Design and Testing of Three Earthing Systems for Micro-Grid Protection during the Islanding Mode

This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current pro-tection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab?/Simulink? environment.

Comparison the Performances of Three Earthing Systems for Micro-Grid Protection during the Grid Connected Mode

This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.

Effects of Grounding (Earthing) on Massage Therapists: An Exploratory Study

It is well known that massage therapists often develop a number of health problems relatively early on in their career. A preliminary study showed that grounding massage therapists during their work may alleviate some of the health problems they encounter. A doubled-blind randomized controlled trial was designed to examine the effects of working and sleeping grounded for 4 weeks on massage therapists’ blood viscosity, stress (through HRV), inflammation (IFN-γ, IL-6, TNF-α, and hsCRP) and oxidative stress (MPO and MDA) biomarkers. The results show stress reduction as measured by heart rate, respir-atory rate and hear rate variability (HRV) and a lowering effect on blood viscosity that lasted for at least one week after ungrounding, with systolic blood viscosity becoming significantly lower at the end of the study. Inflammation markers (IFN-γ, TNF-α, and hsCRP) increased rapidly, within one week, after ungrounding. The findings suggest that grounding is beneficial for massage therapists in multiple domains relevant to health and wellbeing.

Research on the Fault Location Principle for the Earthing Electrode Line of the UHVDC Transmission System

The UHVDC transmission line transports large-capacity power, and its safety operation has very important rule on the safe operation of grid. Currently, in the DC transmission system, the earthing electrode line has the functions of ground potential fixing and bipolar imbalance current circulation during the operation of bipolar balance. Therefore the monitoring to the earthing electrode line operation is very essential. This article firstly introduced the current situation of the research on the earthing electrode line fault location method, then built the relevant PSCAD/EMTDC model for simulation verification of the current using Time Domain Reflectometry for the UHVDC earthing electrode line, and at last analyzed the reasons for the formation of the blind monitoring zones.

EarthingMethod for Protection of a Railway Rail Weighbridge System against Lightning

The rail weighbridge system of a railway freight station is introduced firstly, and then the earthing method for protection of the rail weighbridge system against lightning based on YLG-60 equipotential bonding surge protection device is shown.

Calculation of Earthing System at Bangladesh Storm Water Pumping Station

A Storm Water Pumping Station funded by the World Bank is under construction and commissioning,of which the earthing system design is a crucial part for the electrical design.Based on IEEE and BS standards,this article fully introduces the analysis methodology and calculation of the system within the framework of the World Bank supported project.A solution of this practical case satisfied with the requirements of international standards is shown in order to bring experience and convenience for engineers who are dedicated to projects abroad.

A review on biomedical and dental applications of cerium oxide nanoparticles——Unearthing the potential of this rare earth metal

Nanotechnology deals with particles ranging from 1 to 100 nm in size called as nanoparticles.These nano particles exhibit unique properties which find an application in many industries and medical fields.A growing body of evidence points out the newer developing technologies adopted in the field of medicine in terms of target therapies,imaging systems,drug deliveries,etc.is through the incorporation of nanoparticles.Cerium oxide nanoparticles have gained attention in the last decade due to exceptional properties such as redox activity,biofilm inhibition,antibacterial activity,anti-inflammatory activity,etc.The method of synthesis of cerium oxide nanoparticles plays a pivotal role in its application.It exhibits redox properties and catalytic activity and thus has found its use in biomedical applications.Nanoparticles are incorporated into dental materials such as restorative cements/sealants,adhesives,and denture systems to improve their properties.Among the various metal oxide nanoparticles,ce rium oxide nanoparticles(CeO_(2)NPs)are known to exhibit lower toxicity to mammalian cells and possess unique antibacterial mechanism.In addition,they exhibit potent properties such as antitumor,antiinflammatory,antibacterial activities,and functions as an immunosensor.CeO_(2)NPs have excellent scavenging properties for reactive oxygen species,which is why they are being considered for therapeutic purposes.In this review,various methods of synthesis of CeO_(2)NPs are discussed.Several factors that determine the particle size and morphology of these materials are important for biomedical and dental applications.Emphasis is given to preparation methods and variables such as calcination temperature,which have a profound effect on particle size and morphology.This article also presents various applications of CeO_(2)NPs in the biomedical and dental fields.

