Nitrogen Density Research Articles

Computational prediction of novel two-dimensional tungsten nitride superconductors

Transition metal nitrides are well-known 3D superconductor materials. However, there is a lack of knowledge related to their two-dimensional (2D) counterparts, which have several potential technological applications. In this work, we predict, using an evolutionary algorithm coupled with a first-principles approach, a set of novel 2D superconductive structures based on tungsten nitride. Through a systematic process including energetic and dynamical analysis, three thermodynamically stable compositions along with metastable compounds were studied in the following stoichiometries: W4N2, W2N2, and W2N3. Their superconductive temperature (Tc) values, estimated by means of the Eliashberg superconductive theory and the McMillan equation, range from 2.3 to 21.6 K, where the highestTcvalue corresponds to a W2N3metastable hexagonal system. A systematic analysis of the structural, electronic, vibrational and electron-phonon (e-ph) properties, allowed us to recognize the variables that modulate theTcin theses systems. The superconductive behavior is strongly affected by changes in the nitrogen density of states at Fermi level, the e-ph coupling constant and the lattice symmetry. The present results aim to encourage further theoretical and experimental efforts over non fully explored superconductors in two dimensions.

Optimum Nitrogen and Density Allocation for Trade−Off Between Yield and Lodging Resistance of Winter Wheat

Increasing nitrogen and planting density can enhance crop yield, but it can reduce lodging resistance due to decreased lignin content. There is an urgent need to find feasible measures to balance these conflicting factors. We conducted a two-year field experiment in Tai’an, Shandong Province, China, evaluated SN23 (lodging resistant) and SN16 (lodging sensitive), under three nitrogen applications (120 kg/ha, N1; 240 kg/ha, N2; 360 kg/ha, N3) and four planting densities (75 plants/m2, D1; 225 plants/m2, D2; 375 plants/m2, D3; 525 plants/m2, D4), with N2D2 as the control, and measured lodging resistance related indexes and yield. N2D3 (SN23) increased internode length by 0.40 cm, reduced fresh weight by 0.09 g, resulting in a bending moment reduction of 0.39 g/cm. Lignin, cellulose, and hemicellulose decreased by 18.27, 16.48, and 16.22 mg/g DW, while S and G lignin subunits decreased by 118.09 and 127.34 μg/g DW, and H subunit increased by 23.59 μg/g DW. Eventually, the breaking strength was reduced by 1.74 g/cm resulting in a reduction of 0.09 in the lodging resistance index. The yield reached 10.17 t/ha due to an increase in spike number by 100.33 plants/m2, achieving an optimal balance between yield and lodging resistance in this experiment. This study provides a viable solution for balancing lodging resistance and yield in winter wheat.

Alteration of nitrogen sink and emission by vegetation distribution in a wetland with significant change in water level.

In wetlands, hydrological conditions drive plant community distribution, forming vegetation zones with plant species and material cycling. This mediates nitrogen migration and N2O emissions within wetlands. Five vegetation zones in a large wetland were studied during flooding and drought periods. Zones including mud flat, nymphoides, phalaris, carex, and reeds, distributed sequentially with increasing water level change rate. Carbon and nitrogen densities were higher during drought period. When sediments alternated between source and sink roles annually, N2O emissions varied significantly with zones and water levels. Emission flux decreased with higher C:N ratio in sediments, approximating a threshold at 0.23μgm-2 h-1 when C:N ratio exceeded 25. Denitrifying nirS and nirK genes and anammox hzsB gene varied significantly with water level, most prominently in mud flat and nymphoides zones. Plant distribution under hydrological conditions alters soil stoichiometric ratio, influencing N2O emissions and microbial communities across vegetation zones. Therefore, in freshwater wetlands, hydraulic regulation and reduction in prolonged flooding would be an effective strategy for mitigation of greenhouse gas emissions.

