岩溶水流系统识别方法及其在引调水工程隧洞选线中的应用

某国家重大引调水工程引水隧洞将穿越聚龙山向斜可溶岩地层,可能面临严重岩溶涌突水问题.为了查明隧洞突涌水条件,选择岩溶水害风险较低的引水方案,综合采用岩溶水文地质调查、水化学与同位素分析等方法对聚龙山向斜岩溶水流系统特征进行了识别.结果 表明:聚龙山向斜含水系统具有"两含夹一隔"的多层结构,下部二叠系主要为埋藏型岩溶弱发...     

基于沉积物与文献记录的茈碧湖水文波动与近现代生态环境变化

云南高山湖泊对区域气候变化和流域人类活动十分敏感,部分水体同时面临着污染物增加、生物群落快速演替、生态系统功能降低等问题。位于滇西北高山地区的茈碧湖历史资料表明,该湖近现代以来经历了明显的水文波动与人类活动影响。本研究通过对茈碧湖沉积物进行年代序列测定、元素和粒度等多指标分析,重建了近300年来（对应于钻孔顶部18 cm深度样品）茈碧湖环境变化历史,并结合对硅藻的分析,识别了气候变化和人类活动对生物群落变化的驱动影响。结果表明,沉积物粒度记录了茈碧湖水文变化的长期波动,水库修建与水文调控的增强使得湖泊水位波动明显,与文献记录的水文事件基本一致。硅藻群落结构以浮游种为主,1860年前硅藻组合以对水体扰动力有较强耐受性的Cyclostephanos dubius为主要优势种;1860年以来小型硅藻Cyclotella ocellata占据主要优势,同时Cyclotella comta成为次优势种;1990年开始,底栖硅藻Fragilaria spp.属相对丰度增加并出现明显波动,喜营养盐的Fragilaria crotonensis出现。多变量数理分析显示,气候变暖以及湖泊营养水平变化的共同作用是驱动茈碧湖硅藻组合长期演替的重要因素,分别独立解释了群落变化的27.5%和21.3%;其中湖库改造工程导致的外源物质输入增多,使得营养水平总体上升,是导致20世纪90年代以来硅藻组合出现明显变化的诱因。因此,在气候变暖的背景下,对云南高山湖泊的保护需要进行流域开发和水文调控的综合评价。

     

龙门山冲断隆升及其走向差异的裂变径迹证据

大量的低温年代学研究用来讨论龙门山晚新生代的隆升,但很少涉及其走向差异和中生代隆升。本文分别沿龙门山北、中、南段3条剖面进行了锆石和磷灰石裂变径迹测试,结合已有的热年代学数据,以期揭示整个中 新生代期间龙门山隆升历史及其时空变化。中生代以来,龙门山主要有印支期（约200 Ma）、早白垩世末（约100 Ma）、早新生代（65～30 Ma）以及晚中新世（15～9 Ma）等或快或慢的冷却事件,总体上经历了中生代至早新生代的缓慢冷却和晚新生代快速冷却2个阶段,快速剥露开始于15～9 Ma,剥蚀速率由早期的<0.1mm/a增加到0.15～0.3mm/a左右,局部可达0.9mm/a左右。走向上,龙门山北段相对偏小的锆石裂变径迹年龄和相对偏大的磷灰石裂变径迹年龄反映其在中生代较中、南段隆升更快,而裂变径迹年龄总体上从北段向中、南段减小,表明中、南段在新生代发生了更快的隆升。倾向上,多种热年代学数据显示新生代期间在北川断裂和彭灌断裂两侧存在明显的差异剥露,这种差异在中、南段表现比北段更为突出。龙门山晚新生代快速隆升和剥露是青藏高原区域隆升背景上叠加的冲断活动所致,而非下地壳流动驱动。     

珠江三角洲霾天气的近地层输送条件研究

近年来, 珠江三角洲地区气溶胶污染日趋严重, 霾天气造成能见度恶化和空气质量下降。近地层输送条件即地面流场与大气污染物稀释扩散密切相关。利用2004—2005年广东省466个地面自动气象站资料、广州观象台常规气象资料、珠江三角洲大气成分站网器测能见度资料、珠江三角洲城市环境监测站网的PM10浓度资料等, 使用矢量和分析方法, 分析珠江三角洲近地层风及其对严重霾天气过程和清洁对照过程的影响。结果表明: 2004年霾天气高发季节, 东亚纬向环流比2005年同期显著, 纬向环流不显著的年份, 气流南北交换显著, 冷空气跨越南岭、到达珠江三角洲的机会比较大, 伴随冷空气的大风等天气有利于污染物扩散; 纬向环流显著的年份, 冷空气跨越南岭、到达珠江三角洲的机会比较小, 污染物易于堆积。珠江三角洲霾天气具有区域性特征, 旱季出现最多, 雨季出现最少。严重霾天气过程出现在每年12月至次年4月, 清洁对照过程出现在台风直接影响或冷空气活动频繁的季节。与2004年相比, 2005年的静风频率较低, 且旱季风速较大, 不利于霾天气的形成。矢量和分析表明:区域霾天气过程与区域内静小风过程, 即出现气流停滞区有密切联系, 清洁对照过程与强平流输送有关。     

基于Python的SKA-RASCIL中的天线增益校准实现

天线增益校准是射电天文观测数据处理过程中的一个关键步骤.分析了经典的天线增益校准算法Antsol的基本原理,并基于Python对Antsol算法进行了高性能实现,所完成的程序代码已经集成到平方公里阵列(Square Kilometre Array,SKA)的射电天文模拟校准成像软件(Radio Astronomy Si...     

