Nitrogen Content Distribution Research Articles

Dissimilar welding of high nitrogen stainless steel and low alloy high strength steel under different shielding gas composition: Process, microstructure and mechanical properties

Ar–N2-O2 ternary shielding gas is employed in dissimilar welding between high nitrogen steel and low alloy steel. The effect of O2 and N2 is investigated based on the systematical analysis of the metal transfer, nitrogen escape phenomenon, weld appearance, nondestructive detection, nitrogen content distribution, microstructure and mechanical properties. There are two nitrogen sources of the nitrogen in the weld: high nitrogen base material and shielding gas. The effect of shielding gas is mainly reflected in these two aspects. The change of the droplet transfer mode affects the fusion ratio, N2 in the shielding gas can increase nitrogen content and promote the nitrogen uniform distribution. The addition of 2% O2 to Ar matrix can change the metal transfer from globular transfer to spray transfer, high nitrogen base material is thereby dissolved more to the molten pool, making nitrogen content increase, ferrite decrease and the mechanical properties improve. When applying N2-containing shielding gas, arc stability becomes poor and short-circuiting transfer frequency increases due to the nitrogen escape from droplets and the molten pool. Performance of the joints is improved with N2 increasing, but internal gas pores are easier to appear because of the poor capacity of low alloy steel to dissolve nitrogen, The generation of pores will greatly reduce the impact resistance. 4–8% N2 content in shielding gas is recommended in this study considering the integrated properties of the dissimilar welded joint.

Retrieval of Paddy Crop Nutrient Content at Plot Scale Using Optimal Synthetic Bands of High Spectral and Spatial Resolution Satellite Imagery

The main aim of the present study is to introduce Hyperion narrow band information into high spatial broad band imagery so that it will be helpful for the estimation of crop parameters at small field scale from multispectral data. Here, we are targeting to retrieve the nitrogen content of summer paddy at plot scale. Our findings concluded that paddy crop heterogeneity can be assessed by implementing narrow band index regression model designed for paddy crop from multispectral LISS IV data. Moreover, the proposed models to construct the synthetic narrow bands in green (GS), red (RS) and NIR (NS) regions of the spectrum for high-resolution satellite imagery (LISS IV) are also presented here {\(GS\rho_{LISS \, IV} = 0.032 \cdot G\rho_{IH} + 17.296\); \(RS\rho_{LISS \, IV} = 0.072 \cdot R\rho_{IH} + 16.025\); \(NS\rho_{LISS \, IV} = 0.087 \cdot N\rho_{IH} + 24.923\)}. It showed the spatial variability of nitrogen content ranged from 3.37–6.04% obtained by leaf nitrogen concentration (LNC: R705, R717, R491) index regression model and 3.82–5.96% by simple ratio (SR: R533, R565) index regression model over a rice agriculture system. Thus, the details of spatial variability at crop field level over a rice agriculture system can be assessed from multispectral LISS IV data with 5.6 m spatial resolution through the synthetic broad bands. The results conclude that narrow band-based index regression model derived from Hyperion bands by implementing band average method can effectively evaluate the nitrogen content distribution of croplands subjected to varying field heterogeneity. It confirmed that the proposed methodology can be applied for the variability mapping of crop parameters at plot-scale level within the fields from space platform, which can be beneficial in achieving operational precision farming more efficiently.

Simulation study on performance of nitrogen loss of an improved subsurface drainage system for one-time drainage using HYDRUS-2D

Improved subsurface drainage has been verified as a more efficient drainage technique for solving problems of farmland shortage and frequent floods in South China. However, the environmental effects of improved subsurface drainage with different parameters have rarely been studied. In this study, nitrogen loss in outflow and soil nitrogen content under improved subsurface drainage for one-time drainage is evaluated based on a calibrated HYDRUS model, considering the precipitation process, initial groundwater table depth, initial soil nitrogen content, submerged pipe height, drain spacing, drain depth, filter width, and filter height during a 3-day individual drainage. The results indicate that HYDRUS performed well for the simulation. Under conditions of homogeneous soil and nitrogen content distribution, when rainfall occurred on the first, second, and third days, the total ammonia nitrogen (NH4‒N) and nitrate nitrogen (NO3‒N) losses under a rainfall of 141 mm are approximately 1.26, 1.31, 1.39 and 1.2, 1.25, 1.36 times that under a rainfall of 44 mm, respectively. The NH4‒N and NO3‒N losses in the outflow of the improved subsurface drainage increased significantly 0.5 days after the rain began. Compared with the 10 cm initial groundwater table depth case, the nitrogen loss under a 30 cm initial groundwater table depth reduced by approximately 23%. The NH4‒N losses of the improved subsurface drainage with 20 and 40 cm submerged heights of the pipe reduced by 23% and 48%, respectively, whereas the NO3‒N losses reduced by 24% and 51%, respectively, compared with those under a free outflow. The initial soil nitrogen content contributed primarily to the nitrogen loss of the outflow. The relationship between nitrogen loss per pipe and drain spacing/drain depth can be described as second-degree parabolic/linear. The effects of filter width and height are similar to that of drain spacing. In the improved subsurface drainage, the maximum decrease percentage of soil nitrogen mass occurred in the filter profile at all times, whereas the NH4‒N mass increased at the 0–20 cm soil layer, and the soil NO3‒N mass increased slightly at the 60–80 cm soil layer with increasing drainage time. The results of this study provide a scientific basis for nitrogen management.