Modeling the influence of changes in neutral atmosphere parameters on ionospheric electron density

Based on the modified numerical model of the ionosphere and plasmasphere developed at ISTP SB RAS, we calculated the height profiles of the electron density Ne for the quiet and disturbed thermospheric conditions of January 25, 2009 at the geographical location of Irkutsk (52.4N, 104.3E). The disturbed conditions were simulated by varying the neutral temperature T in the thermosphere. At heights below 180 km and above 250 km, with an increase/decrease in T, an increase/decrease in Ne occurs. At 180–250 km, the opposite pattern is seen: an increase/decrease in T causes a decrease/increase in Ne. The opposite pattern of the change in the Ne profile is associated with the influence of the atomic oxygen to molecular nitrogen density ratio [O]/[N2] at heights of the F-region. Quantitative estimates of the change in Ne at different heights with changes in the neutral temperature were obtained. It has been established that a change in T by 1 K leads to a change in Ne by 0.2–0.3%. The modeling results were compared with observations of the peak electron density NmF2 obtained with the Irkutsk ionosonde during the sudden stratospheric warming in January 2009.

Increasing Planting Density with Reduced Topdressing Nitrogen Inputs Increased Nitrogen Use Efficiency and Improved Grain Quality While Maintaining Yields in Weak-Gluten Wheat

Increasing nitrogen fertilizer will increase wheat grain yield and grain quality at the same time, but the goal of high quality and stable yield in weak-gluten wheat production is to reduce grain protein content and increase grain yield. Our research goal is to reduce nitrogen input while increasing planting density to maintain high quality and stable yield. Field studies were conducted during two successive seasons using a widely planted cultivar, Yangmai 15. We studied the effects of reduced nitrogen topdressing and increased planting density on yield, quality and nitrogen agronomic efficiency. The field experiment was conducted with four nitrogen (N) levels for topdressing at jointing stage: 37.8 (N1), 43.2 (N2), 48.6 (N3) and 54 kg N ha−1 (N4). Moreover, there were three planting densities: 180, 240 and 300 × 104 plants ha−1 (D1, D2 and D3, respectively). When the amount of nitrogen topdressing was reduced, the number of tillers and spikes in each growth period of wheat decreased significantly, and the yield increased first and then decreased, with the highest yield at the level of 48.6 kg N ha−1. When the planting density was increased, the number of tillers and spikes in each growth period of wheat increased significantly, the yield increased significantly, and the yield was the highest at the level of 180 × 104 plants ha−1. Under the same density level, the flag leaf chlorophyll content, leaf area index, nitrogen production efficiency and nitrogen use efficiency decreased with a decrease in the nitrogen application rate. Under the same nitrogen topdressing amount, the nitrogen fertilizer production efficiency and nitrogen fertilizer utilization efficiency increased with the increase in density. The relative chlorophyll content, leaf area index, nitrogen partial factor productivity, nitrogen use efficiency, grain accumulation, grain distribution ratio and grain yield of wheat were the highest under the treatment of a planting density of 300 × 104 plants ha−1 and nitrogen topdressing amount of 48.6 kg N ha−1. The combined decrease in nitrogen recovery and increase in planting density decreased protein content, sedimentation value and wet gluten content. Increasing density significantly improved dry matter accumulation in the population, partially compensating for the yield loss due to nitrogen reduction by increasing the effective number of spikes, thereby further improving grain quality and nitrogen use efficiency. Therefore, agronomic approaches combining low nitrogen and high planting densities may be effective in simultaneously increasing grain yield and nitrogen use efficiency and stabilizing grain processing quality in weakly reinforced wheat.

Permangant-oxidizable carbon as a marker of soil quality in agrolandscapes

Different laboratory methods of soil quality assessment are considered by the example of soils of the North-Pre-Caucasian province. The article presents a detailed protocol for quantitative determination of Permanganate oxidizable carbon (POXC) fraction using 0.2 M potassium permanganate solution. The data are presented for chernozem type soils of Rostov region belonging to different agroecological groups. Samples of ordinary chernozems (Haplic Chernozems) and meadow-chernozems (Gleyic Chernozems) soils of agrolandscapes were used. Data from non-tilled plots were used to estimate background parameters. Correlation POXC with fraction of bichromate-oxidizable carbon, light fraction (LF< 1.6 g/cm3 ) and waterhydrolysable fractions were estimated. It was found that the content of POXC fraction varied in the range of 126–1 006 mg/kg, with maximum values, on average 925 mg/kg, in samples of humus horizons of ordinary chernozems of plakorny agroecological group of untreated plots. The minimum content of POXC fraction was characteristic for samples of AB horizons of arable plakorny and arable low- and medium eroded agroecological soil groups, on average 218 and 137 mg/kg, respectively. POXC has significant correlations with the fraction of bichromate-oxidizable carbon, the content of light fraction, the content of total nitrogen and soil density, and has shown to be a good marker of agro-ecological conditions on the studied set of samples.

