In modern power system, reclosing operation of single phase fault is commonly employed in order to improve operating stability and reliability. However, the successive electrical transients caused by system faults and subsequent switching operations give rise to mechanical stresses nearby electric machines. These stresses may exceed the endurance limit of certain machine parts and bring about slight and severe fatigue damage which is cumulative over the life of machines. In this paper, the sophisticated simulation model, including an infinite grid, lines, breakers, transformers, synchronous machines and mechanical shaft systems etc., is established to identify an interaction between system and machines. A line to ground fault and the single-phase-reclosing processes (SPRP) are simulated for both generator and motor conditions of pumped storage machine (PSM). Electric-magnetic torque characteristics and stator current curves are given. The whole stresses of stator core and frame are calculated by FEM and fatigue loss is predicted. The results show that although there is some fatigue in parts, the impact of SPRP on PSM is acceptable. Thus, the structure of machines can be optimized, and an operating guidance will be achieved to SPRP of PSM.
Reinforcement learning (RL) has been successfully applied to solve path planning problems, but learning is generally slow. The main reason is not making full use of information collected during interaction with the environment. This paper proposes a novel method to solve the discrete space path planning problem in an environment without prior knowledge with intensive obstacles based on RL and heuristic search. Firstly, we apply Dyna-Q algorithm of RL to explore the map and search for the target point and optimize its policy with upper confidence bound (UCB). Then, when the target point is found, we use heuristic search to plan the path from the starting point to the target point and narrow the path to a small range. Finally, we combine Dyna-Q algorithm with the heuristic search recommended path for path planning. We evaluate our algorithm using maze navigation problem. The results verify that heuristic search accelerates Dyan-Q convergence.
The nanomechanical metamaterials offer the possibilities of manipulating exotic electromagnetic properties on demand. Such metamaterial exhibit profound electro-optical, magneto-optical and acousto-optical switching and modulation, optical nonlinearity for modulating light with light, asymmetric transmission, and tunable chirality. The electromagnetic properties of nanomechanical metamaterial structure strongly depend on the spatial arrangement of its building blocks. By constructing metamaterials on elastically deformable scaffolds we can dynamically control the nanoscale spacing among constituent elements across the entire metamaterial array with external stimuli. Based on this approach, we use electrostatic, Lorentz, near field optical forces and sound to drive high-contrast, high-speed active tuning, modulation and switching of photonic metamaterial properties and to deliver exotic electromagnetic properties. We also report a novel approach to the visualization of nanoscale movements of picometre scale Brownian and stimulation movements of the individual building blocks of these functional metamaterials.
Abstract. In 2013, China's government published the Air Pollution Prevention and Control Action Plan (APPCAP) with a specific target for Beijing, which aims to reduce annual mean PM2.5 concentrations in Beijing to 60 µg m−3 in 2017. During 2013–2017, the air quality in Beijing was significantly improved following the implementation of various emission control measures locally and regionally, with the annual mean PM2.5 concentration decreasing from 89.5 µg m−3 in 2013 to 58 µg m−3 in 2017. As meteorological conditions were more favourable to the reduction of air pollution in 2017 than in 2013 and 2016, the real effectiveness of emission control measures on the improvement of air quality in Beijing has frequently been questioned. In this work, by combining a detailed bottom-up emission inventory over Beijing, the MEIC regional emission inventory and the WRF-CMAQ (Weather Research and Forecasting Model and Community Multiscale Air Quality) model, we attribute the improvement in Beijing's PM2.5 air quality in 2017 (compared to 2013 and 2016) to the following factors: changes in meteorological conditions, reduction of emissions from surrounding regions, and seven specific categories of local emission control measures in Beijing. We collect and summarize data related to 32 detailed control measures implemented during 2013–2017, quantify the emission reductions associated with each measure using the bottom-up local emission inventory in 2013, aggregate the measures into seven categories, and conduct a series of CMAQ simulations to quantify the contribution of different factors to the PM2.5 changes. We found that, although changes in meteorological conditions partly explain the improved PM2.5 air quality in Beijing in 2017 compared to 2013 (3.8 µg m−3, 12.1 % of total), the rapid decrease in PM2.5 concentrations in Beijing during 2013–2017 was dominated by local (20.6 µg m−3, 65.4 %) and regional (7.1 µg m−3, 22.5 %) emission reductions. The seven categories of emission control measures, i.e. coal-fired boiler control, clean fuels in the residential sector, optimize industrial structure, fugitive dust control, vehicle emission control, improved end-of-pipe control, and integrated treatment of VOCs, reduced the PM2.5 concentrations in Beijing by 5.9, 5.3, 3.2, 2.3, 1.9, 1.8, and 0.2 µg m−3, respectively, during 2013–2017. We also found that changes in meteorological conditions could explain roughly 30 % of total reduction in PM2.5 concentration during 2016–2017 with more prominent contribution in winter months (November and December). If the meteorological conditions in 2017 had remained the same as those in 2016, the annual mean PM2.5 concentrations would have increased from 58 to 63 µg m−3, exceeding the target established in the APPCAP. Despite the remarkable impacts from meteorological condition changes, local and regional emission reductions still played major roles in the PM2.5 decrease in Beijing during 2016–2017, and clean fuels in the residential sector, coal-fired boiler control, and optimize industrial structure were the three most effective local measures (contributing reductions of 2.1, 1.9, and 1.5 µg m−3, respectively). Our study confirms the effectiveness of clean air actions in Beijing and its surrounding regions and reveals that a new generation of control measures and strengthened regional joint emission control measures should be implemented for continued air quality improvement in Beijing because the major emitting sources have changed since the implementation of the clean air actions.
[Objective] To survey the remission of cancer pain and control of other intractable symptoms by continuous subcutaneous infusion of combined medications,so as to provide scientific basis to establishing a model of palliative care in China and palliative guideline. [Methods] Firstly,we chose 40 advanced cancer patients with pain score ≥ 7 points and the expected survival time more than 30 days. These 40 cases were randomly divided into 2 groups,and each group had 20 cases. Then we applied cross-design analysis of variance method,successively gave oral extended action tablet of morphine and supplied syringe driver combination therapy by syringe driver. Finally,we used statistical software SPSS13.0 to analyze. [Results] We compared analgesic effect and incidence of adverse reactions between subcutaneous morphine by the micro-pump and oral morphine (P﹤0.05) and there was significant difference. The remission rate of other suffering symptoms micro-pump combination was superior to that of oral combination therapy. [Conclusion] The analgesic effect of micro-pump combined medications is superior to oral extended action tablet of morphine. There are less adverse effects and better control pain as well as other intractable distressing in advanced cancer by micro-pump of combined medications.
In this article,through making a contrast analysis of the semantic valence of Chinese and Russian nouns based on Valence Theory. We find that the category of the semantic valence of nouns in Russian is not all the same as that in Chinese. The basic reason for this phenomenon is that in Russian there are a large number of gerunds derived from the verbs of high valence,while there is no gerund,a subcategory of noun,in Chinese. In addition,this article also expounds the manifestation of the valence components of nouns.
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