Nonlinearity-enhanced continuous microwave detection based on stochastic resonance.

In practical sensing tasks, noise is usually regarded as an obstacle that degrades the sensitivity. Fortunately, stochastic resonance can counterintuitively harness noise to notably enhance the output signal-to-noise ratio in a nonlinear system. Although stochastic resonance has been extensively studied in various disciplines, its potential in realistic sensing tasks remains largely unexplored. Here, we propose and demonstrate a noise-enhanced microwave sensor using a thermal ensemble of interacting Rydberg atoms. Using the strong nonlinearity present in the Rydberg ensembles and leveraging stochastic noises in the system, we demonstrate the stochastic resonance driven by a weak microwave signal (from several microvolts per centimeter to millivolts per centimeter). A substantial enhancement in the detection is achieved, with a sensitivity surpassing that of a heterodyne atomic sensor by 6.6 decibels. Our results offer a promising platform for investigating stochastic resonance in practical sensing scenarios.

Development of a droplet digital PCR assay for the detection of BK polyomavirus.

The objective of this study was to establish a more sensitive and specific diagnostic method for detecting plasma BK polyomavirus (BKPyV) DNA load in patients after renal transplantation using droplet digital polymerase chain reaction (ddPCR) and to validate the methodology. The linear range, lower limit of detection, accuracy, precision, and specificity of the detection system were evaluated by using the WHO BKPyV standard (7.2 log10 IU/mL) as a reference, in accordance with the relevant documents of the Clinical and Laboratory Standards Institute. Plasma samples were collected from 74 renal transplantation patients with urinary BKPyV-DNA levels exceeding 7 log10 copies/mL. Quantitative PCR (qPCR) and ddPCR were performed, and their diagnostic efficacy for BKPyV-DNA in the diagnosis of BK polyomavirus-associated nephropathy was evaluated using a receiver operating characteristic (ROC) curve. The coefficients of variation for the repeated detection of BKPyV standard DNA were 2.55 and 4.71 at concentrations of 6.2 and 3.2 log10 IU/mL, respectively. The linear range was 2.2-6.2 log10 IU/mL, and the lowest detection limit was 100 IU/mL. By utilizing histopathological examination of renal biopsy as the gold standard for BKPyV diagnosis, the area under the ROC curve of 74 post-transplantation plasma samples detected by the ddPCR system was found to be 0.875 (95% CI: 0.797-0.953, P < 0.01). The optimal threshold was 512.86 copies/mL, with a sensitivity of 90.0% and a specificity of 67.6%. In comparison, the area under the ROC curve for qPCR was 0.668 (95% CI: 0.583-0.752, P < 0.01), with an optimal threshold of 11,481.54 copies/mL, a sensitivity of 35.0%, and a specificity of 100.0%. Pairwise comparison (Delong test) of the ROC curves of the two systems showed a significant difference in the area under the curve, with a difference of 0.207 and a P-value <0.01. The BKPyV nucleic acid detection system, based on ddPCR, is appropriate for the regular monitoring of the BK polyomavirus, specifically in plasma samples containing low viral DNA loads while it provides the benefits of both absolute quantification and high sensitivity.IMPORTANCEIt was previously believed that droplet digital polymerase chain reaction had limitations, including high cost, limited throughput, and cumbersome operation, which hindered its widespread application in clinical practice. However, the current fully automated digital PCR platform, combined with streamlined operations, can detect 96 samples at once, and the entire process can be completed within an hour, laying a solid foundation for its extensive use.

Effects of ultrasound on bubble dynamic behavior of flow boiling in microchannel.

