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Acid treatment has been proven to effectively reduce the fracture initiation pressure in reservoirs, making it a viable method for stimulating deep tight sandstone reservoirs. However, the underlying mechanism of how sandstone pore structure and mechanical properties vary with acid treatment time remains unknown. Understanding this mechanism is crucial for studying the fracture initiation and propagation in tight sandstone reservoirs. In this study, to quantitatively analyze the changes in pore structure and mechanical properties of sandstone samples treated with acid for different times (0 h, 1 h, 2 h, 4 h, 6 h, 12 h, 24 h, 48 h, 72 h, 120 h, and 168 h), nuclear magnetic resonance and uniaxial compression tests were employed to examine these changes. The results revealed that the number of mesopores and macropores increased rapidly after 6 h and 48 h of acid treatment, respectively. Additionally, the permeability showed a significant increase after 24 h of acid treatment. This can be attributed to the gradual dissolution of intergranular cement, leading to the formation of new pores that connect with the existing pore network. The peak strength of sandstone undergoes stepwise changes with acid treatment time, which can be divided into three stages: stage I (0–6 h), stage II (12–72 h), and stage III (120–168 h). Under the influence of acid treatment and uniaxial compression, the damage and damage change rate of sandstone treated with acid for 24 h reached the minimum. Moreover, a variation mechanism for sandstone after acid treatment was proposed. [ABSTRACT FROM AUTHOR]

Purpose: Rivers transfer eroded sediment with soil organic carbon (SOC) from terrestrial land to ocean basins, playing a key role in the global carbon cycle. During sediment delivery, the coarse particles can be preferentially settled and the fine particles may be transported to downstream depositional sinks. However, the size-specific quantification of soil microbial communities and SOC composition and their roles in SOC stability have not been fully elucidated. Materials and methods: In this study, two soils with similar textures but different aggregate structures were fractionated using a settling tube apparatus into three size classes according to their settling velocities. The individual soil particle-size aggregates and unfractionated soil were analyzed to determine (1) the diversity and composition of the soil microbial communities via 16S rRNA and ITS1, and (2) the SOC composition using mid-infrared diffuse reflectance spectroscopy. Results: The results showed that as the soil aggregate size decreased, the ratio of alkyl groups to carboxyl groups (C−H/COO, C−H/C=O) and soil CO2 emission per gram of SOC significantly decreased; however, the richness and diversity of the soil bacterial and fungal communities increased. Meanwhile, the aggregates of smaller size had lower relative abundances of Proteobacteria and Basidiomycota but higher relative abundances of Actinobacteria and Ascomycota. Rhizobiales was an indicator taxon for bigger soil aggregate communities, while Deinococcales, Capnodiales, and Venturiales were indicator taxa for communities with smaller soil aggregates. SOC composition showed a stronger direct effect on SOC stability in bigger soil aggregates (path coefficient, 0.68). However, SOC composition exerted a greater indirect impact on SOC stability by regulating soil bacterial and fungal community composition in smaller size aggregates (path coefficient, 0.65). Conclusions: Overall, our study provides a fundamental understanding of the chemical and microbial control of SOC stability at the aggregate level and highlights the potential impacts of aggregate-scale SOC decomposition on the fate of eroded SOC. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties of as-extruded Mg-10Li-3Al-3Zn-0.22Si during heat treatment from 473 to 673 K were investigated in this paper, and then the strengthening mechanism and fracture behavior of the studied alloy was also analyzed. Experimental results show that the matrix of as-extruded Mg-10Li-3Al-3Zn-0.22Si alloy mainly consists of α-Mg and β-Li, and dispersive granular phases are AlLi and Li2MgAl. Mg2Si phase shows banded distribution along extrusion direction. The morphology of α-Mg is from long strip to nearly spherical block at 573 K. The α-Mg reprecipitates from β-Li matrix in the orientation relationship: (0001) α-Mg // (110) β-Li, [11 2 - 0] α-Mg // [1 1 - 0] β-Li at 623 K. While the Al-rich granular phase is decomposed and dissolve into the gradually, and then AlLi increase again at 673 K, which may be caused by the dissolution at high temperature and precipitation during air cooling in heat treatment. Besides, the solid solution and dispersion strengthening enhances the strength of alloy after heat treatment. After heat-treated at 573 K for 1 h and then air cooling, alloy presents excellent mechanical properties with the ultimate tensile strength of 253 ± 3 MPa and elongation of 27 ± 3%, respectively. Compared with the extruded state, ultimate tensile strength of alloy can be increased by about 49%. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effect of hot pack rolling and T6 heat treatment on microstructure and mechanical properties of 25 vol% B4CP/6061Al composite fabricated by powder metallurgy. Results show that hot pack rolling process could break the particle agglomeration, refine grain size, decrease porosity and improve the interface bonding quality. Almost 15%, 21% and 328% improvement in ultimate tensile strength, yield strength and elongation for B4CP/6061Al composite were obtained after hot pack rolling. It was also found that the average grain size increased due to the static recrystallization during the T6 heat treatment process. XRD patterns revealed that Mg2Si precipitation hardening phase was formed in the matrix. Compared with the rolled B4CP/6061Al composite, T6 heat treatment resulted in improving the ultimate tensile strength, yield strength and elongation by 7%, 11% and 50%. The strengthening mechanisms and fractured surfaces under different stages were also discussed. The hot pack rolling process could break the particle agglomeration, refine grain size, decrease porosity and improve the interface bonding quality. The properties test indicates that almost 15%, 21% and 328% improvement in ultimate tensile strength, yield strength and elongation for B4CP/6061Al composite were obtained after hot pack rolling. Compared with the roll-ed B4CP/6061Al composite, T6 heat treatment resulted in improving the ultimate tensile strength, yield strength and elongation by 7%, 11% and 50%. [ABSTRACT FROM AUTHOR]

