A moderate-resolution Nasmyth-focus spectrograph of the 6-m BTA telescope

We report on the development of a fast crossed-dispersion spectrograph (CRAB) mounted at the Nasmyth focus of the 6-m telescope. The spectrograph is designed for visible and near-infrared (3800–10 500 Å) CCD observations with the spectral resolution R=4000. We give the basic parameters of the optical scheme and the parameters of the echelle frame. We determined the gain involved in putting the spectrograph into observational practice and discuss the possible range of spectroscopic problems for which the instrument is optimal.     

Biofouling confounds the uptake of trace organic contaminants by semi-permeable membrane devices (SPMDs)

The outer layers of layflat, low density polyethylene plastic tubing (the principal component of semi-permeable membrane devices, SPMDs) were biofouled at a clean site in Hong Kong coastal waters for periods of 1–4 weeks. Following pre-fouling, triolein was added to the SPMDs and, along with control (unfouled) devices, they were exposed to a range of organochlorine pesticides (-HCH, aldrin, p,p^′-DDT) and PAHs (anthracene, fluoranthene and benzo(a)pyrene) under laboratory conditions. Results showed that the uptake of contaminants by SPMDs was severely reduced by as much as 50% under fouling conditions in comparison to unfouled controls. The ultimate utility of SPMDs as passive monitors is thus reduced, although alternative measures, such as the use of permeability reference compounds may compensate, and allow for realistic evaluations of dissolved environmental concentrations in aquatic environments. However, due to the complexities involved in such procedures––especially as they need to be conducted on a case-by-case basis––the utility of SPMDs appears to be limited for estimates of bioavailability unless necessary calibrations are undertaken within each environment that the sampler is used.     

Influence of wave groups on SSC patterns over vortex ripples

Estimates of spatial and temporal variations in suspended sand concentrations (SSC) made with a multi-transducer Acoustic Backscatter Sensor (ABS) under a repeated wave group over a mobile rippled bed in the wave research flume at the National Hydraulics Laboratory in Ottawa, Canada, reveal an number of complex and intriguing patterns. Ensemble averages of 8 nearly identical wave groups provided much more robust estimates of SSC and allowed a detailed examination of the wave group effects. The largest SSC near the bed (< 0.10 m) occurs in phase with the largest waves in the group. Above approximately 0.10 m elevation, SSC lags behind the near bed SSC by as much as 2–3 waves; introducing significant curvature (on a semi-log plot) to the SSC profile. The log linear segments of the SSC profile grow and decay systematically on the scale of the wave group. The range in lengths of log-linear profile segments ( 0.03–0.355 m) suggest that the boundary layer thickness also fluctuates throughout the passage of the wave group. Furthermore, there are significant variations in the patterns of SSC, which occur under the largest and smallest waves in the group. Under the largest waves vertical bands of alternating high and low SSC produce an intra-wave modulation in the upper water column ( 0.075–0.30 m). The equivalent horizontal excursion of these bands scales to the ripple length. Under the smaller waves the intra-wave modulation of the SSC disappears and is replaced by temporally homogenous suspension that expands vertically through several individual wave cycles. The former pattern of homogenous suspension appears to be associated with growth of a boundary layer due to the persistent uni-directional horizontal flow during this part of the group together with the persistence of antecedent bed generated turbulence and vorticity which maintains the suspension. The latter pattern of bands of high and low SSC indicates a strong temporal and spatial constraint on the SSC (phase coupling) induced by the presence of the bedforms which may be enhanced by strong reversals in both flow and vorticity under the large waves in the group.     

高密度空间采样地震数据特点分析

中国陆相沉积盆地的地质结构复杂,储层岩性的多变,需要有高精度的勘探方法。高密度空间采样是提高地震勘探精度的一项新技术。本文简要说明了点激发和点接收技术,分析高密度空间采样的野外工作方法,介绍了Gijs j．o．Vermeer提出的对称采样原理,从波场连续性的角度探讨了高密度空间采样技术。重点分析高密度空间采样数据的特点, 即:高密集的初至波有利于近地表结构的调查,可提高静校正的精度;小偏移距、小点距接收增加了浅层的有效覆盖次数,提高浅层反射的成像精度; 对规则噪声可实现无假频采样,室内的噪声分析和噪声压制的精度随着提高;高密度采集使波场连续性增强,使得各种数学变换的精度提高,有利于不同波场的分离。最后指出高密度空间采样地震勘探技术的难点在于室内数据处理,针对海量数据的分析和处理方法还需要进行深入细致的研究工作。     

