Secondary Cones of the Shatsky Rise and Implications for Late-Stage Volcanism Atop Oceanic Plateaus

Oceanic plateaus are large igneous provinces in the oceans, created by massive underwater eruptions, but their late-stage volcanism is poorly understood. With the addition of recent high-quality bathymetric data to existing data, 286 secondary cones were discovered over Shatsky Rise oceanic plateau. These cones with steeper flank slopes(mean 6.1? ? 4.4?) and smaller sizes(102–1923 m in height) are morphologically distinct from the plateau, and they are thought to have formed after the main volcanic episodes. Cone height and characteristic height(420 m) are close to seamounts in the Pacific Ocean, whereas greater than those in the Atlantic Ocean. Mean flatness of Shatsky Rise's cones(0.25 ? 0.20) are similar to that of seamounts in both Pacific and Atlantic Oceans, but notably density in cone distribution(0.56 km-3) and their mean slope are significantly lower than those of seamounts in the two oceans. Lower slopes of secondary cones within Shatsky Rise may be explained by higher effusion rates of remaining magma. Although cone formation was expected to have a link to rifting by seafloor spreading, weak relationship between cone orientation and magnetic anomaly pattern implies that the expectation is negative. Moreover, weak correlation between the cone height and depth indicates it is not true that volcanic cones grow taller when they occur closer to the massif summits with thicker oceanic crust, which was suggested as the increase in hydraulic pressure. Cone height and flatness are also not strongly related, implying that remaining magma supply was too limited to foster the cones to critical height.     

Response of circular tunnel with imperfect interface bonding in layered ground subjected to obliquely incident plane P or SV wave

A semianalytical procedure is proposed for evaluating the internal forces of circular tunnel with imperfect interface bonding in layered ground subjected to an obliquely incident plane P or SV wave. In this study, the hoop bending moment and hoop axial force are related to the free‐field responses of the ground. A one‐dimensional numerical approach is firstly presented to obtain the free‐field responses of a layered half‐space with an obliquely incident plane P or SV wave propagation. Then, the free‐field stress state is transformed and decomposed in the polar coordinate system. The internal forces of tunnel caused by the isotropic stress state and the pure shear state are calculated and then summed up to obtain the overall analytical solutions. Finally, the validity of the proposed semianalytical procedure is demonstrated by numerical examples.     

卷积神经网络在卫星遥感海冰图像分类中的应用探究

本文以TensorFlow为框架搭建卷积神经网络，基于迁移学习的思想，以经典的手写数字识别作为引入，对不同代价函数和激活函数组合对卷积神经网络模型分类结果影响进行了评价分析。以HJ-1A/B渤海海冰图像为实验数据源，分析了不同函数组合对遥感海冰图像分类的影响，优选出交叉熵代价函数与ReLU激活函数为最佳的组合，证明了卷积神经网络在遥感海冰分类中的应用可行性。对渤海海冰图像分类结果进行验证，其中带标签样本验证精度为98.4%。使用该模型对无标签的测试样本进行识别，讨论了样本的窗口尺寸对海冰分类结果的影响，发现在400×400小范围分类实验中最佳窗口尺寸为2×2；最后对整个渤海海域进行识别验证，效果较好。     

Revisiting gamma-ray burst afterglows with time-dependent parameters

The relativistic external shock model of gamma-ray burst(GRB) afterglows has been established with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ε_e and for the magnetic field ε_B, the number density of the environment n and the index of the powerlaw distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as: the wind medium environment by letting n change with radius,the energy injection model by letting kinetic energy change with time and so on. In this paper, by assuming all four parameters(except p) change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.     

大地电磁资料偏移成像

在研究Zhdanov的二维电磁场偏移成像的基础上, 针对它在某些方面的不足, 研究并提出了改进算法. 首先, 用一维反演结果确定初始背景电阻率, 然后在延拓计算过程中, 利用迭代算法进行逐层修正、 延拓计算, 从而获得较准确的电阻率; 第二, 研究了有限差分方程的改进算法, 根据大地电磁场变化的特点, 设计了纵向以等比级数变网格的迭代算法. 通过以上两方面技术的改进, 经理论模型和实际资料试算验证, 取得了较好的结果.      

