液滴碰撞球形凹曲面复合level set-VOF法的数值分析

采用复合水平集法和流体体积法建立液滴冲击球形凹曲面的数值模型,通过分析计算结果揭示了液滴撞壁流动及破碎机制。研究表明:液滴的撞壁特性与液滴碰撞速度密切相关;液滴凹曲面撞壁与平面撞壁相比,铺展系数较小,回弹射流出现时间超前,回弹射流速度较大。量纲1分析得出:液滴的最大铺展系数和相对最大铺展速度与Reynolds数近似幂递增,液滴的相对最大射流长度与Reynolds数近似对数递增,液滴的相对最大射流速度与Reynolds数近似幂递减。对比分析现有液滴撞壁最大铺展系数理论解析模型,提出了液滴凹曲面撞壁最大铺展系数解析模型的发展方向。

农村人口流动对区域经济发展贡献实证分析——以河南省为例

利用劳动力流动效应模型测度了农村劳动力流动对区域经济发展的贡献,并利用灰色关联度测度了不同类型农村流动人口与经济发展的相关性。结果表明,1进入新世纪以来,中国农村劳动力流动对经济发展贡献显著,对经济增长的平均贡献率达14.7%,但随着时间的推移,农村劳动力流动对经济增长的贡献呈现先增大而后又减小的变化趋势;2区域外流入人口对经济发展的贡献低于区域内流动人口,区域内农村劳动力流动对经济发展的贡献与区域外农村劳动力流动对经济发展的贡献相当,区域外城镇流动人口对经济发展的贡献低于区域内城镇流动人口对经济发展的贡献。

Bayesian analysis for mixed-effects model defined by stochastic differential equations

The nonlinear mixed-effects model with stochastic differential equations （SDEs） is used to model the population pharmacokinetic （PPK） data that are extended from ordinary differential equations （ODEs） by adding a stochastic term to the state equation. Compared with the ODEs, the SDEs can model correlated residuals which are ubiquitous in actual pharmacokinetic problems. The Bayesian estimation is provided for nonlinear mixed-effects models based on stochastic differential equations. Combining the Gibbs and the Metropolis-Hastings algorithms, the population and individual parameter values are given through the parameter posterior predictive distributions. The analysis and simulation results show that the performance of the Bayesian estimation for mixed-effects SDEs model and analysis of population pharmacokinetic data is reliable. The results suggest that the proposed method is feasible for population pharmacokinetic data.

Simulation of astronomical solar radiation over Yellow River Basin based on DEM

Based on the developed distributed model for calculating astronomical solar radiation (ASR), monthly ASR with a resolution of 1 km×1 km for the rugged terrains of Yellow River Basin was calculated, with DEM data as the general characterization of terrain. This model gives an all-sided consideration on factors that influence the ASR. Results suggest that (1) Annual ASR has a progressive decrease trend from south to north; (2) the magnitude order of seasonal ASR is: summer>spring>autumn>winter; (3) topographical factors have robust effect on the spatial distribution of ASR, particularly in winter when a lower sun elevation angle exists; (4) the ASR of slopes with a sunny exposure is generally 2 or 3 times that of slopes with a shading exposure and the extreme difference of ASR for different terrains is over 10 times in January; (5) the spatial differences of ASR are relatively small in summer when a higher sun elevation angle exists and the extreme difference of ASR for different terrains is only 16% in July; and (6) the sequence of topographical influence strength is: winter>autumn>spring>summer.