京津风沙源区NPP时空变化及其对治理工程实施的响应

利用遥感大数据对生态治理工程区域的净初级生产力和固碳能力进行长期动态监测可以实现对治理工程的实施效果的评价,同时为区域“碳中和”目标的实现及可持续发展提供有力支撑。利用Google Earth Engine(GEE)云计算平台,基于改进的CASA模型对京津风沙源治理工程区域的NPP进行计算。运用Sen斜率分析和MK趋势分析方法对2001—2020年间的NPP进行时空变化分析,并分析NPP对京津风沙源治理工程实施的响应。结果表明:1)在京津风沙源工程治理期间,京津风沙源区NPP总体呈波动上升趋势,平均增速为2.21 gC m^(-2)a^(-1),其中极显著增加区域占38.03%,说明京津风沙源治理工程对我国“碳中和”任务起到了积极作用,增加了区域的固碳能力;2)空间尺度上,京津风沙源区NPP和固碳量空间异质性较大,空间分布上主要呈现东部高,西部低的特点,其中,暖温带落叶阔叶林区域最高,温带荒漠区域最低;3)治理工程的实施所带来的NPP增长的速度在不同的区域并不一致,2001—2020年的NPP增速京津冀地区(4.74 gC m^(-2)a^(-1))>山西地区(4.52 gC m^(-2)a^(-1))>陕西地区(3.53 gC m^(-2)a^(-1))>内蒙古地区(1.55 gC m^(-2)a^(-1));4)生态工程实施所带来的生态环境的改善总体呈现先慢后快的特点,绝大部分区域后十年间的变化速率都显著大于前十年,而在生态环境较为恶劣、荒漠区域广布的内蒙古地区,生态环境的改善则具有一定的滞后性,2001—2010年NPP增速仅为0.04 gC m^(-2)a^(-1),直到2011年,NPP才开始有较为明显的增长,2011—2020年NPP增速为1.67 gC m^(-2)a^(-1)。风沙源治理工程需要长期坚持,才能取得更明显的成效。

基于Sentinel-5P的长三角大气NO_(2)污染特征及影响因子分析

基于哨兵-5P(Sentinel-5 Precursor,Sentinel-5P)卫星反演的NO_(2)柱浓度数据,利用Google Earth Engine云平台,结合自然因子和人为社会因子数据,分析长三角地区大气NO_(2)柱浓度的污染特征及影响因素。结果显示:(1)Sentinel-5P卫星反演的NO_(2)柱浓度数据与地面观测站NO_(2)质量浓度具有较好的相关性(r≥0.59,p<0.01),可较为准确地反映长三角地区大气NO_(2)污染状况;(2)长三角的大气NO_(2)柱浓度呈现季节性的周期波动,呈“冬高夏低”变化趋势;(3)大气NO_(2)柱浓度具有显著的空间异质性,整体上东北高,西南低,呈现出一条六安至台州,即“西北—东南”方向的NO_(2)柱浓度分界线,以及一个以环太湖城市群为中心的西南向“U形口”;(4)植被指数、高程、全社会用电量、第二产业产值、第三产业产值是长三角大气NO_(2)柱浓度空间分布的重要影响因子,区域大气NO_(2)柱浓度受因子交互作用显著,高程及植被指数与其他因子的交互作用q均在0.6以上。

耦合时序特征的林分类型遥感识别

【目的】结合多源遥感数据进行特征提取,获取最优分类策略并探究时间序列特征在林分类型识别中的重要性,为遥感林分类型识别提供技术途径。【方法】结合Sentinel-2光谱特征和时间序列特征、Sentinel-1雷达后向散射特征和SRTM DEM地形特征在Google Earth Engine中进行各特征变量的提取,构建不同特征组合使用随机森林分类器进行分类并对不同分类结果进行制图输出和精度评价。【结果】(1)使用Sentinel-2时间序列光谱特征、Sentinel-1雷达后向散射特征和SRTM DEM地形特征的方案分类效果最好,总体精度为84.62%,Kappa系数为0.82;(2)在构建的5个不同特征组合方案中,多特征组合的方案分类效果优于单一特征;(3)地形特征、后向散射特征和时间序列特征对于分类结果非常重要,尤其是时间序列特征的加入能大大提升林分类型识别精度。光谱特征中短红外波段B11和B12最重要,时间序列特征中4月份和10月份为最重要的时间节点。【结论】基于多源遥感数据提取的多特征分类方案能够有效进行研究区林分类型识别,地形特征、后向散射特征和Sentinel-2时间序列特征可以作为光谱特征的有效辅助特征变量提高分类精度,使林分类型识别更为准确,尤其是时间序列特征在提高林分类型识别精度上有突出作用。