Short-Term Impacts of Fire and Post-Fire Restoration Methods on Soil Properties and Microbial Characteristics in Southern China

Wildfires and post-fire restoration methods significantly impact soil physicochemical properties and microbial characteristics in forest ecosystems. Understanding post-fire soil recovery and the impacts of various post-fire restoration methods is essential for developing effective restoration strategies. This study aimed to investigate how fire and soil depth influence soil physicochemical properties, enzymatic activities, and the structure of microbial communities, as well as how these factors change under different post-fire management practices. We sampled 0–10 cm (topsoil) and 10–20 cm (subsoil) in unburned plots, naturally restored plots, and two afforestation plots in southern China. The results showed that fire reduced topsoil soil moisture, nutrient levels, and microbial biomass. The variations in soil physicochemical properties significantly influenced microbial processes. Soil bulk density, nitrate, ammonium, carbon-to-nitrogen ratio, and availability of nitrogen, phosphorus, and potassium availability influenced soil enzyme activities. Soil pH, ammonium nitrogen, and the availability of nitrogen, phosphorus, and potassium were key factors shaping microbial composition. Fire altered the soil microbial communities by reducing the availability of nitrogen. Soil depth alleviated the impact of fire on the soil to some degree. Although artificial interventions reduced soil organic carbon, total nitrogen, and phosphorus, planting nitrogen-fixing species, such as Acacia mangium, promoted microbial recovery.

Ultraviolet NO and Visible O2 Nightglow in the Mars Southern Winter Polar Region: Statistical Study and Model Comparison

AbstractThe Mars NO and the O2 nightglow are produced by the recombination of atoms produced on the dayside by photodissociation and transported to the nightside. These emissions are tracers of the summer to winter pole dynamics in the upper Mars atmosphere. The UV‐visible (UVIS) channel of the Nadir and Occultation for MArs Discovery (NOMAD) spectrometer onboard Trace Gas Orbiter (TGO) is the first instrument able to simultaneously monitor both nightglow emissions. Observations by NOMAD/UVIS during the first part of the Martian year show that both the NO and O2 nightglow emissions are enhanced near the southern winter pole. Their mean brightnesses are 15 and 108 kR, respectively. These nightglow emissions generally occur between 30 and 60 km, the NO emitting layer being consistently located ∼10 km higher than the O2 nightglow layer. Numerical simulations with the Mars Planetary Climate Model (MPCM, v6.1) properly reproduce the nightglow brightness but tend to overestimate the NO peak altitude by ∼10 km. These results suggest that the atomic oxygen density is correctly predicted by the model but that the nitrogen density altitude distribution might not be properly modeled.

Identification of key water environmental factor contributions and spatiotemporal differential characteristics for eutrophication in Dianchi Lake.

