校园网络系统雷击原因分析及防雷措施     

王明亮  徐力泉  吴海 《气象研究与应用》2004,25(3):33

以海南农垦加来师范学校校园网络系统为例,分析了造成雷击事故原因,并提出解决措施。  相似文献   

贵州荔波1.5万年以来石笋高分辨率古气候环境记录   总被引：33，自引：8，他引：25  

张美良  程海  林玉石  覃嘉铭  张会领  涂琳玲  王华  冯玉梅 《地球化学》2004,33(1):65-74

通过对董哥洞石笋进行高精度的 TIMS- U系测年和 C、O同位素分析,建立了贵州省荔波地区 15 470 a以来高分辨率的古气候变化时间序列.研究结果表明,荔波地区 15 470 a以来石笋记录的冷暖事件所反映出的古季风变化,大致可分为 4个气候变化阶段 : (1) 15 470～ 11 350 a期间的晚更新世晚期-- Heinrich (H1)事件和新仙女木 (YD)事件期间,反映本阶段东亚冬季风强盛, 气温降低, 有效大气降水相对减少, 表现为干旱寒冷的气候环境; (2) 11 350～ 9 190 a期间的早全新世--干热期,反映东亚夏季风相对增强,气温升高,有效降水相对较少,表现为干热的气候环境; (3) 9 190～ 3 320 a期间的中全新世--稳定的气候适宜期,反映东亚夏季风相对强盛,气温升高,有效降水相对较大,表现为温暖湿润的气候环境; (4) 3 320～ 130 a期间的晚全新世降温期,反映本阶段东亚夏季风明显减弱,东亚冬季风相对增强,有效降水相对增大,而气候变化的波动频率却在增加 ,越至现代冷温变化时间渐趋缩短.石笋的 C、O同位素记录所揭示的末次冰期最后的 2次冷事件,其冷谷年龄分别为: (15 440± 130) a(H1事件 )和 (11 910± 70) a(YD事件),同时,还确定了终止点Ⅰ的界线年龄为 (11 350± 70) a,并证实了末次冰期在中国南方东亚季风气候区也存在有与北大西洋 H1事件和 YD事件相对应的冷事件.荔波地区的古季风环流变化,反映了东亚夏季风由弱-变强-再逐渐变弱的趋势,有效大气降水由少-增多-变少-再增多,气温由低-变高-再次变低的变化趋势,显示了与北极地区存在着古气候的遥相关关系.  相似文献   

Response analysis of rainfall–runoff processes using wavelet transform: a case study of the alpine meadow belt     

Hai‐Long Liu  An‐Ming Bao  Xi Chen  Ling Wang  Xiang‐liang Pan 《水文研究》2011,25(14):2179-2187

Rainfall–runoff processes appear to be highly nonlinear in Bayinbluk watersheds of the northwestern China. In this study, the time‐scale wavelet transform has been used for the analysis of this nonstationary system. The Haar and Morlet wavelet transform were used to analyse the rainfall–runoff conversion relationship. Wavelet power spectrum and change point methods are also employed to analyse rainfall rates and runoffs measured at daily to half‐hourly sampling rate. The four experimental sites (Luoto, Haer, Kuce and Shengl) are located in the Tianshan Mountains (Xinjiang province, China). Correlation analysis and wavelet transform are first applied to runoff process in different underlying surfaces. Wavelet analyses of rainfall rates and runoffs also give meaningful information on the temporal variability of the rainfall–runoff relationship. Change point and wavelet power spectrum analysis provide simple interpretation of energy distribution between different scales. The results indicate that wavelet transform is a good method for analysing the nonlinear relationship of temporal–spatial responses between rainfall and runoff. This method allowed quantification of the processes affecting runoff and provided an insight into their implications in surface water management. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Physics‐based simulation of multiple interacting crack growth in brittle rocks driven by thermal cooling          下载免费PDF全文

