Gradient bounds for a thin film epitaxy equation

We consider a gradient flow modeling the epitaxial growth of thin films with slope selection. The surface height profile satisfies a nonlinear diffusion equation with biharmonic dissipation. We establish optimal local and global wellposedness for initial data with critical regularity. To understand the mechanism of slope selection and the dependence on the dissipation coefficient, we exhibit several lower and upper bounds for the gradient of the solution in physical dimensions $d\le 3$

Characterizing the stabilization size for semi-implicit Fourier-spectral method to phase field equations

Recent results in the literature provide computational evidence that stabilized semi-implicit time-stepping method can efficiently simulate phase field problems involving fourth-order nonlinear dif- fusion, with typical examples like the Cahn-Hilliard equation and the thin film type equation. The up-to-date theoretical explanation of the numerical stability relies on the assumption that the deriva- tive of the nonlinear potential function satisfies a Lipschitz type condition, which in a rigorous sense, implies the boundedness of the numerical solution. In this work we remove the Lipschitz assumption on the nonlinearity and prove unconditional energy stability for the stabilized semi-implicit time-stepping methods. It is shown that the size of stabilization term depends on the initial energy and the perturba- tion parameter but is independent of the time step. The corresponding error analysis is also established under minimal nonlinearity and regularity assumptions

Cold storage condensation heat recovery system with a novel composite phase change material

© 2016 Elsevier Ltd. Using condensation heat from cold storage refrigeration systems to provide heat for domestic hot water preparation and industrial hot water supply promotes energy conservation. However, few studies have investigated cold storage condensation heat recovery using phase change materials (PCMs). In this study, a cold storage condensation heat recovery system that uses PCMs has been designed and analysed. According to the principle of energy cascade recycling, different operation modes could be effectively switched to recycle condensation heat. Furthermore, a novel and suitable phase change composite material is developed for cold storage condensation heat recovery, which has a relatively large latent heat, high thermal conductivity, and an appropriate phase change temperature (i.e. 80 °C). With carnauba wax (CW) as the PCM and expanded graphite (EG) as the additive, a composite was developed with an optimal mass ratio of CW:EG = 10:1. The thermal and physical properties and the interior structure of the composite were then investigated using a scanning electron microscope (SEM), thermal constants analyser (Hot Disk), differential scanning calorimeter (DSC), and Fourier transform infrared spectrometer (FT-IR). Furthermore, experiments on the melting and solidification processes and accelerated thermal cycling were also conducted. It was found that at the optimal mass ratio of 10:1, the temperatures of the CW/EG composite in the melting and solidification processes were 81.98 °C and 80.43 °C, respectively, while the corresponding latent heats were 150.9 J/g and 142.6 J/g, respectively. During both processes, CW could retain its original worm-like structure after being completely adsorbed by EG. Compared to only CW, the melting and solidification time of the CW/EG composite were reduced by 81.7% and 55.3%, respectively, while its thermal conductivity was 16.4 times higher. After 1000 runs of accelerated thermal cycling, the endothermic/exothermic phase change temperatures of CW and the CW/EG composite increased by only 0.42%/0.42% and 0.23%/0.27%, respectively, while their endothermic/exothermic latent heats decreased by 4.96%/4.78% and 2.05%/3.44%, respectively. These results indicate that both CW and the CW/EG composite have excellent thermal reliability, while the CW/EG composite exhibits a slightly better performance. Finally, the experiments show that the CW/EG composite has desirable thermal and physical properties such as high thermal conductivity and reliability; Hence, it has good potenti al as a material for facilitating condensation heat recovery from cold storage refrigeration systems

Risk evaluation for production-injection recompletion and sidetrack

Using a decision tree and stochastic parameters, expected monetary value is calculated to evaluate optimal sidetrack time. In view of placing a high confidence level on analytical approach to optimal sidetrack time for a waterflooded reservoir based on possible uncertainty of economic and reservoir parameters and probability of sidetrack success, a major assumption on a parameter in a previous study is re-evaluated. Material balance and displacement efficiency are used to re-evaluate this critical waterflood performance parameter. The change in the relative influence of the stochastic parameters to optimal sidetrack time due to re-evaluation calls for much attention with probable need to further reduce assumptions made, however insignificant the parameter may be. This change will affect the degree of acceptability of the analytical approach. The probability of success of sidetrack sums up the geological and technical uncertainties, deconvolution of these will give the analytical approach an edge