The main influencing factors of water environment and the spatiotemporal differences of eutrophication were identified in the Dianchi Lake, the results indicated a comparatively poor and fluctuating the water environmental condition in the Caohai compared to the Waihai, and differences in the correlation between water environment indicators were observed in Caohai and Waihai. The absolute contribution rates of the inner sources to water temperature, pH, electrical conductance, total nitrogen, chlorophyll a and algal density were the largest in Caohai, while offshore sources are pH, electrical conductance, permanganate index, total phosphorus and chlorophyll a in Waihai. The eutrophication level is relatively high near the Xiyuan Suidao section, and the comprehensive trophic level indexes are 61.14, 64.45 and 64.45 in spring, summer and autumn, respectively, which all reach the state of moderate eutrophication; the comprehensive trophic level index is 55.72 in winter, which reaches the state of light eutrophication. The algal density near the Xiyuan Suidao and Luojiaying sections exhibited high levels, reaching a state of moderate algal bloom in summer. Spatial autocorrelation analyses highlighted significant positive and negative spatial autocorrelation for comprehensive Trophic Level Index and algal density, respectively, in Dianchi Lake. The High-High aggregation of the comprehensive Trophic Level Index and algal density was mainly concentrated in the Caohai, while the Low-Low aggregation of the comprehensive Trophic Level Index was primarily observed in the Waihai. Consequently, the risk of eutrophication and algal bloom outbreak in Caohai surpassed that in Waihai. Therefore, it is imperative to propose appropriate treatment measures based on the varying eutrophication level and algal bloom outbreak during different time periods and in distinct regions of the aquatic ecological environment in Dianchi Lake.

Sustainable remediation of piggery wastewater using a novel mixotrophic Chlorella sorokiniana Cbeo for high value biomass production

Piggery wastewater (PW) contains high density of organic carbon (COD), nitrogen (NH4+-N and TN) and phosphorous (TP), which are essential nutrients for microalgae growth. This work was attempted to use a newly isolate Chlorella sorokiniana Cbeo for recovery these compounds into its biomass via mixotrophic cultivation. Critical factors including level of ammonia, C/N ratio, pH, light intensity, sterilized/unsterilized media, and indoor/outdoor cultivations affecting biomass production and nutrients removal efficiencies were investigated. Data revealed that C. sorokiniana Cbeo achieved the optimal growth in the unsterilized medium at NH4+-N concentration, C/N ratio, initial pH, and light intensity of 250 mg/L, 10/1, 7, and 150 μmol/m2/s, respectively. Under the optimal conditions, dry cell weight (DCW) reached the maximal level of 4.30 g/L, which was slightly higher than 4.14 g/L determined for the sterilized medium. In 30 L-scale photobioreactor, C. sorokiniana Cbeo grown under indoor and outdoor achieved DCW of 3.61 and 3.19 g/L, respectively. COD, NH4+-N, TN, TP removal efficiencies for both conditions were determined as 91.9–96.7, 96.6–99.7, 96.2–96.4, and 98.2–100 %, respectively. The C. sorokiniana Cbeo biomass contained 14–27 % lipid, 25–32 % carbohydrate, 44–48 % protein, and 0.25–0.97 % lutein. Interestingly, α-Linolenic acid (C18:3n3) was 19.84 –27.0 % of the total fatty acids. C. sorokiniana Cbeo is the promising algal strain for development of a sustainable biorefinery of PW.

Nitrogen-Site Engineering in Covalent Organic Frameworks for H2O2 Photogeneration via Dual Channels of Indirect Two-Electron O2 Reduction.

Photocatalytic H2O2 production is a green and sustainable route, but far from meeting the increasing demands of industrialization due to the rapid recombination of the photogenerated charge carriers and the sluggish reaction kinetics. Effective strategies for precisely regulating the photogenerated carrier behavior and catalytic activity to construct high-performance photocatalysts are urgently needed. Herein, a nitrogen-site engineering strategy, implying elaborately tuning the species and densities of nitrogen atoms, is applied for H2O2 photogeneration performance regulation. Different nitrogen heterocycles, such as pyridine, pyrimidine, and triazine units, are polymerized with trithiophene units, and five covalent organic frameworks (COFs) with distinct nitrogen species and densities on the skeletons are obtained. Fascinatingly, they photocatalyzed H2O2 production via dominated two-electron O2 reduction processes, including O2-O2 •‒-H2O2 and O2-O2 •‒-O2 1-H2O2 dual pathways. Just in the air and pure water, the multicomponent TTA-TF-COF with the maximum nitrogen densities triazine nitrogen densities exhibited the highest H2O2 production rate of 3343µmol g-1 h-1, higher than most of other reported COFs. The theoretical calculation revealed the higher activity is due to the easy formation of O2 •‒ and O2 1 in different catalytic process. This study gives a new insight into designing photocatalysis at atomic level.