Bubble dynamics is paramount in comprehending the heat transfer mechanisms of flow boiling in the microchannel within ultrasonic field, which is regarded as a promising method to confront challenges of thermal management posed by microelectronic devices. Nevertheless, the impact of ultrasound on bubble behaviors and its underlying mechanisms remain largely unexplored. This study first delves into the effect of ultrasonic parameters on bubble dynamic behaviors and associated mechanisms, subsequently further analyzing the forces acting on bubbles through the constructed force model. The findings suggest that although growth force serves as the significant resistance, the primary Bjerknes force dominates the rapid detachment of bubbles. The secondary Bjerknes force results in the bubble only sliding along the bottom wall rather than lifting off. Furthermore, the elevated ultrasonic pressure amplitude resulting from augmenting ultrasonic power induces a substantial increase in the critical detachment diameter and growth rate by 55.49 % and 59.42 %, respectively. The enhanced primary Bjerknes force, attributed to the rise in ultrasonic frequency, leads to a 71.42 % increase in sliding velocity and a 46.45 % reduction in growth time. The positive impacts arising from ultrasonic power and frequency are anticipated to notably enhance the thermal performance of microchannels. Besides, surface tension acts as the resistance and diminishes slightly with an augmentation of the boiling number, resulting in a moderate variation in sliding velocity and growth time.

Effect of natural astaxanthin on sperm quality and mitochondrial function of breeder rooster semen cryopreservation.

Cryopreservation causes higher reactive oxygen species (ROS) concentrations, leading to oxidative stress and lipid peroxidation damaging sperm, and using antioxidants can improve semen quality after freeze-thaw. Natural astaxanthin (ASTA) can be inserted into cell membranes and its antioxidant properties are stronger than other antioxidants. We aimed to investigate the effects of ASTA supplementation in the Beltsville Poultry Semen Extender (BPSE) on post-thaw rooster semen quality and to explore the potential mechanism of rooster semen quality change. The qualifying semen ejaculates collected from 30 adult male Jinghong No. 1 laying hen breeder roosters (65 wk old) were pooled, divided into four aliquots, and diluted with BPSE having different levels of ASTA (0, 0.5, 1, or 2 µg/mL). Treated semen was cryopreserved and kept in liquid nitrogen. The entire experiment was replicated three times independently. Sperm viability, motility, curvilinear velocity, amplitude of lateral head displacement, straightness, plasma membrane integrity, and acrosome integrity were observed to be highest (P < 0.05) with 1 µg/mL ASTA at freeze-thawing. Higher (P < 0.05) antioxidant enzyme (CAT-like, SOD) activities and free radical (·OH, O2.-) scavenging ability, less ROS and malondialdehyde (MDA) concentrations were recorded with the addition of appropriate concentrations of ASTA compared to control. In addition, the levels of mitochondrial membrane potential (MMP), adenosine triphosphate (ATP), and lactate dehydrogenase (LDH) in the 1 µg/mL ASTA group improved compared to the control group, and decreased the amount of AIF protein level but increased the Bcl-2 protein level (P < 0:05). Collectively, these results demonstrate that adding ASTA in the BPSE promoted rooster freeze-thaw sperm quality, which may be related to reducing ROS levels, protecting the antioxidant defense system, preventing lipid peroxidation, improving mitochondrial structural and functional integrity, and inhibiting sperm apoptosis.

Liver transplantation following two conversions in a patient with huge hepatocellular carcinoma and portal vein invasion: A case report.

BACKGROUND: Surgical resection and liver transplantation (LT) are the most effective curative options for hepatocellular carcinoma (HCC). However, few patients with huge HCC (> 10 cm in diameter), especially those with portal vein tumor thrombus (PVTT), can receive these treatments. Selective internal radiation therapy (SIRT) can be used as a conversion therapy for them because it has the dual benefit of shrinking tumors and increasing residual hepatic volume. However, in patients with huge HCC, high lung absorbed dose often prevents them from receiving SIRT. CASE SUMMARY: A 35-year-old man was admitted because of emaciation and pain in the hepatic region for about 1 month. The computed tomography scan showed a 20.2 cm × 19.8 cm tumor located in the right lobe-left medial lobes with right portal vein and right hepatic vein invasion. After the pathological type of HCC was confirmed by biopsy, two conversions were presented. The first one was drug-eluting bead transarterial chemoembolization plus hepatic arterial infusion chemotherapy and lenvatinib and sintilimab, converted to SIRT, and the second one was sequential SIRT with continued systemic treatment. The tumor size significantly decreased from 20.2 cm × 19.8 cm to 16.2 cm × 13.8 cm, then sequentially to 7.8 cm × 6.8 cm. In the meantime, the ratio of spared volume to total liver volume increased gradually from 34.4% to 55.7%, then to 62.9%. Furthermore, there was visualization of the portal vein, indicating regression of the tumor thrombus. Finally, owing to the new tumor in the left lateral lobe, the patient underwent LT instead of resection without major complications. CONCLUSION: Patients with inoperable huge HCC with PVTT could be converted to SIRT first and accept surgery sequentially.

