opens up a feasible path for the efficient preparation of C/C-(TiZrHfNbTa)C composites. Full article

The Dulong deposit in Wenshan, southeastern Yunnan Province, is rich in zinc, tin, and copper resources, accompanied by rare metals such as indium and silver. It is a particularly important indium production base, with reserves of approximately 7000 tons, ranking first globally. Enrichment and recovery of indium-bearing minerals are mainly achieved through mineral processing technology. However, the recovery rate of indium in the Dulong concentrator remains relatively low, and there is an insufficient understanding of its occurrence state and distribution characteristics, resulting in marked indium resource wastage. Here, we conducted a systematic process mineralogy study on indium-bearing polymetallic ore in the Dulong concentrator. The average grade of indium in the ore is 43.87 g/t, mainly occurring in marmatite (63.63%), supplemented by that in silicate minerals (23.31%), chalcopyrite (7.84%), and pyrrhotite (4.22%). The indium has a relatively dispersed distribution, which is inconducive to enrichment and recovery. The substitution mechanism of indium in marmatite was investigated using laser ablation inductively coupled plasma mass spectrometry. This revealed a positive correlation between indium and copper, allowing us to revise the substitution relationship to: ${\mathrm{Zn}}_x\mathrm{S}+{\mathrm{Cu}}^{+}+{\mathrm{In}}^{3+}\to {\mathrm{Zn}}_{\mathrm{x}-2}\mathrm{CuInS}+2{\mathrm{Zn}}^{2+}$ or ${\mathrm{Zn}}_{\mathrm{x}-1}\mathrm{FeS}+{\mathrm{Cu}}^{+}+{\mathrm{In}}^{3+}\to {\mathrm{Zn}}_{\mathrm{x}-2}\mathrm{CuInS}+{\mathrm{Zn}}^{2+}+{\mathrm{Fe}}^{2+}$. Electron probe microanalysis revealed the presence of roquesite (CuInS₂), an independent indium mineral not previously reported from this deposit. Our detailed investigation of the Dulong concentrator mineral processing technology showed that the recovery rate of indium from marmatite is currently poor, at only 48.01%. To improve the comprehensive utilization rate of indium resources, it will be necessary to further increase the recovery rate from marmatite and explore the flotation recovery of indium from chalcopyrite and pyrrhotite. Full article

Renal cell carcinoma (RCC) is the most prevalent solid organ malignancy among kidney transplant recipients, demonstrating substantially higher incidence rates compared to those in the general population. Although RCC is most commonly diagnosed in native kidneys, its development in transplanted kidneys has an infrequent occurrence. The use of immunosuppressive therapies, pre-existing chronic kidney disease and the unique anatomical characteristics of transplanted kidneys represent considerable therapeutic challenges in managing RCC within this patient cohort. Open radical transplantectomy plays a crucial role in curative treatment for localized RCC, whereas nephron-sparing surgery (NSS), in selected cases, can provide similar oncologic benefits while preserving allograft function. Recently, laparoscopic and robotic surgical procedures have demonstrated favorable outcomes as viable alternatives to conventional open surgery. Furthermore, ablative therapies like radiofrequency ablation and cryoablation can be considered therapeutic alternatives for small renal masses, offering the benefit of preserving allograft function, especially in high-risk surgical candidates. Limited data exist regarding the management of metastatic RCC in transplant recipients. Surgery, withdrawal of immunosuppression and systemic adjuvant therapy could be considered. Management of RCC in transplanted kidneys requires a multidisciplinary approach considering patient-specific characteristics, tumor features and the developing landscape of both surgical and non-surgical options. Further research is needed to refine therapeutic strategies in order to achieve optimal oncological outcomes while preserving allograft function. Full article

