非线性偏振旋转光纤激光器的原理与关键技术

非线性偏振旋转(NPR)锁模光纤激光器以其结构简单紧凑而备受关注,是光通信系统、光传感和光探测等的理想光源。介绍了非线性偏振旋转锁模激光器的研究进展,分析了其工作原理、锁模方法及关键技术,并按其腔内净色散的不同进行分类,分析其各自特点以及通过色散管理获得高能量超短脉冲的方法。     

基才滑模PI控制交流变频钻机旋转系统

钻井过程中钻头粘滑振动会导致钻头失速,钻杆组合故障,增加钻井成本。为此,提出了滑模PI控制策略用于电动钻机交流变频旋转系统。在建立钻机旋转系统模型基础上,将滑模控制与PI控制相结合,用于提高系统的鲁棒性．抑制钻头的粘滑振动。仿真结果表明：基于滑模PI控制的钻机交流变频旋转系统,可有效地控制钻头失速,减少钻柱疲劳损坏．改善旋转系统的动态和静态响应特性。     

Improving Nonlocal Means Method via a No-reference Image Content Metric for MRI Denoising

The patch matching of the traditional Nonlocal means （NLM） filter mainly depends on structure similarity and cannot adapt to the patch rotation or mirroring transformation. Therefore, designing a measure with rorationally invariant similarity is of significant importance for improving the effectiveness of patch comparison of NLM. This paper proposes to apply a no-reference image content metric with the rotation-invariance to NLM for denoising Magnetic resonance （MR） images. The metric measures quantitatively the content of a patch in an image, including sharpness, contrast, and geometric features such as textures and edges. The metric values for every patch are computed and added into the Gaussian matching kernel of NLM so as to effectively perform patch matching. The main advantage of the proposed method is that it does not need to rotate patches in different orientations during patch matching. Experimental results show that the proposed method is superior to the traditional NLM, the state-of-the-art method Block-matching and 3- D （BM3D） filtering and the Unbiased NLM （UNLM） for MRI denoislng.     

模式识别和电视跟踪在前庭功能检查中的应用

应用模式识别和电视跟踪原理测量眼球在视靶信号刺激下的运动,为分析飞行员、车辆驾驶员的前庭功能提供一种先进的检查方法.采用均衡化、形态滤波和形心计算等方法实现了瞳孔区域的自动定位和实时跟踪;通过Harris角点检测和Lucas-Kanade光流跟踪实时测量出虹膜的旋转角度,为前庭功能分析奠定了良好的基础.通过实验验证,所介绍的眼球跟踪算法已达到了预期的效果,并已成功应用在前庭功能检查分析系统中.     

一种基于改进RANSAC的红外图像拼接方法

在一般的红外图像拼接过程中,采用传统随机抽样一致(RANSAC)方法,耗时往往会稍长。为了缩短图像拼接所耗费的时间,提出了基于尺度不变特征转换(SIFT)和改进RANSAC的图像拼接方法。先通过SIFT得到特征点和特征描述,然后用改进的RANSAC对不匹配的特征点进行剔除,通过得到的变换矩阵完成图像的融合。在改进RANSAC中,设置0.95和0.85两个阈值,少量迭代后,选择跳出循环、重新选择或者计算出新的迭代次数,新的迭代次数必定比传统迭代次数小,因而达到减少时间的效果。红外图像拼接后,把实验结果与采用传统RANSAC算法的结果进行多方位比较,可以发现本文方法能够达到减少时间的目的。     

基于小波函数湛江市气象干旱周期分析

选取广东省湛江市作为研究区域,基于区内19个雨量站1966—2015年逐月降雨序列数据,采用6个月时间尺度的标准化降水指数,结合旋转经验正交分解法对区域气象干旱分布进行空间模态分解,利用小波分析对不同空间模态对应的区域进行干旱周期求解。结果表明:湛江市干旱空间分布可分解成6个空间模态,不同模态对应不同区域,区域内干旱周期主要信号最强为9.3 a、最弱为2.1 a,6个模态普遍存在2～6 a震荡周期,与实际干旱发生的周期基本一致。湛江地区干旱呈现周期性变化的原因与厄尔尼诺事件有关,春季降雨和厄尔尼诺的关系更密切,厄尔尼诺对春旱的影响更为持续和显著。     

水利部“948”计划项目——《旋转冲击式多功能钻机》通过验收

2011年3月1日,水利部948项目管理办公室在北京主持召开了由中国水利水电科学研究院承担的《旋转冲击式多功能钻机》验收会。验收专家组由来自水利部、中国地质科学院、中国建筑科学研究院、中国灌排发展中心等单位的专家组成。会议由水利部科技推广中心缪荪处长主持,专家察看了引进的钻机,听取了项目承担单位的成果汇报,审阅了验     

EXPERIMENTS OF SEA ICE SIMULATION

As a substitute for the original displaced pole grids, a simple rotated spherical coordinate system was intro duced into the Community Sea Ice Model version 4（CSIM4）, which is a component of the Community Climate System Model（CCSM） of the American National Center of Atmospheric Researeh（NCAR）, to deal with the ＂pole problems＂. In the new coordinates, both the geographical North Pole and South Pole lie in the model equator and grid sizes near the polar region are more uniform. With reanalysis dataset of American National Centers for Environment Prediction （NCEP） and Levitus dataset without considering sub-mixed layer heat flux, the model was integrated for 100 years with thermodynamics proce.ss involved only in the former 49 years and both dynamic and thermodynamic processes involved in the left time. Inner consistency of model results was checked with no contradiction found. The results of last 10 years＇ model output were analyzed and it is shown that the simulated sea ice seasonal variation is rational whereas sea ice extent in the Barcnts Sea in winter is larger than that of observation, Numerical experiment on influence of sub-mixed layer heat flux was also carried out and it is shown that the sub-mixed layer heat flux can modulate seasonal variation of sea ice greatly. As a model component, the sea ice model with rotated spherical coordinates was coupled with other models （the oceanic general cir culation model is the LASG/IAP Climate System Ocean Model （LICOM） with reduced grid, other models are components of NCAR CCSM2） forming a climate system model and its preliminary results were also given briefly.     

水平旋转内消能泄水道的流态序列、分区特性及临界条件

本文给出竖井进流水平旋转内消能泄水道的基本流态序列、过渡特性及临界水力条件。这种泄水道的流态可根据空腔环流内的气体压强、空腔直径和通气孔的通气量的变化规律分为淹没流流态、吸允流流态和自由流流态；空腔环流形成的水力条件为(H-h)／h大于2．5或Fr大于0．46；各流态转变过程中有明显的过渡段性质；在不同的流态分区内物理量的变化规律是不同的。     

考虑逆压梯度和旋转影响时离心叶轮湍流边界层计算及应用

本文通过计算分析了旋转湍流边界层。提出了一种考虑逆压梯度和旋转影响的双方程湍流模式。通过数值试验,找出了Rocr与Re的关系,并由此建立了逆转捩准则。