多径衰落信道条件下OFDM系统性能研究     

徐昌庆  程琳  宋文涛 《成都信息工程学院学报》2003,18(3):253-257

讨论了正交频分复用系统模型在不同条件下，如加窗和防护段、脉冲整形等，对多径衰落信道条件下正交频分复用系统误码率(BER)性能进行分析。仿真结果表明，加防护段以后系统的BER性能得到改善，但经脉冲整形后，由于载波间的正交性被破坏，因此系统性能几乎没有提高。  相似文献   

Automated suitable drainage network extraction from digital elevation models in Taiwan's upstream watersheds     

Wen‐Tzu Lin  Wen‐Chieh Chou  Chao‐Yuan Lin  Pi‐Hui Huang  Jing‐Shyan Tsai 《水文研究》2006,20(2):289-306

Automatically extracting drainage networks from digital elevation models coupled with the constant stream threshold value is a regular method. These extracted networks can be verified by comparing the channel initiation points with those from real networks. From the results analysed, the differences in channel initiation points will affect the network geometries, geomorphological indices and hydrological responses. This paper develops two automatic algorithms, the headwater‐tracing method and the fitness index, to trace the flow paths from headwaters to the outlet and to calculate the reasonable stream threshold. Instead of the method determined by trial and error or field survey, the accurate channel initiation points can be obtained from airborne photographs coupled with high‐resolution SPOT images for suitable drainage network extraction. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Tidal and subtidal water volume exchange in an estuarine system     

Erick M. Swenson  Wen-Ssn Chuang 《Estuarine, Coastal and Shelf Science》1983,16(3):229-240

Estuarine water movements occur over a broad range of time scales. In this study, moored current meter data were used to investigate water volume exchange in the tidal passes of Lake Pontchartrain, Louisiana on the tidal and subtidal time scales. A calibration technique, employing cross-channel measurements of water velocity, was used to calibrate the moored current meters, thus allowing for calculation of volume flow over a 35-day period. The local diurnal tide accounted for 50% of the total volume exchange, the rest being due to subtidal events (frontal passage). This subtidal exchange occurs primarily as large-scale events characterized by volume fluxes up to six times greater than the normal tidal prism. Neglecting this subtidal component in the determination of the volume fluxes for a system such as Lake Pontchartrain, could result in substantial underestimation (by as much as 50%) of these volume and their corresponding material fluxes.  相似文献   

海水电解质pmv的补充测定及其加和性关系的验证     

季荣  陈国华  冯维  杨育红 《中国海洋大学学报(自然科学版)》1994,(2)

首次用新研制的高精密磁力浮沉子密度计测定ＮａＨＣＯ３，ＫＢｒ，ＫＮＯ３和Ｃａ（ＮＯ３）２在盐度为３０．０和３４．７温度为２９８、１０Ｋ时的偏摩尔体积（即ｐｍｖ）。重新测定了ＮａＣｌ，ＫＣｌ．Ｎａ２ＳＯ４和ＭｇＳＯ４在海水中的ｐｍｖ，并用实验精密验证了海水中主要电解质的ｐｍｖ的加和性关系。  相似文献   

Multistage melt impregnation in Tethyan oceanic mantle: Petrochemical constraints from channelized melt flow in the Naga Hills Ophiolite     

A. Verencar  A. Saha  S. Ganguly  M. Satyanarayanan  B. Doley  M. Ram Mohan 《Chemie der Erde / Geochemistry》2022,82(1):125821