Hai Huang  Paul Meakin  Anders Malthe‐Sorenssen 《国际地质力学数值与分析法杂志》2016,40(16):2163-2177

Crack growth in hot brittle rocks, driven by thermal cooling, was simulated using a coupled two‐dimensional discrete element and heat transport model that explicitly includes the random initiation and subsequent propagation of interacting cracks. The model clearly predicts that a quasi‐hierarchical array of subparallel cracks, oriented along the direction of the temperature gradient, is formed under small to moderately large thermally generated strain load conditions. The simulation results also demonstrate that, after an initial transient, thermal cracks propagate in a stable fashion with a velocity that scales with ~ t^{− 1/2}. However, under large thermal strain loads, a more complicated geometry composed of cracks that curve and coalesce develops during the later stages of crack growth. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

The vertical heterogeneity of soil detachment by overland flow on the water-level fluctuation zone slope in the Three Gorges Reservoir,China     

Ping Guo  Hai Xiao  Feng Gao  Zijuan Li  Huan Hu  Qianheng Zhang  Zhenyao Xia  Mingyi Li  Yueshu Yang 《水文研究》2021,35(7):e14282

Periodic submersion and exposure due to the operation of the Three Gorges Reservoir (TGR) alter the soil properties and plant characteristics at different elevations within the water level fluctuation zone (WLFZ), possibly influencing the soil detachment capacity (D_c), but the vertical heterogeneity of this effect is uncertain. Soil samples were taken from 6 elevation segments (5 m per segment) along a slope profile in the WLFZ of the TGR to clarify the vertical heterogeneity of D_c. Scouring experiments were conducted at 5 slope gradients (17.6%, 26.8%, 36.4%, 46.6%, and 57.7%) and 5 flow rates (10, 15, 20, 25, and 30 L min⁻¹) to determine D_c. The results indicate that the soil properties and biomass parameters of the WLFZ exhibit strongly vertical heterogeneity. D_c fluctuates with increasing elevation, with maximum and minimum average values at elevations of 145–150 m and 165–170 m, respectively. Linear equations accurately describe the relationships between D_c and hydrodynamic parameters, for which the shear stress (τ), stream power (ω), and unit energy of water-carrying section (E) perform much better than the unit stream power (U). Furthermore, a clear improvement is achieved when using a general index of flow intensity to estimate D_c. Furthermore, D_c is significantly and negatively correlated with the mean weight diameter (MWD, p < 0.05) and organic matter content (p < 0.01) but not significantly correlated with other soil properties (p > 0.05). The rill erodibility at elevations of 145–150 m and 170–175 m is greater than that at other elevations. The critical hydraulic parameters were highest in the 165–170 m segments. Both the rill erodibility and the critical parameters fluctuate vertically along the sloping surface. This research highlights the vertical heterogeneity of D_c and is helpful for better understanding the mechanisms responsible for soil detachment in the WLFZ of the TGR.  相似文献   

Speleothem-based chronology and environmental context of deposits from the Mishin Kamik Cave,NW Bulgaria – A contribution to the archaeological study of the Late Pleistocene human occupation in the Balkans     

Sophie Verheyden  Elena Marinova  Stefanka Ivanova  Christian Burlet  Hai Cheng  Lawrence R. Edwards  Thomas Goovaerts  Maria Gurova 《第四纪科学杂志》2021,36(7):1221-1233

The Balkan Peninsula represents one of the most important human pathways into and out of Europe during the Pleistocene. Mishin Kamik cave, located in the karst region of Western Stara Planina, has a rich faunal content and shows promising features indicating a human occupation site with the discovery of potential bone artefacts and an intriguing accumulation of bear skulls and bones. Petrographic study and U-series dating of a stalagmite and other calcite deposits in the cave provide an absolute chronological frame for the detrital infillings and their archaeological content and inform the environmental and climatic context of the cave evolution. Most detrital deposits in the cave were probably deposited before Marine Isotope Stage (MIS) 5 and the cave morphology and sedimentary deposits display current morphologies since ~135 ka. Consequently, the palaeontological and archaeological findings are older than ~135 ka. Calcite dated on and under the accumulation of bear skulls and bones suggests deposition during MIS 7. A first depositional contextualization of the bone accumulation does not allow us to discriminate between a natural or anthropogenic origin. The study emphasizes the added value of speleothem studies in archaeological sites and particularly in bringing a well-constrained chronological and environmental framework.  相似文献   

