Large tropical rivers remain poorly characterized relative to the widely studied large temperate rivers. The Usumacinta River in southern Mexico is North America's most extensive tropical fluvial system. Increasing anthropogenic pressures in the Usumacinta basin (e.g., agriculture, cattle raising, forest fires, deforestation, and urban development) threaten ecosystem health. However, our understanding of the characteristics of the basins, especially on metal(loid) remains limited. To address this, we investigated metal(loid)s in sediments along the Usumacinta River. Thirty-four surface sediments from 17 stations within the Usumacinta's mainstream and principal tributaries were sampled for metal(loid) analysis during the rainy and dry seasons. The sediment grain size and organic matter were analyzed and the concentrations of aluminium (Al), arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), magnesium (Mg), manganese (Mn), nickel (Ni), silver (Ag), selenium (Se), strontium (Sr), antimony (Sb) , thallium (Tl), tin (Sn), vanadium (V), and zinc (Zn) were quantified by Inductively Coupled Plasma Mass Spectrometry. The indices enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), and pollution load index (PLI) were used to assess the health status of metal(loid)s in the surface sediments of the middle and lower basins of the Usumacinta River. Metal(loid) concentrations in Usumacinta River sediments fall within or below the range reported for tropical rivers with comparable geological settings, suggesting limited anthropogenic metal contributions. While the EFs of Ag, Ba, Be, Cu, Sr, Tl, and V was <1.5, suggests that they are linked to weathering, those of As, Co, Mn, Pb, Sb, Sn, and Zn were 1.0 < EF < 10 in various cases, Se was consistently >10 in all stations, seasons, and in the middle and lower basins, evidencing that sediments are Se-enriched. Using four pollution indexes, we found that the sediments of the Usumacinta River are either uncontaminated or moderately contaminated (enriched) with As, Cd, Cu, Cr, Ni, Pb, Sb, V, and Zn. They are consistently enriched in Se from natural sources across both basins and seasons, but this enrichment may be modulated by an anthropogenic signal. In general, results showed that concentrations were higher during the dry than during the rainy season, and that concentrations in the lower basin were higher than in the middle basin. EFs of most elements and stations were <1.5, likely indicating that these metal(loid)s are derived from natural weathering; only the EFs of Se were >10 in all stations and seasons across both basins, suggesting sediment enrichment. This enrichment can be linked specifically to the Cretaceous marine sedimentary rocks or the occurrence of seleniferous in the Sierra de los Cuchumatanes. However, an additional contribution related to phosphate-based agricultural inputs may be added. The patterns thus indicate a superposition of a regional geogenic baseline and a seasonally modulated anthropogenic signal.

