日本沼虾受精卵核行为的初步研究

研究了日本沼虾受精卵的核行为。结果表明 :日本沼虾在 2 1℃水箱中培养时 ,雌虾交配产卵后 0 .5 h,受精卵内仅出现 1个雌原核 ,未见雄原核 ;产卵后 1 .5 h,卵内同时出现雌原核和雄原核 ;产卵后 3 .5 h,雌原核和雄原核接近 ;产卵后 4h,雌原核和雄原核联合 ,形成合子核 ;产卵后 4.5 h,开始第一次有丝分裂 ;产卵后 7h,形成 2个核 ;产卵后 8h,形成 4个核     

变差函数及其在多波段机载成像光谱仪数据处理中的应用

遥感的空间信息反映一定范围内象元在空间上的关系，对成像光谱仪遥感数据而言，空间结构变代表一个局部区域中各象元之间光谱辐射能量的关联状态，在图像上反映为灰度变化，利用空间信息来开拓图像分析技术可获得遥感目标很高的正确识别率，变差函数是联系遥感目标和图像中空间变化特征的有用工具，实验变差函数的计算结果表明遥感目标种类与变差图之间的定量化空间关系，可以在成像光谱图像处理中发挥作用。     

基于旋翼无人机雷达的船只目标成像与类型识别研究进展综述

载有成像雷达的旋翼无人机具有成本低廉、对起降条件要求低、飞行姿态灵活多样等优点，可以在热点区域进行普查、详查或长时间悬停凝视等多模式成像监测，现已成为海上船只目标监测识别的重要手段。本文分别从旋翼无人机雷达硬件系统、无人机载雷达动目标成像、船只目标类型识别和目标三维结构特征提取等四方面开展国内外研究进展综述。总结分析发现当前利用旋翼无人机雷达进行船只目标成像和类型识别，尚存在运动船只成像散焦、三维结构重建难度大、类型识别精度低等问题，迫切需要推动相关技术的发展。     

Imaging spectroscopy as a tool to study sediment characteristics on a tidal sandbank in the Westerschelde

This paper focuses on the use of imaging spectroscopy for the mapping of sediment characteristics on a tidal sandbank in the Westerschelde, called the Molenplaat. On June 8, 2004, during low tide, a HyMap™ scanner recorded the Molenplaat at 4 m pixel resolution. The hyperspectral data were radiometrically calibrated, geometrically corrected, and atmospherically corrected to give apparent surface reflectance data. On the calibrated and corrected dataset a supervised binary classification was performed, based on linear discriminant analysis. Simultaneous to the flight, 25 sediment samples were collected in the field and analysed in the lab to define the median grain size, the water content, the total organic matter content and the chlorophyll-a concentration. These four parameters play a crucial role in sediment stability and macrofaunal habitat definition. Prior to the classification, a feature selection, based on sequential floating forward search (SFFS), was performed. For each of the four parameters two to three bands were retained for the classification. These bands were most frequently selected in the visible and near infrared parts of the spectrum, except for the organic matter content where also SWIR bands were used. The overall classification accuracy was highest for the water content (88%), the median grain size (88%) and the chlorophyll-a concentration (84%). The organic matter content, for which three instead of two classes were distinguished, scored somewhat lower but still reached 80%. The classifications were limited to a small number of classes in order to obtain reliable statistics with a small number of training samples. The spatial patterns in the classified images indicated that the four parameters under study are highly correlated. In most cases coarse sediment coincided with dry conditions, low organic matter and low concentrations of chlorophyll-a. The wet and muddy parts of the Molenplaat were in general characterised by a notably higher amount of organic matter and chlorophyll-a. The individual classification results for the median grain size, the water content and the chlorophyll-a concentration were combined to generate a sediment ecotope map. The presented study illustrates how airborne hyperspectral data can be used to achieve accurate classified maps of intertidal sediment ecotope types, applying feature selection and a binary classification approach.     

