A modified lattice Bhatnagar-Gross-Krook model for convection heat transfer in porous media

The lattice Bhatnagar-Gross-Krook (LBGK) model has become the most popular one in the lattice Boltzmann method for simulating the convection heat transfer in porous media. However, the LBGK model generally suffers from numerical instability at low fluid viscosities and effective thermal diffusivities. In this paper, a modified LBGK model is developed for incompressible thermal flows in porous media at the representative elementary volume scale, in which the shear rate and temperature gradient are incorporated into the equilibrium distribution functions. With two additional parameters, the relaxation times in the collision process can be fixed at a proper value invariable to the viscosity and the effective thermal diffusivity. In addition, by constructing a modified equilibrium distribution function and a source term in the evolution equation of temperature field, the present model can recover the macroscopic equations correctly through the Chapman-Enskog analysis, which is another key point different from previous LBGK models. Several benchmark problems are simulated to validate the present model with the proposed local computing scheme for the shear rate and temperature gradient, and the numerical results agree well with analytical solutions and/or those well-documented data in previous studies. It is also shown that the present model and the computational schemes for the gradient operators have a second-order accuracy in space, and better numerical stability of the present modified LBGK model than previous LBGK models is demonstrated.Comment: 38pages,50figure

Volume-averaged macroscopic equation for fluid flow in moving porous media

Darcy's law and the Brinkman equation are two main models used for creeping fluid flows inside moving permeable particles. For these two models, the time derivative and the nonlinear convective terms of fluid velocity are neglected in the momentum equation. In this paper, a new momentum equation including these two terms are rigorously derived from the pore-scale microscopic equations by the volume-averaging method, which can reduces to Darcy's law and the Brinkman equation under creeping flow conditions. Using the lattice Boltzmann equation method, the macroscopic equations are solved for the problem of a porous circular cylinder moving along the centerline of a channel. Galilean invariance of the equations are investigated both with the intrinsic phase averaged velocity and the phase averaged velocity. The results demonstrate that the commonly used phase averaged velocity cannot serve as the superficial velocity, while the intrinsic phase averaged velocity should be chosen for porous particulate systems

A new model to predict the unsteady production of fractured horizontal wells

Based on the hydraulic fracture width gradually narrows along the fracture length, with consideration of the mutual influences of fracture, non-uniform inflow of fractures segments and variable mass flow in the fracture comprehensively, a spatial separation method and time separation method were used to establish fracture horizontal well’s dynamic coupling model of reservoir seepage and fracture flow. The results showed that the calculation productivity of variable width model is higher than that of the fixed width model, while the difference becomes smaller as time increase. Due to mutual interference of the fractures, the production of outer fracture is higher than that of the inner fracture. When the dimensionless fracture conductivity is 0.1, the middle segment of the fracture dominates the productivity and local peak emerges near the horizontal well. The flow in the fracture is with the ‘double U’ type distribution. As the dimensionless fracture conductivity increase, the fractures productivity mainly through the tips and the flow in the fractures with the ‘U’ type distribution. Using the established fracture width variable productivity prediction model, one can achieve the quantitative optimization of fracture shape

Capillary imbibition of confined water in nanopores

The spontaneous capillary imbibition of confined nanopores is investigated using an analytical model that includes the slip effect, wettability and effective viscosity at the water surface interface. The results show that the effective viscosity of confined water is larger than that of bulk water and decreases with diameter and wettability. The effective slip length is negative for a contact angle of 0◦, and the effective slip length is positive and increases with diameter. The results of the presented model show that the capillary imbibition length for nanoconfined water can vary up to 0.389-1.033 times that determined by the Lucas-Washburn equation with no-slip boundary conditions for nanopores due to the effective viscosity and slippage with various dimensions and contact angles. The enhancement increases with diameter and contact angle. These results elucidate the confined movement through nanopores, which can be used to understand fracturing-fluid flow in the nanopores of shale reservoir formations.Cited as: Zeng, F., Zhang, Q., Guo, J., Meng, Y., Shao, X., Zheng, Y. Capillary imbibition of confined water in nanopores. Capillarity, 2020, 3(1): 8-15, doi: 10.26804/capi.2020.01.0

The rice ERF transcription factor OsERF922 negatively regulates resistance to Magnaporthe oryzae and salt tolerance