Bifunctional MoNi4/nickel foam electro-catalyst for ultra-efficient oxidation of high-concentration 5-hydroxymethylfurfural and HER.

The electro-catalytic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) provides an attractive route to produce 2, 5-furandicarboxylic acid (FDCA) as a substitute for terephthalic acid used in the plastics industry. Herein, we prepared MoNi4 alloy on nickel foam (NF) using a simple hydrothermal method followed by hydrogen reduction. Applied MoNi4/NF as the bifunctional electrodes for the electro-catalytic HMF oxidation reaction (HMFOR) and HER, 98.7% FDCA yield and 97.3% Faraday efficiency (FE) can be achieved even with HMF concentration as high as 200 mM. Notably, no obvious deactivation was observed after ten consecutive cycles. In-situ Raman, XANES and EXAFS results show that the nickel species of MoNi4/NF is first oxidized to Ni3+ species under the applied voltage, and after undergoing the electro-catalytic HMFOR, then reduced to Ni2-δ state (with a valence between 0 and +2) due to the electron-donating effect from Mo. MoNi4/NF with more than one electron transfer between Ni3+ and Ni2-δ during the HMFOR enables it to have excellent electro-catalytic oxidation ability toward HMFOR.

Estimation of skin surface roughness in vivo based on optical coherence tomography combined with convolutional neural network.

The texture of human skin is influenced by both external and internal factors, and changes in wrinkles can most directly reflect the state of the skin. Skin roughness is primarily used to quantify the wrinkle features of the skin. Therefore, effective and accurate quantification of skin roughness is essential in skincare, medical treatment, and product development. This study proposes a method for estimating the skin surface roughness using optical coherence tomography (OCT) combined with a convolutional neural network (CNN). The proposed algorithm is validated through a roughness standard plate. Then, the experimental results revealed that skin surface roughness including arithmetic mean roughness and depth of roughness depends on age and gender. The advantage of the proposed method based on OCT is that it can reduce the effect of the skin surface's natural curvature on roughness. In addition, the method is combined with the epidermal thickness and dermal attenuation coefficient for multi-parameter characterization of skin features. It could be seen as a potential tool for understanding the aging process and developing strategies to maintain and enhance skin health and appearance.

Temporomandibular joint CBCT image segmentation via multi-view ensemble learning network.

Accurate segmentation of the temporomandibular joint (TMJ) from cone beam CT (CBCT) images holds significant clinical value for diagnosing temporomandibular joint osteoarthrosis (TMJOA) and related conditions. Convolutional neural network-based medical image segmentation methods have achieved state-of-the-art performance in various segmentation tasks. However, 3D medical images segmentation requires substantial global context and rich spatial semantic information, demanding much more GPU memory and computational resources. To address these challenges in 3D medical image segmentation, we propose a novel network- the MVEL-Net (Multi-view Ensemble Learning Network) for TMJ CBCT image segmentation. By resampling images along three dimensions, we generate multiple weak learners with different spatial semantic information. A subsequent strong learning network effectively integrates the outputs from these weak learners to achieve more accurate segmentation results. We evaluated our network model using a clinical dataset comprising 88 subjects with TMJ CBCT images. The average Dice similarity coefficient (DSC) was 0.9817 ± 0.0049, the average surface distance was 0.0540 ± 0.0179 mm, and the 95% Hausdorff distance was 0.1743 ± 0.0550 mm. Our proposed MVEL-Net demonstrates excellent segmentation performance on TMJ from CBCT images, while using fewer GPU memory resources compared to other 3D networks. The effectiveness of this method in capturing spatial context could be leveraged for tasks like organ segmentation from volumetric scans. This may facilitate wider adoption of AI-based solutions for automated analysis of 3D medical images.

Central nervous system crystal-storing histiocytosis: A case report and literature review.