Hot compression tests of Hastelloy C-276 alloy were conducted at the temperature ranging from 1000 to 1250 °C and strain rate ranging from 0.01 to 10 s−1. The constitutive relation and critical points of dynamic recrystallization (DRX) of the Hastelloy C-276 alloy were analyzed. The flow stress curves were corrected to tackle the problems of the influence of the adiabatic heating and friction. It was revealed that a five-order polynomial was suitable to solve the problem of the influence of strain. The critical strains of DRX could be expressed by the calculation from strain hardening rate as ε c = 7.67 × 10 - 4 Z 0.144 and ε c ≈ 0.78 ε p . Microstructural evolution revealed that the development of DRX of the alloy was complete at high temperature and low strain rate and the DRX grain size increased with the increase in temperature. The volume fraction of DRX was increased, and the grain size of DRX was also slightly increased with the increase in strain. The main nucleation mechanism of DRX was discontinuous dynamic recrystallization (DDRX), which was characterized by the grain boundary bowing nucleation mechanism coupled with the twinning-induced nucleation mechanism. Σ3 twins also contribute to the grain refinement and homogenization during hot deformation. The grains of C-276 alloy were refined significantly, and the microstructural homogeneity was improved effectively during hot deformation at high temperature and low strain rate. By choosing the suitable hot working processing parameters, the refinement and uniform distribution of grains of Hastelloy C-276 alloy could be obtained. [ABSTRACT FROM AUTHOR]

Purpose: Erosion processes spatially redistribute soil particles and the associated carbon across landscapes. Their spatial redistribution pattern is governed by the transport distances of individual displaced soil particles, which is not only dependent on their settling velocity, but also affected by slope topography. However, the potential impacts of fine-scale variation of slope topography on the erosion-induced lateral and carbon fluxes are often over-generalized by coarse digital elevation models. Material and methods: In this study, two topo-sequences, convex and concave, over a long gentle slope in the northeast China were investigated. Surface soils were sampled at predetermined space intervals from upslope to downslope along the two toposequences, and then fractionated by the settling velocity of individual fractions into four classes: > 250, 63 – 250, 20 – 63 and < 20 μm. The soil organic carbon (SOC) and δ13 C of the unfractionated soils and all the settling classes were measured, and their CO2 emission rates were also determined at six temperature gradients: 5°C, 10°C, 15°C, 20°C, 25°C and 30°C. Results and disucssion: Our results show that: 1) The soil fractions along the upper lying convex segment showed a coarsening effect toward the knee point and then a fining trend at the slope toe, whilst the soil compositions along the lower lying concave segment stayed fairly comparable as the slope descended. 2) The net loss of surface soil along the eroding convex segment resulted in depleted SOC and more positive δ13 C signatures than that along the depositional concave segment. 3) The CO2 emission rates of almost all the settling fractions were enhanced compared with that of the unfractionated soil, and the settling class-specific CO2 emission rates and their temperature sensitivity (Q10) also differed along the two topo-sequences. Conclusions: This demonstrates that fine scale topographic variations had a strong control over the lateral and vertical carbon fluxes, which has been often disguised by coarse grid size in digital elevation models or average sediment delivery ratios. Topography-dependency must be properly accounted for when calculating slope-scale carbon balances. [ABSTRACT FROM AUTHOR]