Recent exploration has achieved significant breakthroughs in dolomite reservoirs within the third member of the Middle Triassic Leikoupo Formation (T2l3) in the northwestern Sichuan Basin. However, limited understanding persists about the sources of dolomitizing fluids, dolomite genesis, and diagenetic-porosity evolution, hindering research on high-quality reservoir formation. This study integrates petrographic, geochemical (C-O-Sr isotopes, major and trace elements, rare earth elements), and cathodoluminescence analyses to clarify the origins of diagenetic fluids and formation mechanisms of various dolomite types in T2l3 and establishes a diagenetic-porosity evolution model for high-quality reservoirs. The results indicate that (1) the T2l3 dolostones in the northwestern Sichuan Basin can be classified into four types: Mud-microcrystalline dolostone (D1), algal dolostone (D2), grain-dominated dolostone (D3), and crystalline dolostone (D4). (2) The δ13C values and 87Sr/86Sr ratios of the four dolostone types generally fall within the ranges of coeval seawater, and their Z values are approximately 130. Their rare-earth element distribution patterns are also broadly comparable to those of contemporaneous seawater, showing relative enrichment in light rare-earth elements and depletion in heavy rare-earth elements. These characteristics suggest that the dolomitizing fluids of the four dolostone types were derived predominantly from highly saline, concentrated coeval seawater. (3) D1 formed at temperatures of approximately 33-41 °C. Its relatively high Sr, Na, and Fe contents and δ18O values, together with relatively low Mn contents and dolomite ordering, suggest that D1 was formed by evaporative dolomitization in a near-surface, oxidizing environment during the penecontemporaneous stage. D2 and D3 formed at approximately 43-56 °C and are characterized by moderate dolomite ordering, negatively shifted δ18O values, and generally low Fe and Mn contents. These features indicate that they were formed mainly through reflux dolomitization under shallow-burial conditions. D4 formed at approximately 61-76 °C. Its elevated Fe and Mn contents and higher degree of dolomite ordering are consistent with increasing burial depth, whereas its relatively low Sr and Na contents and δ18O values collectively suggest formation or substantial modification through burial dolomitization under intermediate- to deep-burial conditions. (4) The diagenetic-pore evolution of the high-quality reservoirs was controlled by multiple constructive and destructive diagenetic processes. Penecontemporaneous dissolution generated the initial pore system, whereas cementation and compaction during shallow burial caused substantial reservoir densification. During intermediate to deep burial, burial-related dissolution represented the principal constructive process responsible for secondary pore regeneration. The ultimate development of high-quality reservoirs depended on late-stage dissolution exceeding the destructive effects of earlier diagenesis, together with the pore-preserving effect of hydrocarbon charging. These findings provide new insights into the genesis of dolostones and the formation mechanisms of high-quality carbonate reservoirs and offer a geological basis for future hydrocarbon exploration and development in the T2l3 of the northwestern Sichuan Basin.

Interfacial thermalized and non-thermalized charge transfer between CsPbBr3 nanocomposites and carbon dots is studied using steady-state spectroscopy. Two types of carbon dots (CDs) were synthesized and characterized: one derived from amine-functionalized pyrene, and the other prepared using citric acid and ortho-phenylenediamine as precursor materials. Fourier transform infrared and X-ray photoelectron spectroscopy measurements have shown that the carbon dot synthesized from pyrene is amine-rich, whereas the carbon dot synthesized from citric acid is carboxylic acid-rich. The PL of CsPbBr3 nanocomposites is quenched by both CDs, indicating charge transfer between perovskite nanocomposites and the carbon dots. Transient absorption measurements have shown ultrafast charge transfer from perovskite nanocomposites to bound CDs from non-thermalized and thermalized excitonic states. We observed non-thermalized charge transfer from CsPbBr3 to CDs, with nearly 44% hot-hole transfer from CsPbBr3 to CD- Pyr and 25% hot-electron transfer from CsPbBr3 to CD- Cyan. The charge transfer from thermalized states is monitored from the bleach recovery kinetics of CsPbBr3 with CDs, and the rates of charge transfer fall in the normal and inverted regions of the Marcus bell-shaped curve.

The flexibility of generative artificial intelligence (AI), and specifically large language models (LLMs), holds promise to transform healthcare by offering new tools to improve patient care and enhance clinician efficiency. However, this flexibility introduces new challenges, as LLM applications might inadvertently be used in ways that do not align with the intended purpose of the manufacturer, raising patient safety concerns and liability issues. We have identified a regulatory gap whereby LLM applications that could be repurposed, malfunction or be inadvertently misused for medical purposes fall outside the scope of the Medical Device Regulation (MDR) because they lack a medical intended purpose, and outside meaningful AI Act safety obligations because they do not qualify as high-risk systems, yet still present patient safety risks without adequate regulatory guidance. In this manuscript, we aim to address this regulatory gap for LLM applications in healthcare by identifying these ambiguous grey-area applications and providing four recommendations-validation, mitigation, compliance and alignment-focused on prevention and risk mitigation rather than reclassification as medical devices. These recommendations are intended to advance the responsible implementation of LLM applications in healthcare while ensuring patient safety.