Mineral N stock and nitrate accumulation in the 50 to 200 m profile on the Loess Plateau

Nitrogen (N) stored in deep profiles is important in assessing regional and/or global N stocks and nitrate leaching risk to groundwater. The Chinese Loess Plateau, which is characterized by significantly thick loess deposits, potentially stores immense stocks of mineral N, posing future threats to groundwater quality. In order to determine the vertical distributions of nitrate and ammonium content in the region, as well as to characterize the potential accumulation of nitrate in the deep loess profile, we study loess samples collected at five sites (Yangling, Changwu, Fuxian, An'sai and Shenmu) through a 50 to 200 m loess profile. The estimated storage of mineral N varied significantly among the five sites, ranging from 0.46 to 2.43 × 104 kg N ha−1. Ammonium exhibited fluctuations and dominated mineral N stocks within the whole profile at the sites, except for the upper 20–30 m at Yangling and Changwu. Measured nitrate content in the entire profile at Fuxian, An'sai and Shenmu is low, but significant accumulations were observed to 30–50 m depth at the other two sites. Analysis of δ15N and δ18O of nitrate indicates different causes for accumulated nitrate at these two sites. Mineralization and nitrification of manure and organic N respectively contribute nitrate to the 0–12 and 12–30 m profile at Changwu; while nitrification of NH4+ fertilizer, NO3− fertilizer and nitrification of organic N control the nitrate distribution in the 0–3, 3–7 and 7–10 m layer at Yangling, respectively. Furthermore, our analysis illustrates the low denitrification potential in the lower part of the vadose zone. The accumulated nitrate introduced by human activities is thus mainly distributed in the upper vadose zone (above 30 m), indicating, currently, a low nitrate leaching risk to groundwater due to a high storage capacity of the thick vadose zone in the region

Undoped Strained Ge Quantum Well with Ultrahigh Mobility Grown by Reduce Pressure Chemical Vapor Deposition

We fabricate an undoped Ge quantum well under 30 nm Ge0.8Si0.2 shallow barrier with reverse grading technology. The under barrier is deposited by Ge0.8Si0.2 followed by Ge0.9Si0.1 so that the variation of Ge content forms a sharp interface which can suppress the threading dislocation density penetrating into undoped Ge quantum well. And the Ge0.8Si0.2 barrier introduces enough in-plane parallel strain -0.41% in the Ge quantum well. The heterostructure field-effect transistors with a shallow buried channel get a high two-dimensional hole gas (2DHG) mobility over 2E6 cm2/Vs at a low percolation density of 2.51 E-11 cm2. We also discover a tunable fractional quantum Hall effect at high densities and high magnetic fields. This approach defines strained germanium as providing the material basis for tuning the spin-orbit coupling strength for fast and coherent quantum computation.Comment: 11 pages, 5 figure

A predictive scoring model to select suitable patients for surgery on primary tumor in metastatic esophageal cancer

Abstract Background Surgery on primary tumor (SPT) has been a common treatment strategy for many types of cancer. Aims This study aimed to investigate whether SPT could be considered a treatment option for metastatic esophageal cancer and to identify the patient population that would benefit the most from SPT. Methods Data from 18 registration sites in the Surveillance, Epidemiology, and End Results Program database (SEER database) were analyzed to select patients with metastatic esophageal cancer. Multivariate Cox regression analysis was used to identify potential risk factors for pre‐treatment survival. Variables with a p‐value of less than 0.05 were used to construct a pre‐treatment nomogram. A pre‐surgery predictive model was then developed using the pre‐surgery factors to score patients, called the “pre‐surgery score”. The optimal cut‐off value for the “pre‐surgery score” was determined using X‐tile analysis, and patients were divided into high‐risk and low‐risk subsets. It was hypothesized that patients with a low “pre‐surgery score” risk would benefit the most from SPT. Results A total of 3793 patients were included in the analysis. SPT was found to be an independent risk factor for the survival of metastatic esophageal cancer patients. Subgroup analyses showed that patients with liver or lung metastases derived more benefit from SPT compared to those with bone or brain metastases. A pre‐treatment predictive model was constructed to estimate the survival rates at one, two, and three years, which showed good accuracy (C‐index: 0.705 for the training set and 0.701 for the validation set). Patients with a “pre‐surgery score” below 4.9 were considered to have a low mortality risk and benefitted from SPT (SPT vs. non‐surgery: median overall survival (OS): 24 months vs. 4 months, HR = 0.386, 95% CI: 0.303–0.491, p < 0.001). Conclusion This study demonstrated that SPT could improve the OS of patients with metastatic esophageal cancer. The pre‐treatment scoring model developed in this study might be useful in identifying suitable candidates for SPT. The strengths of this study include the large patient sample size and rigorous statistical analyses. However, limitations should be noted due to the retrospective study design, and prospective studies are needed to validate the findings in the future

