加强区域数字地震台网建设推进数字地震学的应用研究

简要回顾了数字地震学诞生以来所取得的科学成果。结合我国地震观测系统大规模数字化改造的实践,着重阐述了区域数字化地震台网的观测优势,以及在台网建设目标、观测资料的充分利用和高素质人才培养方面存在的劣势和不足。还提出了对关于区域数字地震台网建设和发展过程中的指导思想、“软件”和“硬件”的关系、基础和应用研究与地震预报的关系、数字地震学的发展与高素质人才培养的关系等等问题的思考和建议。     

竖向质量分布对框架结构动力特性影响的研究

在框架结构动力分析中,往往是把填充墙质量集中在楼层处进行求解.文中考虑填充墙实际分布对结构自振特性的影响,通过传递矩阵法求解结构自振频率和振型,并进一步分析了高阶频率的分布规律.结果表明,与采用集中质量模型的振型叠加法相比,填充墙的竖向质量分布会对框架结构高阶频率产生很大影响;框架结构的高阶模态具有局部性和密集分组的特...     

Demeter观测的电离层非震变化特征研究

利用法国电磁卫星Demeter装载的ICE(电场探针)及IAP(等离子体分析仪)探测数据,分析研究2006年不同季节、不同地方时顶部电离层电场及各等离子参量的全球空间分布特征,结果发现,电场x分量及H+离子浓度、O+离子浓度、He+离子浓度、等离子体温度具有显著的季节变化和地方时变化,而电场y分量及z分量全球分布的季节...     

几种降低锥束CT辐射剂量的方法

千伏级锥束CT在放射治疗、外科手术、口腔疾病诊断等领域都有广泛的应用。然而,频繁地使用千伏级锥束CT,也会给患者甚至医生带来额外的射线辐射损伤。相关统计结果表明,X射线辐射能够诱发癌症,特别是儿童和女性对射线辐射异常敏感。因此,合理使用锥束CT,同时降低锥束CT辐射剂量,对于降低射线辐射并发症风险显得非常重要。本文总结了降低锥束CT辐射剂量的常用措施,包括降低管电流、局部扫描、脉冲扫描、短扫描以及少投影扫描。辐射剂量的降低有可能会在重建图像中引入噪声、伪影。针对特定的问题,本文也提出了对应的补偿方法。     

陇中黄土高原夏季陆面辐射和热量特征研究

利用兰州大学半干旱气候与环境观测站(SACOL)的观测资料,分析了陇中黄土高原夏季陆面辐射和热量收支的特征.通过研究不同典型天气条件对陆面过程微气象特征的影响,发现地表反射率在晴天会出现早晨偏大的不对称结构;晴天与多云天气相比不平衡量较大,而阴天时的阵性降水会使局地能量收支出现不平衡.利用最小二乘法(OLS)线性回归得到的夏季平均不闭合度是19.6%.在半干旱区云和降水对辐射和能量收支的影响不容忽视,达到约25%的削弱程度,比极端干旱的敦煌荒漠区要大,又进一步证明了半干旱区夏季的平均气候特征与云量较多的多云天气(5≤Mean total cloud amount<8)接近.另外,7月日平均波恩比最大是4.1,平均是1.95,比极端干旱区的敦煌波恩比小1个数量级,说明榆中所处的黄土高原半干旱区比敦煌所处的极端干旱区在气候上要湿润很多.     

椭圆度-凹坑双缺陷海底管道局部屈曲特性研究

海底管道在制造、埋设以及使用过程中极易产生椭圆度-凹坑双缺陷,双缺陷影响管道局部屈曲,对含椭圆度-凹坑双缺陷海底管道的局部屈曲特性研究十分必要。现行规范中采用等效椭圆度对含椭圆度-凹坑海底管道进行评估,该方法无法准确评估不同缺陷形式的屈曲特性。采用形状系数对含椭圆度-凹坑双缺陷的海底管道进行评估,运用有限元软件ABAQUS进行数值模拟,并进行试验验证。在此基础上对含有不同凹坑深度、不同椭圆度的海底管道进行局部屈曲的数值模拟,计算不同形状椭圆度、含有不同凹坑深度海底管道的形状系数,对其进行敏感性分析。计算结果表明:形状系数对海底管道椭圆度、凹坑深度、径厚比敏感性较强;对凹坑宽度敏感性较弱。     