During the operation of a solid rocket motor, the nozzle, which is a key component, is subjected to extreme conditions, including high temperatures, high-speed gas flow, and discrete-phase particles. For composite nozzles incorporating a carbon/carbon (C/C) throat liner and a carbon/phenolic expansion section, thermochemical ablation and the formation of ablation steps during the ablation process significantly hinder nozzle performance and engine operational stability. In this study, the fluid and solid domains and the physicochemical interactions between them during nozzle operation were analyzed. An innovative thermochemical ablation model for composite nozzles was developed to account for wall recession. The coupled model covered multi-component gas flow, heterogeneous chemical reactions on the nozzle surface, structural heat transfer, variations in material parameters induced by carbon/phenolic pyrolysis, and the dynamic recession process of the nozzle profile due to ablation. The model achieved coupling between gas flow, heterogeneous reactions, and structural heat transfer through interfacial mass and energy balance relationships. Based on this model, the distribution of the nozzle’s thermochemical ablation rate was analyzed to investigate the mechanisms underlying ablation step formation. Furthermore, detailed calculations and analyses were performed to determine the effects of the gas pressure, temperature, H₂O concentration, and aluminum concentration in the propellant on the ablation rate of the throat liner and the thickness of the ablation steps. This study provides a theoretical foundation for the thermal protection design and performance optimization of composite nozzles, improving the reliability and service life of solid rocket motor nozzles and advancing technological development. Full article

Thermal protection materials with excellent performance are critical for hypersonic vehicles. Carbon fiber/phenolic resin composites (C_f/Ph) have been widely used as thermal protection materials due to their high specific strength and ease of processing. However, oxidative failure limits the extensive applications of C_f/Ph in harsh environments. In this paper, a novel hafnium carbide (HfC) and boron carbide (B₄C)-modified C_f/Ph was fabricated via an impregnating and compression molding route. The synergistic effect of HfC and B₄C on the thermal stability, flexural strength, microstructure, and phase evolution of the ceramizable composite was studied. The resulting ceramizable composites exhibited excellent resistance to oxidative corrosion and ablation behavior. The residual yield at 1400 °C and the flexural strength after heat treatment at 1600 °C for 20 min were 46% and 54.65 MPa, respectively, with an increase of 79.59% in flexural strength compared to that of the composites without ceramizable fillers. The linear ablation rate (LAR) and mass ablation rate (MAR) under a heat flux density of 4.2 MW/m² for the 20 s were as low as −8.33 × 10⁻³ mm/s and 3.08 × 10⁻² g/s. The ablation mechanism was further revealed. A dense B–C–N–O–Hf ceramic layer was constructed in situ as an efficient thermal protection barrier, significantly reducing the corrosion of the carbon fibers. Full article

The recovery of gold in metallurgical processes is significantly influenced by the presence of refractory minerals. This study investigates the mineralogical characteristics of refractory gold in the Pituca II ore deposit, with a focus on identifying the sulfide minerals that encapsulate gold particles and understanding their impact on gold recovery rates via cyanidation leaching. To establish a theoretical basis for optimizing gold recovery, a comprehensive suite of analytical techniques including electron microprobe analysis, petrographic analysis, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and X-ray diffraction was employed to characterize the ore’s composition and mineralogical properties. The primary ore minerals identified were pyrite, galena, chalcopyrite, and sphalerite, with hessite occurring as an accessory phase. Gold was observed as fine-grained particles (<40 µm), predominantly enclosed within pyrite and galena, contributing to its refractory nature. Cyanidation tests revealed a strong correlation between particle size and leaching efficiency: material ground to D₈₀ = 170 mesh (90 μm) achieved a recovery rate of 81.2%, compared to 72.2% for material at D₈₀ = 100 mesh (150 μm). These findings elucidate the mineralogical constraints on gold recovery and underscore the necessity of appropriate particle size reduction to enhance leaching performance. The study provides practical insights and targeted recommendations for pretreatment strategies, thereby contributing to more efficient exploitation of refractory gold ores in similar geological settings. Full article

