Search

Surfactants are widely used in the tertiary recovery of oilfields， and it is of great significance to study the mechanism of surfactant flooding from the microscopic point of view. In recent years， molecular dynamics （MD） simulation has become essential for oil and gas field development research. The use of MD simulation to study surfactants has become a hot spot. Through MD simulation， the numerical solutions of Newton’s equations are calculated for all the moving particles in the system， and the change in atomic positions with time is analyzed， from which some laws are found. MD simulation can be used to study the microscopic behavior of surfactant molecules to explore the properties of surfactant molecules and the microscopic flooding mechanism. MD simulation of the movement and aggregation state of surfactants at the interface and the analysis of the influence of surfactant molecules at the interface on the interfacial system are of some guiding significance for the field application of surfactants. To this end， based on the principle overview of MD simulation， firstly， the force field， boundary conditions， system types， and numerical algorithms in MD simulation are summarized； secondly， the microscopic mechanisms of MD simulation of surfactant flooding are highlighted， including the reduction of oil-water interfacial tension， the change in surface wettability， the increase in interfacial charge and emulsification， etc.； then， examples of the application of MD simulation in surfactant flooding are presented. Finally， the development directions of MD simulation technology in surfactant flooding are proposed， including the flooding environment similar to production， the design of new surfactants， the relationship between theory and experiment， the selection of molecular force field and potential energy model， and the research and development of composite and multifunctional integrated surfactants.

Objective To explore the effects of store-operated calcium entry(SOCE) on oxidized low-density lipoprotein (ox-LDL)-induced hyperpermeability in human umbilical vein endothelial cells(HUVECs). Methods HUVECs at passage 3 were divided into the control group and the ox-LDL(10, 25, 50 and 100 μg/mL) intervention groups (n=3) for the examination of transendothelial electrical resistance (TER). HUVECs cultured in slides were randomly divided into the control group, the ox-LDL 24 h group and the ox-LDL 48 h group. The distribution of F-actin and VE-cadherin were detected by immunofluorescence, and the protein content of VE-cadherin was detected by Western blotting. Incubated with calcium fluorescence probe (Fluo-3/AM), intracellular free Ca2+ concentration (control group, ox-LDLgroup, ox-LDL+2-APB group) and SOCE (control group, ox-LDL 24 h group, ox-LDL 48 h group) were detected by laser confocal microscopy. Results Low dose of ox-LDL(10, 25 μg/mL) exerted no effect on TER. High dose of ox-LDL (50, 100 μg/mL) also had no effect on TER within 6 h, but after 6 h showed no effect on TER. However, high dose of ox-LDL(50, 100 μg/mL) reduced the decrease of TER in 12 h (P < 0.05), and the decrease was more significant in 24 h and 48 h. After the incubation with ox-LDL(100 μg/mL) 24 h and 48 h, the expression level of VE-cadherin decreased(P < 0.05), while the form and distribution of F-action changed; Intracellular free Ca2+ concentration increased obviously which was interrupted by 2-APB the SOCE inhibitor (P < 0.05), and the 2-APB can decrease the effect of ox-LDL on TER. After incubation with ox-LDL(100 μg/mL) 48 h, the amplitude of SOCE decreased (P < 0.05). The descending artery flow velocity of SOCE showed a slightly decreased trend after incubation with ox-LDL 24 h and a more significant decrease in 48 h(P < 0.05). Conclusion Ox-LDL up-regulate the intracellular free Ca2+ concentration of vascular endothelial cells by extending the duration of SOCE to effect the arrangement of cytoskeleton and cell junction, which increases the cell permeability.

Asynchronous injection–production cycle (AIPC) in a horizontal–vertical well pattern is an efficient strategy for enhancing water injection in tight reservoirs. However, current studies lack consideration of waterflood-induced fractures (WIFs) caused by long-term water injection. This paper takes block Z in the Ordos Basin, China, as the research object and first clarifies the formation conditions of WIFs considering the horizontal principal stress and flow line. Then, the pressure-sensitive permeability equations for the induce-fracture region between wells are derived. Finally, the WIFs characteristics in a horizontal–vertical well network with different injection modes are discussed by numerical simulation. The results show that WIFs preferentially form where flow aligns with the maximum principal stress, influencing permeability distribution. Controlling the injection rate of vertical wells on the maximum principal stress and flow line and cyclically adjusting the production rate of horizontal wells can regulate the appropriate propagation of WIFs and expand the swept areas. The parallel injection mode (PIM) and the half-production injection mode are superior to the full-production injection mode. This study can provide theoretical support for the effective development of tight oil reservoirs. [ABSTRACT FROM AUTHOR]

The shape and structure of helicopter fuselage are complex, and it is difficult for a finite element method (FEM) to investigate helicopter fuselage projectile damage in a multi-projectile environment. An efficient analysis method for helicopter fuselage projectile damage is then proposed by coupling the projectile breakdown theory, which is derived from the existing empirical formula for penetrating ductile metals, and the model of projectile impact. Then, the characteristics of the helicopter fuselage impact coordinate, residual velocity, and fuselage damage area under a multi-projectile attack are investigated. The results show that the predicted residual velocities agree with the experiments. The maximum errors of the residual velocity and the fuselage damage area are 4.7% and 9.56%, respectively. Compared with the FEM, the computational time of the proposed method is reduced by 92.1%, and its efficiency is obviously improved. As the incidence angle increases, the residual velocity decreases, and the damage area increases. When the incidence angle of the projectile body is large, the projectile body cannot penetrate the surface of the fuselage, resulting in flume skid damage and a large area of damage. [ABSTRACT FROM AUTHOR]

