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排序方式: 共有961条查询结果,搜索用时 17 毫秒
1.
现有毒品滥用流行病模型假设吸毒者康复后对毒品拥有永久"免疫"力,而忽视了其再次成为毒品易感者的可能性。针对这一问题,通过考虑社区治疗和隔离治疗两种措施,分析了毒品滥用人群的演化过程,提出了基于暂时"免疫"力的毒品滥用流行病模型,并计算了模型的基本再生数,讨论了模型平衡点的存在性和稳定性。当基本再生数小于1时,模型存在一个局部渐进稳定的无毒平衡点;当基本再生数大于1时,模型存在唯一的地方病平衡点,并利用几何方法证明了地方病平衡点的全局稳定性;当基本再生数等于1时,如果满足一定条件,模型出现后向分支现象。数值模拟验证了上述所有结果。研究结果表明提高隔离治疗率、改善社区治疗效果和降低接触传染率可以有效抑制毒品滥用的流行。 相似文献
2.
Aspen Plus has become one of the most common process simulation tools for both academia and industrial applications. In the last decade, the number of the papers on Aspen Plus modeling of biomass gasification has significantly increased. This review focuses on recent developments and studies on modeling biomass gasification in Aspen Plus including key aspects such as tar formation and model validation. Accordingly, challenges in modeling due to specific assumptions and limitations will be highlighted to provide a useful basis for researchers and end-users for further process modeling of biomass gasification in Aspen Plus. 相似文献
3.
《Ceramics International》2020,46(2):1545-1550
Ti-bearing blast furnace slags have been regarded as an important secondary material in modern society, and the efficient recycling of Ti oxides from it is of key interest. For this reason, more thermodynamic data is needed regarding the phase relations in different composition ranges and sections. Therefore, the equilibrium phase relations of CaO–MgO–SiO2–Al2O3–TiO2 system in a low w(CaO)/w(SiO2) ratio of 0.6–0.8 at 1250 °C in air and fixed concentrations of MgO and Al2O3, were investigated experimentally using a high temperature equilibration and quenching method followed by SEM-EDS (Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer) analyses. The equilibrium solid phases of perovskite (CaO·TiO2), a pseudo-brookite solid solution (MgO·2TiO2, Al2O3·TiO2)ss, and anorthite (CaO·Al2O3·2SiO2) were found to coexist with the liquid phase at 1250 °C. The calculated results of Factsage and MTDATA were used for comparisons, and significant discrepancies were found between predictions and the experimental results. The 1250 °C isotherm has been constructed and projected on the CaO–SiO2–TiO2-8 wt.% MgO-14 wt% Al2O3 quasi-ternary plane of the phase diagram. The obtained results provide new fundamental data for Ti-bearing slag recycling processes, and they add new experimental features for thermodynamic modeling of the high-order titanium oxide-containing systems. 相似文献
4.
This paper presents a conjectural-variation-based equilibrium model of a single-price electricity market. The main characteristic of the model is that the market equilibrium equations incorporate the effect of the voltage constraints on the companies’ strategic behavior. A two-stage optimization model is used to solve the market equilibrium. In the first stage, an equivalent optimization problem is used to compute the day-ahead market clearing process. In the second stage, some generation units have to modify their active and reactive power in order to meet the technical constraints of the transmission network. These generation changes are determined by computing an AC optimal power flow. 相似文献
5.
Ahmad Hosseini-Bandegharaei Mohammad Karimzadeh Masoud Sarwghadi Aliasghar Heydarbeigi Seyyed Hossein Hosseini Mehdi Nedaie Hassan Shoghi 《Chemical Engineering Research and Design》2014
Adsorption of Pb(II) ion by a novel extractant-impregnated resin, EIR, was studied as a function of various experimental parameters using batch adsorption experiments. The new EIR was prepared by impregnating gallocyanine (GCN) onto Amberlite XAD-16 resin beads. The EIR was characterized by nitrogen analysis and SEM micrographs. The new EIR showed excellent selectivity factor values (α) for Pb(II) adsorption respect to other metal ions. The effects of some chemical and physical variables were evaluated and the optimum conditions were found for Pb(II) removal from aqueous solutions. The equilibrium adsorption isotherm was fitted with the Langmuir adsorption model. The maximum adsorption capacity (qmax) of EIR for Pb(II) ions was found to be 367.92 mg g−1. The kinetic studies showed that the intra-particle diffusion is the rate-controlling step. Also, the intra-particle diffusion coefficients, Dip values, were of the order of 10−12 m2 s−1. The values of enthalpy (ΔH°) were positive, which confirms the endothermic nature of adsorption process. Also, the positive entropy changes (ΔS°) were showed that the randomness increased along with the adsorption process. In addition, the obtained negative values of Gibbs free energy (ΔG°) indicated feasible and spontaneous nature of the adsorption process at different temperatures. The new adsorbent was very stable so that it can be successfully used for many consecutive cycles without significant loss in its adsorption capacity. 相似文献
6.