Modeling Canopy Carbon and Water Fluxes Using a Multilayered Model over a Temperate Meadow in Inner Mongolia

To incorporate canopy vertical structure in a process-based model over a temperate meadow, a multilayered model estimated canopy carbon flux (Fc) and water flux (LE) was applied by comparing with eddy covariance measurements in Inner Mongolia, China. Simulations of diurnal, seasonal CO2 and H2O fluxes and model sensitivity to parameters and variables were analyzed. The results showed that the model underestimated Fc and LE by about 0.6% and 5.0%, respectively. It was able to simulate the diurnal and seasonal variation of Fc and LE and performed well during the day and in the growing season, but poorly at night and early in the growing season. Fc was more sensitive to the leaf nitrogen content distribution coefficient and maximum catalytic activity of Rubisco, whereas LE showed greater sensitivity to the stomatal conductance parameter a1, empirical coefficient of stomatal response to saturated vapor pressure difference Vpds0, and minimum stomatal conductance of CO2gsc0. The response of Fc to environmental factors was ranked as air CO2 concentration (Ca) > air temperature (Ta) > photosynthetically active radiation (PAR) > soil water content (θsm) > vapor pressure deficit (VPD) > wind speed (u0). The response of LE to environmental factors was ranked as Ta > VPD > θsm> PAR> Ca> u0. The response of LE to vegetation characteristic parameters was greater than that of Fc.

Top soil physical and chemical properties in Kazakhstan across a north-south gradient

Kazakhstan’s soil properties have yet to be comprehensively characterized. We sampled 40 sites consisting of ten major soil types at spring (wet) and late-summer (dry) seasons. The sample locations range from semi-arid to arid with an annual mean air temperature from 1.2 to 10.7 °C and annual precipitation from less than 200 to around 400 mm. Overall topsoil total (STC), organic (SOC), and inorganic (SIC) carbon did not change significantly between spring and late summer. STC and SOC show a wave like pattern from north to south with two maxima in northern and southern Kazakhstan and one minimum in central Kazakhstan. With a few exceptions SIC content at northern sites is generally low, whereas at Lake Balkhash SIC can exceed 75% of STC. Independent of the seasons, SOC significantly differed among soil types. Total nitrogen content distribution among our sampling sites followed a similar pattern as SOC with significant differences between soil types occurring in northern, central and southern Kazakhstan.

Optimization of process parameters in the RF-DC plasma N2-H2 for AISI420 molds and dies

The RF-DC plasma N2-H2 was used to make precise AISI420 molds and dies have complex textured geometry. The quality of the molds and dies directly affect the quality of the produced parts. The excellent examples of molds were used for injection molding lenses and dies used for the precision forging of automotive drive train components. In this study, a temperature, DC bias, and duration as process parameters of the RF-DC plasma N2-H2 have been optimized for molds and dies fabrication. The mask-less micro-patterned method was utilized to draw the initial 2D micro patterns directly onto the AISI420 substrate surface. The unprinted substrate surfaces were selectively nitrided by the RF-DC plasma N2-H2 at 673 K for 5400 s by 70 Pa with hollow cathode device. Energy Dispersive X-ray was utilized to describe the nitrogen content distribution at the vicinity of the border between the unprinted surfaces. This exclusive nitrogen mapping proves that only the unprinted parts of the substrate have high content nitrogen solutes. XRD analysis was performed to investigate whether the iron nitrides were precipitated by RF-DC plasma N2-H2 in the AISI420.