The agro-pastoral ecotone serves as an important ecological transition zone between grassland and cropland. It plays a crucial role in providing forage and maintaining the ecological security of Northern China. China has initiated many ecological restoration projects in the agro-pastoral ecotone. Separating the affecting factors of anthropogenic activities and natural factors change on grassland may help guide future ecological restoration projects. This study investigated the grassland change over the agro-pastoral ecotone in Inner Mongolia (APEI) using land use data, vegetation index, and monthly climate data, social and economic data from 2010 to 2020. Two indicators were introduced to evaluate the grassland change in quality and quantity. The average annual maximum NDVI of grassland within each sample was used as a proxy for grassland quality, and the proportion of grassland within each sample was used as a proxy for grassland quantity. The driving mechanisms of grassland quality were examined on different types of grassland. The results showed that (1) from 2010 to 2020, the quantity of grassland in APEI slightly decreased while the quality of the grassland significantly improved; (2) the change in grassland quality was jointly caused by natural factors and human activities, with 66.77% being attributed to natural factors and 33.23% to human activities. In some areas, the alteration in grassland quality was solely determined by either the impacts of natural factors or human-induced disturbances; and (3) temperature and precipitation played different roles in affecting grassland quality among different types of grassland. In some areas, anthropogenic activities, such as farmland and population, would affect grassland quality. The findings of this study would contribute to the understanding of the mechanism of ecological environmental changes in the agro-pastoral ecotone and guide the planning and implementation of future ecological restoration projects in agro-pastoral areas. [ABSTRACT FROM AUTHOR]

With the characteristics of high transmission delay and mobility, distributed time synchronization of underwa-ter sensor networks can be very challenging. The existing works cannot get high accuracy, because most of them ignore the long transmission latency, or dynamic changing tra ission delay caused by the mobility. A mobility model was built considering the effect of mobility and long transmission latency on time synchronization, and a time synchronization parameters equation was formed according to the mobili model. Thus, based on the equation, a time synchronization algorithm (MM-sync) was proposed. The experiment results show that MM-sync can reduce the consumption of energy, and can get higher accuracy than state-of-art solutions in high density underwater sensor networks with rapid movement.

In recent years, wild morel mushroom species have begun to be widely cultivated in China due to their high edible and medicinal values. To parse the medicinal ingredients, we employed the technique of liquid-submerged fermentation to investigate the secondary metabolites of Morehella importuna. Two new natural isobenzofuranone derivatives (1–2) and one new orsellinaldehyde derivative (3), together with seven known compounds, including one o-orsellinaldehyde (4), phenylacetic acid (5), benzoic acid (6), 4-hydroxy-phenylacetic acid (7), 3,5-dihydroxybenzoic acid (8), N,N′-pentane-1,5-diyldiacetamide (9), and 1H-pyrrole-2-carboxylic acid (10), were obtained from the fermented broth of M. importuna. Their structures were determined according to the data of NMR, HR Q-TOF MS, IR, UV, optical activity, and single-crystal X-ray crystallography. TLC-bioautography displayed that these compounds possess significant antioxidant activity with the half DPPH free radical scavenging concentration of 1.79 (1), 4.10 (2), 4.28 (4), 2.45 (5), 4.40 (7), 1.73 (8), and 6.00 (10) mM. The experimental results would shed light on the medicinal value of M. importuna for its abundant antioxidants. [ABSTRACT FROM AUTHOR]

Accurate monitoring of bare soil land (BSL) is an urgent need for environmental governance and optimal utilization of land resources. High-resolution imagery contains rich semantic information, which is beneficial for the recognition of objects on the ground. Simultaneously, it is susceptible to the impact of its background. We propose a semantic segmentation model, Deeplabv3+-M-CBAM, for extracting BSL. First, we replaced the Xception of Deeplabv3+ with MobileNetV2 as the backbone network to reduce the number of parameters. Second, to distinguish BSL from the background, we employed the convolutional block attention module (CBAM) via a combination of channel attention and spatial attention. For model training, we built a BSL dataset based on BJ-2 satellite images. The test result for the F1 of the model was 88.42%. Compared with Deeplabv3+, the classification accuracy improved by 8.52%, and the segmentation speed was 2.34 times faster. In addition, compared with the visual interpretation, the extraction speed improved by 11.5 times. In order to verify the transferable performance of the model, Jilin-1GXA images were used for the transfer test, and the extraction accuracies for F1, IoU, recall and precision were 86.07%, 87.88%, 87.00% and 95.80%, respectively. All of these experiments show that Deeplabv3+-M-CBAM achieved efficient and accurate extraction results and a well transferable performance for BSL. The methodology proposed in this study exhibits its application value for the refinement of environmental governance and the surveillance of land use. [ABSTRACT FROM AUTHOR]