基于导频序列的OFDM信道估计性能分析     

陈玮玮  王天宝  王保强 《成都信息工程学院学报》2007,22(3):352-354

正交频分复用(OFDM)作为一种可以有效对抗符号间干扰(ISI)的高速传输技术,得到了广泛的应用,而信道估计技术作为其重要技术之一得到了很大的发展.信道估计分为盲信道估计、半盲信道估计和基于导频的信道估计.主要研究基于导频的最小平方(LS)信道估计和线性最小均方误差(LMMSE,Linear Minimum Mean Square Error)信道估计,在不同的信道环境和不同的循环前缀(CP)和导频子载波数下的性能比较并得出结论.  相似文献   

汶川地震断裂带科学钻探项目WFSD-3-P孔钻探施工概况   总被引：3，自引：0，他引：3       下载免费PDF全文

赵远刚  樊腊生  杨明奇 《探矿工程》2012,39(9):18-21

主要介绍了汶川地震断裂带科学钻探项目WFSD-3-P孔的地层情况、施工过程、钻井液技术、事故的处理与预防技术。在钻探施工中,采取了高密度低失水泥浆体系和反复扫孔、起钻中途回灌泥浆的措施,解决了断层泥缩径、岩层破碎、钻孔坍塌扩径的技术难题,并取得了原状性完好的岩心。  相似文献   

煤矿井筒检查孔施工工艺探讨          下载免费PDF全文

董润平  胡忠义 《探矿工程》2012,39(10):12-15

煤矿井筒检查孔不同于普通的煤田勘探孔及水文地质钻孔,它既需要全孔取心,又需要分层（段）进行抽水试验,技术要求高,施工难度大。如果工艺设计不合理,施工措施不得力,极易出现孔内事故,影响钻孔质量,加大施工成本。就煤矿井筒检查孔的钻探成孔、起下套管及抽水试验等方面总结了经验及教训,为今后类似工程施工提供借鉴。  相似文献   

Discrimination of Seafloor Sediment Properties by VWA     

Bo Lu  Ganxian Li  Shaojian Huang  Qiang Liu 《Marine Georesources & Geotechnology》2013,31(1):53-66

Analytical results of sound velocity and spectrum for seafloor sediment ore obtained by VWA (velocity-wave-amplitude) discrimination technique. Based on velocity-wave-amplitude, an understanding is gained of the physical condition and structural characteristics of seafloor sediment, which is combined with other geological information of the sedimentary layer to synthetically discriminate the properties of seafloor sediment. Experimental results show that, by using the relationship between sound velocity, wave form envelope, amplitude shape and size, and such parameters as sedimentary structure, microstructure, bedding, grain composition, mineral composition, and physical-mechanics, etc., the basic properties of the shallow surface seafloor sediment in the experimental sea area can be discriminated and the burial depth of traces of ancient marine transgression and regression events in the borehole cores of seafloor sediment can be divided, thus making an attempt of and contribution to the practice of acoustically remote-sensing and telemetering seafloor sediment.  相似文献   

A study of stability of the seafloor foundation on a gently sloping continental shelf     

Liang Yuanbo  Lu Bo  Huang Shaojian  Li Tinghuan  Yang Weiguang  Wen Yaolin 《Marine Georesources & Geotechnology》2013,31(3-4):189-201

Abstract

The possibility of seafloor failure under external loadings on a gently sloping continental shelf is controlled, to a large extent, by the geotechnical characters of subbottom sediments (e.g., shear strength, compressibility, and liquefaction potential) and structural factors (e.g., sedimentary stratification). By means of undis‐turbing coring, in‐situ acoustic measurement, and subbottom profiling, the authors conducted an investigation into the seafloor instabilities and possibilities of sediment slope failure within the continental shelf off the Pearl River mouth, which is one of the most important areas for offshore development in the northern South China Sea. Based on in‐situ and laboratory measurements and tests for sediment physical properties, static and dynamic behavior, and acoustic characteristics, the analyses indicate: (1) subbottom sediments that originated from terrigenous clay during the Pleistocene are compact and overconsolidated, and the mean sound velocity in such sediments is relatively high; (2) the maximum vertical bearing capacity of subbottom sediments is efficiently conservative on the safe side for dead loads of light structures, and the trench walls are stable enough while trenching to a depth of about 2 m below the seafloor under still water; and (3) it is quite improbable that the subbottom sediments liquefy under earthquake (M ≤ 6) or storm wave loading.  相似文献   

The autumn occurrence and spatial distribution of cetaceans in the waters of Mauritania during a geophysical survey in 2012     