BACKGROUND: Crystal-storing histiocytosis (CSH) is a rare form of histiocytosis with intralysosomal accumulations of immunoglobulins or paraproteins that aggregate as crystals. Central nervous system (CNS) involvement of CSH is uncommon but should be considered in cases of persistent parenchymal enhancement on neuroimaging. METHODS: We describe one local case of CNS CSH and 10 additional cases identified by literature review. RESULTS: Among 11 CSH patients, lesions involved either the dura (2/11) or brain parenchyma (9/11). Two cases had leptomeningeal enhancement. One case had spinal cord involvement. Two cases were associated with marginal zone lymphoma; one case was associated with an immunoglobulin A-plasma cell dyscrasia. Eight of 11 cases had outcome data available: 7/8 cases had clinical and/or radiological improvement and 1/8 had radiological stability. CONCLUSIONS: Central nervous system involvement of CSH is rare. Potential cases should be comprehensively evaluated for lymphoma or myeloma with positron emission tomography/computed tomography (CT) of the body or alternatively, CT of the chest, abdomen, pelvis and nuclear bone scan, bone marrow biopsy, serum protein electrophoresis, and cerebrospinal fluid protein electrophoresis. Treatment is targeted toward the underlying malignancy.

Lignin-polyurea/luffa seed oil microcapsules for anti-mold modification of bamboo.

Bamboo has shown enormous potential across construction, furniture, and other fields as an efficient replacement for wood. However, during its application, bamboo is susceptible to microbial infection and mildew, resulting in damage to the internal structure that adversely affects its mechanical properties. In the present study, lignin-based polyurea resin/luffa seed oil (LSO) microcapsules (LSO@LPMC) were prepared by interfacial polymerization method. These microcapsules were then applied on bamboo for mold-prevention modification through vacuum impregnation and epoxy resin-microcapsule coating, which significantly improved the mold resistance of bamboo. Microcapsules could alleviate the excessive release of carbon and nitrogen sources within the LSO. The prepared LSO@LPMC exhibited a high encapsulation efficiency (90.76 %) and excellent sustained release performance. LSO benefited from active functional groups including aldehyde and carboxyl groups, thus the enzymes and proteins on the cell surface could be easily deactivated, ultimately leading to microbial lysis and death. The bamboo samples modified with microcapsule coating exhibited excellent antifungal activity and mechanical properties. The processing technology of these microcapsules provides a theoretical reference and practical foundation for the promotion and application of LSO in the field of anti-mold modification of bamboo.

Pretreatment of artesunate promoted hepatocyte proliferation by activating the PI3K/Akt/mTOR signaling pathway in mice.

PURPOSE: Artesunate (ART) has been implicated in regulating the many processes of liver injury, but its roles in liver regeneration still need to be illustrated. METHODS: In the present study, ART was used to pretreat hepatocyte cell line NCTC1469 to study the effect of ART on hepatocyte proliferation in vitro. Furthermore, the potency of ART as a regimen to promote liver regeneration and restore liver function was evaluated following partial hepatectomy (PH) on C57BL/6 mice. RESULTS: ART concentration-dependently promoted hepatocyte proliferation and reduced apoptosis. Cell cycle and Ki-67 immunohistochemical analyses demonstrated that ART supplementation promoted the proliferation of hepatocytes and accelerated liver regeneration. Our results provided evidence that ART improved liver function in a dose-dependent manner, as indicated by decreased serum alanine aminotransferase, aspartate aminotransferase, and increased albumin, and hepatocyte growth factor levels in PH mice. Meanwhile, ART promoted the PI3K/Akt/mTOR signaling in NCTC1469 cells and liver tissue of PH mice. In addition, PI3K inhibitor LY294002 blocked the promotion effect of ART on hepatocyte proliferation and cell cycle progression. CONCLUSION: ART promoted hepatocyte proliferation via activation of the PI3K/Akt/mTOR pathway, which was beneficial to liver regeneration of PH-induced liver injury.

Buckling cluster-based H-bonded icosahedral capsules and their propagation to a robust zeolite-like supramolecular framework.