基于GEE的Landsat-8与Sentinel-2影像在棉花种植提取中差异性分析及提取方法对比研究

棉花作为南疆地区重要的经济作物之一,在经济工作中起着至关重要的作用。及时、准确地获取棉花种植面积,对农业政策和经济发展具有重要意义。为了实现这一目标,需要综合分析不同方法和遥感数据对最终棉花种植面积制图精度的影响。本研究以新疆阿克苏地区棉花种植区为例,借助Google Earth Engine云平台,采用随机森林法(RF)、支持向量机法(SVM)、最小距离分类法(MDC)等3种机器学习方法,利用2类中分辨率影像提取棉花种植信息,充分评估使用的档案数据和官方统计数字。结果表明,采用Sentinel-2方法和RF获得了最优棉花图,随机森林法分类器的总体精度、Kappa系数和用户精度分别高达97.4%、96.7%和91.1%,分别比Landsat-8图像和RF模型的结果高出7.3百分点、0.081、2.8百分点。与官方统计数据相比,采用RF、SVM、MDC对Sentinel-2和Landsat-8图像的棉花种植面积估算图的精度分别为98.4%、95.8%、79.6%和90.3%、83.7%、72.5%。很明显,Sentinel-2和RF模型的组合与官方数据的一致性最高。对比分析结果表明,Landsat-8和Sentinel-2数据可用于大范围复杂种植结构的棉花高精度测绘。本研究结果有望为棉花大面积鉴别提供一定的理论指导和实践指导。

滇池蓝藻水华时空变化特征及环境影响因素

[目的]明晰滇池流域水体富营养化演变特征和水体综合治理状况及其主要驱动因素,为滇池流域水污染治理和水生态修复提供科学支撑。[方法]以滇池为研究对象,采用Google Earth Engine(GEE)和遥感监测分析2002—2021年期间滇池蓝藻水华的时空变化,并探讨了蓝藻水华与环境因子之间的关系。[结果]2002—2021年,滇池蓝藻水华面积变化具有显著的年际特征,在2006年、2013年和2016年出现峰值,分别为1.952×10^(7),2.010×10^(7),1.743×10^(7) m^(2);在2005年、2010年和2014年出现谷值,分别为1.243×10^(7),1.156×10^(7),1.163×10^(7) m^(2)。2016年后蓝藻水华面积稳定波动,整体无明显变化趋势,2021年面积为1.709×10^(7) m^(2)。在月份尺度,蓝藻水华主要发生在7—12月,8月达到峰值,11—2月持续降低,2月达谷值。蓝藻水华与气温、降水量之间呈现正相关关系,与风向呈现显著负相关关系(p<0.05),与风向呈现最为密切的显著相关关系(p<0.05),受滇池地形等因素影响,4种气象因子中风向因子重要性最高,偏东的风向对滇池蓝藻水华覆盖率具有显著促进作用。[结论]滇池蓝藻整体保持稳定波动无显著演变趋势,未来滇池水生态修复应深入考量风向、风速对蓝藻爆发的重要驱动作用。

