Modeling of multiphase flow in low permeability porous media:Effect of wettability and pore structure properties

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications.However,a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability.To address this issue,based on the digital rock of low permeability sandstone,a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process.In addition,a dual-porosity pore network model(PNM)is constructed to obtain the water-oil relative permeability of the sample.The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties.Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability.The injected water breaks through the outlet earlier with a large mass flow,while thick oil films exist in rough hydrophobic surfaces and poorly connected pores.The variation of water-oil relative permeability is significant,and residual oil saturation is high in the oil-wet system.The flooding is extensive,and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces;thus,water relative permeability is lower in the water-wet system.While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity.Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance,and a large microporosity corresponds to low residual oil saturation.This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

A model‑free approach to do long‑term volatility forecasting and its variants

Volatility forecasting is important in financial econometrics and is mainly based on the application of various GARCH-type models.However,it is difficult to choose a specific GARCH model that works uniformly well across datasets,and the traditional methods are unstable when dealing with highly volatile or short-sized datasets.The newly pro-posed normalizing and variance stabilizing(NoVaS)method is a more robust and accu-rate prediction technique that can help with such datasets.This model-free method was originally developed by taking advantage of an inverse transformation based on the frame of the ARCH model.In this study,we conduct extensive empirical and simu-lation analyses to investigate whether it provides higher-quality long-term volatility forecasting than standard GARCH models.Specifically,we found this advantage to be more prominent with short and volatile data.Next,we propose a variant of the NoVaS method that possesses a more complete form and generally outperforms the current state-of-the-art NoVaS method.The uniformly superior performance of NoVaS-type methods encourages their wide application in volatility forecasting.Our analyses also highlight the flexibility of the NoVaS idea that allows the exploration of other model structures to improve existing models or solve specific prediction problems.

Prevalence of Congenital Heart Disease at Extremely High Altitudes in Tibet and the Establishment of a New Free Treatment Model

Background: This study aimed to illustrate the prevalence of CHD by screening children in extremely high-altitudeareas (over 4000 m to even 5000 m above sea level) and explore an aid model for early diagnosis and treatmentfor the Tibetan population. Methods: A total of 2242 students from different schools in Ngamring County,Xigaze City, Tibet from September 2019 to September 2020 were selected for screening. The students were examinedthrough the inquiry of their current medical history and family history, cardiac auscultation and a physicalexamination, in order to screen out the suspected cases of CHD, and then the suspected cases were confirmed bycardiac color ultrasound examinations. After that, positive patients were be transferred to Shandong Province forfree treatment. Results: The prevalence of CHD among children in Ngamring County was 3.70% (83 cases),which is the highest incidence rate ever reported. The most common type of CHD was patent ductus arteriosus(PDA), accounting for 55.42% of the total number of cases screened, followed by atrial septal defect (ASD) andventricular septal defect (VSD), accounting for 28.92% and 12.05%, respectively. The prevalence of CHD in childrenat high altitude was significantly higher than that in children at low altitude. The children with CHD weretransferred to Shandong Province for surgery, the operations were successful and their recoveries went well.Conclusions: The results show that high altitude is closely related to the prevalence of CHD, and the incidencein Ngamring County is much higher than that in previous reports.

DYNAMIC FREE ENERGY HYSTERESIS MODEL IN MAGNETOSTRICTIVE ACTUATORS

A dynamic free energy hysteresis model in magnetostrictive actuators is presented. It is the free energy hysteresis model coupled to an ordinary different equation in an unusual way. According to its special structure, numerical implementation method of the dynamic model is provided. The resistor parameter in the dynamic model changes according to different frequency ranges. This makes numerical implementation results reasonable in the discussed operating frequency range. The validity of the dynamic free energy model is illustrated by comparison with experimental data.