《African Journal of Marine Science》2013,35(4):371-381

This study aimed to identify the occurrence and spatial distribution of cetaceans in Mauritanian waters (eastern Atlantic). A geophysical survey was conducted over 92 days between September and December 2012. Over 967 km was surveyed, with 1 017 h of observer effort recorded. Visual watches for marine mammals resulted in 228 cetacean sightings of 16 different species, including 12 odontocetes and 4 mysticetes. The short-finned pilot whale Globicephala macrorhynchus was the most frequently encountered odontocete, followed by the Atlantic spotted dolphin Stenella frontalis. Of the mysticetes, the sei whale Balaenoptera borealis and blue whale B. musculus were encountered most frequently. We used generalised additive models and generalised linear models to examine the relationships between environmental factors and cetacean distribution. The results showed depth had a significant influence on presence of the short-finned pilot whale, which preferred waters deeper than 1 800 m. The model for mysticetes identified bathymetry as a significant environmental predictor, whereas slope of the ocean floor had a positive effect but was not significant. This study contributes to our understanding of cetaceans in Mauritanian waters, using data from a platform of opportunity.  相似文献   

Relationship between Formation of Zhongyebei Basin and Spreading of Southwest Subbasin, South China Sea     

Gao Hongfang  Zhou Di  Qiu Yan 《中国地质大学学报(英文版)》2009,20(1)

The Zhongyebei (中业北) basin (ZYBB) is an NE-striking,narrow and small sedimentary basin superimposing the southern 1/2 segment of the proposed spreading axes of the SW subbasin of the South China Sea (SCS).More than 4 500 m strata were identified in the Zhongyebei basin,including the Paleogene lower structure layer and the Neogene upper structure layer.The SW subbasin of the South China Sea has been regarded as an oceanic basin opened by seafloor spreading,as evidenced by the fiat and deep (＞ 4 000 m mostly) seafloor with linear magnetic anomalies,and by the shallow Moho depth of ＜ 12 km as estimated from gravity modeling.The classic model of seafloor spreading predicts that sediments on the oceanic crust are younger and thinner towards the spreading axes.But in the southwestern segment of the SW subbasin,contradictions appear.Firstly,the thick sedimentation in the ZYBB is along the proposed spreading axes.Secondly,the sediments are thinner (500-1 500 m) and younger away from the proposed spreading axes.Thirdly,geological elements of the two sides of spreading axes develop asymmetrically in the southwestern SW subbasin.Two models,the early opening model and the limited modeling model,are suggested for resolving this paradox.The former suggests that the opening of the SW subbasin was in Late Eocene and earlier than the oldest sediment in the ZYBB.The latter proposes that the opening of the SW subbasin was limited to its northeastern portion,and did not extend to the southwest portion.The ZYBB is a rift basin survived from the spreading but subjected to severe syn-spreading magmatic disturbance.The SW subbasin and the ZYBB of the SCS provide a unique opportunity for studying the structural evolution and dynamic mechanism at the tip of a propagating seafloor spreading.Both models have unresolved questions,and further studies are needed.  相似文献   

He, Ne and Ar isotope compositions of fluid inclusions in hydrothermal sulfides from the TAG hydrothermal field Mid-Atlantic Ridge   总被引：7，自引：2，他引：7  

ZENG ZHIGANG  QIN Yunshan  ZHAI Shikui 《中国科学D辑(英文版)》2001,44(3):221-228

Helium, neon and argon isotope compositions of fluid inclusions have been measured in hydrothermal sulfide samples from the TAG hydrothermal field at the Mid-Atlantic Ridge. Fluid-inclusion³He/⁴He ratios are 2.2—13.3 times the air value (Ra), and with a mean of 7.2 Ra. Comparison with the local vent fluids (³He/⁴He=7.5—8.2 Ra) and mid-ocean ridge basalt values (³He/⁴He=6—11 Ra) shows that the variation range of³He/⁴He ratios from sulfide-hosted fluid inclusions is significantly large. Values for²⁰Ne/²²Ne are from 10.2 to 11.4, which are significantly higher than the atmospheric ratio (9.8). And fluid-inclusion⁴⁰Ar/³⁶Ar ratios range from 287 to 359, which are close to the atmospheric values (295.5). These results indicate that the noble gases of fluid inclusions in hydrothermal sulfides are a mixture of mantle- and seawater-derived noble gases; the partial mantle-derived components of trapped hydrothermal fluids may be from the lower mantle; the helium of fluid inclusions is mainly from upper mantle; and the Ne and Ar components are mainly from seawater.  相似文献   

ZDY4000LS型煤矿用履带式全液压坑道钻机的研制          下载免费PDF全文

胡海峰  魏斌斌  陆惠明 《探矿工程》2017,44(6):28-32

一般传统钻机主要由主机、操作台、泵站三大件组成,质量大,搬运不方便。ZDY4000LS型煤矿用履带式全液压坑道钻机是一种新型的钻机,结构布置合理,辅助功能齐全,它能有效地改善中小煤矿钻孔施工效率,提高钻掘产量,降低工人劳动强度。主要介绍了ZDY4000LS型煤矿用履带式全液压坑道钻机的主要技术参数、结构布局特点、液压系统及生产试验情况。试验应用表明,对于巷道较小或者有运输皮带限制的煤矿巷道,该钻机具有推广价值。  相似文献   

一种分层海底反向散射模型   总被引：1，自引：1，他引：0  

于盛齐  刘保华  于凯本  杨志国  阚光明 《海洋学报(英文版)》2017,36(7):56-65

In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency(0.1–10 kHz) is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency(below 1.0 kHz). While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency(10–100 kHz) bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.  相似文献