Numerical Investigation on 1,3-Butadiene/Propyne Co-pyrolysis and Insight into Synergistic Effect on Aromatic Hydrocarbon Formation

A numerical investigation on the co-pyrolysis of 1,3-butadiene and propyne is performed to explore the synergistic effect between fuel components on aromatic hydrocarbon formation. A detailed kinetic model of 1,3-butadiene/propyne co-pyrolysis with the sub-mechanism of aromatic hydrocarbon formation is developed and validated on previous 1,3-butadiene and propyne pyrolysis experiments. The model is able to reproduce both the single component pyrolysis and the co-pyrolysis experiments, as well as the synergistic effect between 1,3- butadiene and propyne on the formation of a series of aromatic hydrocarbons. Based on the rate of production and sensitivity analyses, key reaction pathways in the fuel decomposition and aromatic hydrocarbon formation processes are revealed and insight into the synergistic effect on aromatic hydrocarbon formation is also achieved. The synergistic effect results from the interaction between 1,3-butadiene and propyne. The easily happened chain initiation in the 1,3-butadiene decomposition provides an abundant radical pool for propyne to undergo the H-atom abstraction and produce propargyl radical which plays key roles in the formation of aromatic hydrocarbons. Besides, the 1,3-butadiene/propyne co-pyrolysis includes high concentration levels of C3 and C4 precursors simultaneously, which stimulates the formation of key aromatic hydrocarbons such as toluene and naphthalene.

Exploring the Low-Temperature Oxidation Chemistry of Cyclohexane in a Jet-Stirred Reactor:an Experimental and Kinetic Modeling Study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry （SVUV-PIMS） was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window （-80 K） was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 （2013）], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the de- composition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-l-al and OH radical.

Stability analysis of the rotating tribological pair system on circular-disc end faces

In order to study the stability of friction and contact of the rotating tribological pair system,considering the influence of the changeable factors on the stability,the system dynamics analysis model based on the Lagrange equation is firstly established.The surface contact stiffness model is determined on the basis of the fractal theory.The model of the friction torque with velocities is created by using the Stribeck friction effect.The Lyapunov indirect method is employed to explore the eigenvalue problem of the system state equation.The effects of the applied load,the fractal dimension,the fractal scaling coefficient and the Stribeck coefficient on the system stability are investigated in detail.The numerical simulation results demonstrate that the tribological pair system is prone to causing system instability at low speed,and the system instability boundary value decreases when the Stribeck coefficient decreases.The fractal dimension and the fractal scaling coefficient impact the system stability slightly when fractal dimensions are large,and the system instability can be reduced by properly increasing the surface smoothness.Moreover,the system instability evidently increases with the increase in the applied load and the Stribeck coefficient.These achievements can provide a reference and theoretical support for the analysis of the dynamic performance of the tribological pair system.

Dynamic Characteristics of the Crankshaft System with Coupling Effect

The nonlinear dynamic model of the marine diesel crankshaft system with a propeller and 6 cranks is established, in which the variable moment of inertia of the linkage and the piston, coupling effect between torsional and axial vibration, the actuating force applied on the piston, the actuating torque and force applied on the propeller is included. The governing equations of the model denote a strong nonlinear and non autonomous system. By numeric simulation, the dynamic response of the system to initial displacement and initial speed, variable moment of inertia, the pressure applied on the piston by combustion gas, the torque and the axial force applied on the propeller by fluid is researched respectively. According to the research results, the variable moment of inertia and coupling effect between torsional and axial vibration are the fundamental reason for nonlinear vibration. Different actuating factors can not only result in different frequency components of the response, but make the same frequency component have different vibration amplitude. The dynamic behavior of the system is not influenced obviously by the actuating torque and force applied on the propeller. There is obvious difference in sensitivity of the dynamic response in the different direction to the same actuating factor.