Plant Photosynthetic and Respiration Rates Are Key Populational Traits to Improve Yield and Quality for Good-Tasting Double-Cropped Rice

Improving the yield and quality for tasty rice varieties is a great challenge. In the present study, different nitrogen rates and plant density were utilized to form differential rice populational structures, which were determined to clarify key traits determining grain yield and quality for tasty rice varieties in a double-cropped rice system in subtropical China. The present results showed that the plant photosynthetic rate, leaf area index and plant respiration rate had important and significant impacts on the grain yields of both early and late rice, though the late rice yield was also significantly affected by the canopy temperature. In addition, among the studied populational traits, plant photosynthetic and/or respiration rates had significant effects on all quality traits. Consistently, grain yield and quality were significantly improved with the increasing plant photosynthetic and respiration rates through correlative analysis, which was also observed in principal components analysis. Overall, the present study suggests that both the grain yield and milling and appearance qualities could be improved through the optimal management of nitrogen and plant density through increasing plant photosynthetic and respiration rates.

Enhanced degradation of aqueous caffeine via cylindrical dielectric barrier discharge plasma: Efficacy and toxicity insights

An environmentally friendly approach for caffeine degradation was explored in this study utilizing cylindrical dielectric barrier discharge (CDBD) plasma. The current-voltage characteristics and the plasma parameters of the CDBD, such as the electron temperature, electron density, density of nitrogen excited states, vibrational temperature, and rotational temperature, were assessed through electrical and optical characterization respectively. Fourier-transform infrared spectroscopy (FTIR) was employed to evaluate the reactive oxygen and nitrogen species (RONS) in the plasma-treated air. The physicochemical properties of deionized water (DW) were measured. To gain a deeper insight into the role of RONS in caffeine degradation, their concentrations in DW were analyzed. Furthermore, the effects of initial concentration, sample volume, and pH on caffeine degradation were investigated. The highest degradation of caffeine was 94% at initial concentration of 50 mg L−1, sample volume 50 mL and in neutral pH. Liquid chromatography–mass spectrometry (LC-MS) was then used to propose the degradation pathway for caffeine. The major reactive species involved in caffeine degradation was ozone. Finally, the phytotoxicity and cytotoxicity of caffeine were assessed before and after plasma treatment with plasma-treated caffeine (PTC) showing minimal toxicity to both plants and cells.

Knowledge‐Based Deep Learning to Predict Vegetation Carbon, Nitrogen and Phosphorus Densities in China’s Shrublands

AbstractAccurate estimations of carbon (C), nitrogen (N), and phosphorus (P) densities in shrublands are pivotal for assessing terrestrial ecosystem carbon sequestration. Combining in‐situ investigations and machine learning facilitates large‐scale patterns mapping, however, which often overlooks underlying ecological regulations. Here we utilize data from 1,122 survey plots across China's shrublands and develop a novel knowledge‐based deep learning framework that integrates a structural equation model (SEM) to elucidate mechanisms and construct an artificial neural network (ANN) based on these causal relationships. Results show that biomass allocation to different organs follows allometric regulations and that N and P concentrations maintain a degree of stoichiometric homeostasis following biological stoichiometry theory. This insight guides the construction of our ANN, which outperforms both SEM and other prevalent machine learning methods. By leveraging ecological theories to inform model construction, our framework not only enhances prediction accuracy and explainability but also provides a methodological blueprint for ecological research.

Effect of 67-years of manuring, fertilization and amendments on fractions of soil organic carbon, nutrient dynamics and yield sustainability in an acidic Alfisol

