阳泉高瓦斯大采长综放面瓦斯涌出规律研究     

郭有慧  ;魏建平 《中国煤炭地质》2014,(11):34-38

适当加大综放工作面长度已成为煤矿高产高效主要发展方向之一,但工作面采长加大后,瓦斯的涌出量加大,对安全生产带来隐患。通过分析阳泉煤矿三矿综放工作面采长增加后瓦斯涌出量的变化特征,对采长200m以下和200m以上的综放工作面瓦斯涌出影响因素进行了对比研究,认为综放工作面采长增大后,邻近层垮落卸压范围增大,吨煤瓦斯涌出量增加27%;瓦斯涌出总量的增加主要取决于卸压影响范围体积的增加和煤层开采产量的增大。  相似文献   

基于NARX回归神经网络的岸基GNSS-IR有效波高反演模型分析     

张一  周立 《测绘通报》2022,(2):90-94

有效波高是海洋动力环境的主要参数,针对现有岸基双天线GNSS-R有效波高反演方法必须使用专用型接收机,以及相关测站布设较少、数据获取困难等限制,本文提出了一种利用普通单天线测量型GNSS接收机的GNSS-IR数据反演有效波高的方法。首先,利用NARX回归神经网络构建潮高反演误差与有效波高大小之间的相关模型,并给出了从数据选取、数据集制作到反演模型构建的相关流程与方法。然后,使用斯坦福大学哈勃肯斯海洋实验站中P231站两年的数据,开展了基于NARX回归神经网络的岸基单天线GNSS-IR有效波高反演模型试验。试验结果表明,该模型适用于0.1~2.5 m （即二～四级海况之间）范围内有效波高的反演应用,反演有效波高的MSE最小为0.01 m。  相似文献   

近55年来河西地区季节开始日及长短变化特征   总被引：4，自引：0，他引：4  

张克新  刘普幸  张锐  霍华丽  曹立国 《地理研究》2011,30(3):547-554

利用河西地区15个气象站点1955～2009年日平均气温资料,采用5d滑动平均、气候倾向率、Mann-Kendall和滑动t检验,ArcGIS中的反距离加权插值等方法分析河西地区四季开始日及其长短变化特征,以揭示气候季节变化对全球气候变暖的响应.结果表明:近55年来,河西地区四季开始日主要表现为春、夏和秋季提早,冬季推...  相似文献   

时间序列数字滤波后自由度的确定--应用于日长变化与南方涛动指数的相关分析     

闫昊明  钟敏  朱耀仲 《天文学报》2003,44(3):324-329

原始观测时间序列进行数字滤波后，其自由度将大大降低，对各种数字滤波器都可以通过Monte Carlo方法模拟获得对应置信水平的相关系数临界值，从而得到时间序列滤波后的自由度，如果滤波后的频段宽度与Nyquist频率之比为Z，那么对于理想的单边和双边滤波器，时间序列滤波后的自由度为原始值的Z／2和Z倍，非理想滤波器一般不符合此规律。  相似文献   

Determination of longitudinal dispersivity in an unconfined sandy aquifer     

Dong‐Ju Kim  Joung‐Souk Kim  Seong‐Taek Yun  Sang‐Hoon Lee 《水文研究》2002,16(10):1955-1964

Study of the mobility of contaminants in an aquifer is an important issue for the proper remediation of contaminated groundwater. Determination of associated solute transport parameters therefore is essential for investigation of the extent to which groundwater can be contaminated. This study aimed at determining solute transport parameters for an unconfined sandy aquifer at a laboratory scale through various tracer tests using a conservative solute as a tracer. Tracer tests consisted of both well‐tracer tests (single and double wells) and an aquifer tracer test using a plume‐capturing device such as time domain reflectometry (TDR). The results showed that longitudinal dispersivities estimated from the single and double well‐tracer tests were 2·2 cm and 13·5 cm for a travel distance of 9·3 cm and 13·5 cm from the injection point respectively. These results agreed reasonably well with the results of the aquifer tracer test. The solute transport parameters obtained at multiple points in the aquifer through the aquifer tracer test revealed that the dispersivity length was proportional to the travel distance by a factor of 0·3, which was moderately higher than the value of 0·1 given in the literature. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Modeling mineral dust emissions from Chinese and Mongolian deserts   总被引：6，自引：0，他引：6  