Re-evaluation of organic carbon pool from land surface down to bedrock on China's Loess Plateau

Large reservoirs of organic carbon (OC) store in deep soils ( > 1 m below land surface) are not usually included in regional and global terrestrial C inventories. Chinaos Loess Plateau (CLP), which has the worldos deepest loess deposit and has experienced long-term, intensive agricultural and revegetation activities, could contain large stores of OC. In this study, the distribution of OC concentration and stock across the entire loess profile from the ground surface down to the bedrock (56-205 m) was assessed at five sites (Yangling, YL; Changwu, CW; Fuxian, FX; Anosai, AS; and Shenmu, SM) under three land use types (farmland, grassland and shrubland). There was pronounced decrease in mean OC concentration with increasing depth along loess profiles at all the investigated sites. OC concentration in the topmost 20 m of the loess was much higher and fluctuated more significantly than that in the deeper layers at YL, CW, FX and AS, where mean annual precipitation was > 550 mm. In contrast, OC concentration was low and stable at SM with mean annual precipitation < 450 mm. The restoration of vegetation with deep roots following the abandonment of farmlands resulted in deep OC accumulation at YL and AS, whereas natural grassland recovery did not result in the accumulation of OC at SM. Our results suggested that land use change could alter OC distribution in deep soils, of which degree depended on climatic condition and vegetation type. The estimated OC storage varied significantly across the sites (859-5044 Mg ha(-1)), which mainly depended on the thickness of loess deposit. OC store on the CLP and other areas around the world with deep soils or sediments could be underestimated and need re-consideration in future C budget studies. This is the first estimate of regional OC stock across loess profile, spanning from the land surface down to the bedrock. The findings could have significant implications for biogeochemical cycling of C in surface and deep soil layers down to the bedrock

Types and sedimentary genesis of barriers and interlayers in the composite turbidite sand bodies of a deep-water canyon: A case study of the Central Canyon in the Qiongdongnan Basin