基于GEE的苹果园地遥感信息提取研究——以陕西省渭北旱塬区为例

准确掌握苹果园空间分布及动态变化对苹果产业发展及规划具有重要意义。以陕西主要种植区———渭北旱塬区14个县(区)为研究区,基于Google Earth Engine(GEE)云计算平台,以2020年Sentinel-2卫星影像的Level-2A级数据为数据源,结合实地采样获得的461个苹果园样本点,构建包含光谱特征、遥感植被指数、纹理特征和地形特征等共计21个特征作为分类特征集,利用随机森林分类方法对研究区苹果园地空间信息进行提取。结果表明,研究区苹果种植面积为23.03万hm^(2),连片种植的苹果园主要分布于延安市洛川县、渭南市白水县、咸阳市淳化县和咸阳市彬州市,种植面积分别为3.54、3.21、2.90万hm^(2)和2.51万hm^(2);包含光谱特征、遥感植被指数、纹理特征和地形特征的分类特征集在提取苹果园空间格局方面效果最优,苹果园地提取的总体精度和Kappa系数分别为94%和0.86,高于其他分类特征组合。研究成果可为未来陕西省苹果产业合理规划及果园精细化管理提供科学依据和数据支撑。

基于GEOVIS Earth Studio的高中地理教学案例开发——以“河流地貌”为例

信息技术与教学的融合发展是教育改革发展的方向,地理信息技术在教育信息化2.0时代给地理教育提供了丰富的教学资源,可有效提高教学效果。本文通过挖掘GEOVIS Earth Studio平台在地理教学中的功能优势,构建其教学应用模式,以人教版必修《地理1》“河流地貌”为例阐明平台操作过程并进行案例教学设计,创新地理教学技术手段,促进中学地理教学的信息化进程。

On the apparent line-of-sight alignment of the peak X-ray intensity of the magnetosheath and the tangent to the magnetopause,as viewed by SMILE-SXI

The Soft X-ray Imager(SXI)on board the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)spacecraft will be able to view the Earth’s magnetosheath in soft X-rays.Simulated images of the X-ray emission visible from the position of SMILE are created for a range of solar wind densities by using 3 years of the SMILE mission orbit,together with models of the expected X-ray emissivity from the Earth’s magnetosheath.Results from global magnetohydrodynamic simulations and a simple model for exospheric neutral densities are used to compare the locations of the lines of sight along which integrated soft X-ray intensities peak with the lines of sight lying tangent to surfaces(defined here to be the magnetopause)along which local soft X-ray intensities peak or exhibit their strongest gradients,or both,for strongly southward interplanetary magnetic field conditions when no depletion or low-latitude boundary layers are expected.Where,in the parameter space of the various times and seasons,orbital phases,solar wind conditions,and magnetopause models,the alignment of the X-ray emission peak with the magnetopause tangent is good,or is not,is presented.The main results are as follows.The spacecraft needs to be positioned well outside the magnetopause;low-altitude times near perigee are not good.In addition,there are seasonal aspects:dayside-apogee orbits are generally very good because the spacecraft travels out sunward at high altitude,but nightside-apogee orbits,behind the Earth,are bad because the spacecraft only rarely leaves the magnetopause.Dusk-apogee and dawnapogee orbits are intermediate.Dayside-apogee orbits worsen slightly over the first three mission years,whereas nightside-apogee orbits improve slightly.Additionally,many more times of good agreement with the peak-to-tangent hypothesis occur when the solar wind is in a high-density state,as opposed to a low-density state.In a high-density state,the magnetopause is compressed,and the spacecraft is more often a good distance outside the magnetopause.

全球红树林时空变化及演变趋势

红树林是全球重要的生态系统,了解红树林的时空变化特征及演变趋势对开展红树林的保护、恢复及可持续管理具有重要意义。基于谷歌地球工程(Google Earth Engine,GEE)云平台,利用全球红树林分布数据和陆地卫星(Landsat)系列光学影像特征指数数据,结合Theil-Sen中值趋势分析、Mann-Kendall检验、Hurst指数等方法,分析了全球红树林的时空分布特征、时空演变趋势及其可持续特征。结果表明:1990—2020年全球红树林面积呈先下降后上升趋势,总面积减少52174.18km^(2),年平均流失率达1.2%,红树林面积减少最多的地区为东南亚,其次为澳大利亚和新西兰、南美洲和东南非洲;红树林呈退化趋势变化的面积(81.44%)明显多于改善区域的面积(17.43%),其中澳大利亚和新西兰的退化趋势最为明显;2015—2020年全球红树林变化趋势有所改善,有73.85%的区域在未来是可持续的,持续改善区域面积(38.58%)大于持续退化区域面积(33.06%),且改善区域的可持续性明显高于不可持续性,表明2020年之后全球红树林整体上呈改善趋势变化。全球红树林时空变化特征和演变模式,可为生物多样性保护、沿海经济发展、生态环境的可持续改善提供重要支撑,对评估联合国2030可持续发展目标实现的状况具有重要影响。

