关键词： business models   circular economy   finance  

摘要： Capitalism, as we know it, is the result of the industrial revolution, when resources were perceived as abundant and limitless. The population was much smaller and the environmental impact of the industrial activity was perceived as minimal. As the world population increased exponentially and more countries emerged from poverty to join the middle-income rank, demand for products increased leading to a rapid industrialization with no concerns for its environmental and societal impact. Capitalism is also based on the idea of free markets that adjust automatically to new information about scarcity, demand, and processes of production to allocate resources in the most efficient way possible. However, free market implies that possibly unobservable factors are taken into consideration to lower the potential impact of negative externalities by imbedding them in the pricing process. Unfortunately, free markets failed in this task and the list of environmental disasters from the Gulf oil spill of BP, the tobacco health issue are good examples of the inability of the markets to gauge the impact of these negative externalities.

关键词： Model   Bovine fasciolosis   Economic   Nigeria  

摘要： Bovine fasciolosis is a zoonotic infection transmitted by infected freshwater snail-Lymnaea(Radix)natalensis-in tropical regions. The prevalence of bovine fasciolosis in Nigeria is overwhelming with huge financial cost. In the chronic form of the disease, hyperplastic cholangitis and calcification of bile ducts occur with severe liver damage. The aim of the study was to estimate annual economic losses of bovine fasciolosis in Nigeria. Disease prevalence was estimated at 18.3% (8.5-30.6), average annual disease incidence is maintained at 2.5%, an estimated mortality rate of 1.5%, a total liver condemnation rate of 11.1% were estimated from affected liver due to fasciolosis, annual slaughter rate of 10.5% and a total cattle population of 20 million. A total of 7.3% livestock owners consider fasciolosis as a threat, while only 4.3% have ever used molluscicide. Treatment cost of controlling fasciolosis is estimated at US$375,000, which puts the total annual loss due to fasciolosis at US$26.02 million. Both direct and indirect sources of production losses have an impact on the livestock industry in Nigeria. Bovine fasciolosis threatens food security in Nigeria;therefore, further awareness among livestock owners is needed on control strategies to improve the income base for small-scale livestock farmers.

关键词： Stochastic simulation   Stochastic modelling   Crop yield uncertainty   Macroeconomic uncertainty   Aglink-Cosimo  

摘要： The analysis of uncertainty in large-scale agricultural economic models has gained attention from a policymakers and researchers' viewpoint. The different methodologies available vary depending on data availability and the nature of the variables subject to analysis, which in turn influences the outcomes. When evaluating the results of previously applied partial stochastic methodologies to partial equilibrium models, underperformance and generation of biases have been observed. This paper evaluates different stochastic methods for introducing yield and macroeconomic uncertainty in a large-scale agricultural economic model and proposes a new methodology for partial uncertainty analysis consisting of a combination of parametric and non-parametric estimators chosen to minimize the statistical prediction error and distributional assumptions. Results suggest that the best methodologies are those relaxing distributional assumptions and allowing for a better representation of historical variability. For uncertainty extraction, the cubic polynomial (for yields) and the multivariate vector auto-regression (for macroeconomic variables) methods perform best. For uncertainty simulation, tests favor semi parametric methods against parametric approaches. These methods are applied to the ex-ante analysis of global agricultural commodity markets and supplement the traditional deterministic analysis with a statistical representation of stochastic uncertainty.y

关键词： Bifurcation analysis   Neimark-Sacker   Fold   Period-doubling   Resonance   Chenciner  

摘要： This paper studies bifurcation analysis of an economic model by using the critical normal form coefficients method which is one of the most influential methods in bifurcation theory. This method advantageously checks the non-degeneracy condition without computing the central manifold and converting the linear part of the map into Jordan form. In this study, the codimension one and codimension two bifurcations of the model are investigated by considering different parameters and for each bifurcation, the normal form coefficients are computed. The obtained results conclude that the model undergoes bifurcations such as flip (period-doubling), Neimark-Sacker, resonance 1:3, resonance 1:4, Chenciner and period-doubling Neimark-Sacker. Furthermore, to accomplish symmetric bifurcation analysis of the model, the normal form of the Z(3)-symmetric double-1 multiplier bifurcation is utilized. The bifurcation curves of the model are drawn with the aid of the numerical continuation method. From the mathematical point of view, these bifurcation curves and numerical simulations not only support the theoretical results but also reveal more details of the dynamic system under study, especially after higher iterations. The achieved results directly can be applied to design and optimize many types of economic models. (c) 2020 Elsevier Ltd. All rights reserved.