Effects of Chuanxiongqin hydrochloride on increasing the fluidity of brain cell membrane and scavenging free radicals in model rats with ischemia/reperfusion injury

BACKGROUND: The fluidity of cell membrane can be affected by various factors. Many experiments have confirmed that the ischemia/reperfusion of organic tissue can increase the contents of free radicals, which lead to high rigidity and low fluidity of cell membrane, and the conditions can be changed by Chuanxiongqin. OBJECTIVE: To observe the effect and mechanism of Chuanxiongqin hydrochloride on the fluidity of brain cell membrane in rat models of ischemia/reperfusion. DESIGN: A completely randomized controlled animal trial. SETTINGS: Institute of Brain Sciences; Department of Physiology, Medical College, Datong University. MATERIALS: Twenty male grade Ⅰ Wistar rats of 170-220 g were randomly divided into model group (n =10) and control group (n =10). Chuanxiongqin hydrochloride (molecular mass was 172.2) was purchased from the National Institute for the Control of Pharmaceutical and Biological Products (batch number: 0817-9803); Spin labelers: 5-doxyl-stearlic acid methylester (5DS), 16-doxyl-stearlic acid methylester (16DS), xanthine, xanthine oxidase (XOD) and 5,5-dimeth-1-pyrroline- N-oxide (DMPO) from Sigma Company; Bruker ESP 300 electron paramagnetic resonance (EPR) spectrometer by Bruker Company (Germany). METHODS: The experiments were carried out in the State Key Laboratory of Natural and Biomimetic Drugs, Peking University from June 2001 to July 2002. In the model group, rats were made into models of cerebral ischemia by 30-minute ligation and 2-hour reperfusion of common carotid arteries; The rats in the control group were not made into models. The order parameter (S) and rotational correlation time (τc) were detected with the ESR spectrometer by means of spin labeling. The greater the S and τc, the smaller the fluidity. Meanwhile, the clearance rate of free radicals was detected with ESR spin trapping. The measurement data were compared using the t test. MAIN OUTCOME MEASURES: The S, τc and clearance rates of O2 · and OH· free radicals were compared between the model group and control group. RESULTS: The S and τc in the model group [0.738 4±0.003 5; (8.472±0.027)×10-10 s/circle] were obviously different from those in the control group [0.683 9±0.008 3; (7.945±0.082)×10-10 s/circle, t =5.731, 5.918, P < 0.05], which suggested that ischemia/reperfusion injury decreased the fluidity of brain cell membrane. After adding Chuanxiongqin hydrochloride, there were no obvious differences between the model group [0.688 5±0.030 5; (7.886±0.341)×10-10 s/circle] and control group (P > 0.05), indicating that Chuanxiongqin hydrochloride could recover the fluidity of brain cell membrane after ischemia/reperfusion injury close to the level in the normal control group. Chuanxiongqin hydrochloride could directly scavenge the O2 · and OH· free radicals, and the maximal clearance rates were 83.92% and 44.99% respectively. CONCLUSION: Chuanxiongqin hydrochloride increases the fluidity of membrane of ischemia-injured brain cell by scavenging both O2 ·and OH· free radicals.

Model Free Adaptive Predictive Control of Desulfurization Slurry pH Based on CPS Framework

In order to improve the slurry pH control accuracy of the absorption tower in the wet flue gas desulfurization process,a model free adaptive predictive control algorithm for the desulfurization slurry pH which is based on a cyber physical systems framework is proposed.First,aiming to address system characteristics of non-linearity and pure hysteresis in slurry pH change process,a model free adaptive predictive control algorithm based on compact form dynamic linearization is proposed by combining model free adaptive control algorithm with model predictive control algorithm.Then,by integrating information resources with the physical resources in the absorption tower slurry pH control process,an absorption tower slurry pH optimization control system based on cyber physical systems is constructed.It is turned out that the model free adaptive predictive control algorithm under the framework of the cyber physical systems can effectively realize the high-precision tracking control of the slurry pH of the absorption tower,and it has strong robustness.