Hydrogen-bonded assembly of multiple components into well-defined icosahedral capsules akin to virus capsids has been elusive. In parallel, constructing robust zeolitic-like cluster-based supramolecular frameworks (CSFs) without any coordination covalent bonding linkages remains challenging. Herein, we report a cluster-based pseudoicosahedral H-bonded capsule Cu60, which is buckled by the self-organization of judiciously designed constituent copper clusters and anions. The spontaneous formation of the icosahedron in the solid state takes advantage of 48 charge-assisted CH···F hydrogen bonds between cationic clusters and anions (PF6-), and is highly sensitive to the surface protective ligands on the clusters with minor structural modification inhibiting its formation. Most excitingly, an extended three-periodic robust zeolitic-like CSF, is constructed by edge-sharing the resultant icosahedrons. The perpendicular channels of the CSF feature unusual 3D orthogonal double-helical patterns. The CSF material not only keeps its single-crystal character in the desolvated phase, but also exhibits excellent chemical and thermal stabilities as well as long-lived phosphorescence emission.

The Interfacial Ni/Fe─O─Y Bonds Contribute to High-Efficiency Water Splitting.

Developing economical and efficient electrocatalysts is critical for hydrogen energy industrialization through water electrolysis. Herein, a novel dual-site synergistic NiFe/Y2O3 hybrid with abundant interfacial Ni/Fe─O─Y bonds is designed by density functional theory (DFT) simulations. In situ Raman spectra combined with DFT calculations reveal that the interfacial Ni/Fe─O─Y units greatly promote H2O dissociation and optimize the adsorption of both H* and oxygen species, achieving excellent activity and durability for hydrogen evolution reaction. As expected, NiFe/Y2O3 exhibits a low overpotential of 27 mV at 10 mA cm-2 and robust stability of over 200 h at 1000 mA cm-2, and also outstanding water splitting performance with a low cell voltage of 1.64 V at 100 mA cm-2, showing significant potential for real-world applications.

Tumor therapy utilizing dual-responsive nanoparticles: A multifaceted approach integrating calcium-overload and PTT/CDT/chemotherapy.

The advancement of rational nano drug delivery systems offers robust tools for achieving synergistic therapeutic outcomes in tumor treatment. In this study, we present the development of pH and near-infrared laser dual-responsive nanoparticles (DOX-CuS@CaCO3@PL-PEG, DCCP NPs) based on calcium carbonate, utilizing a one-pot gas diffusion reaction. These nanoparticles enable combined photothermal therapy (PTT), chemodynamic therapy (CDT), chemotherapy, and Ca2+-overloading synergistic therapy. Doxorubicin (DOX) and copper sulfide (CuS) NPs were co-loaded in CaCO3, followed by PEG surface functionalization. The presence of PEG enhanced the stability of DCCP NPs in aqueous environments. Controlled release of DOX, CuS NPs, and Ca2+ occurs specifically in the acidic tumor microenvironment. Released DOX enhances chemotherapy efficiency, while CuS NPs, upon laser irradiation, induce thermal damage, promoting further drug release and cellular uptake. Additionally, CuS NPs in our system consume excess GSH and generate toxic hydroxyl radicals (·OH) through a Fenton-like reaction, contributing to CDT. These radicals not only directly eliminate tumor cells but also disrupt mitochondrial Ca2+ buffering capacity. Furthermore, Ca2+ released from CaCO3 induces Ca2+-overloading, intensifying mitochondrial disruption and oxidative damage. The synergistic combination of PTT, CDT, chemotherapy, and Ca2+-overloading showcases significant therapeutic potential, indicating broad applications in tumor therapy. This multifaceted approach holds promise for advancing the field of tumor therapeutics.

Overexpression of PRDM16 attenuates acute kidney injury progression: genetic and pharmacological approaches.