湘西北2008年初持续冰雪灾害及对椪柑影响分析

2008年初湘西北出现了自1956年有气象记录以来低温持续时间最长、冰冻范围最大、强度最强的一次低温雨雪冰冻天气过程,罕见的特大冰冻灾害给当地支柱产业之一的椪柑生产带来严重影响.本文从天气学和农业气象学角度出发,对低温雨雪造成的椪柑冻害及椪柑成果的贮藏、销售影响进行了详细评估,旨在为湘西北椪柑生产恢复与制定防灾减灾措施提出科学依据.     

控制中国汽车交通燃油消耗和温室气体排放的技术选择与政策体系

 中国的汽车交通面临着燃油短缺和温室气体排放上升的双重压力,本文从中国经济发展的背景和中国汽车平均燃油消耗量的国际差距入手,通过分析汽车行业的技术选择,建立了汽车交通的燃油消耗和温室气体排放的分析框架。分析后认为,要控制中国汽车交通的燃油消耗和温室气体排放,就要运用一系列技术手段和政策手段控制汽车保有量、降低汽车平均行驶里程、提高单车的燃油经济性水平和降低汽车排放水平。最后,对所提出的政策体系进行了分析和评价。     

近56年我国暖冬气候事件变化

对冬季平均气温序列采用三分位方法确定单站暖冬阈值, 并将单站暖冬分为弱和强两个等级。以此为基础, 确定区域暖冬和全国暖冬的界定方法和等级划分标准。区域暖冬采用站点相对比例确定, 全国暖冬采用暖冬面积相对比例界定。对我国1952— 2007年的暖冬事件变化特征的分析结果表明:南方暖冬频率高于北方, 强暖冬多发区出现在我国中西部地区; 北方单站暖冬指数上升幅度大于南方, 表明北方暖冬事件上升趋势更加明显; 以1986年为界, 前期 (1952— 1985年) 南、北方各区域均很少出现暖冬, 南方各区暖冬频率略高于北方各区, 后期 (1986—2007年) 各区暖冬年大为增加, 北方各区增加最明显且超过了南方; 56年中, 全国性暖冬共发生15次 (年), 其中强暖冬共有5次 (年); 全国暖冬指数呈显著上升趋势, 在有效面积不变的情况下, 暖冬面积每10年增加10%。     

沙瓦特指数的一种迭代算法

为了提高沙瓦特指数的计算精度, 在沙瓦特指数计算方案中引入二分法:先用于计算抬升凝结高度上的要素, 进而计算假相当位温, 再依据假相当位温守恒性质用于计算500 hPa气块温度。与其他方案对比表明, 该迭代算法计算的沙瓦特指数精度较高; 与查表法所得的气块温度对比表明, 该迭代算法得到的气块温度的最大绝对误差为1.36 ℃, 平均误差 (-0.68 ℃) 与平均绝对误差 (0.69 ℃) 数值接近; 迭代算法与查表法之间以系统性偏差为主; 此外, 该迭代算法计算量小, 收敛速度快, 具有推广应用价值。     

区域性极端低温事件的识别及其变化特征

区域性极端低温事件的客观识别方法主要包括4个部分:极端低温阈值的确定、极端低温事件空间区域的识别、空间区域的连续性过程提取和指标体系,结合个例分析验证了该方法在实际低温事件检测中的有效性。从空间分布和时间变化趋势等角度分析了近50年区域性极端低温事件的变化特征:区域性极端低温事件的发生频次较高的纬度带主要位于32°N和42°N附近,区域性极端低温事件的发生频次、强度和最大覆盖面积等存在总体减弱的趋势,在20世纪80年代后期存在显著的转折,90年代后期以来变化逐渐趋于平缓。此外,对各种单一指标与我国冷冻害造成的经济损失和受灾人口之间的相关分析,构建了体现区域性极端低温事件多方面影响的综合指标。