B. Laurent  B. Marticorena  G. Bergametti  F. Mei   《Global and Planetary Change》2006,52(1-4):121

The present study investigates the frequency and intensity of mineral dust emissions over the deserts of eastern Asia from 1996 to 2001. Mineral dust emissions are simulated using a physical dust emission scheme over a region extending from 35.5°N to 47°N and from 73°E to 125°E. The input parameters required by the dust emission model are (1) surface features data including aerodynamic roughness length, soil dry size distribution and texture; and (2) meteorological surface data, mainly wind speed, soil moisture and snow cover. The way by which these surface features and meteorological data can be assessed is described and discussed. The influence of soil moisture and snow cover is taken into account and their effects on simulated dust emission are quantified.The simulations reproduce on a daily basis the location and intensity of the severe events of April 1998 and spring 2001 as recorded by the meteorological stations and/or described in various studies. Based on 6 yr of simulations, the main dust source regions are identified and their relative contributions to the total dust emissions are quantified.The seasonal cycle of the dust storms frequency is well reproduced with a maximum in spring. The simulations suggest that it is mainly controlled by the emissions occurring in the Taklimakan desert in latter spring and in summer, and by those occurring in the northern deserts of China in winter. The Taklimakan desert appears to be the most frequent and steady source of dust emissions during the studied period. On the other hand, in the Gobi desert, only a few dust emission events are simulated, but the dust amount emitted during each event is generally very large. In the northern deserts of China, dust emissions are frequent and their intensity is variable.These results show an important annual and inter-annual variability of the emitted dust (between 100 Mt yr^− 1 and 460 Mt yr^− 1), mainly controlled by the occurrence of severe events in the Gobi desert and in the northern deserts of China.  相似文献   

Comparison Of Upwind Land Use And Roughness Length Measured In The Urban Boundary Layer   总被引：1，自引：1，他引：0  

G. G. Rooney 《Boundary-Layer Meteorology》2001,100(3):469-485

The results of wind measurements taken in two studies at an urban sitein Birmingham (UK) are presented. Displacement heights and roughnesslengths are calculated that compare well with previous measurements inthe urban canopy. Dimensionless windshear and vertical-velocity standarddeviation are also shown to obey Monin–Obukhov similarity theory. Themean roughness lengths measured at the highest measuring position (45 m)increase with the fraction of upwind urban cover calculated using asource-area model.  相似文献   

地貌分形理论模型的数值模拟   总被引：2，自引：0，他引：2  

李锰  朱令人  龙海英 《大地测量与地球动力学》2002,22(2):47-52

利用简单分形模型和分数布朗运动模型，分别对分形地貌研究中的多度域分形曲线和外营力作用下地貌剖线自仿射分形进行了模拟计算。模拟结果显示，不同机制作用下的地貌形态分维值差异不大的时候，从分维结构图上无法获得相应的多度域分维值，这时需要借助其它手段进行分析；不同起伏的地表形态可以具有相同的分维值，夷平作用并不改变由地表侵蚀作用形成的分维值，表现出外营力作用的相对稳定性，要全面描述曲线的起伏特性需要引入渡越长度。  相似文献   

Absence of initial singularities in superstring cosmology     

Sanjay Jain 《Journal of Astrophysics and Astronomy》1997,18(4):363-379

In a universe whose elementary constituents are point particles there does not seem to be any obvious mechanism for avoiding the initial singularities in physical quantities in the standard model of cosmology. In contrast in string theory these singularities can be absent even at the level where spacetime is treated classically. This is a consequence of the basic degrees of freedom of strings in compact spaces, which necessitate a reinterpretation of what one means by a very small universe. We discuss the basic degrees of freedom of a string at the classical and quantum level, the minimum size of strings (string uncertainty principle), the t-duality symmetry, and string thermodynamics at high energy densities, and then describe how these considerations suggest a resolution of the initial singularity problem. An effort has been made to keep this writeup self-contained and accessible to non-string theorists.  相似文献   

平面贴片天线的研究     

付传兴  杜国宏 《成都信息工程学院学报》2006,21(Z1):30-35

介绍了半波谐振贴片的理论,并利用HFSS分别对采用微带和同轴两种方式馈电的中心频率为12GHZ的平面贴片天线进行了仿真.仿真结果表明:当改变微带与同轴传输线馈电位置时,对于微带馈电方式,要实现单频点,取贴片的长边中点效果较好;如果偏离该中心点,将具有双频点特性.而采用同轴馈电时,所研究的几个馈电点位置中也是贴片长边中点相对较好,如偏离该中心点,频率将偏离中心频率.  相似文献