A new mask-antimask coded-aperture telescope for hard X-ray astronomy

A new imaging balloon-borne telescope for hard X-rays in the energy range from 30 to 100 keV is described. The imaging capability is provided by the use of an extended URA-based coded-mask. With only one motor and suitable stop pins, we can rotate a carbon-fiber wheel with most of the mask elements attached to it by 180°, and a bar, which is also part of the mask pattern and is allowed to rotate freely over the wheel, by 90°; this combined rotation creates an antimask of the original mask, except for the central element. This is a novel and elegant manner of providing an antimask without additional weight and complex mechanical manipulations. We show that the use of antimasks is a very effective method of eliminating systematic variations in the background map over the position-sensitive detector area. The expected sensitivity of the instrument for the 30–100 keV range is of the order of 7 × 10^-5 photons cm^-2 s^-1 keV^-1, for an integration time of 10⁴ seconds at a residual atmosphere of 3.5 g cm^-2. This telescope will provide imaging observations of bright galactic hard X-ray sources with an angular resolution of 2° in a 10° by 10° FOV, which is defined by a collimator placed in front of the detector system. We are particularly interested in the galactic center region, where recent imaging results in X-rays have shown the presence of an interesting source field. Results of computer simulations of the imaging system are reported.     

Advances in interpretation of subsurface processes with time‐lapse electrical imaging

Electrical geophysical methods, including electrical resistivity, time‐domain induced polarization, and complex resistivity, have become commonly used to image the near subsurface. Here, we outline their utility for time‐lapse imaging of hydrological, geochemical, and biogeochemical processes, focusing on new instrumentation, processing, and analysis techniques specific to monitoring. We review data collection procedures, parameters measured, and petrophysical relationships and then outline the state of the science with respect to inversion methodologies, including coupled inversion. We conclude by highlighting recent research focused on innovative applications of time‐lapse imaging in hydrology, biology, ecology, and geochemistry, among other areas of interest. Copyright © 2014 John Wiley & Sons, Ltd.     

The shape, topography, and geology of Tempel 1 from Deep Impact observations

Deep Impact images of the nucleus of Comet Tempel 1 reveal pervasive layering, possible impact craters, flows with smooth upper surfaces, and erosional stripping of material. There are at least 3 layers 50-200 m thick that appear to extend deep into the nucleus, and several layers 1-20 m thick that parallel the surface and are being eroded laterally. Circular depressions show geographical variation in their forms and suggest differences in erosion rates or style over scales >1 km. The stratigraphic arrangement of these features suggests that the comet experienced substantial periods of little erosion. Smooth surfaces trending downslope suggest some form of eruption of materials from this highly porous object. The Deep Impact images show that the nucleus of Tempel 1 cannot be modeled simply as either an onion-layer or rubble pile structure.     

Digital spatial cracking behaviors of fine-grained sandstone with precracks under uniaxial compression

X-ray computed tomography (CT) imaging and digital image correlation techniques are applied to study spatial cracking behaviors of sandstone under uniaxial compression, in which the angle between precracks is 45°, 90°, and 135° and the crack depth is 7.5 mm and 10 mm, respectively. Layered anisotropy damages and spatial cracking evolution are quantitatively analyzed by the defined digital layered anisotropy index and digital damage ratio, respectively. Three cases with different array of precracks evidence the depth effects of precracks on spatial crack propagation. Results show that the failure process of samples is first controlled by the coalescence of surface cracks in 2D space and then the samples are failed by the propagation of coalesced cracks (shear cracks with different shapes). The crack types for samples with precrack depth of 7.5 mm are all shear cracks for Cases 1‑3. Nevertheless, the crack types for samples with precrack depth of 10 mm are, respectively, the half X-shape crack for Case 1, X-shape crack for Case 2, and double shell crack for Case 3. The precrack has a significant promotion effect on the failure process when the angle between the two precracks is β = 90°, and the precrack has little to no effect on the failure process when the angle between the two precracks is β = 135°. As the depth of precrack increases to 10 mm, the crack types are changed in this study. The peak strength of sample subjected to uniaxial compression decreases with increasing depth of precracks, implying the decrease of the rock strength by the discontinuity.