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1.
碳达峰和碳中和的提出对城市群发展提出新的要求,城市群高速发展与环境问题间的矛盾日益加剧,绿色低碳发展路径亟待研究.以京津冀城市群为研究对象,在梳理城市群发展影响因素的基础上,分析城市群循环系统构成中要素间的关联关系,并通过量化模型,搭建基于系统动力学的城市群绿色低碳发展系统;重点从经济、能源、环境和城市聚合4个角度构建仿真系统,建立要素间量化函数,设定基本场景,以2010—2019年数据为基础,对系统进行仿真运行.算例结果表明,构建的仿真系统通过了检验,拟合程度较好;通过设计不同场景,验证相关参数变化时对系统运行的影响程度,发现综合场景对未来系统运行效益最佳,兼顾了经济发展与碳减排问题,能够促进城市向群绿色低碳发展.  相似文献   
2.
为了提高双离合变速器在车辆上的换挡品质,提升电气化换挡执行机构的工作效率,给出执行机构性能与换挡品质评价准则;通过两种不同双离合变速器电控电动执行机构的工作原理与性能分析,基于MATLAB数值仿真方法优化出最高效率进行试验.基于车辆6个维度的换挡工况对二者所搭载的变速器分别进行试验与CAN线数据采集,对比研究两种机构优缺点,通过雷达图的方式进行优劣说明.结果表明,两种执行机构传动效率可达70%且换挡品质相当.可见Tip in tip out工况对二者要求最为严格.  相似文献   
3.
《Journal of Retailing》2022,98(2):277-293
This research examines how consumers’ intentions to purchase food change depending on the visualisation mode (3D vs. AR) and product format (served vs. packaged). In three studies, we demonstrate that mental simulation of eating experiences (process and outcome) mediate these effects. Study 1 shows that AR visualisation of a served food improves simulation of the eating process over 3D visualisation, with a positive effect on purchase intention. Study 2 reveals that 3D visualisation improves purchase intention for packaged products (high instrumental properties) over served products (low instrumental properties) while the opposite is true for AR visualisation. In addition, interactivity and immersion mediate the effects of 3D (vs. AR) on mental simulation of the eating process for packaged products. Study 3 extends these results by showing that 3D increases purchase intention by eliciting mental simulation of the eating outcome, when the food is visible due to transparent (vs. opaque) packaging (displaying both sensory and instrumental properties), but that no such differences emerge for AR. This research highlights the importance of using different visualisation modes to promote food depending on the product format. The findings have important implications for both offline and online retailers.  相似文献   
4.
In the context of personal income tax (PIT) reform in China in 2018, this paper examines some of the major issues of concern regarding the reform and income distribution. Using the China Personal Income Tax Micro‐simulation model, the paper compares the differences between the 2011 and 2018 PIT systems, and finds that residents relying on different income sources may face a large degree of real tax rate change. Once the tax system is altered to PIT 2018, the coverage of PIT for wage earners will decrease from 46.9 to 23.4 percent, the income redistributive effect will drop from 1.95 to 1.22 percent and the PIT's role in fiscal revenue will also be negatively affected. Nevertheless, if individual income continues to grow, the share of PIT in fiscal revenue is expected to return to the 2018 level in 2022, but its income redistribution function is difficult to recover in the short term. The paper finds that the effect of PIT on income distribution depends on the tax structure. Gradual transition to an “entirely comprehensive” tax system when conditions are appropriate will achieve better income redistribution results at a lower average tax rate.  相似文献   
5.
The construction of an importance density for partially non‐Gaussian state space models is crucial when simulation methods are used for likelihood evaluation, signal extraction, and forecasting. The method of efficient importance sampling is successful in this respect, but we show that it can be implemented in a computationally more efficient manner using standard Kalman filter and smoothing methods. Efficient importance sampling is generally applicable for a wide range of models, but it is typically a custom‐built procedure. For the class of partially non‐Gaussian state space models, we present a general method for efficient importance sampling. Our novel method makes the efficient importance sampling methodology more accessible because it does not require the computation of a (possibly) complicated density kernel that needs to be tracked for each time period. The new method is illustrated for a stochastic volatility model with a Student's t distribution.  相似文献   
6.