改良检测血浆中3种双酯型乌头碱含量的UPLC/Q Exactive MS方法学研究

目的:改良UPLC/Q Exactive MS用于同时测定大鼠血浆中乌头碱、次乌头碱和新乌头碱含量的方法学。方法:采用Dionex UltiMate 3000快速超高效液相色谱仪和Q Exactive四极杆-静电场轨道阱高分辨质谱系统检测。采用HypersilGOLD色谱柱分离,流动相A(0.1%甲酸-水):流动相B(乙腈)=35∶65,通过全扫描/选择离子监测(FullMS/SIM)模式进行定性筛查和定量检测。结果:此检测方法专属性高,绝对基质效应在99.22%~100.79%;线性相关系数r≥0.9995,次乌头碱、乌头碱和新乌头碱在1~64ng/mL范围内线性关系良好,定量下限(S/N=10),次乌头碱为0.2ng/mL,乌头碱和新乌头碱为0.5ng/mL;准确度RE%在-2.3800%~2.131%,精密度RSD%在0.0971%~8.8111%,符合生物样本定量分析要求;稳定性考察结果表明室温放置8h、-20℃冻存2周的条件下稳定,-20℃冻融3次后将不再适合生物样本测定。结论:改良后的方法更适合同时测定大鼠血浆中3种双酯型乌头碱的含量。

Population pharmacokinetic of losartan and its active metabolite E-3174 in five different ethnic populations of China

The aim of this study was to develop a combined population pharmacokinetic （PPK） model for losartan and its active metabolite E-3174 in five Chinese ethnicities for individualized drug therapy in clinical practice. HPLC method was used to determine the blood levels of losartan and E-3174 simultaneously. One-, two- and three-compartment models were fitted to plasma concentration time data of 50 Chinese healthy subjects （including Han, Mongolian, Korean, Hui and Uigur） using nonlinear mixed-effect modeling （NONMEM）. From the basic model of losartan, the effects of demography and biochemical covariates were investigated, which were added one by one by the forward inclusion and backward elimination. The final models of losartan and E-3174 were connected by first order or transit compartment model. Pharmacokinetic parameters of losartan and its active metabolite E-3174 were assessed simultaneously in one integrated model with the plausible covariates on the key pharmacokinetic parameters of E-3174. Nonparametric bootstrap was used for the model stability validation. The data of losartan were best described using a two-compartment model with linear elimination. The time to reach Cmax of losartan and E-3174 were obtained to be 0.9 and 3.8 h, respectively. Two transit compartments were chosen with adequate fit of the delayed Tmax of E-3174. The population estimates for transformation of losartan to E-3174 was about 73.9%. Ethnicity factor showed significant influence on the non-metabolizing E-3174 clearance CL10, the peripheral compartment clearance CL2 and the central compartment volume Vj of losartan and also has a significant effect on the transit rate （Kt）. A total of 925 out of 1000 iterations succeeded in minimization. The PPK models were steady and reliable. Ethnicity factor showed significant influence on both losartan clearance and the transition from losartan to E-3174, no covariate influencing the PK parameters of E-3174 was identified.

Modeling of growth stress gradient effect on the oxidation rate at high temperature

A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By introducing the growth stress gradient we modify the classical oxidation parabolic law. The modified factor of the oxidation rate constant is a function of growth strain, environment oxygen concentration, and temperature. The modeling results show that the stress gradient effect on the oxidation rate cannot be ignored. Growth strain will dominate whether the stress gradient effect promotes or slows down the oxidation process. The stress gradient effect becomes weaker at higher temperature. This effect is amplified at higher concentrations of environmental oxygen. Applied mechanical loads do not affect the oxidation rate. This model is available for high temperature oxidation of metals and alloys.

Phase-field modeling of epitaxial growth with the Ehrlich-Schwoebel barrier: Model validation and application

In this paper,we introduce different forms of mobility into a quantitative phase-field model to produce arbitrary Ehrlich-Schwoebel(ES)effects.Convergence studies were carried out in the one-side step-flow model,which showed that the original mobility not only induces the ES effect,but also leads to larger numerical instability with increase of the step width.Thus,another modified form of the ES barrier is proposed,and is found to be more suitable for large-scale simulations.Model applications were performed on the wedding-cake structure,coarsening and coalescence of islands and spiral growth.The results show that the ES barrier exhibits more significant kinetic effects at the larger deposition rates by limiting motions of atoms on upper steps,leading to aggregation on the top layers,as well as the roughening of growing surfaces.