Ophiolitic sequences obducted onto continental margins allow field based observations coupled with petrochemical interrogations of upper mantle lithologies thereby aiding evaluation of compositional heterogeneity of oceanic mantle, depletion-enrichment events and geodynamic conditions governing oceanic lithosphere formation. The Naga Hills Ophiolite (NHO) suite preserves a segment of the Neotethyan oceanic lithosphere encompassing a package of mantle and crustal lithologies. This paper for the first time reports the occurrence of melt flow channels traversing the mantle section near Molen of the NHO and presents a comprehensive study involving chromite-spinel chemistry, bulk rock major, trace and PGE geochemistry to understand the petrogenesis and evolution in a geodynamic transition from mid oceanic ridge (MOR) to suprasubduction zone (SSZ). The spinel chemistry of peridotitic melt channels depicts both MOR-type and SSZ signatures underlining a transitional tectonic frame. Chromite chemistry and high Al₂O₃/TiO₂ ranging from 15.98–35.70 in concurrence with low CaO/Al₂O₃ ranging from 0.03–0.53; and chondrite normalised LREE > MREE < HREE patterns confirm the influx of boninitic melts into the refractory mantle. The boninitic signature shared by melt channels and host rock invokes a geochemical and geodynamic transition from anhydrous melting of depleted mantle to hydrated fluid flux melting resulting in boninitic melts, that subsequently impregnate and refertilise the fore arc mantle wedge in a SSZ regime at the nascent stage of subduction. The high Ba/Nb, Ba/Th, and Ba/La for the studied peridotites highlight the influx of subduction derived fluids in the supra subduction mantle. Further higher Zr/Hf and Nd/Hf with respect to primitive mantle values in concurrence with lower Nb/Ta suggest progressive refertilisation due to fluid- and melt-driven metasomatism of the refractory fore arc mantle wedge. The chondrite normalised PGE patterns suggest positive Ir and Ru anomalies stipulating the source to be refractory while enriched Pt and Pd underpins the mobilisation of these elements by subduction derived fluids and melts. The elevated abundances of PPGEs than IPGEs as cited by PPGE/IPGE > 1; and Pd/Pt avg. 0.85 for melt channels and 0.84 for host peridotites indicate fluid-fluxed metasomatism of fore arc mantle wedge with a S-undersaturated trend coupled with boninitic affinity. The mineral, trace, REE and PGE chemistry collectively emphasizes that the mantle peridotites of the NHO formed in a transitional geodynamic tectonic setting caused by fore arc extension during subduction initiation followed by rejuvenation by subduction derived fluids and boninitic melts, which typically are of the SSZ tectonic regime. The harzburgitic melt channels and host rock are refractory in nature, reflecting multiple episodes of melt extraction of about 5–15% and ~10–20% respectively from a spinel peridotite mantle source. The occurrences of these melt channels indicate segregation and percolation of melt through porous and channelized network in upper mantle peridotites.  相似文献   

宁陕地震台体应变仪观测质量及映震能力分析     

张雪娟  王玥明  张国华  杨浩东  王鲲鹏 《地震地磁观测与研究》2022,43(3):74-80

选取2016—2020年宁陕地震台TJ-Ⅱ型体积式钻孔应变仪观测资料,基于观测质量和映震能力,系统分析应变仪运行状况及地震监测效能。结果表明：该台体应变观测资料质量整体较好,但数据连续率及完整率尚有待提升;体应变仪映震能力较强,可记录国内M_S≥7.0和国外M_S≥7.4地震;同震形变响应分析结果表明,同震响应最大变幅与震中距满足A = ae^{blg D}的负相关关系,与震级满足A = ae^bM的正相关关系。  相似文献   

地震地球物理观测台网地应变数据集     

吴凯  施贺青  张燕  赵莹  余晨晖 《地震地磁观测与研究》2022,43(2):214-218

作为地壳形变监测的一种手段,地应变观测可监测微尺度下的地表应变变化,其分辨率一般为10-9。目前地震地球物理观测台网在网运行的洞体应变观测台站有111个,分量钻孔应变观测站59个,钻孔体应变测站有68个,产出数据包括原始观测数据、台站预处理数据和产品数据,可为地震研究、地球动力学研究提供重要的数据支撑。  相似文献   