Cu-Ag alloy is widely used as conductive material for high-field pulsed magnets in electrical industry. The cryorolling technique is considered as the most applicable severe plastic deformation technique. Therefore, in this study, cryorolling and subsequent annealing process were used to prepare Cu-4Ag (in wt.%) alloy sheets. The strength, ductility and electrical conductivity of Cu-4Ag alloy sheets were investigated. Microstructure of Cu-4Ag alloy was also studied by OM, SEM, XRD and TEM. As a result, the cryorolling specimens after annealing at temperature of 300 °C display a good combination of tensile strength of 652.2 ± 6.0 MPa, moderate elongation of 12.5 ± 0.7% and electrical conductivity of 80.6 ± 0.2% IACS. This is due to the presence of dislocations, dislocation cells, nanograins and nanotwins in the non-recrystallized regions and fine nanoscaled silver precipitates. Besides, a good ductility is achieved in this condition due to its desirable ductile fracture characteristics. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen (N) is not only a major regulator of productivity in terrestrial systems but can also be a pollutant. While the effects of fertilizer addition to soil N cycling processes and the associated soil microbial groups have been extensively studied, little attention has been paid to the interaction of fertilizer amendment and the intrinsic fertility of the soil. Methods: We conducted a filed study on the Chinese Loess Plateau with soils of two fertility levels (low fertility and high fertility), amended with or without synthetic fertilizer (N and phosphorus, NP). Soil samples were collected three times in a continuous winter wheat cropping system and analyzed for soil potential nitrification (PNA) and denitrification (DEA) rates, nitrifiers and denitrifiers. Results: Populations of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and the resulting PNA were increased by the NP application regardless of intrinsic soil fertility. The NP application increased DEA by 15–228% in the low fertility soil, but decreased DEA by 18–46% in the high fertility soil. Soil denitrifiers also showed divergent responses to NP application in low and high fertility soils, i.e., the abundance of nirS-nitrite reducers increased in the low fertility soil, while nirS- and nirK-nitrite reducers were unchanged in the high fertility soil. The narG-nitrate reducers, AOB and AOA were more responsive to the NP application in the tillering stage (BBCH 25–26) than in other periods, whereas PNA, DEA and denitrifier gene abundance (nirS and nirK) varied more in the flowering stage (BBCH 65). Conclusions: Our results suggest that the responses of soil nitrification/nitrifiers and denitrification /denitrifiers to NP application varied with intrinsic soil fertility levels. The contrasting responses of nitrification and denitrification to NP application in high fertility soil indicate a decoupling of both processes. [ABSTRACT FROM AUTHOR]

Frictional torque is an important mean for momentum exchange between the atmosphere and earth, and significantly influences the variation in atmospheric angular momentum. Using NCEP-NCAR reanalysis data for the period 1948-2011, we examined the spatial and temporal patterns of frictional torque. It was found that the globally integrated frictional torque turned from positive to negative in 1972, suggesting that angular momentum was transferred from the earth to the atmosphere before 1972, but from the atmosphere to the earth thereafter. The global frictional torque steadily declined from 1948 to 1994, but has been increasing since 1995. It was also found that the global frictional torque is mainly determined by the wind systems in the mid and low latitudes of the Southern Hemisphere (SH), where large changes in frictional torque occurred during the study period. Westerly wind increased continuously in the midlatitudes after 1948, while easterly wind decreased in the tropics of the SH after the 1980s. [ABSTRACT FROM AUTHOR]

Although small-scale spatial variation of soil respiration has been studied in a wide variety of ecosystems, there are few studies investigating the spatial variation of soil respiration at tree-scale. An inaccurate estimation of soil respiration would be obtained if the spatial variation of soil respiration was ignored. Soil respiration, soil temperature, soil moisture and fine roots biomass were measured in different directions (0, 120, and 240°) at different distances (0.5 and 2 m radial distance) from the trunk of three representative trees for the period 2011-2013 in a mature apple orchard established on the Loess Plateau in 2000. The mean soil respiration rate at 0.5 m-distance was 21, 35 and 42 % higher, respectively. The cumulative soil respiration at 0.5 m-distance was 20, 31, and 38 % higher; and the temperature sensitivity of soil respiration ( Q) at 0.5 m-distance was 15, 30 and 12 % higher than that at 2 m-distance in 2011, 2012, and 2013, respectively. There was no significant difference in soil temperature and moisture between 0.5 m- and 2 m-distance, whereas fine root biomass at 0.5 m-distance was 64, 108, and 114 % higher than that at 2 m-distance in 2011-2013, respectively. Fine root biomass had a positive linear relationship with accumulative soil respiration and Q. Mean annual cumulative soil respiration was 0.46, 0.45, and 0.57 kg C m year in 2011-2013, respectively. Fine root biomass contributed to the spatial variation of soil respiration in apple orchard, and soil respiration at 2 m-distance could represent the C respired in orchard level. [ABSTRACT FROM AUTHOR]