Meandering Spiral Waves Induced by Time-Periodic Coupling Strength

Effects of time-periodic coupling strength （TPCS） on spiral waves dynamics are studied by numerical computations and mathematical analyses. We find that meandering or drifting spirals waves, which are not observed for the case of constant coupling strength, can be induced by TPCS. In particular, a transition between outward petal and inward petal meandering spirals is observed when the period of TPCS is varied. These two types of meandering spirals are separated by a drifting spiral, which can be induced by TPCS when the period of TPCS is very close to that of rigidly rotating spiral. Similar results can be obtained if the coupling strength is modulated by a rectangle wave. Furthermore, a kinetic model for spiral movement suggested by Diet al., [Phys. Rev. E 85 （2012） 046216] is applied for explaining the above findings. The theoretical results are in good qualitative agreement with numerical simulations.

Asymptotic dynamics of a modified discrete Leslie-Gower competition system

We propose a modified discrete-time Leslie-Gower competition system of two popula- tions to study competition outcomes. Depending on the magnitude of a particular model parameter that measures intraspecific competition between individuals within the same population, either one or both populations may be subject to Allee effects. The resulting system can have up to four coexisting steady states. Using the theory of planar compet- itive maps, it is shown that the model has only equilibrium dynamics. The competition outcomes then depend not only on the parameter regimes but may also depend on the initial population distributions.

Self-trapping and Macroscopic Tunnelling of Superfluid Fermi Gases in Multi-well Potentials

We study the tunnelling dynamics of superfluid Fermi gases trapped in multi-well system along the BEC-BCS crossover. Within the hydrodynamical model and by using the multi-mode approximation, the self-trapping dynamics of superfluid Fermi gases in multi-well system are obtained numerically. We find that the self-trapping to diffusion transition strongly depends on the well number. When the well number is less than three, the self-trapped state takes place easier on the BEC side than that on the BCS side. However, when the well number is larger than three, the self-trapped state takes place easier on the BCS side instead of the BEC side. Furthermore, by considering a superfluid of 40K atoms, we obtain the zero-mode and π-mode Josephson frequencies of coherent atomic oscillations in double-well system. It is noteworthy that the Josephson mode, especially, the existence of π-mode frequency strongly depends on the atoms number on the BCS side.

Neural network representation of electronic structure from ab initio molecular dynamics

Despite their rich information content,electronic structure data amassed at high volumes in ab initio molecular dynamics simulations are generally under-utilized.We introduce a transferable high-fidelity neural network representation of such data in the form of tight-binding Hamiltonians for crystalline materials.This predictive representation of ab initio electronic structure,combined with machinelearning boosted molecular dynamics,enables efficient and accurate electronic evolution and sampling.When it is applied to a one-dimension charge-density wave material,carbyne,we are able to compute the spectral function and optical conductivity in the canonical ensemble.The spectral functions evaluated during soliton-antisoliton pair annihilation process reveal significant renormalization of low-energy edge modes due to retarded electron-lattice coupling beyond the Born-Oppenheimer limit.The availability of an efficient and reusable surrogate model for the electronic structure dynamical system will enable calculating many interesting physical properties,paving the way to previously inaccessible or challenging avenues in materials modeling.

Electrostatic Surface Waves on Semi-Bounded Quantum Electron-Hole Semiconductor Plasmas

The electrostatic surface waves on semi-bounded quantum electron-hole semiconductor plasmas are studied within the framework of the quantum hydrodynamic model, including the electrons and holes quantum recoil effects,quantum statistical pressures of the plasma species, as well as exchange and correlation effects. The dispersion characteristics of surface electrostatic oscillations are investigated by using the typical values of Ga As, Ga Sb and Ga N semiconductors. Numerical results show the existence of one low-frequency branch due to the mass difference between the electrons and holes in addition to one high-frequency branch due to charge-separation effects.