火灾烟颗粒分形模型和球形模型光散射的比较研究

对烟颗粒的光散射进行模拟计算是研究火灾烟颗粒光散射特性的重要手段,目前对于火灾烟颗粒光散射的数值计算多采用球形或椭球模型.实际上,火灾烟颗粒的形貌与球形和椭球均存在着显著差异.扫描电子显微镜图像表明,烟颗粒具有近似分形的结构.本文利用离散偶极近似方法计算了随机取向的火灾烟颗粒分形凝团以及同体积的球形颗粒的光散射Muller矩阵,并对两者的归一化Muller矩阵元素随散射角的分布进行了比较.研究表明:火灾烟颗粒分形模型和球形模型的归一化矩阵元素F₁₁(θ)/F_{11相似文献}   

双层钙钛矿La1.8 Ca1.2 Mn2 O7 磁性相关I-V非线性与电输运性质

采用传统固相反应法制备了双层钙钛矿结构锰氧化物La_1.8Ca_1.2Mn₂O₇陶瓷,并用X射线粉末衍射法,扫描电镜,HL5500PC Hall效应分析仪和综合物性测量系统(PPMS)对其磁、电性质进行了表征.结果表明:经过两次高温烧结可合成具有双层Sr₃Ti₂O₇型四方结构的La_1.8Ca_1.2Mn_2<     

Time-domain analysis of second-harmonic generation of primary Lamb wave propagation in an elastic plate

Within the second-order perturbation approximation, this paper investigates the physical process of generation of the time-domain second harmonic by a primary Lamb wave waveform in an elastic plate. The present work is performed based on the preconditions that the phase velocity matching is satisfied and that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero. It investigates the influences of the difference between the group velocities of the primary Lamb wave and the double frequency Lamb wave, the propagation distance and the duration of the primary Lamb wave waveform on the envelope shape of the time-domain second harmonic. It finds that the maximum magnitude of the envelope of the second-harmonic waveform can grow within some propagation distance even if the condition of group velocity matching is not satisfied. Our analyses also indicate that the maximum magnitude of the envelope of the second-harmonic waveform is kept constant beyond a specific propagation distance. Furthermore, it concludes that the integration amplitude of the time-domain second-harmonic waveform always grows with propagation distance within the second-order perturbation. The present research yields new physical insight not previously available into the effect of generation of the time-domain second harmonic by propagation of a primary Lamb wave waveform.     

Seismic imaging of gas hydrates in the northernmost South China sea

Horizon velocity analysis and pre-stack depth migration of seismic profiles collected by R/V Maurice Ewing in 1995 across the accretionary prism off SW Taiwan and along the continental slope of the northernmost South China Sea were implemented for identifying gas hydrates. Similarly, a survey of 32 ocean-bottom seismometers (OBS), with a spacing of about 500 m, was conducted for exploring gas hydrates on the accretionary prism off SW Taiwan in April 2006. Travel times of head wave, refraction, reflection and converted shear wave identified from the hydrophone, vertical and horizontal components of these OBS data were applied for imaging P-wave velocity and Poisson’s ratio of hydrate-bearing sediments. In the accretionary prism off SW Taiwan, we found hydrate-bearing sediment, with a thickness of about 100–200 m, a relatively high P-wave velocity of 1.87–2.04 km/s and a relatively low Poisson’s ratio of 0.445–0.455, below anticlinal ridges near imbricate emergent thrusts in the drainage system of the Penghu and Kaoping Canyons. Free-gas layer, with a thickness of about 30–120 m, a relatively low P-wave velocity of 1.4–1.8 km/s and a relatively high Poisson’s ratio (0.47–0.48), was also observed below most of the bottom-simulating reflectors (BSR). Subsequently, based on rock physics of the three-phase effective medium, we evaluated the hydrate saturation of about 12–30% and the free-gas saturation of about 1–4%. The highest saturation (30% and 4%) of gas hydrates is found below anticlines due to N–S trending thrust-bounded folds and NE-SW thrusting and strike-slip ramps in the lower slope of the accretionary prism. We suggest that fluid may have migrated through the relay-fault array due to decollement folding and gas hydrates have been trapped in anticlines formed by the basement rises along the thrust faults. In contrast, in the rifted continental margin of the northernmost South China Sea, P-wave velocities of 1.9–2.2 km/s and 1.3–1.6 km/s, and thicknesses of about 50–200 m and 100–200 m, respectively, for a hydrate layer and a free-gas layer were imaged below the remnant and erosional ridges in the upper continental slope. High P-wave velocity of hydrate-bearing sediment below erosional ridges may also indicate high saturation of hydrates there. Normal faults due to rifting in the South China continental crust may have provided conduits for gas migration below the erosional ridges where P-wave velocity of hydrate-bearing sediment in the passive continental margin of the northernmost South China Sea is greater than that in the active accretionary prism off SW Taiwan.