大豆油催化热解动力学分析

为了优化油脂类热解工艺,测量了大豆油催化热解的热重及差示扫描量热曲线,催化剂为碳酸钠、α型氧化铝及γ型氧化铝,反应温度由室温升至600℃。曲线表明催化剂的加入改变了热解反应的历程。利用不同升温速率(5、10和20 K/min)的热重数据,采用Vyazovkin算法计算了反应的活化能。活化能计算结果与DSC、DTG曲线的变化趋势相一致;大豆油的热解起始活化能为204.33 kJ/mol,碳酸钠、α型氧化铝、γ型氧化铝可将起始活化能分别降至137.3、98.455和182.06 kJ/mol,但随反应的进行,催化热解的活化能会逐步升高。依据活化能计算结果预测了等温裂解反应时间,温度的升高能有效降低反应时间,接近转化终点所用反应时间由6 h以上缩短至40 min以内。反应时间的计算结果表明催化剂的加入可以使反应较为温和的进行。

Triangular domain extension of algebraic trigonometricB′ezier-like basis

In computer aided geometric design （CAGD）, B′ezier-like bases receive more andmore considerations as new modeling tools in recent years. But those existing B′ezier-like basesare all defined over the rectangular domain. In this paper, we extend the algebraic trigono-metric B′ezier-like basis of order 4 to the triangular domain. The new basis functions definedover the triangular domain are proved to fulfill non-negativity, partition of unity, symmetry,boundary representation, linear independence and so on. We also prove some properties of thecorresponding B′ezier-like surfaces. Finally, some applications of the proposed basis are shown.

Fe2O3/氮掺杂石墨烯复合材料的热分解动力学

对Fe2O3/氮掺杂石墨烯(NG)的热解行为进行热重研究,分析出物质的热分解特性和机理函数。通过水热法制备Fe2O3/NG样品,在氮气氛围的保护下分别以5、10、15、20 K/min的升温速率线性升温到1473.15 K。使用Kissinger Akahira and Sunose(KAS)、Flyn n-Wal l-Ozawa(FWO)两种“model free”方法和Coat s-Redfern模型拟合法进行热动力学拟合,结果表明:FWO和KAS两种拟合法估算的表观活化能变化范围分别为404.08~424.65 kJ/mol和405.52~427.10 kJ/mol,且表观活化能随着转化率的增大而增加;FWO和KAS两种拟合法估算的表观活化能平均值分别为410.92 kJ/mol和412.74 kJ/mol,相差0.4%;Mample Power(P3)是最能反映Fe2O3/NG分解机理的函数。

显式自由表面模型时间分裂格式的一个积分方案(英文)

Errors due to split time stepping are discussed for an explicit free–surface ocean model. In commonly used split time stepping, the way of time integration for the barotropic momentum equation is not compatible with that of the baroclinic one. The baroclinic equation has three–time–level structure because of leapfrog scheme. The barotropic one, however, has two–time–level structure when represented in terms of the baroclinic time level, on which the baroclinic one is integrated. This incompatibility results in the splitting errors as shown in this paper. The proper split time stepping is therefore proposed in such a way that the compatibility is kept between the barotropic and baroclinic equations. Its splitting errors are shown extremely small, so that it is particularly relevant to long–term integration for climate studies. It is applied to a free–surface model for the North Pacific Ocean.

Study on the Bubble Growth and Departure with A Lattice Boltzmann Method

For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain to deal with the no-slip boundary condition. Effects of the viscosity, surface tension, gas inertial force and buoyancy on the characteristics of bubbles when they grow and departure from an orifice in quiescent liquid are studied. The releasing period and departure diameter of the bubble are influenced by the residual gas at the orifice, and the interaction between bubbles is taken into consideration. The relations between the releasing period or departure diameter and the gravity acceleration show fair agreements with previous numerical and theoretical results. And the influence of the gas outflow velocity on bubble formation is discussed as well. For the bubbles growing in cross-flow field, effects of the cross-flow speed and the gas outflow velocity on the bubble formation are discussed, which is related to the application in ship resistance reduction. And optimal choice of the ship speed and gas outflow velocity is studied. Cases in this paper also prove that this high density ratio LBM model has its flexibility and effectiveness on multiphase flow simulations.