Doping and reduction of graphene oxide using chitosan-derived volatile N-heterocyclic compounds for metal-free oxygen reduction reaction

We developed a fast, simple, scalable and safe method for the metal-free reduction and nitrogen-doping of graphene oxide (GO) using volatile nitrogen-containing heterocyclic compounds. In this method, chitosan and graphene oxide were simultaneously annealed without making any physical contact between them under a flow of argon using chemical vapor deposition (CVD). Based on the established knowledge of chitosan thermal decomposition, in-situ formed volatile nitrogen-containing heterocyclic compounds interact with graphene oxide to produce N-doped reduced graphene oxide (NrGO). In order to study the effect of temperature on the nitrogen content distribution and on the carbon/oxygen ratio, we annealed the graphene oxide and chitosan at 300, 450 and 600 °C. We fully characterized the synthesized materials (NrGOs) by XPS, Raman, FT-IR, HR-SEM, AFM, XRD and UV–Vis techniques. On the basis of XPS analysis, we achieved the highest nitrogen-doping level at 4.3 atom % at 450 °C with an atomic ratio of C/O as high as 16, which, to our knowledge, is the highest value reported so far at this temperature. Electrochemical characterizations demonstrate electrocatalytic activity of this NrGO towards the oxygen reduction reaction (ORR) in alkaline electrolytes, with a high reaction onset potential of 0.78 V vs. RHE.

Effects of Gas Nitriding Temperature on the Surface Properties of a High Manganese TWIP Steel

The effects of gas nitriding temperature on the cross section morphology, element nitrogen distribution, and surface layer compositions of a cold rolled and pre-strained high manganese austenitic TWIP steel 25Mn-3Cr-3Al-0.3C-0.01N and the corresponding anti-corrosion ability have been studied. The results show that, depending on nitriding temperature, the distribution of element nitrogen and main phase compositions are significantly different in the nitriding layers. At a temperature lower than 500 °C, the main composition in the modified layer is S-phase and the nitrogen concentration linearly decreases from the surface to the center, while Fe4N forms with S-phase and a step-like distribution of nitrogen content is present at nitriding temperature of 600 °C. Caused by the increasing of modified layer thickness and the formation of S-phase and Fe4N, the surface hardness was obviously enhanced. Anodic polarization curves in 3.5 wt. % NaCl solution indicate that the nitrided processes have a tremendous modification effect on anti-corrosion ability. Moreover, the increase of (111) oriented grain, caused by the elevated nitriding temperature, has a positive effect on the corrosion resistance.

Two-dimensional amine-functionality gradient by plasma polymerization

A two-dimensional (2D) gradient was created by employing two-step diffusion-controlled plasma polymerization of allylamine on polypropylene membrane, with varied deposition durations composed of two stages. The wettability gradient was examined by water contact angle measurements which clearly demonstrated that the gradient was well manipulated by varying the treatment duration, thus controlled the surface coverage and resulted in the average water contact angle ranged from 110° to 25°. On the created 2D gradients, the cell responses toward the distribution of nitrogen content were imaged by confocal laser microscopy. Moreover, a correlation based on experimental data revealed a linear relationship between the nitrogen content and water contact angle. The addition of serum proteins assisted also the adhesion and growth of L-929 cells. The methodology in fabricating the 2D gradient demonstrated the flexibility of the plasma technique which can be further used to create different types of well-defined gradients for applications in surface functionalization, biomedical devices, and material screening.

角倍蚜虫瘿对盐肤木光合特性和总氮含量的影响

Chinese gallnut which formed by some aphids is a special local product of China and valued as a commercial product for export. Schlechtendalia chinensis is the main commercial species which induces horned gall on Rhus chinensis and its shares about 75% more Chinese gallnut yield of the world. Effects of horned gall on photosynthetic characteristics and total nitrogen content of R. chinensis were analysed in Kunming,Yunnan province. The result indicated that photosynthetic characteristics of R. chinensis were disturbed by the horned gall. Compared to the control plants,( 1) maximum photosynthesis rates( Amax) of the leaves induced gall of treatment plant rose to 14. 49%,32. 17%,and 42. 01% by horned galls in the initial,middle and late gall stages,respectively. Maximum photosynthesis rates of the nearby leaves without gall were also raised but declined after middle gall stage.( 2) light-compensation points( Lcp) of the leaves induced gall were raised,but the Lcp of the leaves without gall were declined in middle gall stages. Light-saturation points( Lsp) of the leaves induced gall were raised,but the Lsp of the leaves without gall were declined in initial and middle gall stages.( 3) dark respiration rate( Rd) of the leaves both induced gall and without gall were raised in the initial gall stages,but no significant influences in the middle and late gall stages. Effects of horned gall on photosynthetic characteristics of R. chinensis leaves were correlated to the leaflet positions and the gall growth stages. At the same time, the total nitrogen content distribution of R. chinensis leaves had been changed by the horned gall. Total nitrogen contents of gall,leaves induced gall and leaves without gall were 1. 13%,1. 98%,and 2. 14%,respectively. It is the possible reasons that nutrition flows to the leaves which induced gall and finally to the galls from leaves without gall,and supplied to the gall and galling aphids need.

