基于有上下界风量约束的矿井风量极值流算法研究

为解决既有方法不能准确求出矿井最大通风量与最小配风量,从而导致矿井通风系统产生能源浪费或难以满足矿井通风需求,出现安全隐患与改造难度大、潜力低等问题,提出1种基于有上下界风量约束的矿井风量极值流算法.该算法首先利用最大流算法求解满足节点流量平衡与分支上下界容量限制条件的可行流问题,若存在可行流,在求得可行流基础上,再利...     

Trends in Raindrop Kinetic Energy with Modeled Climate Warming in the Lake Tahoe Basin

Two means by which climate change may increase surface soil erosion in mountainous terrain are: (1) increasing the frequency of extreme rainfall events and (2) decreasing the duration of snow cover on bare soil. We used output from four general circulation models (GCMs) and two greenhouse gas trajectories to produce a suite of hydrologic variables at a daily time‐step for historic and projected 21st Century conditions. We statistically disaggregated the daily rainfall to hourly, using hourly rainfall from a network of nine weather stations in the Tahoe Basin, and filtered out rain falling on a snowpack. We applied published equations to convert hourly intensity to raindrop kinetic energy (KE) for each day and grid cell in the Basin, averaged across grid cells, and created time series of total annual and maximum annual hourly kinetic energy (TKE and MKE) on snow‐free ground. Using the Generalized Extreme Value distribution, we calculated the significance of long‐term trends in KE on snow‐free ground, and estimated energy levels for return periods of 2, 20, and 100 years. We then detrended the snowpack data and compared the resulting trends in KE with the trends resulting from changes in both rainfall energy and snowpack under two GCMs. Principal findings include (1) upward trends in MKE, (2) stronger upward trends in TKE; and (3) an effect of increasing rainfall intensities on KE in some cases, and a strong effect of reduced snowpack in all cases examined.     

The effect of summer drought on the predictability of local extinctions in a butterfly metapopulation

The ecological impacts of extreme climatic events on population dynamics and community composition are profound and predominantly negative. Using extensive data of an ecological model system, we tested whether predictions from ecological models remain robust when environmental conditions are outside the bounds of observation. We observed a 10-fold demographic decline of the Glanville fritillary butterfly (Melitaea cinxia) metapopulation on the Åland islands, Finland in the summer of 2018 and used climatic and satellite data to demonstrate that this year was an anomaly with low climatic water balance values and low vegetation productivity indices across Åland. Population growth rates were strongly associated with spatiotemporal variation in climatic water balance. Covariates shown previously to affect the extinction probability of local populations in this metapopulation were less informative when populations were exposed to severe drought during the summer months. Our results highlight the unpredictable responses of natural populations to extreme climatic events.     

SVD在串联故障电弧检测及选相中的应用*

煤矿井下发生串联故障电弧易引发火灾等安全事故,为了预防电气火灾、指导线路维修,利用三相电动机及变频器负载开展不同线路、不同电流条件下的串联故障电弧实验,研究三相串联故障电弧的检测及选相方法。首先,对单相电流进行一阶差分处理后,建立改进的吸引子轨迹矩阵作为故障特征矩阵;其次,对故障特征矩阵进行奇异值分解,采用特征矩阵的奇异值构建串联故障电弧检测及选相的特征向量;最后,利用极限学习机建立故障电弧检测及选相模型,并测试检测及选相准确率。研究结果表明:提出的SVD方法可以利用单相电流实现三相电动机及变频器负载回路中的串联故障电弧检测及选相。     

2000年全球气象灾害评价

2000年,全球气候持续较常年偏暖。赤道中,东太平洋地区强拉尼娜事件在1月再次达到峰值后,迅速减弱,强拉尼娜事件对全球,特别是对热带地区产生了较大的影响,北半球许多地区冬季出现严寒天气,夏季又遭热浪袭击,严重的高温、干旱、森林大火困扰全球。而亚洲南部、西欧、南部非洲、南美北部的许多地区暴雨频繁。估计气象自然灾害造成全球经济损失达上千亿美元。数亿人口受灾。     

灰霾天气城市空气污染程度判据指标体系建立的探讨

灰霾天气加重空气污染程度,是空气污染呈现区域性、复合型污染的重要天气污染现象,对视觉空气质量以及人体健康造成很大影响与危害.针对灰霾天气下城市空气污染加重程度判据系统建立,对灰霾天气下空气污染程度评估方法及建立污染程度与能见度量化相关关系进行了初步探讨.     