Structure of radio sources at wavelengths 10.5 and 12.0 cm from observations of the Solar eclipse on March 29, 2006

The eclipse observations were performed at the Laboratory of Radio Astronomy of the CrAO in Katsiveli with stationary instrumentation of the Solar Patrol at wavelengths of 10.5 and 12.0 cm. The data obtained were used to determine the brightness temperature of the undisturbed Sun at solar activity minimum between 11-year cycles 23 and 24: T _d10.5 = (43.7 ± 0.5) × 10³ K at 10.5 cm and T _d12.0 = (51.8 ± 0.5) × 10³ K at 12.0 cm. The radio brightness distribution above the limb group of sunspots NOAA 0866 was calculated. It shows that at both wavelengths the source consisted of a compact bright nucleus about 50 × 10³ km in size with temperatures T _b10.5 = 0.94 × 10⁶ K and T _b12.0 = 2.15 × 10⁶ K located, respectively, at heights h _10.5 = 33.5 × 10³ km and h _12.0 = 43.3 × 10³ km above the sunspot and an extended halo with a temperature T _b = (230–300) × 10³ K stretching to a height of 157 × 10³ km above the photosphere. The revealed spatial structure of the local source is consistent with the universally accepted assumption that the radiation from the bright part of the source is generated by electrons in the sunspot magnetic fields at the second-third cyclotron frequency harmonics and that the halo is the bremsstrahlung of thermal electrons in the coronal condensation forming an active region. According to the eclipse results, the electron density near the upper boundary of the condensation was N _e ≈ 2.3 × 10⁸ cm^?3, while the optical depth was τ ≈ 0.1 at an electron temperature T _e ≈ 10⁶ K. Thus, the observations of the March 29, 2006 eclipse have allowed the height of the coronal condensation at solar activity minimum to be experimentally determined and the physical parameters of the plasma near its upper boundary to be estimated.     

Spatial Variation of Sea Level Trend Along the Bangladesh Coast

The Bangladesh coast is threatened by rising sea level due to various factors. The results based on the analysis of past 22 years of tidal data of the Bangladesh coast reveal that the annual mean tidal level in the eastern Bangladesh coast is rising at an alarmingly high rate of 7.8 mm/year, which is almost twice the observed rate in the western region. This type of sea level trend seems to be the result of changing local conditions like increased precipitation and land subsidence during the recent decades. It seems that the higher rate of land subsidence in the eastern Bangladesh coast is the main causative factor for the steeper sea level trends there. The differential sea level trends show that the subsidence component in the sea level rise may be as high as 4 mm/year in the eastern Bangladesh coast. However, this needs to be verified with actual geological observations.     

Retracking of Jason-1 Data

We present the results of retracking 18 cycles (15 from the Jason-TOPEX collinear period) of Jason-1 data. We used the retracking method of Rodriguez which simultaneously solves for all relevant waveform parameters using a 26 Gaussian model of the altimeter point target response. We find significant differences from the Jason-1 Project retracking in the key parameters of range and significant wave height (SWH) in the second version of the Project SGDRs. The differences from the Jason-1 data have a strong dependence on off-nadir angle and some dependence on SWH. The dependence of range on SWH is what is called sea state bias. The retracking technique also estimates surface skewness. For Jason-1 with its very clean waveforms we make the first direct estimates of the skewness effect on altimeter data. We believe that the differences found here and thus in overall sea surface height are the result of the standard project processing using a single Gaussian approximation to the Point Target Response (PTR) and not solving simultaneously for off nadir angle. We believe that the relatively large sea state bias errors estimated empirically for Jason-1 during the cal/val phase result from sensitivity of quantities, particularly SWH, in project GDRs to off nadir angle. The TOPEX-Jason-1 bias can be determined only when a full retracking of Jason-1 is done for the collinear period.