Experimental, numerical and sensitive analysis of nitrogen dynamics in soils irrigated with treated sewage

An ammonia volatilization submodel and a crop-growth submodel have been set up and incorporated to the 2D nitrogen transport and transformation simulation model Nitrogen-2D. The coupled model Nitrogen-2D considers all the important nitrogen transformation processes such as mineralization, immobilization, denitrification, nitrification, volatilization, root uptake and soil adsorption in the soil. The model was used to simulate the nitrogen dynamics for the experiment in four lysimeters under sewage irrigation. Simulation results show that the model can describe the water content and ammonium nitrogen content distribution well but simulate the change of the nitrate nitrogen poorly. Sensitivity analysis shows that the simulation results are influenced by the soil water characteristic parameters severely, especially by the parameter of n. The model is much less sensitive to N dynamic parameters.

Quantitative inverse modeling of nitrogen content from hyperion data under stress of exhausted coal mining sites

Monitoring and evaluating the nutritional status of vegetation under stress from exhausted coal mining sites by hyper-spectral remote sensing is important in future ecological restoration engineering. The Wangpingcun coal mine, located in the Mentougou district of Beijing, was chosen as a case study. The ecological damage was analyzed by 3S technology, field investigation and from chemical data. The derivative spectra of the diagnostic absorption bands are derived from the spectra measured in the field and used as characteristic spectral variables. A correlation analysis was conducted for the nitrogen content of the vegetation samples and the first derivative spectrum and the estimation model of nitrogen content established by a multiple stepwise linear regression method. The spatial distribution of nitrogen content was extracted by a parameter mapping method from the Hyperion data which revealed the distribution of the nitrogen content. In addition, the estimation model was evaluated for two evaluation indicators which are important for the precision of the model. Experimental results indicate that by linear regression and parameter mapping, the estimation model precision was very high. The coefficient of determination, R 2, was 0.795 and the standard deviation of residual (SDR) 0.19. The nitrogen content of most samples was about 1.03% and the nitrogen content in the study site seems inversely proportional to the distance from the piles of coal waste. Therefore, we can conclude that inversely modeling nitrogen content by hyper-spectral remote sensing in exhausted coal mining sites is feasible and our study can be taken as reference in species selection and in subsequent management and maintenance in ecological restoration.

Leaf nitrogen distribution in relation to leaf age and photon flux density in dominant and subordinate plants in dense stands of a dicotyledonous herb.

We studied the effects of photon flux density (PFD) and leaf position, a measure of developmental age, on the distribution of nitrogen content per unit leaf area (N area) in plants of different heights, in dense stands grown at two nitrogen availabilities and in solitary plants of the erect dicotyledonous herb Xanthium canadense. Taller more dominant plants received higher PFD levels and experienced a larger difference in relative PFD between their youngest and oldest leaves than shorter subordinate plants in the stands. Differences in PFD between leaves of solitary plants were assumed to be minimal and differences in leaf traits, found for these plants, could thus be mainly attributed to an effect of leaf position. In the solitary plants, N area decreased with leaf position while in the plants from the stands it decreased with decreasing relative PFD, indicating both factors to be important in determining the distribution of N area. Due to the effect of leaf position on N area, leaves of subordinate plants had a higher N area than older leaves of dominant plants which were at the same height or slightly higher in the canopy. Consequently, the N area distribution patterns of individual plants plotted as a function of relative PFD were steeper, and probably closer to the optimal distribution which maximizes photosynthesis, than the average distribution in the stand. Leaves of subordinate plants had a lower mass per unit area (LMA) than those of dominant plants. In the dominant plants, LMA decreased with decreasing relative PFD (and with leaf position) while in the subordinate plants it increased. This surprising result for the subordinate plants can be explained by the fact that, during the course of a growing season, these plants became increasingly shaded and newer leaves were thus formed at progressively lower light availability. This indicates that LMA was strongly determined by the relative PFD at leaf formation and to a lesser extent by the current PFD. Leaf N content per unit mass (N mass) was strongly determined by leaf position independent of relative PFD. This indicates that N mass is strongly ontogenetically related to the leaf-aging process while changes in N area, in response to PFD, were regulated through changes in LMA.