Acute kidney injury (AKI) presents as a condition marked by a sudden and rapid decrease in kidney function over a short timeframe, resulting from diverse causes. As a transcription factor, PR domain-containing 16 (PRDM16), has recently been implicated in brown fat biogenesis and heart diseases. Our recent works indicated that PRDM16 could suppress the occurrence of renal interstitial fibrosis in diabetic kidney disorder. Nonetheless, the effect and regulatory mechanism of PRDM16 in AKI remain elusive. Our study demonstrated that PRDM16 inhibited apoptosis induced by ischemic/reperfusion (I/R) in BUMPT (Boston University mouse kidney proximal tubular) cells and HK-2(Human Kidney-2) cells. Mechanistically, PRDM16 not only bound to the promoter region of S100 Calcium Binding Protein A6 (S100A6)and upregulated its expression but also interacted with its amino acids 945-949, 957-960, and 981-984 to suppress the p38MAPK and JNK axes via inhibition of PKC-η activity and mitochondrial reactive oxygen species (ROS) production. Furthermore, cisplatin- and I/R-stimulated AKI progression were ameliorated in PRDM16 proximal-tubule-specific knockin mice, whereas exacerbated in PRDM16 knockout proximal-tubule-specific mice). Moreover, we observed that formononetin ameliorated I/R- and cisplatin-triggered AKI progression in mice. Taken together, these findings reveal a novel self-protective mechanism in AKI, whereby PRDM16 regulates the S100A6/PKC-η/ROS/p38MAPK and JNK pathways to inhibit AKI progression.

Pancreatic agenesis and altered m6A methylation in the pancreas of PDX1-mutant cynomolgus macaques.

As an essential transcriptional activator, PDX1 plays a crucial role in pancreatic development and ß-cell function. Mutations in the PDX1 gene may lead to type 4 maturity-onset diabetes of the young (MODY4) and neonatal diabetes mellitus. However, the precise mechanisms underlying MODY4 remain elusive due to the paucity of clinical samples and pronounced differences in pancreatic architecture and genomic composition between humans and existing animal models. In this study, three PDX1-mutant cynomolgus macaques were generated using CRISPR/Cas9 technology, all of which succumbed shortly postpartum, exhibiting pancreatic agenesis. Notably, one tri-allelic PDX1-mutant cynomolgus macaque (designated as M4) developed a pancreas, whereas the two mono-allelic PDX1-mutant cynomolgus macaques displayed no anatomical evidence of pancreatic formation. RNA sequencing of the M4 pancreas revealed substantial molecular changes in both endocrine and exocrine functions, indicating developmental delay and PDX1 haploinsufficiency. A marked change in m6A methylation was identified in the M4 pancreas, confirmed through cultured PDX1-mutant islet organoids. Notably, overexpression of the m6A modulator METTL3 restored function in heterozygous PDX1-mutant islet organoids. This study highlights a novel role of m6A methylation modification in the progression of MODY4 and provides valuable molecular insights for preclinical research.

Application of coal-based solid waste artificial soil in the restoration of saline alkali land-taking the saline alkali land restoration of the Emao River in China as an example.

In this paper, coal-based solid waste, including fly ash, desulfurization gypsum, furnace bottom slag, and coal washing sludge in the ratio of 3:2:3:2 with a total of 200 tons/0.07 hm2, were used as the specialized main material for restoring the saline alkali land of Emao River in Huairen of China. The remediation effect and safety of solid waste artificial soil were evaluated by testing the soil samples before and after the remediation. The results showed that the pH value of the soil after remediation decreased from 9.98 to 7.60, which was close to the neutral value and suitable for crop growth. The total amount of water-soluble salts decreased from 8.30 g kg-1 to 4.80 g kg-1 with a decrease of 42.2 %. The organic matter increased from 6.5 g kg-1 to 39.1 g kg-1 with a 5-fold increase. Compared to the original soil, the heavy metal content in the restored soil did not increased, but instead decreased, indicating that the restoration technology was feasible and meets environmental requirements. Corn planting experiment results showed that corn's emergence rate in the original saline alkali soil was extremely low (about 1 %), while in the restored soil reached over 99 %. The average yield of corn in restoration field was 16.56 % higher than the average local yield level. The residual content of heavy metals and organic toxic substances in corn and potatoes grown on restored soil were analyzed, and the results showed that the detected heavy metal content was far lower than the standard values, and the residual organic toxic substances were basically not detected, indicating that the agricultural fruits grown on restored soil were safe, harmless, and edible. This approach could achieve large-scale consumption of coal-based solid waste, increase arable land, and reduce the cost of restoring saline alkali land.