Hot compression tests of the commercial Inconel 625 were performed in the temperature range of 950-1200 °C and strain rate range of 0.01-10 s. The flow behavior and processing maps were investigated using the corrected flow stress data to eliminate effects of the friction and adiabatic heating. The processing maps have exhibited a domain in the temperature range of 1100-1200 °C and strain rate range of 0.01-10 s corresponding to the higher efficiency of power dissipation. Microstructural observations reveal that the full dynamic recrystallization (DRX) occurs in this domain, which is optimum processing window for hot working to obtain a homogeneous microstructure. DRX grain growth occurs in the temperature range of 1150-1200 °C and strain rate range of 0.01-0.1 s. In view of the refined and uniform grains obtained by hot deformation, the finish forming processing should be selected the deformation conditions in which the full DRX occurs without the grain growth. The small regimes of flow instability are noticed at temperature below about 970 °C at the different strains. The material undergoes flow instability manifesting as bands of flow localizations and high density deformation twins. In addition, it is found that the undissolved second-phase particles and carbides can promote the DRX processing and be helpful to restrict the DRX grain growth. [ABSTRACT FROM AUTHOR]

The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate. [ABSTRACT FROM AUTHOR]

Aims: Concerns over food security and global climate change require an improved understanding of how to achieve optimal crop yields whilst minimizing net greenhouse gas emissions from agriculture. In the semi-arid Loess Plateau region of China, as elsewhere, fertilizer nitrogen (N) inputs are necessary to increase yields and improve local food security. Methods: In a dryland annual cropping system, we evaluated the effects of N fertilizers on crop yield, its long-term impact on soil organic carbon (SOC) concentrations and stock sizes, and the distribution of carbon (C) within various aggregate-size fractions. A current version (RothC) of the Rothamsted model for the turnover of organic C in soil was used to simulate changes in SOC. Five N application rates [0 (N0), 45 (N45), 90 (N90), 135 (N135), and 180 (N180) kg N ha] were applied to plots for 25 years (1984-2009) on a loam soil (Cumulic Haplustoll) at the Changwu State Key Agro-Ecological Experimental Station, Shaanxi, China. Results: Crop yield varied with year, but increased over time in the fertilized plots. Average annual grain yields were 1.15, 2.46, 3.11, 3.49, and 3.55 Mg ha with the increasing N application rates, respectively. Long-term N fertilizer application increased significantly ( P = 0.041) SOC concentrations and stocks in the 0-20 cm horizon. Each kilogram of fertilizer N applied increased SOC by 0.51 kg in the top soil from 1984 to 2009. Using RothC, the calculated annual inputs of plant C (in roots, stubble, root exudates, etc.) to the soil were 0.61, 0.74, 0.78, 0.86, and 0.97 Mg C ha year in N0, N45, N90, N135 and N180 treatments, respectively. The modeled turnover time of SOC (excluding inert organic C) in the continuous wheat cropping system was 26 years. The SOC accumulation rate was calculated to be 40.0, 48.0, 68.0, and 100.0 kg C ha year for the N45, N90, N135 and N180 treatments over 25 years, respectively. As aboveground biomass was removed, the increases in SOC stocks with higher N application are attributed to increased inputs of root biomass and root exudates. Increasing N application rates significantly improved C concentrations in the macroaggregate fractions (>1 mm). Conclusions: Applying N fertilizer is a sustainable practice, especially in carbon sequestration and crop productivity, for the semiarid Loess Plateau region. [ABSTRACT FROM AUTHOR]

We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the '1111' iron-based superconductors. The joint hole doping via (Ba,K) substitution &spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments. [ABSTRACT FROM AUTHOR]

Aims: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Methods: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Results: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Conclusions: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands. [ABSTRACT FROM AUTHOR]