《Chemical Engineering Research and Design》2014,92(12):2861-2866
This work aims of the determination of a series of vapor–liquid equilibrium (VLE) experimental data at low pressure (70 kPa) for binary mixtures of ethyl acetate with methanol and ethanol. The Fischer's ebulliometer was used for the measurements of VLE data. A complete series of equilibrium data was obtained such as pressure, temperature and compositions of the liquid and vapor phases (PTxy). The two VLE data sets were submitted to a thermodynamic consistence test, where the deviations were evaluated in all variables, using the UNIQUAC activity coefficient equation. The magnitude of the average deviations was within the experimental uncertainty satisfying the Gibbs–Duhen equation. The data sets were also used to test the prediction of the UNIFAC model in its original and modified editions and the results were also within experimental uncertainties. Then a series of binary systems containing alcohols (methanol and ethanol) and esters (methyl and ethyl acetate) were collected from the literature for testing systematically the capability of the UNIFAC contribution method for this type of mixtures. 相似文献
7.
The equilibrium and dynamic surface tension of three sulfosuccinate surfactants at the air/aqueous solution interface were investigated. Wilhelmy plate method was used to determine critical micelle concentration (CMC) and the equilibrium surface tension (γ eq). The dynamic surface tensions in the range 10–100 s were measured by maximum bubble pressure method. The well-known Ward–Tordai equation was employed to analyze the adsorption of the sulfosuccinate surfactants. The parameters and effective diffusion coefficients (D eff) of dynamic surface tension have been calculated and analyzed. The equilibrium surface tension results showed that disodium laureth (3) sulfosuccinate (AEO3-SS), disodium laureth (6) sulfosuccinate (AEO6-SS) and disodium alkyl ethoxy glucoside sulfosuccinate (AEG-SS) are surfactants possessing strong surface activity, adsorbing to the interface rapidly and their γ eq values were in the range 25–32 mN/m. CMC of the three surfactants increases with the number of hydrophilic groups and AEO3-SS has the lowest CMC. According to the values of some dynamic surface tension parameters, AEG-SS is the most hydrophilic surfactant of them and AEO3-SS is energetically more favorable to adsorb to the interface than the others. According to Ward–Tordai equation, the D eff values were calculated, the adsorption mechanism was diffusion controlled at short times and toward the end good evidence was found for an activated-diffusion mechanism with an energy barrier. 相似文献
8.
Mg ion-exchanged samples were prepared with acid-washed Shengli lignite. The chemical composition of the ash of the raw sample was determined by X-ray fluorescence. The equilibrium adsorption water contents of sam-ples were determined in a range of relative humidity. The ion-exchange process was characterized by FT-IR, ash content, and pH value. A possible mechanism is proposed for equilibrium adsorption water of ion-exchanged samples at different humidities. The extent of ion-exchange reaction between Mg2+and lignite is control ed by the concentration of Mg2+in MgSO4 solution. The effect of Mg2+on equilibrium adsorption water content varies with relative humidity and content of Mg2+. The factor that controls equilibrium adsorption water content at low relative humidity is water interactions with sorption sites, which are Mg2+–carboxyl group complex. At middle relative humidity capil ary force between Mg2+–water clusters Mg+(H2O)n and capil ary is more impor-tant. At high relative humidity, free water–free water interactions are more significant. 相似文献
9.
10.
《Calphad》2020
Herein the phase equilibria in the Si–Fe–Ca–O–S–Cu system in equilibrium with matte at controlled P(SO2) of 0.3 and 0.6 atm and fixed matte grade of 72 wt % Cu were experimentally investigated in the spinel primary phase field. The high-temperature equilibrations were realized in spinel substrate and the sample after quenching were characterized using Electron Probe Micro-analysis (EPMA). The effect of CaO on the liquidus temperature of slags was quantified with varying CaO content from 0 to 6 wt %. It was found that, the presence of CaO increased the liquidus temperature of slags and moreover, the increment effect got enhanced with increasing CaO content in the present range. The influence of P(SO2) was further clarified and it was found that, the equilibrium SiO2 content in the liquid phase, at the same temperature, remarkably increased with increasing P(SO2). The present study will not only deepen the understanding of the equilibration in the present liquid/spinel/matte/gas system, but also provide useful guidance for the industrial operations. 相似文献