Amending a problem soil in addition to nutrient input is crucial for maintaining a healthy and productive soil in the long run. The study aimed at evaluating the long-term impact of manuring and fertilization with or without liming on different soil attributes and crop yield in an acidic Alfisol. Surface soil samples (0–15 cm) were collected from selected 7 treatments, viz. Control; N; FYM; ½(N+FYM)+PX/2+KY/2; NPK; NPK+L; and P(A-X)K(B-Y)+FYM+L of the Permanent Manurial Trial (PMT) of Birsa Agricultural University, Ranchi, after the harvesting of rainy (kharif) maize (Zea mays L.) at the 67th crop cycle (2023 and 2024) and assessed for various fractions of soil organic carbon (SOC), available nutrients and yield attributes. The experiment was laid out in a randomized block design (RBD) and replicated thrice. The treatments which received manures either alone or in combination with chemical fertilizers recorded significantly higher amount of all the fractions of SOC, available nitrogen and lower bulk density as compare to the unfertilized plot or treatment with inorganic alone. The study also revealed that, addition of lime helped maintaining an optimum pH level, enhanced microbial activities and nutrient availability in the soil leading to a higher crop yield. Therefore, integrated use of manures and fertilizers in addition to lime for a prolonged period would have significant positive impact on soil health and sustaining its productivity.

Effects of occasional tillage on soil physical and chemical properties and weed infestation in a 10-year no-till system

Few studies have investigated how one-time targeted tillage of long-term no-till fields impacts topsoil properties and weed dynamics. An on-farm trial was implemented in 2020 to test the effects of occasional tillage (OT) in Morocco with a long-term no-tillage (NT) system and rainfed field crops: durum wheat (Triticum durum), faba bean (Vicia faba minor), and chickpea (Cicer arietinum). Four treatments were established, namely, continuous NT with crop residues maintained (“NT + residue”); continuous NT with crop residues not maintained (“NT-residue”); shallow inversion tillage (“shallow OT”); and deep non-inversion tillage (“deep OT”). We assessed the effect of these treatments on soil physical and chemical properties in 0–10 and 10–20 cm soil depths after crop harvest of the 2020–2021 (year 1) and 2021–2022 (year 2) growing seasons corresponding to 1 and 2 years after OT, respectively. In addition, we evaluated the effect of the treatments on weed populations and the effect of the legume crop rotated with wheat on soil nitrogen (N) and weed density. In year 1, deep OT reduced the water content at field capacity and available water capacity at 0–10 cm compared to continuous NT; the cation-exchange capacity (CEC) under deep OT was lower than in NT-residue and NT + residue at 0–10 cm and 10–20 cm, respectively. Furthermore, deep OT increased ammonium-N (NH4-N) at 0–10 and 10–20 cm compared to NT + residue but reduced exchangeable potassium (K) at 10–20 cm depth compared to NT-residue. In year 2, shallow OT had lower total porosity at 10–20 cm than NT + residue, while shallow and deep OT recorded higher water-stable aggregates at 0–10 cm than NT + residue; at 10–20 cm, deep OT recorded lower CEC than NT + residue. However, deep OT had higher nitrate-N (NO3-N) and available sulfur (S) than NT-residue at 10–20 cm. Occasional tillage did not significantly affect 10 out of 19 of the soil properties evaluated, including soil organic matter (SOM), in all the years and did not help reduce the stratification of soil nutrients in NT. In year 1, 50 days after OT, deep OT reduced the weed density by 46% compared to NT + residue, while in year 2, 406 days after OT, shallow OT reduced weed density by 53% compared to NT-residue. Regarding the effect of the legume rotated with wheat, faba bean appeared to be the better preceding or following wheat crop as it resulted in higher residual soil mineral N and lower weed infestation than chickpea.

Ir-Catalyzed Asymmetric Hydrogenation of N-Fused Heteroarenes with High Nitrogen Density: An Access to Chiral 2,5-Disubstituted 5,6-Dihydropyrrolo[1,2-a][1,2,4]triazolo[5,1-c]pyrazines.

A highly enantioselective Ir-catalyzed asymmetric hydrogenation of 2,5-disubstituted pyrrolo[1,2-a][1,2,4]triazolo[5,1-c]pyrazines containing four nitrogen atoms has been first realized. Under additive-free conditions, a variety of chiral 2,5-disubstituted 5,6-dihydropyrrolo[1,2-a][1,2,4]triazolo[5,1-c]pyrazines can be afforded in high yields (86-98%) with excellent enantioselectivities of up to 99% ee. This method provides a straightforward strategy for the efficient synthesis of chiral multinitrogen polyheterocyclic compounds.