关键词： Offshore transmission   Interconnectors   Wind energy   Uncertainty   Net present value  

摘要： The inherent uncertainties associated with offshore wind are substantial, as are the investments. Therefore, investors are keen to identify and evaluate the risks. This paper presents a model to economically evaluate projects from an offshore transmission owner's perspective by considering the revenue streams, capital costs, and operational expenditure. To allow a more realistic economic evaluation, data, regulatory information, and expert knowledge are collected, curated and, where necessary, combined with statistical techniques. A generic 1.2 GW project is used as a case study. This research contributes to a deeper understanding of the severe uncertainties involved in offshore transmission planning and their impact on a project's expected profit. Understanding their impact, through a sensitivity analysis where individually one factor is varied within an interval, supports informed decision making with limited information. Uncertainty in interest rates, planned operational expenditure and, particularly, cable failure rates were found to be critical to an investor's return. For the case study considered, comparing cable failure rates based on operational experience to inputs based on literature, resulted in a 64.2% lower net present value. In conclusion, further research into cable failures, and addressing the uncertainty in inputs used for economic evaluations could be beneficial to the industry. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Model predictive control   Lyapunov stability   Descriptor system and differential algebraic equation  

摘要： A large number of physical applications such as electrical circuits, chemical processes and multibody systems can be accurately described by a set of differential algebraic equations (DAEs). For instance, sustainable water desalination techniques such as membrane distillation (MD) is an example of a chemical process that is described by DAEs. Optimal control strategies such as economic model predictive control (EMPC) has many operational advantages (e.g., maximizing process economics and enhancing operational safety) for chemical applications. However, constructing EMPC schemes for a general class of nonlinear DAEs systems while ensuring closed-loop stability and recursive feasibility is an open research challenge that has not been considered. Motivated by the above considerations, this note introduces a Lyapunov-based economic model predictive control (LEMPC) design that can economically operate nonlinear descriptor systems while satisfying input and states constraints. To guarantee closed-loop stability and recursive feasibility of the proposed control design, a Lyapunov-based control law is introduced to characterize the stability region at which the LEMPC can maximize the process economics. Finally, a chemical batch process modeled by nonlinear differential algebraic equations (DAEs) is utilized to demonstrate the applicability of the proposed framework. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

关键词： 增长曲线   经济模型   VIP   运营利润   竞争激烈   线上教育   作业帮   赛道  

摘要： 打破了亏损"魔咒"的VIPKID,从上一个竞争激烈的赛道又闯进了另一个血腥的赛道K12教育,它要面对的是猿辅导、作业帮等"烧钱"更凶猛的对手线上教育热闹厮杀,沉寂了半年的VIPKID也决定释放一些消息。VIPKID总裁兼联合创始人张月佳不久前对外宣布,VIPKID单位运营利润(UE,Unit Economic model,即单位经济模型)已经连续6个月为正,同时90%的渠道首单实现盈利,获客成本同比降低45%。

关键词： 天然气   管道   放空立管   高度   数学模型  

摘要： 天然气长输管道站场、阀室均设有放空立管,用于天然气的事故放空和计划放空。现有标准和规范未考虑管道所在地区等级的差异所导致的放空立管高度差异,造成在低等级地区的放空立管建设投资过大。针对这一问题,考虑天然气放空立管的技术可靠性、安全性和经济性,提出了一种新的天然气放空立管高度计算模型及求解方法。结合西部天然气管道工程实例,将计算结果与相关现行国内外相关标准的规定值进行了对比。结果表明:根据本方法可计算得到与地区等级相关的放空立管高度,不仅能保证放空的工艺安全性,还能够节约放空管建设投资和运行维护费用。

关键词： 概率统计教学   经济模型   课程  

摘要： 概率统计是一门经济管理类专业理论性和应用性很强的课程,在概率统计教学中融入经济模型的介绍能够提高学生对概率统计思想的理解,同时又能够锻炼学生利用理论知识建立模型解决实际问题的能力,达到学以致用。

关键词： cost-effectiveness analysis   dementia   non-communicable disease   public health   simulation  

摘要： Objectives Economic evaluations of lifestyle interventions, which aim to prevent diabetes/cardiovascular disease (CVD), have not included dementia. Lifestyle interventions decrease dementia risk and extend life expectancy, leading to competing effects on health care costs. We aim to demonstrate the feasibility of including dementia in a public health cost-effectiveness analysis and quantify the overall impacts accounting for these competing effects. Methods The School for Public Health Research (SPHR) diabetes prevention model describes individuals' risk of type 2 diabetes, microvascular outcomes, CVD, congestive heart failure, cancer, osteoarthritis, depression, and mortality in England. In version 3.1, we adapted the model to include dementia using published data from primary care databases, health surveys, and trials of dementia to describe dementia incidence, diagnosis, and disease progression. We estimate the impact of dementia on lifetime costs and quality-adjusted life years (QALYs) gained of the National Health Service diabetes prevention program (NHS DPP) from an NHS/personal social services perspective with 3 scenarios: 1) no dementia, 2) dementia only, and 3) reduced dementia risk. Subgroup, parameter, and probabilistic sensitivity analyses were conducted. Results The lifetime cost savings of the NHS DPP per patient were 145 pound in the no-dementia scenario, 121 pound in the dementia-only scenario, and 167 pound in the reduced dementia risk scenario. The QALY gains increased by 0.0006 in dementia only and 0.0134 in reduced dementia risk. Dementia did not alter the recommendation that the NHS/DPP is cost-effective. Conclusions Including dementia into a model of lifestyle interventions was feasible but did not change policy recommendations or modify health economic outcomes. The impact on health economic outcomes was largest where a direct impact on dementia incidence was assumed, particularly in elderly populations.