Large variations of δ13C values in stalagmites from southeastern China during historical times: implications for anthropogenic deforestation          下载免费PDF全文

Haiwei Zhang  Yanjun Cai  Liangcheng Tan  Hai Cheng  Shijiang Qin  Zhisheng An  R. Lawrence Edwards  Le Ma 《Boreas: An International Journal of Quaternary Research》2015,44(3):511-525

Variations in speleothem δ¹³C values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined δ¹³C variations in two stalagmites growing for the last 2200 years in Shennong Cave, Jiangxi Province, SE China. The two δ¹³C records corroborate well one another and show a prominent 6‰ enrichment of the δ¹³C values from AD 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between δ¹⁸O and δ¹³C values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between Mg/Ca and Sr/Ca ratios and divergent changes between δ¹³C values and Mg/Ca and Sr/Ca ratios from AD 700 to 1100 reveal that the prior calcite precipitation (PCP) and water–rock interaction did not dominate the increase of δ¹³C values. It is plausible that the obvious δ¹³C variation was largely influenced by the changes in vegetation cover overlying the cave. Our δ¹³C results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to AD 700, small fluctuations in relatively light δ¹³C values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during AD 700–1100, the drastic increase in δ¹³C values indicates persistent and massive deforestation associated with large‐scale immigration into northern Jiangxi after the Rebellion of An & Shi (AD 755–763) in the Tang Dynasty and the subsequent development of agriculture and economic activity; and (iii) since AD 1100, fluctuations in relatively high δ¹³C values suggest that local vegetation during the last millennium has been sparse. Since the Rebellion of An & Shi, southeastern China was progressively developed, coincident with deforestation and vegetation deterioration caused by human disturbance in the form of deforestation and cultivation.  相似文献   

Potential influence of the November–December Southern Hemisphere annular mode on the East Asian winter precipitation: a new mechanism     

Zhiwei Wu  Juan Dou  Hai Lin 《Climate Dynamics》2015,44(5-6):1215-1226

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Mercury concentration in ecosystem components in water bodies and streams in Khanh Hoa province (Central Vietnam)     

N. V. Lobus  V. T. Komov  Nguyen Thi Hai Thanh 《Water Resources》2011,38(6):799-805

Total mercury concentration in water, seston, soils, and muscle tissues of fish in water bodies in Khan Hoa province was determined. Hg concentration in water does not exceed 40 ng/l. It migrates in water mostly in dissolved form. Hg concentration in soils of the examined water bodies varies from 0.01 to 0.05 mg/(kg dry mass) and that in the muscle tissues of fish on the average does not exceed 1.4 mg/(kg dry mass).  相似文献   

新城金矿蚀变带构造与地球化学特征   总被引：4，自引：0，他引：4  

吕承训  吴淦国  陈小龙  张迎春  张迅与  赵海 《大地构造与成矿学》2011,35(4):618-627

通过新城金矿的构造和蚀变岩剖面实测、构造测量和岩石地球化学分析,获得以下构造和岩石地球化学同步变化特点:(1)以焦家断裂为中心蚀变岩分带为断层泥-硅化带-黄铁绢英岩带-强钾化花岗岩带-弱钾化花岗岩带-未蚀变花岗岩带;(2)金矿化主要集中在硅化带及黄铁绢英岩带;(3)断裂下盘依次发育糜棱岩-碎裂岩-花岗质碎裂岩-碎裂花岗...  相似文献