Expansion of C4 plants in the tropical Leizhou Peninsula during the Last Glacial Maximum: Modulating effect of regional sea-level change

Due to the lack of relatively long-term, high-resolution terrestrial records in tropical southern China, there is limited published research on terrestrial vegetation changes and their responses to regional and/or global climate forcings since the last glacial period. In this study, a 170-cm-long peat core (covering the interval from ~44.1 to 9.3 cal kyr BP) recovered from the Xialu peatland in Leizhou Peninsula, South China, was analyzed for organic carbon isotope (δ13Corg), along with total organic carbon, total nitrogen, and bulk dry density, to investigate past vegetation and hydroclimatic changes. Our results showed that C4 plants dominated the study region during Marine Isotope Stage (MIS) 2 (29–14 cal kyr BP), indicating generally cooler and drier conditions during MIS 2 relative to late MIS 3 (~ 44.1–29 cal kyr BP) and early MIS 1 (14–9.3 cal kyr BP). In particular, the driest conditions occurred during the Last Glacial Maximum (~ 25–19 cal kyr BP) when sea level was at its lowest. In addition, several millennial-scale climatic events associated with the expansion of C4 plants were clearly identified. Our record is sensitive to a variety of glacial-interglacial forcings, including regional processes and global forcing, among which the inundation history of Beibu Gulf due to sea-level change during the late Quaternary, which has been neglected in previous studies, may have played an important role in modulating paleo-hydroclimatic changes in tropical southern China.

Exploring soil nitrogen and sulfur dynamics: implications for greenhouse gas emissions on the Qinghai-Tibet Plateau.

The Qinghai-Tibet Plateau is particularly vulnerable to the effects of climate change and disturbances caused by human activity. To better understand the interactions between soil nitrogen and sulfur cycles and human activities on the plateau, the distribution characteristics of soil nitrogen and sulfur density and their influencing factors for three soil layers in Machin County at depths of 0-20cm, 0-100cm, and 0-180cm are discussed in this paper. The results indicated that at depths of 0-180cm, soil nitrogen density in Machin County varied between 1.36 and 16.85kg/m2, while sulfur density ranged from 0.37 to 4.61kg/m2. The effects of three factors-geological background, land use status, and soil type-on soil nitrogen and sulfur density were all highly significant (p < 0.01). Specifically, natural factors such as soil type and geological background, along with anthropogenic factors including land use practices and grazing intensity, were identified as decisive in causing spatial variations in soil nitrogen and sulfur density. Machin County on the Tibetan Plateau exhibits natural nitrogen and sulfur sinks; However, it is crucial to monitor the emissions of N2O and SO2 into the atmosphere from areas with high external nitrogen and sulfur inputs and low fertility retention capacities, such as bare land. On this basis, changes in the spatial and temporal scales of the nitrogen and sulfur cycles in soils and their source-sink relationships remain the focus of future research.

Helium metastable density determination in the COST reference source by absolutely calibrated optical emission spectroscopy

Helium metastable densities in the COST Reference Microplasma Jet are estimated for a variety of He/N2 admixtures and dissipated powers by applying a collisional-radiative model to absolutely calibrated optical emission spectroscopy measurements. This is accomplished by delineating the excitation mechanisms that result in the N2(C–B) and N2+(B–X) emission bands, the latter of which is strongly coupled to the presence of helium metastables. A number of other plasma parameters are established and discussed for each operating condition including the electron energy distribution function, reduced electric field, rate constants, and electron density. With these parameters, the reaction rates for the primary ionization pathways are also calculated, emphasizing the importance of helium metastables for discharge sustainment. Good agreement with the existing literature is found for most plasma parameters and for helium metastable densities, in particular. A clear [N2]−1 relationship between the nitrogen concentration and density of helium metastables is demonstrated, as has been identified in previous studies in analogous atmospheric pressure plasma jets. This validates the efficacy of this optical technique for determining helium metastable densities and establishes it as a viable, and in many cases, more accessible alternative to other means of quantifying helium metastables in low-temperature plasmas.