北京城区春季空气污染物垂直分布与气象条件观测分析

分析了北京城区春季污染物 (SO2 、NOX)垂直分布与相应的气象条件之间的关系 ,结果表明 ,不同高度的 SO2 浓度差异不显著 ,而不同高度的 NOX 浓度有明显的差异 ,知春路低层浓度高于中、高层 ,潘家园则是低层低于中、高层。一日中 ,特别是当无大的天气系统影响 ,地面呈典型的山谷风日变化时不同高度的 SO2 和 NOX浓度均呈明显的峰谷变化。工作日污染物浓度比休息日浓度高 50 %。     

Standardisation of Temperature Observed by Automatic Weather Stations

Daily mean, maximum and minimum surface airtemperature data were gathered from a network ofautomatic weather stations (AWS) within the Moor HouseNational Nature Reserve in northern England. Five AWSwere installed next to the official EnvironmentalChange Network weather station at Moor House. Datawere compared graphically and correction constantswere calculated to adjust data from each AWS to thestandard of the official station by optimising theconcordance correlation coefficient. Each correctedstation was re-located next to one of five in-situstations in and around the reserve, allowingcorrection of all temperature sensors to a commonstandard. The mean error associated with measureddaily mean, maximum and minimum temperature for eachsensor does not exceed ±0.2 K. The procedurequantifies a source of systematic measurement error,improving the identification of spatial temperaturedifferences between stations.     

基于天气分型的北京地区雷电潜势预报预警系统

对1997-2006年457个雷暴过程的环流形势进行对比分析,将北京地区的雷暴天气分为东北低涡低槽、贝蒙低涡低槽、西来槽等11种雷暴天气型;利用南郊观象台(54511站)的探空资料计算对流有效位能、抬升指数和相对风暴螺旋度等33个对流参数,通过与北京地区SAFAIR3000获取的闪电定位资料进行统计分析,提取BCAPE、BLI、MDCI、BIC、KNEW和SWISS等6个对流参数作为北京地区潜势预报参数;采用事件概率回归(REEP)方法,利用获取的6个对流参数作为变量,形成了11种雷暴天气型下的潜势预报方法。利用WRF模式的预报场,建立适用于北京地区3～36 h雷电潜势预报系统。个例实验结果表明其具有较好准确性。由于该系统建立过程中使用了高分辨率探测资料和中尺度模式的输出结果,实现了雷电潜势预报由点到面,由粗到细的突破,对北京地区雷电预警预报具有一定的应用价值。     

基于标准化降水蒸散指数的华南干旱趋势研究

最近几年华南地区干旱频发,为探讨该地区的干旱趋势,用标准化降水蒸散指数(SPEI)和1961-2010年华南地区具有代表性的50个站点的月降水及月平均气温资料,分析了该地区近50年来的干旱趋势、干旱空间分布、极端干旱事件发生频次和干旱持续时间。结果表明,华南地区普遍存在干旱事实,最近10年是干旱最严重的10年,Mann-Kendall检验表明该地区平均SPEI指数从1998年开始突变;干旱化最严重的区域是海南岛、广西南部和西部地区,广东的干旱化趋势最轻。20世纪70年代干旱和极端干旱事件较少,其后明显增多,干旱持续时间也有所延长。由于该地区降水呈现弱增加趋势而温度升高显著,因此推测温度升高导致蒸散增加可能是华南地区干旱化的主要原因。另外,降水频次的减少和集中也是导致近来极端干旱事件增多的原因之一。SPEI指数较好地体现了气候变暖导致的干旱化趋势。