油源断裂油气成藏期优势通道输导能力综合评判方法及其应用     

袁红旗  魏鸣禄  于英华 《吉林大学学报(地球科学版)》2021,51(3):694-703

本文通过油气成藏期油源断裂不同部位古活动速率相对大小分布,确定其油气输导的优势通道。并基于优势输导通道的断裂古活动速率、古倾角、目的层古埋深和源岩古剩余地层压力等指标,建立了一套油源断裂在油气成藏期优势通道输导能力的综合评判方法。以渤海湾盆地冀中坳陷廊固凹陷为靶区,对大柳泉区块旧州油源断裂带在成藏期沙三中下亚段内的优势通道进行了厘定和油气输导能力综合评判。评判结果表明：旧州油源断裂6条分支断裂油气成藏期——沙二段沉积时期发育了10个优势通道,其油气输导能力以F₁和F₂分支断裂的6个优势通道输导油气能力相对较强,有利于油气运移,F₃、F₄、F₅和F₆分支断裂发育4个优势通道,其输导油气能力相对较弱,不利于油气运移。此评判结果与目前旧州断裂带附近沙三中下亚段内的油气分布现状相吻合,表明用此方法进行油源断裂成藏期优势通道的输导能力综合评判是可行性的。  相似文献   

乌鲁木齐市日最大边界层高度变化特征分析及其与空气质量的关系     

贾健  杨佩琪  蒋慧敏 《气象与环境学报》2019,(2):55-60

利用2007—2017年乌鲁木齐市L波段探空雷达和地面常规观测数据,以Holzworth干绝热曲线原理,估算该地逐日最大边界层高度,并计算对应的边界层平均风速和通风量等数据。同时,应用2015—2017年空气污染指数(AQI),探讨空气质量与大气边界层参数的关系。结果表明:乌鲁木齐市日最大边界层年均高度为1415 m,总体上呈下降趋势,平均降幅为5. 9 m·a^-1。时间序列上,日最大边界层高度分布呈明显周期性。逐月数据呈"抛物线"状,1月平均高度最低(336 m),6月平均高度最高(2400 m)。冬季边界层平均风速最小,为2. 6 m·s^-1,春季和夏季最大,均为5. 6 m·s^-1。一年中,1月平均通风量最小,为977. 0 m^2·s^-1,5月平均通风量最大,为14835. 9 m^2·s^-1,4—9月为平均通风量大值期,平均通风量为13282. 3 m^2·s^-1。大气污染物在风速弱、边界层高度低和通风量小条件下的累积,易造成中度以上污染。冬季,乌鲁木齐常处于蒙古高压后部或底部,为造成冬季污染严重的重要原因之一。  相似文献   

基于植被分布的河道糙率分区及率定方法          下载免费PDF全文

吴乔枫  蔡奕  刘曙光  蔡万贤 《水科学进展》2018,29(6):820-827

天然河流的河道综合糙率呈现出空间上的差异性和随水位（或流量）变化的动态性,但目前缺乏相关参数化方法来定量描述河道糙率的动态变化规律。尝试通过参数化方法开展受河道植被影响显著河流的糙率反演研究,用以提升模型精度。基于植被分布将河道断面划分为若干糙率不同的子区,通过率定河道断面各分区的糙率,从而反演糙率—水位曲线。在此基础上通过分析河道植被覆盖情况与河道断面特点对糙率曲线变化的影响,推求了基于分区糙率的河道断面综合糙率计算公式,从而定量描述分区糙率与综合糙率的关系。以漓江干流为例,采用该方法率定漓江干流（大溶江至阳朔段）水动力模型。结果表明:漓江干流综合糙率随水位在0.022~0.180间变化;在1.5 m的临界水深下,断面可划分为底床植被区（n=0.210）与非植被区（n=0.006）,能较好地反演糙率—水位曲线并获得理想的水位模拟效果。漓江底床植被繁茂是糙率随水位变化的根本原因,断面边滩的坡度变化是糙率与水位曲线梯度变化的主要驱动因素,两者的共同作用使得糙率随着水位呈现两段式的非线性变化。  相似文献