地下线状长导体对激发极化场的影响——以胶东地区为例     

董寿志 《山东地质》2012,(1):31-33,38

线状长导体,如金属管道、裸金属线、光缆等,其直径相对于埋深虽然很小,但受到激发时,能够产生很大的极化场,生产实践中对极化率的影响很大。该文主要研究了中梯和联剖2种装置下地下线状长导体的异常特征,分析了异常产生的原因,并提出了辨别这种干扰因素的方法。  相似文献   

航磁垂直梯度调整ΔT水平方法研究   总被引：2，自引：1，他引：1       下载免费PDF全文

骆遥  王平  段树岭  程怀德 《地球物理学报》2012,55(11):3854-3861

使用中国自主研发、具有完全自主知识产权的航磁全轴梯度勘查系统首次试飞获得的资料,利用航磁垂直梯度数据进行ΔT水平调整研究,讨论了航磁及航磁梯度资料水平调整的原则,提出梯度资料长波水平的调平方法.对经长波水平调整后的垂直梯度数据进行位场转换,获得不受地磁场随时间变化影响的磁异常,并通过恢复磁异常的长波信息,实现了ΔT的水平调整和增强.实际资料处理表明调平过程具有物理意义、效果明显.  相似文献   

Theory and application of nonlinear river dynamics     

Yu-chuan BAI  Zhao-yin WANG 《国际泥沙研究》2014,29(3):285-303

A theoretical model for river evolution including riverbed formation and meandering pattern formation is presented in this paper.Based on nonlinear mathematic theory,the nonlinear river dynamic theory is set up for river dynamic process.Its core content includes the stability and tropism characteristics of flow motion in river and river selves＇ evolution.The stability of river dynamic process depends on the response of river selves to the external disturbance,if the disturbance and the resulting response will eventually attenuate,and the river dynamics process can be restored to new equilibrium state,the river dynamic process is known as stable;otherwise,the river dynamic process is unstable.The river dynamic process tropism refers to that the evolution tendency of river morphology after the disturbance.As an application of this theory,the dynamical stability of the constant curvature river bend is calculated for its coherent vortex disturbance and response.In addition,this paper discusses the nonlinear evolution of the river peristaltic process under a large-scale disturbance,showing the nonlinear tendency of river dynamic processes,such as river filtering and butterfly effect.  相似文献   

中国极端温度的群发性研究   总被引：1，自引：0，他引：1  

赵俊虎  王启光  支蓉  封国林 《气象学报》2012,70(2):302-310

从极端事件再现时间的角度研究了中国极端高、低温事件再现时间序列的长程相关性、群发性以及二者的关系。发现极端温度事件再现时间序列具有长程相关性,表征长程相关性的标度指数分布存在着明显的区域性特征,并与大气环流有关,当中国大陆在盛夏或隆冬稳定的西风环流控制下,极端温度的长程相关性较好,标度指数较大。通过定义极端事件的群发指数,对极端高、低温进行研究,发现具有长程相关性再现时间序列的极端温度呈现群发现象,且极端温度再现时间序列的标度指数和群发指数二者在空间分布上有较好的对应,极端温度再现时间序列的长程相关性可能是导致极端温度群发性的原因。从年际变化的角度看,极端高温Ⅰ级群发区域的群发指数增长趋于平缓,而极端低温Ⅰ级群发区域的群发指数有下降趋势,这与近几十年来全球变暖一致。在年代际尺度上,群发指数分布的演变特征明显,极端高温Ⅰ级群发区域总体面积变化不大,而极端低温Ⅰ级群发区域面积明显减少。因此,极端低温事件群发性减弱很可能是年代际气候变暖的主要原因。  相似文献   

热带低压远距离对西南涡稳定加强的作用     

李云川  张迎新  马翠平  田秀霞  李宗涛  赵娜  赵利品 《高原气象》2012,31(6):1551-1561

利用地面观测资料、FY-2C卫星红外云图及中尺度数值模式WRF对2010年7月19-20日河北省南部和中东部一次区域性大暴雨过程进行了诊断分析和数值模拟研究。结果表明,海上热带低压对西南涡的稳定和维持有远距离作用。由于热带低压的存在而促使西南低涡的发展,使西南低空急流在河北突然增强,降水得以再度加强;冷空气从高空侵入、下沉,加强了大气斜压性,迫使对流层中层空气的抬升,为西南涡的发展提供了动力条件;暖湿气流主要来自西南涡携带的西南气流及海上低压和西太平洋副热带高压的东南气流输送,为暴雨加强提供了充沛的水汽和热力条件。  相似文献   

Population ecology of the snail Melampus bidentatus in changing salt marsh landscapes          下载免费PDF全文

Roman Zajac  Erin Kelly  Danielle Perry  Ivana Espinosa 《Marine Ecology》2017,38(2)

We studied the population ecology of the snail Melampus bidentatus in relation to patch composition and landscape structure across several salt marsh systems in Connecticut, USA. These marshes have changed significantly over the past 40–50 years including loss of total area, increased areas of short Spartina alterniflora, and decreased areas and fragmentation of Spartina patens. These changes are consistent with tidal inundation patterns that indicate frequent flooding of high marsh areas. Melampus bidentatus densities were highly variable, both among different salt marsh systems and locations within specific marshes, but were generally similar among short Sp. alterniflora and Sp. patens patches within locations. Densities were lowest where the marsh was regularly inundated at high tide and only remnant Sp. patens patches remained. Almost no snails were found in bare patches. Areas that had large Sp. patens patches adjacent to short Sp. alterniflora supported the highest M. bidentatus densities. Population size‐structure varied significantly among patch types, with higher proportions of large individuals in short Sp. alterniflora and hummocked Sp. patens patches than in large and remnant Sp. patens patches. This was likely due to size‐selective predation and/or higher snail growth rates due to better food resource conditions in short Sp. alterniflora patches. Egg mass densities and the number of eggs per egg mass were highest in short Sp. alterniflora. Our results indicate that M. bidentatus is resilient to the level and patterns of salt marsh change evident at our study sites. Indeed, snail densities were significantly higher than reported in other field studies, suggesting that increased patch areas of short Sp. alterniflora and associated environmental conditions at our study sites may provide more favorable habitats than previously when marshes were dominated by extensive Sp. patens meadows. However, there may be threshold conditions that could overwhelm the ability of M. bidentatus to maintain itself within salt marsh systems where changes in hydrology, sedimentation and other factors lead to increased numbers of bare patches and ponds and loss of short Sp. alterniflora and Sp. patens. Studies of the responses of resident and transient fauna to salt marsh change are critically needed in order to better understand the implications for salt marsh ecosystem dynamics and services.  相似文献   