Symmetrical adhesion of two cylindrical colloids to a tubular membrane

With the full treatment of the Helfrich model we theoretically study the symmetrical adhesion of two cylindrical colloids to a tubular membrane. The adhesion of the rigid cylinders with different radius from the membrane tube surface can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. These significant structural behaviors can be obtained by analyzing the system energy. A second order adhesion transition from the desorbed to weakly adhered states is found, and a first order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered states can be obtained as well.

Fusion Equation of Metals

An expression of initial slope of melting curve of pure metals was obtained as follows: (dT_m/dP)_o=T_(mo)/c, where c=1.09 (N_(at))^(5/3)z^(-1/3), the unit of c is GPa, N_(at) is the atomic concentra- tion (in 10^(28) m^(-3)), z is the valence, T_(mo) is the melting temperature (in k) of metal under one atmosphere. The calculated results for thirty-one metals agree well with experiments. It has also been proved that by using the free electron model of melting, the fusion equation of metals is Simon equation (T_m/T_(mo))q=1+(p/d). Two parameters q and d, which have to fit with experiments in Simon's empirical equation, now can be predicted theoretically, e.g. for Mg, giving q=1.56, d=7.88GPa, the calculated melting curve in a fairly wide pressure range (0～60GPa) is shown to be close to the experimental one.

Research of testing method based on UML statecharts

Unified modeling language （UML） is a powerful graphical modeling language with intuitional meaning. It provides various diagrams to depict system characteristics and complex environment from different viewpoints and different application layers. UML-based software development and modeling environments have been widely accepted in industry, including areas in which safety is an important issue such as spaceflight, defense, automobile, etc. To ensure and improve software quality becomes a main concern in the field. As one of the key techniques for software quality, software testing can effectively detect system faults. UML based software testing based is an important research direction in software engineering. The key to software testing is the generation of test cases. This dissertation studies an approach to generating test cases from UML statecharts.

Appraisal of pollution and health risks associated with coal mine contaminated soil using multimodal statistical and Fuzzy-TOPSIS approaches

The present study assesses the concentration,probabilistic risk,source classification,and dietary risk arising from heavy metal(HMs)pollution in agricultural soils affected by coal mining in eastern part of India.Analyses of soil and rice plant indicated significantly elevated levels of HMs beyond the permissible limit in the contaminated zones(zone 1:PbSoil:108.24±72.97,CuSoil:57.26±23.91,CdSoil:8.44±2.76,CrSoil:180.05±46.90,NiSoil:70.79±25.06 mg/kg;PbGrain:0.96±0.8,CuGrain:8.6±5.1,CdGrain:0.65±0.42,CrGrain:4.78±1.89,NiGrain:11.74±4.38 mg/kg.zone 2:PbSoil:139.56±69.46,CuSoil:69.89±19.86,CdSoil:8.95±2.57,CrSoil:245.46±70.66,NiSoil:95.46±22.89 mg/kg;PbGrain:1.27±0.84,CuGrain:7.9±4.57,CdGrain:0.76±0.43,CrGrain:8.6±1.58,NiGrain:11.50±2.46 mg/kg)compared to the uncontaminated zone(zone 3).Carcinogenic and non-carcinogenic health risks were computed based on the HMs concentration in the soil and rice grain,with Pb,Cr,and Ni identified as posing a high risk to human health.Monte Carlo simulation,the solubility-free ion activity model(FIAM),and severity adjusted margin of exposure(SAMOE)were employed to predict health risk.FIAM hazard quotient(HQ)values for Ni,Cr,Cd,and Pb were>1,indicating a significant non-carcinogenic risk.SAMOE(risk thermometer)results for contaminated zones ranged from low to moderate risk(CrSAMOE:0.05,and NiSAMOE:0.03).Fuzzy-TOPSIS and variable importance plots(from random forest)showed that Ni and Cr were mostly responsible for the toxicity in the rice plant,respectively.A self-organizing map for source classification revealed common origin for the studied HMs with zone 2 exhibiting the highest contamination.The positive matrix factorization model for the source apportionment identified coal mining and transportation as the predominant sources of HMs.Spatial distribution analysis indicated higher contamination near mining sites as compared to distant sampling sites.Consequently,this study will aid environmental scientists and policymakers controlling HM pollution in agricultural soils near coal mines.