Review on Quantitative Assessment of Corporate Governance

Recently a lot of different institutions and research centers around the world gradually launch their corporate governance assessment system, making each interested party to get to know the corporate governance level and making reasonable decisions. This essay is based upon corporate governance and assessment connotation, summarizes and concludes the research progress of domestic and overseas corporate governance quantitative assessment, finding that corporate governance quantitative assessment mainly relies on composite indicator assessment, but there is still big difference in the starting point, targeted object and assessment indicator of assessment indicator system, so some people question the validity and applicability of this assessment indicator system. Based on this, this essay points out that the existent literature review has some problems such as assessment subject is vague, missing out some key indicators, weighting subjectively and failing to abide the principle of “ substance over form”, thus bringing up corresponding suggestion.Recently a lot of different institutions and research centers around the world gradually launch their corporate governance assessment system, making each interested party to get to know the corporate governance level and making reasonable decisions. This essay is based upon corporate governance and assessment connotation, summarizes and concludes the research progress of domestic and overseas corporate governance quantitative assessment, finding that corporate governance quantitative assessment mainly relies on composite indicator assessment, but there is still big difference in the starting point, targeted object and assessment indicator of assessment indicator system, so some people question the validity and applicability of this assessment indicator system. Based on this, this essay points out that the existent literature review has some problems such as assessment subject is vague, missing out some key indicators, weighting subjectively and failing to abide the principle of “ substance over form”, thus bringing up corresponding suggestion

GIS based aquifer vulnerability assessment in Hangzhou-Jiaxing-Huzhou plain, China

Hangzhou-Jiaxing-Huzhou plain is among the regions which faces the shortage of water due to its increasing population, industrialization, agriculture and domestic use; hence there is high dependence on ground water. In China, the exploitation of aquifers has been historically undertaken without proper concern for environmental impacts or even the concept of sustainable yield. In order to maintain basin aquifer as a source of water for the area, it is necessary to find out whether certain locations in this ground water basin are susceptible to receive and transmit pollution, this is why the main objective of this research is to find out the ground water vulnerable zones using Geographical Information System (GIS) model in Hangzhou-Jiaxing-Huzhou plain. GIS was used to create ground water vulnerability map by overlaying hydro-geological data. The input of the model was provided by the following seven data layers: Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity. This study showed that Hangzhou-Jiaxing-Huzhou area is grouped into three categories: Highvulnerable zone with 27.4% of the total area, moderate vulnerable zone which occupy the greatpart of that area 60.5% and low vulnerable zone with 12.1%. This research suggests first theprioritization of high vulnerable areas in order to prevent further pollution to already pollutedareas; next the frequent monitoring of vulnerable zones to monitor the changing level ofpollutants; and finally suggests that this model can be an effective tool for local authorities whoare responsible for managing ground water resources in that area. Keywords: Hangzhou-Jiaxing-Huzhou plain, Ground water vulnerability, GIS, DRASTIC model, shallow aquife

Case Study of the Impact of Cold and Hot Waterflooding Performance by Simulation and Experiment of High Pour Point Oil Reservoir,, Liaohe Oilfield, North-East China

Block Shen-95 has been under cold waterflooding for 17 years. Of particular interest is the low recovery of 11.27% for the North Block due to crude oil cloud point being very close to the reservoir temperature. Formation damage near the wellbore region is controlled at production wells by hot-oiling and low injection rates of non-isothermal waterflooding. Optimizing production necessitated looking at core-scale experiment and reservoir-scale simulation waterflooding performance at different temperatures. The intent also, is basically to condition core-scale flooding observations to properly initialize the numerical model. Based on experiment carried out on core samples, sharp decline in oil displacement efficiency occurred, increase in residual oil saturation and increase in the intensity of formation damage below the cloud point. Reservoir simulation depicted decline in production with decreasing flooding temperature captured specifically by change in viscosity around the wellbore region. Change in flow dynamics due to change in relative permeability was not efficiently captured and formation damage impact on porosity and permeability. Reservoir-scale performance for high pour point oil reservoir can better be understood by considering the effects of formation damage on storativity and transmissibility, and fluid rheology. The irreversible process of wax precipitation may cause permanent damage if further from the wellbore regio

Numerical modeling of the environment impact of landfill leachate leakage on groundwater quality-A field application

There are more than 372 big uncontrolled landfill areas in China. Waste disposal facilities are mainly responsible for the gradual quality degradation of groundwater. This paper reports an integrated study undertaken to develop an environmental assessment of the uncontrolled sanitary landfill area of the city of Jiaxing, Zhejiang, China. The USGS modular 3D finite difference groundwater flow model (Mod- flow) and Modular 3D Finite Difference Mass Transport Model (MT3D) software were used to simulate groundwater flow and contaminant transport modeling. The results indicated that landfill leachate leakage has significant effect on groundwater quality