Northern Aegean Earthquake (Mw=6.9): Observations at three seismic downhole arrays in Istanbul     

《Soil Dynamics and Earthquake Engineering》2015

The Northern Aegean Earthquake (M_w=6.9\M_L=6.5) took place on May 24, 2014 between the islands of Gokceada, Turkey and Samothraki, Greece. The tremors were felt as far as in Istanbul, about 300 km on the East – Northeast (ENE) side of the epicenter. Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University, Turkey operate three downhole arrays in Istanbul, namely Atakoy (ATK), Fatih (FTH) and Zeytinburnu (ZYT) arrays. In this study, waveforms and site response observed at the KOERI operated seismic downhole arrays during the May 2014 Northern Aegean Earthquake (NAE2014) are analyzed in detail and presented. Evaluation of the acceleration records have shown low amplitude but long period and long duration motions at Istanbul. Furthermore, the analyses of the recordings suggest that V_s30 alone may not be a sufficient parameter for the characterization of site amplification.  相似文献   

Numerical simulation of laboratory experiments in detention pond routing with long rainfall duration     

Yao-Ming HONG 《国际泥沙研究》2008,23(3):233-248

This paper establishes a numerical detention pond volume model based on the hydrological continuity equation and the Runge-Kutta numerical method. Experiments for the conditions of both steady and unsteady flow have been used to verify the model. In unsteady flow cases, the outflow hydrograph by numerical simulation are fairly consistent with experimental value. Both experimental and numerical results indicate that wider rectangular sharp-crested weirs or larger rectangular slot tend to induce greater outflow discharges, which undesirably cut down the detention volume. Experiments show that the necessary detention volume of rectangular slot is smaller than that of the rectangular sharp-crested weir for a constant flood peak reduction. That is, the rectangular slot is the recommended outflow device when flood peak reduction is the design criteria. The study also shows that necessary detention volume of the short rainfall duration is less than that of the long rainfall duration under constant allowable maximum discharge.  相似文献   

Sediment transport and beach morphodynamics induced by free long waves,bound long waves and wave groups   总被引：1，自引：0，他引：1  

T.E. Baldock  P. ManoonvoravongKim Son Pham 《Coastal Engineering》2010

New laboratory data are presented on the influence of free long waves, bound long waves and wave groups on sediment transport in the surf and swash zones. As a result of the very significant difficulties in isolating and identifying the morphodynamic influences of long waves and wave groups in field conditions, a laboratory study was designed specifically to enable measurements of sediment transport that resolve these influences. The evolution of model sand beaches, each with the same initial plane slope, was measured for a range of wave conditions, firstly using monochromatic short waves. Subsequently, the monochromatic conditions were perturbed with free long waves and then substituted with bichromatic wave groups with the same mean energy flux. The beach profile changes and net cross-shore transport rates were extracted and compared for the different wave conditions, with and without long waves and wave groups. The experiments include a range of wave conditions, e.g. high-energy, moderate-energy, low-energy waves, which induce both spilling and plunging breakers and different turbulent intensities, and the beaches evolve to form classical accretive, erosive, and intermediate beach states. The data clearly demonstrate that free long waves influence surf zone morphodynamics and promote increased onshore sediment transport during accretive conditions and decreased offshore transport under erosive conditions. In contrast, wave groups, which can generate both forced and free long waves, generally reduce onshore transport during accretive conditions and increase offshore transport under erosive conditions. The influence of the free long waves and wave groups is consistent with the concept of the relative fall velocity, H/w_sT, as a dominant parameter controlling net beach erosion or accretion. Free long waves tend to reduce H/w_sT, promoting accretion, while wave groups tend to increase the effective H/w_sT, promoting erosion.  相似文献   

一种测定并置站垂线偏差的小网参数转换法          下载免费PDF全文

马小辉  张志斌  孙中苗  米立功  雷鸣  张阿丽  王广利  王宏  谷守周 《天文学报》2021,62(2):18

推导了传统全球卫星导航定位系统(GNSS)测定垂线偏差(Deflection of the Vertical, DOV)形式误差的表达式;提出一种可用以解算并置站DOV的小网参数转换法.利用乌鲁木齐南山多技术并置站控制网观测信息,开展了算法验证,并对该站内多个地点DOV开展了实测.结果表明,高精度的小网DOV仅由点位观测精度最高、覆盖面积最广的3个站点决定.个别精度较差的点会为DOV的测定值带来较大的不确定性;采用小网转换法所解算的DOV与实测值间的一致性分别为-2.3′′±4.3′′(子午分量)和0.2′′±4.6′′(卯酉分量);小网转换求取DOV的方法在精度上与经典的GNSS水准方法相当,但步骤更加简便.鉴于多技术并置站会不定期地开展本地测量,可利用该方法实现多技术并置站DOV的零成本长期监测.  相似文献