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30 result(s) for "Tan, Dong-Bo"
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Supercritical fluid in deep subduction zones as revealed by multiphase fluid inclusions in an ultrahigh-pressure metamorphic vein
Due to their low viscosity, high mobility, and high element contents, supercritical fluids are important agents in the cycling of elements. However, the chemical composition of supercritical fluids in natural rocks is poorly understood. Here, we investigate well-preserved primary multiphase fluid inclusions (MFIs) from an ultrahigh-pressure (UHP) metamorphic vein of the Bixiling eclogite in Dabieshan, China, thus providing direct evidence for the components of supercritical fluid occurring in a natural system. Via the 3D modeling of MFIs by Raman scanning, we quantitatively determined the major composition of the fluid trapped in the MFIs. Combined with the peak-metamorphic pressure–temperature conditions and the cooccurrence of coesite, rutile, and garnet, we suggest that the trapped fluids in the MFIs represent supercritical fluids in a deep subduction zone. The strong mobility of the supercritical fluids with respect to carbon and sulfur suggests that such fluids have profound effects on global carbon and sulfur cycling.
Carbonic Fluids Drive Continental Carbon Cycling as Revealed by the Geochemistry of the Eclogite‐Garnet Peridotite Interface
Subduction zones regulate Earth's carbon distribution, yet the mechanism of carbon transfer from continental crust to mantle remains elusive. We examined an eclogite‐garnet peridotite interface from the Chinese Continental Scientific Drilling Program in the Sulu orogen, representing the slab–mantle wedge boundary formed during continental subduction. Whole‐rock magnesium (Mg) isotopic and major‐trace element data, together with in situ mineral analyses, identify the presence of carbonic fluids characterized by notably light Mg isotopic compositions (−0.54 to −0.36‰) and elevated Ca, Mg, Sr, and rare earth elements contents. These fluids, generated by slab decarbonation during prograde metamorphism, mobilized carbon from the subducted crust and enriched the mantle wedge. Modeling indicates that continental subduction rivals oceanic systems in transporting carbon to mantle. However, the paucity of mantle‐derived magmatism limits carbon return, promoting long‐term retention of continental carbon in mantle and establishing continental subduction as a major sink in the global carbon budget.
Sulfur-enriched sub-arc fluids drive deep sulfur cycling in subduction zones
Arc magmas are enriched in sulfur relative to mid-ocean ridge basalts, commonly attributed to slab-derived sulfur inputs during subduction. However, the contribution of slab fluids remains debated because sulfur concentrations in sub-arc fluids have not been directly measured. Here we quantify sulfur in slab-derived fluids preserved as multiphase fluid inclusions composed of H 2 O, calcite, and chalcopyrite in omphacite from ultrahigh-pressure eclogites in the Sumdo orogenic belt. Three-dimensional Raman spectroscopy reveals high sulfur concentrations averaging ~6 wt.%. Mass-balance calculations indicate that such fluids can efficiently enrich the mantle wedge and supply up to ~70% of the sulfur emitted by arc volcanism. We further suggest that chalcopyrite formed through post-entrapment reduction of oxidized sulfur species by host omphacite, followed by precipitation with co-entrapped copper and iron. Our findings identify sub-arc depths as a critical window for slab sulfur release and provide key constraints on deep sulfur cycling and copper mobilization in arc systems. Three-dimensional Raman modelling of multiphase inclusions in Sumdo eclogites reveals sulfur rich slab-derived fluids at sub-arc depths, providing direct constraints on deep sulfur cycling and copper mobilization in subduction zones.
Formation and evolution of supercritical geofluid
In this work, we provide a comprehensive review on the formation, evolution, properties, and effects of supercritical geofluid. In Earth’s interior, enhanced miscibility between H 2 O and silicate by the addition of special components or by the increase of pressure and temperature gives rise to supercritical geofluid with a significant amount of both H 2 O and silicate solute. The formation of supercritical geofluid in magmatic-hydrothermal systems, typified by pegmatite system, is governed by meltfluid critical curve. The formation of supercritical geofluid in metamorphic systems, typified by subducted slab, is governed by the second critical end point. Experimental results suggest that the presence of boron and fluorine in pegmatite system makes it possible to form supercritical geofluid at crustal depths, but the release of supercritical geofluid from subducted slab is withheld until almost 100 km depth. A major presence of both H 2 O and depolymerized structural units (monomers, dimers, etc.) endows supercritical geofluid with unique physical properties including low density, low elastic moduli, low viscosity, high diffusivity, and high electrical conductivity. Supercritical geofluid can effectively mobilize a variety of elements even including high field strength elements and heavy rare earth elements. The chemical signatures of supercritical geofluid can be inherited by metasomatized mantle and mantle-derived melts, and this could give an explanation of the oxidation of arc magmas. Phase separation of supercritical geofluid through the mechanism of spinodal decomposition leads to formation of a melt network. Multiphase fluid inclusions recovered from subduction zone rocks and pegmatites are possible relics of supercritical geofluid. Supercritical geofluid can cause electrical anomaly and low seismic velocity near the top of subducted slab, and can be linked with intermediate-focus earthquakes. Supercritical geofluid may have played a crucial role in the formation of pegmatites and associated ore deposits.