[Characteristics of Vegetation and Soil of Degraded Grasslands and Their Relationships in Xizang].

To investigate the characteristics of grassland degradation on a regional scale in Xizang, data on grassland degradation from the second grassland survey of Xizang and 12 vegetation and soil indicators from the National Tibetan Plateau Data Center were collected. Using ArcMap, 10 000 random sample points were selected on raster data （excluding non-grassland, desertification, and salinization data, leaving 7 949 valid sample points）. The multi-value extraction to-point method was applied to extract degradation and indicator data for each sample point. The characteristics of degraded grassland vegetation and soil and their relationships were analyzed in Xizang. Moreover, random forest modeling was conducted to predict the trend of grassland ecosystem changes. The results indicated that： ① The grasslands in Xizang were primarily composed of alpine steppe and alpine meadow types, accounting for 45.83% and 41.15% of the valid sample points, respectively. ② With the intensification of grassland degradation, the number of steppe-type species among the 17 grassland types gradually decreased, and the proportion of steppe dominated by species such as Stipa purpurea and Carex moorcroftii decreased, whereas the proportion of miscellaneous grasses and Dasiphora fruticosa increased. ③ As the degree of degradation increased, vegetation indicators generally showed a declining trend, with soil total nitrogen, total phosphorus, total potassium, and organic carbon decreasing, whereas soil pH and bulk density increased, and soil moisture content was not significant. ④ A positive correlation exists between soil moisture content, total nitrogen, total phosphorus, total potassium, organic carbon, vegetation cover, net primary productivity of vegetation, normalized difference vegetation index, aboveground biomass, and habitat quality. However, there was a negative correlation between pH and soil bulk density, and the correlation coefficients among various indicators decreased with the intensification of degradation. ⑤ The random forest simulation results showed that during the degradation process, the contribution rates of soil bulk density and habitat quality both exceeded 12%, with the model prediction accuracy reaching 78%. The study revealed that grassland degradation in Xizang was closely related to soil bulk density and habitat quality, indicating that higher soil bulk density or lower habitat quality may correspond to more severe grassland degradation. This provides a scientific basis for future grassland conservation and management.

Patterns of nitrate load variability under surface water-groundwater interactions in agriculturally intensive valley watersheds.

Nitrate pollution is a significant environmental issue closely related to human activities, complicated hydrological interactions and nitrate fate in the valley watershed strongly affects nitrate load in hydrological systems. In this study, a nitrate reactive transport model by coupling SWAT-MODFLOW-RT3D between surface water and groundwater interactions at the watershed scale was developed, which was used to reproduce the interaction between surface water and groundwater in the basin from 2016 to 2019 and to reveal the nitrogen transformation process and the evolving trend of nitrate load within the hydrological system of the valley watershed. The results showed that the basin exhibited groundwater recharge to surface water in 2016-2019, particularly in the northwestern and northeastern mountainous regions of the valley watershed and the southern Beishan Reservoir vicinity. Groundwater recharge to surface water declined by 20.17 % from 2016 to 2019 due to precipitation. Nitrate loads in the hydrologic system of the watershed are primarily derived from human activities (including fertilizer application from agricultural activities and residential wastewater discharges) and the nitrogen cycle. Nitrate loads in surface water declined 16.05 % from 2016 to 2019. Nitrate levels are higher in agricultural farming and residential areas on the eastern and northern sides of the watershed. Additionally, hydrological interactions are usually accompanied by material accumulation and environmental changes. Nitrate levels tend to rise with converging water flows, a process that becomes more pronounced during precipitation events and cropping seasons in agriculturally intensive valley watersheds. However, environmental changes alter nitrogen transformation processes. Nitrogen fixation, nitrification, and ammonification intensify nitrogen inputs during river pooling, enhancing nitrogen cycling fluxes and elevating nitrate loads. These processes are further enhanced during groundwater recharge to surface water, leading to evaluated nitrate load. Enhanced denitrification, dissimilatory nitrate reduction to ammonium (DNRA), anaerobic ammonia oxidation, and assimilation promote the nitrogen export from the system and reduce the nitrate load during surface water recharge to groundwater.