A numerical study of sea level and current responses to Hurricane Frederic using a coastal ocean model for the Gulf of Mexico

A three-dimensional, nonlinear, primitive equation ocean general circulation model is used to study the response of the Gulf of Mexico to Hurricane Frederic. The model has free surface dynamics and a second order turbulence closure scheme for the mixed layer. Realistic coastlines, bottom topography and open boundary conditions are used in the study. The model has a vertical sigma coordinate with 18 levels, and a horizontal resolution of 0.2°×0.2° for the entire Gulf. The study focuses on hurricane generated sea level, current, and coastally trapped wave (CTW) responses of the Gulf. Time series of sea levels from U.S. coastal tide gauge stations and the numerical model simulation of sea levels and currents on the shelf are used to study sea level, current and CTW responses. Both model sea levels and observations from tide gauge stations show a westward progression of the surge as a CTW response. The results of the study of sea levels and currents indicate that CTW propagate to the west with phase speeds of 7–10 m s^–1. There is also a strong nonlinear interaction between the Loop Current and hurricane induced currents. The surface current attains a maximum of 200 cm s^–1 in the eastern Gulf. The model surface elevation at several locations is compared with tide gauge data. The current meter data at three moorings are also compared with the model currents. The model simulations show good agreement with observed data for the hurricane induced coastally trapped wave, storm surge, and current distribution in the Gulf.     

Kinetic investigation of the OH + CH3Br reaction between 248 and 390 K

The rate parameters for the reaction of the OH radical with CH₃Br have been measured using the discharge flow-electron paramagnetic resonance method. The result isk ₁=(1.86±0.48)×10^–12 exp[–(1230±150)/T] cm³ molecule^–1 s^–1. This value is compared to earlier data and is found to be in excellent agreement with the most recent results, which greatly increases the accuracy of the ozone depletion potential of CH₃Br which can be derived from these kinetic data.     

山西河南间第三纪末及第四纪地层研究

从汾河谷中观察与从潼关以下黄河谷中所见者相符即此二谷中第四纪地层显然分为二段在下者为三门系其时代为上新统之上部或更新统即洪积统之下部在上者为主要黄土(以後续成者不计)其时代属更新统之中部或上部在汾河谷之中心山门系砂砾较多每呈洪水冲积之状但在岸旁斜坡则成黄土例如插图3A 所示者其黄土之下部似实与三门系相当盖此带红色之黄土中曾得含有?齿类骨之结核此物昔曾见于甘肃陕西黄土之底部而呈曾经搬移之状可见含此之层当在真正黄土之前动物骨中又有一种与泥河湾所见同凡此皆证明其非真正黄士也因此可知三门系同一时代能呈不同之状态在三门者为河成在泥河湾者为湖成而在汾河谷中则又见其有洪水冲积及黄土状之二态为三门系之下为蓬蒂层)Pontien)亦能呈诸状态成土状时则为含三趾马之红土成洪水冲积老汾河峡谷及河南新安陕西榆林曾见之潼关含Melania 之层为其湖成态茲将蓬蒂期三门期及黄土期三期之各种变态列表如下蓬蒂期之蜗牛往往较大壳呈被溶状中有方解石结晶壳色深褐若黄土中之蜗牛则常极洁白热河以北达贲诺尔在三趾马红土以上复有白色土层亦含三趾马此系局部特别现象蓬蒂三门黄土三期为同一地质现象之错见或复见即北方各大流域之?成及充积是也三期间之分隔则似前二期间视後二期间为较显     

New challenges for adaptive optics: extremely large telescopes

The performance of an adaptive optics (AO) system on a 100-m diameter ground-based telescope working in the visible range of the spectrum is computed using an analytical approach. The target Strehl ratio of 60 per cent is achieved at 0.5 μm with a limiting magnitude of the AO guide source near R   magnitude~10, at the cost of an extremely low sky coverage. To alleviate this problem, the concept of tomographic wavefront sensing in a wider field of view using either natural guide stars (NGS) or laser guide stars (LGS) is investigated. These methods use three or four reference sources and up to three deformable mirrors, which increase up to 8-fold the corrected field size (up to 60 arcsec at 0.5 μm). Operation with multiple NGS is limited to the infrared (in the J band this approach yields a sky coverage of 50 per cent with a Strehl ratio of 0.2). The option of open-loop wavefront correction in the visible using several bright NGS is discussed. The LGS approach involves the use of a faint ( R ~22) NGS for low-order correction, which results in a sky coverage of 40 per cent at the Galactic poles in the visible.     