Rice OsERF922, encoding an APETELA2/ethylene response factor (AP2/ERF) type transcription factor, is rapidly and strongly induced by abscisic acid (ABA) and salt treatments, as well as by both virulent and avirulent pathovars of Magnaporthe oryzae, the causal agent of rice blast disease. OsERF922 is localized to the nucleus, binds specifically to the GCC box sequence, and acts as a transcriptional activator in plant cells. Knockdown of OsERF922 by means of RNAi enhanced resistance against M. oryzae. The elevated disease resistance of the RNAi plants was associated with increased expression of PR, PAL, and the other genes encoding phytoalexin biosynthetic enzymes and without M. oryzae infection. In contrast, OsERF922-overexpressing plants showed reduced expression of these defence-related genes and enhanced susceptibility to M. oryzae. In addition, the OsERF922-overexpressing lines exhibited decreased tolerance to salt stress with an increased Na+/K+ ratio in the shoots. The ABA levels were found increased in the overexpressing lines and decreased in the RNAi plants. Expression of the ABA biosynthesis-related genes, 9-cis-epoxycarotenoid dioxygenase (NCED) 3 and 4, was upregulated in the OsERF922-overexpressing plants, and NCED4 was downregulated in the RNAi lines. These results suggest that OsERF922 is integrated into the cross-talk between biotic and abiotic stress-signalling networks perhaps through modulation of the ABA levels

Effect of Bone Morphogenetic Protein-2 on Proliferation and Apoptosis of Gastric Cancer Cells

Objective: To investigate the effects of bone morphogenetic protein-2 (BMP-2) on the proliferation, differentiation and apoptosis of normal human gastric mucosal cells and gastric cancer cells

Bed strength in sheared beds of mono- and bi-disperse particles : Dependence on geometrical and mechanical properties of constituent particles

Acknowledgments This work is financially supported by National Science Foundation (U21A20105), China Scholarship Council, China Postdoctoral Science Foundation (2021M692695). FZ thanks LEPS Technology Company, Chengdu, China for providing the temporary plugging materials used in the present experiments and unpublished product specifications. The authors thank the two anonymous reviewers for their comments.Peer reviewe

Effectiveness of neoadjuvant immunochemotherapy compared to neoadjuvant chemotherapy in non-small cell lung cancer patients: Real-world data of a retrospective, dual-center study

BackgroundStudying the application of neoadjuvant immunochemotherapy (NICT) in the real world and evaluating its effectiveness and safety in comparison with neoadjuvant chemotherapy (NCT) are critically important.MethodsThis study included the II-IIIB stage non-small cell lung cancer (NSCLC) patients receiving NCT with or without PD-1 inhibitors and undergoing surgery after neoadjuvant treatments between January 2019 to August 2022. The clinical characteristics and treatment outcomes were retrospectively reviewed and analyzed.ResultsA total of 66 patients receiving NICT and 101 patients receiving NCT were included in this study. As compared to NCT, NICT showed similar safety while not increasing the surgical difficulty. The ORR in the NICT and NCT groups was 74.2% and 53.5%, respectively, P = 0.009. A total of 44 patients (66.7%) in the NICT group and 21 patients (20.8%) in the NCT group showed major pathology response (MPR) (P <0.001). The pathology complete response (pCR) rate was also significantly higher in NICT group than that in NCT group (45.5% vs. 10.9%, P <0.001). After Propensity Score Matching (PSM), 42 pairs of patients were included in the analysis. The results showed no significant difference in the ORR between the two groups (52.3% vs. 43.2%, P = 0.118), and the proportions of MPR (76.2%) and pCR (50.0%) in NICT group were significantly higher than those of MPR (11.9%) and pCR (4.7%) in the NCT group (P <0.001). The patients with driver mutations might also benefit from NICT.ConclusionsAs compared to NCT, the NICT could significantly increase the proportions of patients with pCR and MPR without increasing the operation-related bleeding and operation time

Construction of Yeast One-hybrid Bait Reporter Vector for Screening the Binding Proteins of Cassava MeCWINV1

Cellwall invertase (CWIN) hydrolyzes sucrose into glucose and fructose irreversibly, playing key roles in carbohydrate partitioning and plant defence. MeCWINV1 is one of the CWINs in cassava, which contains several light-responsive elements and stress-responsive elements in promoter region. To analyze the regulatory function of MeCWINV1 in the cassava starch accumulation and stress defense response, a 865 bp MeCWINV1 promoter fragment was cloned and inserted into yeast one-hybrid bait vector to construct pCW1-AbAi vector, then was transformed to Y1HGold yeast strains to screen the binding proteins. It might provide a framework for further investigation on the regulation mechanism of MeCWINV1 gene in cassava