Previous reviews by authors indicate the continuing development and improvement of thermal protective systems through the introduction of polymer nanocomposites into polymer matrix composites. These materials perform as thermal protective systems for a variety of aerospace applications, such as thermal protection systems (TPSs), solid rocket motor (SRM) nozzles, internal insulation of SRMs, leading edges of hypersonic vehicles, and missile launch structures. A summary of the most recent global technical research is presented. Polymeric resin systems continue to emphasize phenolic resins and other materials. New high-temperature organic resins based on phthalonitrile and polysiloxane are described and extend the increased temperature range of resin matrix systems. An important technical development relates to the transformation of the resin matrix, primarily phenolic resin, into an aerogel or a nanoporous material that penetrates uniformly within the reinforcing fiber configuration with a corresponding particle size of <100 nm. Furthermore, many of the current papers consider the use of low-density carbon fiber or quartz fiber in the use of low-density felts with high porosity to mimic NASA’s successful use of rigid low-density carbon/phenolic known as phenolic impregnated carbon ablator (PICA). The resulting aerogel composition with low-density non-wovens or felts possesses durability and low density and is extremely effective in providing insulation and preventing heat transfer with low thermal conductivity within the aerogel-modified thermal protective system, resulting in multiple features, such as low-density TPSs, increased thermal stability, improved mechanical properties, especially compressive strength, lower thermal conductivity, improved thermal insulation, reduced ablation recession rate and mass loss, and lower backside temperature. The utility of these TPS materials is being expanded by considering them for infrastructures and ballistics besides aerospace applications. Full article

The vigorous development of micro–nano satellites urgently requires satellite-borne propulsion systems as support. Pulsed laser ablation micro-propulsion can meet these high demands. Ammonium dinitramide (ADN), as a green monopropellant, can serve as the working substance for laser ablation. This work investigated the micro-propulsion performance of liquid propellants composed of ADN and water with different ADN mass fractions, aiming to clarify the enhancement effect of chemical energy. Through the single-pulse impulse measurement, the results show that the 70 wt.% ADN had a maximum specific impulse of 167.55 s, a 19% increase compared to H₂O. The established semi-empirical model of the micro-propulsion performance fits well with the experimental data and can effectively explain the variations in the patterns of the propulsion’s parameters. The chemical energy’s actual rate of contribution to the increase in the kinetic energy was positively correlated with the ADN’s mass fraction and negatively correlated with the laser energy, with an actual contribution rate of 36% for 70 wt.% ADN at a laser energy of 60 mJ. Furthermore, based on the relationship between the ablation efficiency, chemical-specific energy, and laser specific energy, it was found that the ablation efficiency can be improved by increasing the chemical specific energy and reducing the laser specific energy while ensuring the breakdown. This work provides a scientific approach to quantitatively analyze the enhancement in the propulsion’s performance by chemical energy in laser micro-ablation, which is expected to be extended to other energetic liquid propellants. Full article

Temperate glaciers in the Kangri Karpo region of the southeastern Qinghai–Tibet Plateau (QTP) have experienced significant ablation in recent decades, increasing the risk of glacier-related hazards and impacting regional water resources. However, the spatial and temporal pattern of mass loss in these glaciers remains inadequately quantified. In this study, we used ASTER L1A stereo images to construct a high-resolution elevation time series and provide a comprehensive spatial–temporal assessment of glacier elevation change from 2000 to 2024. The results indicate that almost all glaciers have experienced rapid ablation, with an average surface elevation decrease of −18.35 ± 5.13 m, corresponding to a rate of −0.76 ± 0.21 m yr⁻¹. Glaciers in the region were divided into the northern and southern basins, with average rates of −0.79 ± 0.17 m yr⁻¹ and −0.72 ± 0.13 m yr⁻¹, respectively. A notable difference in acceleration trends between the two basins was observed, with the elevation rate increasing from −0.78 ± 0.17m yr⁻¹ to −1.04 ± 0.17 m yr⁻¹ and from −0.52 ± 0.13 m yr⁻¹ to −0.92 ± 0.13 m yr⁻¹, respectively. The seasonal cycle was identified in glacier surface elevation change, with an accumulation period from November to March followed by a prolonged ablation period. The seasonal amplitude decreased with elevation, with higher elevations exhibiting longer accumulation periods and less ablation. Correlation analysis with meteorological data indicated that higher summer temperatures and increased summer rainfall intensify elevation loss, while increased spring snowfall may reduce ablation. Our analysis highlights distinct variations in glacier elevation changes across different locations, elevations, and climatic conditions in the Kangri Karpo region, providing valuable insights into glacier responses to environmental changes on the Tibetan Plateau. Full article