文章尝试将商业生态系统理论与互联网相结合,解释互联网商业生态系统内部结构的静态和动态演化过程,从理论上深度探索了互联网商业生态系统内部生态发展的内在机理和运行机制,并运用计算机仿真方法模拟了互联网商业生态系统的内部演化过程。研究发现:互联网生态结构的演化过程经历了萌芽期、成长期、繁殖期、分化期四个主要阶段,商圈发展经历了平台、商家、消费者三主体到平台、商家、消费者、专业服务商、增值服务商五主体的进化过程,并不断进化和繁殖生成新的专业服务商和增值服务商,随之产生新的互联网商业生态系统。最后,文章以阿里巴巴电子商务生态系统为案例从经验上对其内部生态系统的发展和演化构成进行了分析。  相似文献   
7.
This study proposes an integrated simulation approach, which consists of a microscopic traffic simulation model, a vehicle dynamics model, and an emission estimation model, in order to estimate emissions based on more reliable vehicle performance measures. The vehicle performance measures such as engine power and engine speed significantly relate to the amount of emissions, and road curvatures and inclinations are the core inputs affecting these vehicle performance measures. Therefore, providing reliable vehicle performance measures reflecting the road geometric attributes is critical for a reliable emission estimation. This study proposes to use the microscopic traffic simulation model for generating vehicle trajectories, which is advantageous in modeling various traffic situations, and the vehicle dynamics model for producing the vehicle performance measures based on the vehicle trajectories. Finally, the outputs from the vehicle dynamics model are fed into the emission estimation model to compute emission measures. This study conducted a case-study using two road sections, one is a hypothesized road section, including various curvatures and inclinations with regular variations, and the other is a Kesselberg road section, which is an actual geometry in Bayern, Germany. The emission measures are estimated in these case-study road sections using both an existing simulation approach and the proposed integrated simulation approach. The difference between these two emission estimation approaches is discussed in terms of the emission measures, including fuel consumption, nitrogen oxides, and particulate matters.  相似文献   
8.
We use stock market data to analyze the quality of alternative models and procedures for forecasting expected shortfall (ES) at different significance levels. We compute ES forecasts from conditional models applied to the full distribution of returns as well as from models that focus on tail events using extreme value theory (EVT). We also apply the semiparametric filtered historical simulation (FHS) approach to ES forecasting to obtain 10-day ES forecasts. At the 10-day horizon we combine FHS with EVT. The performance of the different models is assessed using six different ES backtests recently proposed in the literature. Our results suggest that conditional EVT-based models produce more accurate 1-day and 10-day ES forecasts than do non-EVT based models. Under either approach, asymmetric probability distributions for return innovations tend to produce better forecasts. Incorporating EVT in parametric or semiparametric approaches also improves ES forecasting performance. These qualitative results are also valid for the recent crisis period, even though all models then underestimate the level of risk. FHS narrows the range of numerical forecasts obtained from alternative models, thereby reducing model risk. Combining EVT and FHS seems to be best approach for obtaining accurate ES forecasts.  相似文献   
9.
在复杂电磁环境下,由于民航地空通信大频偏的要求,滤波器无法滤除波道内的干扰。针对此问题,提出了一种自适应抗干扰系统设计方法。对于落在波道内且与地空通信信号有效频带不重叠的干扰,首先对通信信号进行载波频率估计,然后使用自适应滤波方法进行干扰抑制;对于落在波道内且与地空通信信号有效频带重叠的恒包络干扰,首先重构载波信号,消除对恒包络信号估计的影响,然后根据恒包络信号的特性重构干扰信号并进行干扰分离。实验结果表明,该系统设计方法在不改变民航地空通信架构的前提下,抗有效频带外干扰的能力最大可以提升23.8 dB,抗恒包络干扰的能力最大可以提升39.4 dB,从而可以大幅提高航空飞行安全水平。  相似文献   
10.
We develop extensions to auction theory results that are useful in real life scenarios.1. Since valuations are generally positive we first develop approximations using the log-normal distribution. This would be useful for many finance related auction settings since asset prices are usually non-negative.2. We formulate a positive symmetric discrete distribution, which is likely to be followed by the total number of auction participants, and incorporate this into auction theory results.3. We develop extensions when the valuations of the bidders are interdependent and incorporate all the results developed into a final combined realistic setting.4. Our methods can be a practical tool for bidders and auction sellers to maximize their profits. The models developed here could be potentially useful for inventory estimation and for wholesale procurement of financial instruments and also non-financial commodities.All the propositions are new results and they refer to existing results which are stated as Lemmas.  相似文献   
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