Modelling sulphate-enhanced cadmium uptake by Zea mays from nutrient solution under conditions of constant free Cd^(2+) ion activity

A controlled hydroponic experiment was undertaken to investigate Cd uptake in relation to the activity of Cd species in solution other than the free ion （Cd^2＋） by maintaining a constant Cd^2＋ activity under variable SO4^2- and Cl^- concentrations exposed to maize （Zea mays vat. Cameron） plants. The objectives of these experiments were： （1） to distinguish and quantify the different uptake rates of free and inorganic-complexed Cd from nutrient solution, and （2） to model the uptake of Cd by maize with a Biotic Ligand Model （BLM） in a system which facilitates the close examination of root characteristics. Results of the current experiments suggest that, in addition to the free ion, CdSO4^0 complexes are important factors in determining Cd uptake in nutrient solution by maize plants. Higher nominal SO4^2- concentrations in solution generally resulted in a greater Cd accumulation by maize plants than predicted by the Cd^2＋ activity. A better integration of the complete dataset for the 3 harvest times （6, 9 and 11 days after treatment） was achieved by including consideration of both the duration of Cd exposure and especially the root surface area to express Cd uptake. Similarly, the fit of the BLM was also improved when taking into account exposure time and expressing uptake in terms of root morphological parameters.

THE APPLICATIONS AND STUDY OF NUMERICAL SIMULATION OF TURBULENCE FLOW WITH FREE SURFACE IN HYDRAULIC SPILL WAYS STRUCTURE

The turbulence flow Free Surface has important applications in hydraulic spillways structure, such as the hydraulic jump, energy dissipation flow etc. This is being considered as very complicated flow, and has not yet been solved quite well by numerical method. In this paper, a Large-scale computational software package are developed for numerical laboratory of hydraulic spillway structure. Some methods,such as turbulence model, free surface and irregular boundary treating techniques,scientific computer visualization are put forward and performed.

Triangular domain extension of linear Bernstein-like trigonometric polynomial basis

In computer aided geometric design(CAGD),the Bernstein-Bézier system for polynomial space including the triangular domain is an important tool for modeling free form shapes.The Bernstein-like bases for other spaces(trigonometric polynomial,hyperbolic polynomial,or blended space) has also been studied.However,none of them was extended to the triangular domain.In this paper,we extend the linear trigonometric polynomial basis to the triangular domain and obtain a new Bernstein-like basis,which is linearly independent and satisfies positivity,partition of unity,symmetry,and boundary represen-tation.We prove some properties of the corresponding surfaces,including differentiation,subdivision,convex hull,and so forth.Some applications are shown.

Numerical investigation of full scale coaxial main rotor aerodynamics in hover and vertical descent

The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State(VRS)area was performed.The calculations were carried out under the condition of variable blade pitch angle values providing a fixed timeaverage thrust value.Visualization data of free vortex wake shapes,flow structures,and velocity fields were obtained and analyzed.The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed.The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations,growth of rotor power consumption relative to the hover,growth of rotor induced velocities relative to the hover,and growth of the required rotor blade pitch angles values.The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.

Inference after covariate-adaptive randomisation:aspects of methodology and theory

Covariate-adaptive randomisation has a more than 45 years of history of applications in clinical trials,in order to balance treatment assignments across prognostic factors that may have influence on the outcomes of interest.However,almost no theory had been developed for covariate-adaptive randomisation until a paper on the theory of testing hypotheses published in 2010.In this article,we review aspects of methodology and theory developed in the last decade for statistical inference under covariate-adaptive randomisation.Wefocus on issues such as whether a conventional procedure valid under the assumption that treatments are assigned completely at random is still valid or conservative when the actual randomisation is covariateadaptive,how a valid inference procedure can be obtained by modifying a conventional method or directly constructed by stratifying the covariates used in randomisation,whether inference procedures have different properties when covariate-adaptive randomisation schemes have different degrees of balancing assignments,and how to further adjust covariates in the inference procedures to gain more efficiency.Recommendations are made during the review and further research problems are discussed.