Hypersonic flight in the atmosphere is associated with high thermal flux impacting the vehicle surface. The nose, leading edges, and some elements of the engine typically require the implementation of highly refractory materials or an active thermal protection system to maintain structural stability during the vehicle mission. Carbon–carbon (C–C) composites are commonly considered for the application thanks to their unique thermal and mechanical properties. However, C–C composites’ ablation and oxidation under long cruise flights at high speeds (Mach number > 5) are the limiting factors for their application. In this paper, the results of an experimental study of C–C composite thermal ablation and oxidation with test article surface temperatures up to 2000 K are presented. The tests were performed under atmospheric conditions and hypersonic flow in the ND_ArcJet facility at the University of Notre Dame. The test articles were preheated with CW laser radiation and then exposed to M = 6 flow at stagnation pressures up to 14 bar. It was found that C–C composite oxidation and mechanical erosion rates are significantly increased in hypersonic airflow compared to those at ambient conditions and nitrogen M = 6 flow. Compared to atmospheric air, mass loss occurred at a rate of 1.5 orders of magnitude faster for M = 6 airflow. During high-speed flow conditions, rapid chemical oxidation and the mechanical destruction of weakened C-fibers likely cause the accelerated degradation of C–C composite material. In this study, a post-mortem microscopic analysis of the morphology of the C–C surface is used to explain the physical processes of the material destruction. Full article

Supraglacial debris cover considerably influences sub-debris ablation patterns and the surface morphology of glaciers by modulating the land–atmosphere energy exchange. Understanding its spatial distribution and temporal variations is crucial for analyzing melting processes and managing downstream disaster mitigation efforts. In recent years, the overall slightly positive mass balance or stable state of eastern Pamir glaciers has been referred to as the “Pamir-Karakoram anomaly”. It is important to note that spatial heterogeneity in glacier change has drawn widespread research attention. However, research on the spatiotemporal changes in the debris cover in this region is completely nonexistent, which has led to an inadequate understanding of debris-covered glacier variations. To address this research gap, this study employed Landsat remote sensing images within the Google Earth Engine platform, leveraging the Random Forest algorithm to classify the supraglacial debris cover. The classification algorithm integrates spectral features from Landsat images and derived indices (NDVI, NDSI, NDWI, and BAND RATIO), supplemented by auxiliary factors such as slope and aspect. By extracting the supraglacial debris cover from 1994 to 2024, this study systematically analyzed the spatiotemporal variations and investigated the underlying drivers of debris cover changes from the perspective of mass conservation. By 2024, the area of supraglacial debris in eastern Pamir reached 258.08 ± 20.65 km², accounting for 18.5 ± 1.55% of the total glacier area. It was observed that the Kungey Mountain region demonstrated the largest debris cover rate. Between 1994 and 2024, while the total glacier area decreased by −2.57 ± 0.70%, the debris-covered areas expanded upward at a rate of +1.64 ± 0.10% yr⁻¹. The expansion of debris cover is driven by several factors in the context of global warming. The rising temperature resulted in permafrost degradation, slope destabilization, and intensified weathering on supply slopes, thereby augmenting the debris supply. Additionally, the steep supply slope in the study area facilitates the rapid deposition of collapsed debris onto glacier surfaces, with frequent avalanche events accelerating the mobilization of rock fragments. Full article