1990—2020年黄土高原典型县域植被覆盖变化及影响因素

为探究吉县近30 a植被动态演变规律及其影响因素,本研究基于Landsat影像,结合气象、土地利用、夜间灯光等数据,采用趋势分析、偏相关分析、随机森林、残差分析等方法探究吉县植被覆盖度时空变化特征及气候和人为因素对植被变化的影响。结果显示:(1)1990—2020年研究区植被覆盖度(FVC)整体呈显著上升趋势,FVC年均增长速率约为0.49%,植被质量明显改善。(2)吉县FVC具有明显的“低值-高值”交错分布的空间特征。1990—2020年FVC显著增加区占51%,FVC显著减少区占7%。(3)气候因素对部分FVC高值区和建筑区植被生长起抑制作用,对其余地区植被覆盖起促进作用。将人类活动作为全域影响因素考虑时气候和人类活动对植被动态的贡献率分别为53.43%、46.57%,将其作为局域变量时相对贡献率减少至13.07%。人类活动在特定地区如吉县中部和东部是植被退化的重要影响因素,西侧和南部的植被恢复也与之相关。研究结果可为区域生态修复工作进一步开展提供科学依据。

Lateral earth pressure of granular backfills on retaining walls with expanded polystyrene geofoam inclusions under limited surcharge loading

Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.

基于Google earth engine渭-库绿洲果园遥感提取

针对干旱区果园大面积遥感提取困难、识别精度低等问题,本研究基于GEE(Google earth engine)平台,综合应用Sentinel-1/Sentinel-2影像构建特征集。通过对比原始特征组合、Jeffries-Matusita(J-M)距离、属性重要度3种优化方式,结合随机森林(Random forest,RF)分类方法,对比得到最佳优化方式,探索果园最优分类特征集。结果表明:识别效果最好的方案为G17 JM,总体精度为91.25%,kappa系数为0.89,面积精度为82.55%。最优特征集为B8_asm、B8_ent、B8_idm、NDVI re3、B6、B7、a、e、b、EVI、B11、B8A、B8、VV。使用J-M距离进行特征集优化,有效降低数据量、提高计算效率,更有利于精确遥感识别果园种植面积。表明GEE快速、准确获取果园种植面积的可行性,为获取果园动态变化提供强有力的基础。

中国西南山地城市生态环境质量长时序变化及其评价——以重庆市为例

为研究中国西南地区山地城市的生态环境质量,选择以重庆市为例,利用遥感技术和Google Earth Engine(GEE)平台,构建遥感生态指数(RSEI,remote sensing ecological index),评价重庆市2000年~2021年的生态环境质量及其长时序变化。为探讨山地城市生态环境质量的主要影响因素,选取海拔、坡度、气温和降水四个影响因子,得到RSEI的海拔依赖性与坡度依赖性以及RSEI与气候因子的响应关系。结果表明:①遥感生态指数RSEI总体呈上升趋势,生态质量为“优”的面积增加了130.27%,生态质量为“差”的面积减少了65.68%,生态环境有明显的改善;②从RSEI随海拔、坡度变化曲线可以看出,0 m~1800 m范围内RSEI缓慢增加,1800 m~2800 m范围内开始减小,RSEI随坡度增加而增长,坡度>40°之后RSEI趋于平稳;③从RSEI与气候因子的响应曲线可以看出,温度和RSEI呈负相关,温度越高,RSEI越低;随着降水的增加,RSEI指数逐渐上升。研究表明,使用GEE平台可以对多云雾、植被覆盖度高的西南山地城市的生态环境质量进行长时序的监测和评价。研究结果可为中国西南地区山地城市的生态环境保护提供精细化管理,从而根据区域特色进行环境治理,实现生态环境与经济的协调发展。