Deep-water oil and gas is currently the hot spot and difficulty of global oil and gas exploration, and the complex flow process inside the turbidite channels of deep-water canyons makes it difficult to characterize reservoir structures, identify barriers and interlayers and clarify the spatial distribution laws of reservoirs, which restricts the development of deep-water oil and gas. Taking the Central Canyon of the Qiongdongnan Basin as an example, this paper identifies and characterizes the barriers and interlayers of composite channel scale by means of seismic sedimentology, based on three-dimensional seismic and core data. Then, based on the turbidite filling process, barriers and interlayers are classified, and their genesis and control factors are analyzed. Finally, a development model of deep-water barriers and interlayers is established based on the quantitative analysis of sediment transportation system parameters. And the following research results are obtained. First, based on sedimentary genesis, barriers and interlayers are classified into four types, namely mudstone interlayers of lateral (aggradational) turbidite channel genesis (type A), mudstone interlayers of fine-grained turbidite channel genesis (type B), barriers of hemipelagic deep-water sediment genesis (type C), and calcareous petrophysical interlayers (type D). Second, based on the filling stage, barriers and interlayers are divided into four combination sequences, i.e., the initial canyon formation stage with strong sediment supply conditions (type A + type C and type B+ type C), the initial canyon formation stage with weak sediment supply conditions (type B + type C), the stable canyon development/late reworking stage with strong sediment supply conditions (types A + type D), and the stable canyon development/late reworking stage with weak sediment supply conditions (type D). Third, the development types and combination sequences of barriers and interlayers are controlled by the change of sediment transportation volume and terrain slope in the canyon. In the initial canyon formation stage, there is sufficient space for the development of turbidite, and the development of thin barriers and interlayers is controlled by sediment dischage volume, while the development of thick barriers and interlayers is controlled by terrain slope change. In the stable canyon development/late reworking stage, turbidite undergoes superimposed development and overbank. The sediment supply is the primary control factor of barrier and interlayer thickness, and the terrain slope change is the secondary factor. In conclusion, the development model of barriers and interlayers can be used to describe and predict the reservoir structure models under the same sedimentary background and provides a technical support for the exploration and development of deep-water oil and gas

Mechanistic Study of Oil/Brine/Solid Interfacial Behaviors during Low-Salinity Waterflooding Using Visual and Quantitative Methods

Despite the many studies of low-salinity waterflooding (LSWF), its underlying mechanisms are not well understood as a result of the complexity of the oil/brine/solid interfacial behaviors. Moreover, the widely held belief that LSWF is effective only under certain conditions has not been conclusively proven. Therefore, the static and dynamic interfacial behaviors during LSWF were visually and quantitatively studied in this work to elucidate the underlying mechanism(s). The results showed that LSWF effectively promotes oil recovery by causing double-layer expansion (DLE) and hydrocarbon solubilization. The DLE resulted from multicomponent ion exchange (MIE), as revealed by contact angle, ζ potential, and conductivity measurements. Emulsions prepared with low-salinity brines (≤0.21 wt %) were noticeably heavier and quite stable, demonstrating the significant solubilization effect of LSWF. The oil displacement dynamics observed in a visual micromodel indicated that LSWF increased the oil recovery factor by 4% (secondary) and 1.7% (tertiary) in water–wet porous media, whereas in oil-wet porous media, LSWF was even more efficient than high-salinity waterflooding (HSWF) when employed as the secondary mode. Moreover, the macroscopic sweep and microscopic displacement efficiencies were quantitatively determined using an image analysis technique to verify the proposed mechanisms

Influence of Individual Ions on Oil/Brine/Rock Interfacial Interactions and Oil–Water Flow Behaviors in Porous Media

The low salinity effect (LSE) in enhanced oil recovery (EOR) is widely accepted. However, its underlying mechanisms remain unclear due in part to the complex interactions at the oil/brine/rock interface. The chemistry of brine largely depends on the ionic composition. Thus, in this work, attention was placed on the roles of individual ions and salinity in LSE through direct measurements of oil/brine/rock interfacial behaviors, oil displacement efficiencies, and oil–water relative permeability in sandstone porous media. The results showed that the oil/water interfacial tensions (IFTs) were weakly dependent on ion and the lowest IFTs were generated at the salinities of 0.2–0.5 wt %. In contrast, the interfacial dilational modulus varied significantly with ion types and salinities due to the adsorption of polar components at the oil/water interface. Moreover, wettability alteration of the sandstone surface was found to be associated with the divalent ions in our work. As a result of the viscoelastic interfaces, the breakage of oil column into oil droplets or ganglia was delayed, which subsequently led to the improvement of the oil–water relative permeability and oil displacement efficiencies. Based on the analysis, it was concluded that HCO₃^–, Mg²⁺, and SO₄^2– were potential-determining ions (PDIs) in LSE. The results of the tests, to our knowledge, are the first that particularly emphasize the roles of individual ions at the interfaces and oil–water flow patterns in porous media