遥感数据的高斯金字塔尺度上推方法研究

尺度转换是遥感信息科学领域的研究热点,其传统研究方法大多局限于统计模型,对数据的空间结构信息考虑较少,很难满足遥感数据的多尺度表达要求。基于此,针对遥感数据的尺度不一致问题,本文提出了一种利用高斯金字塔的图像模糊特性进行遥感数据尺度上推的方法,在对金字塔每一层的数据高斯模糊的基础上,通过多次连续的降采样,得到一系列不同尺度的数据,从而满足实际应用的空间分辨率要求。为了验证本文所提方法的有效性,本文选择Landsat7 ETM影像和ASTER GDEM为研究数据进行尺度上推,并与传统的最邻近、双线性以及立方卷积等方法进行了实验对比,采用均值、方差、均方根误差、平均绝对误差等评价指标,以及相同分辨率的ASTER GDEM和SRTM DEM的等高线套合结果来衡量高斯金字塔方法的性能。实验结果表明,本文使用的高斯金字塔尺度上推方法能够有效地实现连续遥感数据的尺度转换,在保持遥感数据局部细节特征的基础上,较好地保持了原始遥感数据的信息量以及空间结构特征。     

Side-scan sonar image matching

This paper presents a method for the matching of underwater images acquired with acoustic sensors. As a final objective, the system aims at matching data from two-dimensional scenes. The proposed approach carries out a hypothetical reasoning based on objects, represented by shadows and echoes in the sonar images, and their available features. The problem of determining measures which are invariant to changes in sonar settings and noise characteristics is addressed by mapping robust features for sonar images to a qualitative representation. To cope with the viewpoint charging appearance, the method is based on the conservation of objects' relative position from one image to another. We attempt to match geometrical structures formed by the association of three objects. The hypothetical reasoning is conducted in a decision tree framework. A tree node is generated by two objects' association, each one belonging to a respective image. Hypotheses propagation consists of creating new nodes from neighboring associations. The matching solution is determined by the selection of the decision tree's longest branch. Thus, the association mechanism is a depth-first procedure. The proposed method has been applied to real high-resolution side-scan sonar images. The matching process has shown successful and promising results which have been further improved. In particular, the parceled shadows (during the segmentation procedure) problem has been tackled     

潮汕海岸带河-海交互区沉积环境及小型底栖动物群落结构研究

河口三角洲是人类活动最为剧烈的区域, 陆海作用复杂, 生态环境脆弱。2021年6月以潮汕韩江三角洲河口群为研究区, 开展了河-海交互区沉积环境和小型底栖动物群落综合研究。结果表明, 研究区沉积物以黏土质粉砂为主, 中值粒径为6.66~1 301.34 μm; 盐度为15.91~35.11, 具有典型的河-海交互区特征; 有机碳(TOC)、叶绿素a (chl a)、脱镁叶绿酸含量(Phaeo)均呈现由陆向海减少趋势。重金属Cu和Zn、Phaeo、透明度和砂含量是造成沉积环境差异的主要因素。共鉴定出13个小型底栖动物主要类群, 其中自由生活海洋线虫在丰度和生物量上均为最优势类群(90%和38%), 桡足类和多毛类居次。小型底栖动物的平均丰度和生物量(干重)分别为(295±195) inds./10 cm²和(277.8±202.8) μg/10 cm²,整体上从陆向海呈增加趋势, 在不同河口断面间差异显著。盐度和河口也是控制小型底栖动物群落空间分布的主要因素, 真盐区(盐度>30)的群落相似性较高。小型底栖动物丰度、生物量和物种数与Phaeo和重金属(Cu、Zn、Pb、Cd)呈负相关关系; 解释小型底栖动物群落结构差异的最佳环境组合是盐度和重金属Cd含量。基于重金属、有机污染指数及海洋线虫与桡足类比值三种环境评价方法, 其结果均显示污染较严重的区域位于河口入海口门处。研究结果可为海岸带资源保护、生态监测以及基于生态系统实施综合管理提供基础数据支撑。     

Wavelet Analysis of Several Important Periodic Properties in the Relative Sunspot Numbers

We investigate the wavelet transform of yearly mean relative sunspot number series from 1700 to 2002. The curve of the global wavelet power spectrum peaks at 11-yr, 53-yr and 101-yr periods. The evolution of the amplitudes of the three periods is studied. The results show that around 1750 and 1800, the amplitude of the 53-yr period was much higher than that of the the 11-yr period, that the ca. 53-yr period was apparent only for the interval from 1725 to 1850, and was very low after 1850, that around 1750, 1800 and 1900, the amplitude of the 101-yr period was higher than that of the 11-yr period and that, from 1940 to 2000, the 11-yr period greatly dominates over the other two periods.     

Preliminary results on VLT K-band imaging observations of GRB host galaxies

We have obtainedK-band imaging observations of Gamma-Ray Burst (GRB) host galaxies with the near-infrared spectro-imager ISAAC installed on the Very Large Telescope at Paranal (Chile). The derivedK magnitudes, combined with other photometric data taken from the literature, are used to investigate theR-K colors of GRB hosts. We do not find any extremely reddened starbursts in our sample, despite the capability of GRBs to trace star formation even in dusty regions. The observedR-K colors are on the contrary typical of irregular and spiral blue galaxies at high redshift.