Abrasive Wear Behaviors of Light-weight Austenitic Fe-24Mn-7Al-1C Steel and Mn13Cr2 Steel
The impact abrasive wear behaviors of light-weight austenitic Fe-24Mn-7Al-1Csteel with increasing impact wear conditions were studied by comparing with the modified Hadfield(Mn13Cr2)steel.Wear tests were performed with the MLD-10 abrasive wear testing machine.Main parameters such as impact energy,impacting frequency and wear time were evaluated.To explore the abrasive wear behaviors under different impact energies,the parameters including mass loss,wear resistance and hardness were evaluated in detail.The microstructures of the steels were further analyzed using optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).Results showed that the light-weight austenitic Fe-24Mn-7Al-1Csteel had a better wear resistance than Mn13Cr2 steel under the impact energy tested.The wear resistance of light-weight austenitic Fe-24Mn-7Al-1Csteel was about 1.09-1.17 times as high as that of Mn13Cr2 steel under low and medium impact energy(0.5-2.0J)conditions,and 1.41 times under high impact energy(4.0J)condition.In Mn13Cr2 steel,the evolution of dislocation substructure with increasing impact energy showed typical stacking fault,interaction of twins and dislocations,as well as mechanical twins.The high work-hardening rate in Fe-24Mn-7Al-1Csteel was caused by Taylor lattice and high density of dislocation tangles.
Anisotropic flexibility and rigidification in a TPE-based Zr-MOFs with scu topology
Tetraphenylethylene (TPE)-based ligands are appealing for constructing metal-organic frameworks (MOFs) with new functions and responsiveness. Here, we report a non-interpenetrated TPE-based scu Zr-MOF with anisotropic flexibility, that is, Zr-TCPE (H 4 TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), remaining two anisotropic pockets. The framework flexibility is further anisotropically rigidified by installing linkers individually at specific pockets. By individually installing dicarboxylic acid L 1 or L 2 at pocket A or B, the framework flexibility along the b -axis or c -axis is rigidified, and the intermolecular or intramolecular motions of organic ligands are restricted, respectively. Synergistically, with dual linker installation, the flexibility is completely rigidified with the restriction of ligand motion, resulting in MOFs with enhanced stability and improved separation ability. Furthermore, in situ observation of the flipping of the phenyl ring and its rigidification process is made by 2 H solid-state NMR. The anisotropic rigidification of flexibility in scu Zr-MOFs guides the directional control of ligand motion for designing stimuli-responsive emitting or efficient separation materials. Metal-organic frameworks (MOFs) with adjustable porosity and tunable functionality have attracted considerable attention, but the directional control of intermolecular and intramolecular motion of TPE-based ligands in the non-interpenetrated flexible MOFs has not yet been studied. Here, the authors report a non-interpenetrated tetraphenylethylene-based MOF with anisotropic flexibility.
Conditional survival and recurrence of remnant gastric cancer after surgical resection: A multi‐institutional study
The present study was designed to evaluate the dynamic survival and recurrence of remnant gastric cancer (RGC) after radical resection and to provide a reference for the development of personalized follow‐up strategies. A total of 298 patients were analyzed for their 3‐year conditional overall survival (COS3), 3‐year conditional disease‐specific survival (CDSS3), corresponding recurrence and pattern changes, and associated risk factors. The 5‐year overall survival (OS) and the 5‐year disease‐specific survival (DSS) of the entire cohort were 41.2% and 45.8%, respectively. The COS3 and CDDS3 of RGC patients who survived for 5 years were 84.0% and 89.8%, respectively. The conditional survival in patients with unfavorable prognostic characteristics showed greater growth over time than in those with favorable prognostic characteristics (eg, COS3, ≥T3: 46.4%‐83.0%, Δ36.6% vs ≤T2: 82.4%‐85.7%, Δ3.3%; P < 0.001). Most recurrences (93.5%) occurred in the first 3 years after surgery. The American Joint Committee on Cancer (AJCC) stage was the only factor that affected recurrence. Time‐dependent Cox regression showed that for both OS and DSS, after 4 years of survival, the common prognostic factors that were initially judged lost their ability to predict survival (P > 0.05). Time‐dependent logistic regression analysis showed that the AJCC stage independently affected recurrence within 2 years after surgery (P < 0.05). A postoperative follow‐up model was developed for RGC patients. In conclusion, patients with RGC usually have a high likelihood of death or recurrence within 3 years after radical surgery. We developed a postoperative follow‐up model for RGC patients of different stages, which may affect the design of future clinical trials. Patients with RGC usually have a high likelihood of death or recurrence within 3 years after radical surgery. We developed a postoperative follow‐up model for RGC patients of different stages.
Obesity-related asthma and its relationship with microbiota
Obesity and asthma are global public health problems. Obesity-related asthma is a special phenotype of asthma with a complex pathogenesis. Its occurrence and development are related to mechanical compression, inflammatory response, metabolic regulation, gene regulation, and vitamin D deficiency. Different treatment strategies used in the process of weight loss have a beneficial impact on asthma. Alterations in gut and airway microbial community structure and their metabolites may also contribute to obesity-related asthma. The role of the Th17/Treg balance in the gut microbiota regulating the immune responses and host metabolism is important. Therapeutic measures associated with the gut microbiota variety may contribute to improving chronic inflammation associated with obesity by regulating the Th17/Treg balance. An early reduction in microbial diversity can predict the development of asthma and lead to allergy through an imbalance of Th2/Th1 responses. Short-chain fatty acids (SCFAs) regulate the differentiation and activation of regulatory T cells, thereby regulating immune homeostasis in the lung to suppress allergic inflammation and weight gain. Therefore, clarifying the microbial mechanism of obesity-related asthma has important guiding significance for clinical treatment. In this review, we used the following terms: “asthma and obesity” and “obesity-related asthma”, combining “phenotype”, “airway inflammation” and “lung function”, and reviewed the characteristics and pathogenesis of obesity-related asthma, the relationship between the gut and airway microbiota and obesity-related asthma, and the current treatment measures for the disease.