涡旋诱发磁重联模型的解析研究

在磁流体中涡旋诱发重联的线性过程的解析研究过程中,主要运用了渐近匹配展开方法．结果表明,如果流体粘性远大于磁粘性,流场马赫数Ma～1,重联的线性增长率正比于Vv为无量纲化流体粘性,这与数值模拟结果一致．此结论表明,流体粘性能够促进磁场重联,在理论上支持涡旋诱发重联模式．本文还研究了周期分布多电流片系统中涡旋诱发重联的线性增长率;随电流片之间距离的减小,反对称和对称情形的增长率分别增大和减小．     

基于Gmsh的起伏地形下井—地直流电法正演模拟

采用Gmsh软件对起伏地形下的异常体模型进行建模和不规则网格剖分,将剖分网格数据应用到2.5D有限元正演程序中,并使用井—地联合观测方法对正演计算结果进行分析.分析结果表明:采用不规则网格剖分拟合起伏地形和使用井—地联合观测方法来进行起伏地形下的地质情况勘探能得到较好的结果,同时还研究了使用不同观测装置时山谷地形对下方...     

连续小波变换识别位场场源法的噪声影响分析与尺度因子的选择

为提高连续小波变换识别位场场源准确度,研究噪声对场源识别结果的影响和尺度因子优选方法问题。根据连续小波变换识别位场场源的基本原理,用该方法对不同噪声水平的合成数据进行场源识别,分析噪声对于场源识别结果的影响,研究小波变换的尺度因子对噪声压制的效果,讨论连续小波变换进行场源识别时尺度因子的选取方法。理论模型和实测资料场源识别结果表明,噪声会降低连续小波变换场源识别结果的准确度,笔者提出的尺度因子优选方法能有效压制噪声干扰,提高场源识别结果的准确度。     

新型旋转减冲装置对桩基局部冲刷防护试验研究

为减轻海上风电单桩基础周围局部冲刷对其结构安全的影响,提出了一种新型旋转减冲装置。在波流水槽中开展物理模型试验,改变波流条件、装置安装高度、安装距离,记录桩周冲刷发展历时,运用激光地形仪扫描冲刷坑形态,分析各工况下冲刷坑形态差异,验证装置不同安装距离、安装高度下的冲刷防护效果,提出了不同安装位置下的防护效率公式。结果表明：新型旋转减冲装置具有较好的冲刷防护效果,本试验工况下,桩周最大冲刷深度可减小44%左右。装置安装距离对冲刷防护效果影响较小,波流作用下的冲刷防护效果受装置安装高度影响显著,冲刷防护效果随装置安装高度的增加而减弱。     

基于A- CGAN的深反射地震数据随机噪声压制方法研究

基于深度学习的地震数据噪声压制方法是当前地震数据去噪处理的重要方向。深度学习方法突破了传统滤波处理的局限,在对常规地震数据的噪声压制中表现出效率高、信噪分离效果好的特点。但针对深部弱有效反射数据,当前的深度学习方法特征提取能力有限,难以取得较好的去噪效果。笔者等结合深反射地震数据特点,针对当前深度学习噪声压制方法在特征提取及对数据集依赖上的局限,提出了基于注意力循环生成对抗网络(Attention Cycle- Consistent Generative Adversarial Networks,A- CGAN)的深反射地震数据随机噪声压制方法。借助循环一致生成对抗网络(Cycle- Consistent Generative Adversarial Networks,Cycle- GAN)的域映射思想,降低对数据集的要求。为了构建适用于深反射地震数据的去噪网络,从3个方面对Cycle- GAN进行改进：在Cycle- GAN的生成器（去噪器）中加入残差结构和注意力机制,用于加深网络深度和提高其特征提取能力;在Cycle- GAN的鉴别器中使用块判决,提高鉴别精度和准确度;在损失函数部分加入感知一致性损失函数,提升网络模型恢复纹理细节信息的能力。通过合成地震数据和实际深反射地震数据测试,验证了优化算法的有效性,体现了良好的应用价值。     

噪声抑制的多极化SAR海冰图像分割

合成孔径雷达(SAR)海冰图像分割对全球气候研究和保证船舶航行安全具有重要意义。现有的基于区域的马尔可夫随机场(MRF)多极化SAR分割方法,由于受相干斑噪声影响,其区域划分不尽合理,不能有效完成分割。因此,提出一种噪声抑制的多极化SAR海冰图像分割算法,首先在极化总功率图上引入降低噪声的滤波算法,合理划分初始区域,其次考虑区域之间的差异度,从而实现多极化SAR海冰图像的准确分割。以RADARSAT-2和SIR-C获得的全极化海冰图像为实验数据进行验证,结果表明:和其他较先进算法相比,本文算法优势明显,既能高效保持图像连通性,又能增强图像的细节信息,具有更高的分割精度。