Background: Atrial fibrillation (AF) is prevalent among obese patients, and cryoballoon ablation (CBA) is an effective strategy for the rhythm control of AF. The impact of body mass index (BMI) on the clinical outcomes of CBA for AF is not fully explored. Methods: 85 consecutive patients with paroxysmal AF were enrolled and were categorized into three groups as per their BMI: normal weight (BMI 18.5–25 kg/m²), overweight (BMI 25–30 kg/m²), and obese patients (BMI > 30 kg/m²). The primary study endpoint was a late (12 month) recurrence of AF. Early recurrence of AF, symptom improvement, and procedural outcomes were some key secondary outcomes. Results: 20 patients had normal weight, 35 were overweight, and 30 were obese. Obese patients featured a higher prevalence of diabetes mellitus, heavier exposure to smoking, and worse baseline symptoms (as assessed through EHRA class at admission and 12 months before CBA) compared to overweight and normal weight patients. Both late and early (<3 months) AF recurrence rates were comparable across the three groups. Of note, obese patients showed greater improvement in their symptoms post-CBA, defined as improvement by at least one EHRA class, compared to normal weight patients; this might be explained by improved diastolic function. Total procedure time and dose area product were significantly increased in obese patients. The multivariate logistic regression analysis indicated that early AF recurrence and the duration of hypertension are independent predictors of late AF recurrence. Conclusion: CBA is effective in overweight and obese patients with paroxysmal AF. Procedure time and radiation exposure are increased in obese patients undergoing CBA. Full article

Assessing changes of the mass balance in the Antarctic ice sheet in the context of global warming is a key focus in polar study. This study analyzed the spatiotemporal variation in the Antarctic ice sheet’s mass balance, both as a whole and by individual basins, from 2003 to 2016 and from 2018 to 2022 using GRACE RL06 data published by the Center for Space Research (CSR) and ERA-5 meteorological data. It explored the lagged relationships between mass balance and precipitation, net surface solar radiation, and temperature, and applied the random forest method to examine the relative contributions of these factors to the ice sheet’s mass balance within a nonlinear framework. The results showed that the mass loss rates of the Antarctic ice sheet during the study periods were −123.3 ± 6.2 Gt/a and −24.8 ± 52.1 Gt/a. The region with the greatest mass loss was the Amundsen Sea in West Antarctica (−488.8 ± 5.3 Gt/a and −447.9 ± 14.7 Gt/a), while Queen Maud Land experienced the most significant mass accumulation (44.9 ± 1.0 Gt/a and 30.0 ± 3.2 Gt/a). The main factors contributing to surface ablation of the Antarctic ice sheet are rising temperatures and increased surface net solar radiation, each showing a lag effect of 1 month and 2 months, respectively. Precipitation also affects the loss of the ice sheet to some extent. Over time, the contribution of precipitation to the changes in the ice sheet’s mass balance increases. Full article

Accurately predicting the payload movement and ensuring efficient control during dynamic tower crane operations are crucial for crane safety, including the ability to predict payload mass within a safe or normal range. This research utilizes deep learning to accurately predict the normal and abnormal payload movement of tower cranes. A scaled-down tower crane prototype with a systematic data acquisition system is built to perform experiments and data collection. The data related to 12 test case scenarios are gathered, and each test case represents a specific combination of hoisting and slewing motion and payload mass to counterweight ratio, defining tower crane operational variations. This comprehensive data is investigated using a novel attention-based deep neural network with Tree-Structured Parzen Estimator optimization (TPE-AttDNN). The proposed TPE-AttDNN achieved a prediction accuracy of 0.95 with a false positive rate of 0.08. These results clearly demonstrate the effectiveness of the proposed model in accurately predicting the tower crane payload moving condition. To ensure a more reliable performance assessment of the proposed AttDNN, we carried out ablation experiments that highlighted the significance of the model’s individual components. Full article

To study the ablation properties and differences of plain-woven SiC/SiC composites under single and cyclic ablation. The ablation test of plain-woven SiC/SiC composites was conducted under an oxyacetylene torch. The results indicate that the mass ablation rate of cyclic ablation is lower than that of single ablation, whereas the line ablation rate is higher. Macro-microstructural characterization revealed the presence of white oxide formed by silica on the surface of the ablation center region. The fibers in the central region of the ablation were ablated layer by layer, and the broken fiber bundles exhibited a spiky morphology with numerous silica particles attached. The oxide layer on the surface and the silica particles on the fibers, which are in the molten state formed in the high-temperature ablation environment, contribute to resisting ablation. Thermal shock during cyclic ablation also played a role in the ablation process. The thermal shock causes cracks in the fiber bundles and matrix of the SiC/SiC composites. This study helps to apply SiC/SiC composite to complex thermal shock environments. Full article