Numerical study of the effect of tortuosity and mixed wettability on spontaneous imbibition in heterogeneous porous media

Spontaneous imbibition in porous media plays an important role in numerous industrial processes, but its underlying mechanisms are still poorly understood due to the complicated structure and multiple surface properties of natural porous media. In order to fill this gap, a quasi-three-dimensional color-gradient lattice Boltzmann model is applied to simulate the spontaneous imbibition in heterogeneous porous media micromodels, where the influence of viscosity ratio, tortuosity and mixed wettability is systematically investigated. Results show that the tortuosity has less influence on imbibition than the viscosity ratio, which leads to unstable displacement for viscosity ratios smaller than unity and to stable displacement for viscosity ratios greater than unity. By establishing the power-law relationship between wetting fluid saturation and time, it is found that the scaling exponent is not only affected by tortuosity, but also related to pore throat structure of the micromodel. In addition, the mixed wettability is found to significantly influence the stability of displacement, especially when the contact angle difference of two constituents is large. Specifically, the greater the mixing degree of two wettabilities, the more unstable the displacement will become, which results in an enhanced interface roughening. Accordingly, the scaling exponent deviates more from the prediction from the Lucas-Washburn equation. Due to the reduced connectivity of flow paths, the wetting fluid imbibition rate in mixed wettability condition is lower than that in uniform wettability condition, no matter whether the latter theoretically corresponds to a slow displacement or not.Cited as: Diao, Z., Li, S., Liu, W., Liu, H., Xia, Q. Numerical study of the effect of tortuosity and mixed wettability on spontaneous imbibition in heterogeneous porous media. Capillarity, 2021, 4(3): 50-62, doi: 10.46690/capi.2021.03.0

A New Targeted Password Guessing Model

TarGuess-I is a leading targeted password guessing model using users\u27 personally identifiable information(PII) proposed at ACM CCS 2016 by Wang et al. Owing to its superior guessing performance, TarGuess-I has attracted widespread attention in password security. Yet, TarGuess-I fails to capture popular passwords and special strings in passwords correctly. Thus we propose TarGuess-I$^+$: an improved password guessing model, which is capable of identifying popular passwords by generating top-300 most popular passwords from similar websites and grasping special strings by extracting continuous characters from user-generated PII. We conduct a series of experiments on 6 real-world leaked datasets and the results show that our improved model outperforms TarGuess-I by 9.07\% on average with 1000 guesses, which proves the effectiveness of our improvements

Diet-Intestinal Microbiota Axis in Osteoarthritis: A Possible Role

Intestinal microbiota is highly involved in host physiology and pathology through activity of the microbiome and its metabolic products. Osteoarthritis (OA) is a common form of arthritis characterized by articular cartilage destruction and osteophyte formation. Although various person-level risk factors, such as age, sex, and obesity, have been proposed for the pathogenesis of OA, the underlying links between these person-level factors and OA are still enigmatic. Based on the current understanding in the crosstalk between intestinal microbiota and these risk factors, intestinal microbiota could be considered as a major hidden risk factor that provides a unifying mechanism to explain the involvement of these person-level risk factors in OA

Research Progress, Hotspots, and Trends of Using BIM to Reduce Building Energy Consumption: Visual Analysis Based on WOS Database

With the development of engineering technology, building information modeling (BIM) has attracted more and more attention and has been studied by many experts on building energy consumption in recent years. It is necessary to analyze and forecast the application trend and prospect of BIM technology in building energy consumption. Based on 377 articles published in the WOS database, this study adopts the technique of combining scientometrics and bibliometrics to obtain relevant research hotspots and quantitative analysis results. The findings demonstrate that the building energy consumption field has made extensive use of BIM technology. However, there are still some limitations that can be improved, and the use of BIM technology in construction renovation projects should be emphasized. This study can help readers better understand the application status of BIM technology and its trajectory of development with regard to building energy consumption, providing a valuable reference for future research

Design of the water-cooling structure for the 100 kA DC mechanical switch in the CRAFT quench protection system

The DC mechanical switch is connected in series with the superconducting magnet in the quench protection system. As the main switch that carries the magnet current for a long time, the temperature of its conductive unit, especially the contact part, inevitably increases significantly during operation. It is necessary to design a water-cooled structure to control the temperature rise. This article introduces the structural design of the conductive unit of the DC mechanical switch for the Comprehensive Research Facility for Fusion Technology quench protection system and uses a combination of theoretical calculation, thermal-electrical coupling simulation, and Fluent simulation to analyze the thermal stability characteristics at a current level of 100 kA. By comparing and studying the temperature rise characteristics of switches under different cooling paths, diameters of water-cooling pipe, and water flow rates, a design basis is provided for determining a 15 mm diameter “∏” shaped cooling water path structure for the mechanical switch. The DC mechanical switch water-cooled structure designed in this article is expected to effectively control the temperature rise level of the contact

Experimental Study on Pore Structure Evolution of Unloaded Rock Mass during Excavation of Reservoir Slope under Dry–Wet Cycle

There is a long sequence of periodic characteristics of reservoir water storage and discharge in large hydropower stations. The unloaded rock mass formed by blasting and excavation in the reservoir slope of the reservoir fluctuation zone is not only subjected to the penetration erosion caused by the change of the water level of the reservoir slope, but also the dry–wet cycle caused by the reservoir water storage and discharge. There is an obvious process of crack derivation and pore structure expansion, and the subsequent strength degradation breeds reservoir slope risks, which is one of the important factors restricting the operation safety of power stations. To study the pore structure evolution law of unloaded rock mass in reservoir slope excavation of reservoir fluctuation zones, the dry–wet cycle test simulating the periodic storage and discharge environment was carried out with samples of equal unloading amount obtained by indoor triaxial unloading test. The variation law of mesoscopic parameters such as wave velocity, mass, and nuclear magnetic resonance spectrum under dry–wet cycle was compared and analyzed, and the physical and mechanical mechanism of the pore structure evolution of the unloaded specimen under dry–wet cycles was explored. The results show that: (1) With the increase of dry–wet cycles, the evolution of wave velocity and dry mass of unloaded samples has obvious stage characteristics, which generally presents a rapid change in the early stage, moderate in the middle stage, and gradually stable in the late stage; (2) nuclear magnetic resonance (NMR) shows that the number of macropore structures in unloaded samples increases gradually with the dry–wet cycles; (3) the smaller the initial confining pressure, the larger the first peak area and the peak value of unloaded samples, and the spectral area corresponding to each peak under low confining pressure is significantly larger than that under medium and high confining pressure; (4) the unloading amount affects the overall proportion of macropores in the sample, which determines the deterioration process and evolution law of the mesostructure of the sample under dry–wet cycles

Modified Password Guessing Methods Based on TarGuess-I

TarGuess−I is a leading online targeted password guessing model using users’ personally identifiable information (PII) proposed at ACM CCS 2016 by Wang et al. It has attracted widespread attention in password security owing to its superior guessing performance. Yet, after analyzing the users’ vulnerable behaviors of using popular passwords and constructing passwords with users’ PII, we find that this model does not take into account popular passwords, keyboard patterns, and the special strings. The special strings are the strings related to users but do not appear in the users’ demographic information. Thus, we propose TarGuess−I+KPX, a modified password guessing model with three semantic methods, including (1) identifying popular passwords by generating top-300 lists from similar websites, (2) recognizing keyboard patterns by relative position, and (3) catching the special strings by extracting continuous characters from user-generated PII. We conduct a series of evaluations on six large-scale real-world leaked password datasets. The experimental results show that our modified model outperforms TarGuess−I by 2.62% within 100 guesses