脉冲激光引信烟雾后向散射特性研究

激光引信的探测性能容易受到烟雾的干扰,引起虚警和漏警。为研究脉冲激光引信在烟雾环境中的传输特性,基于Mie散射理论和Monte Carlo方法,建立脉冲激光引信烟雾后向散射模型,仿真905 nm脉冲激光在不同烟雾环境下的回波特性,进行相关试验,对比仿真归一化峰值强度与实测峰值电压,进行相关性分析,验证模型的准确性。分析不同烟雾质量浓度、烟筒长度与距离下脉冲激光引信在烟雾环境中的后向散射特性,得到不同条件对回波的影响规律,研究结果可为脉冲激光引信抗烟雾干扰提供支撑。     

Hybridization of Bimetallic Molybdenum‐Tungsten Carbide with Nitrogen‐Doped Carbon: A Rational Design of Super Active Porous Composite Nanowires with Tailored Electronic Structure for Boosting Hydrogen Evolution Catalysis

An ecofriendly and robust strategy is developed to construct a self‐supported monolithic electrode composed of N‐doped carbon hybridized with bimetallic molybdenum‐tungsten carbide (Mo_xW_2?xC) to form composite nanowires for hydrogen evolution reaction (HER). The hybridization of Mo_xW_2?xC with N‐doped carbon enables effective regulation of the electrocatalytic performance of the composite nanowires, endowing abundant accessible active sites derived from N‐doping and Mo_xW_2?xC incorporation, outstanding conductivity resulting from the N‐doped carbon matrix, and appropriate positioning of the d‐band center with a thermodynamically favorable hydrogen adsorption free energy (ΔG_H*) for efficient hydrogen evolution catalysis, which forms a binder‐free 3D self‐supported monolithic electrode with accessible nanopores, desirable chemical compositions and stable composite structure. By modulating the Mo/W ratio, the optimal Mo_1.33W_0.67C @ NC nanowires on carbon cloth achieve a low overpotential (at a geometric current density of 10 mA cm^?2) of 115 and 108 mV and a small Tafel slope of 58.5 and 55.4 mV dec^?1 in acidic and alkaline environments, respectively, which can maintain 40 h of stable performance, outperforming most of the reported metal‐carbide‐based HER electrocatalysts.     

Spherical Gaussian-based Lightcuts for Glossy Interreflections

It is still challenging to render directional but non-specular reflections in complex scenes. The SG-based (Spherical Gaussian) many-light framework provides a scalable solution but still requires a large number of glossy virtual lights to avoid spikes as well as reduce clamping errors. Directly gathering contributions from these glossy virtual lights to each pixel in a pairwise way is very inefficient. In this paper, we propose an adaptive algorithm with tighter error bounds to efficiently compute glossy interreflections from glossy virtual lights. This approach is an extension of the Lightcuts that builds hierarchies on both lights and pixels with new error bounds and new GPU-based traversal methods between light and pixel hierarchies. Results demonstrate that our method is able to faithfully and efficiently compute glossy interreflections in scenes with highly glossy and spatial varying reflectance. Compared with the conventional Lightcuts method, our approach generates lightcuts with only one-fourth to one-fifth light nodes therefore exhibits better scalability. Additionally, after being implemented on GPU, our algorithms achieve a magnitude of faster performance than the previous method.     

An improved kernel correlation filter for complex scenes target tracking

Multimedia Tools and Applications - Video tracking technology employed to achieve efficient and accurate tracking of targets in complex scenes has often been one of the challenges to be tackled....     

泄洪雾化对天气环境影响的松弛同化方法研究

为实现在综合考虑地形和环境背景场条件下,模拟泄洪期间局地区域天气环境的变化情况,以数值天气预报系统为基础,建立了泄洪雾化对天气环境影响的松弛同化方法。结合大岗山水电站一次降雨过程和实际观测资料,拟定了泄洪雾化同化数据分类设置的参考值范围。运用泄洪雾化对天气环境影响的松弛同化方法,对大岗山水电站泄洪期间的天气环境变量进行了同化计算。由于大岗山水电站仅有2015年9月14日15∶30—16∶40泄洪数据,选取2015年9月14日16∶00时刻模拟数据分析得到,在考虑风向变化的条件下,风速变化值为8.76 m/s,纵向影响范围约2.1 km;温度降低了3.32℃,纵向影响范围约2 km;相对湿度升高了8.71%,纵向影响范围约2.8 km。模拟结果表明,风速受水舌风影响风向改变、风速升高,温度受泄洪雾化降雨影响降低,相对湿度受雨雾蒸发影响升高。同化模拟的结果均向观测数据趋近,模拟结果符合实际的观测情况。     

The Contributions of Climate Changes and Human Activities to Long-Term Variations in Lake Sediments Based on Results from Generalized Additive Models

Water Resources Management - Climate changes and human activities can influence lake sediments, which may lead to disruptions in aquatic environments. A better understanding of these effects is...     

电动帆改进推力模型及深空探测性能分析

电动太阳风帆(简称电动帆)是一种利用太阳风动能冲力飞行的新兴无质损飞行器.针对电动帆传统推力模型中忽略了姿态对推力幅值影响的问题,本文推导得出了一种解析形式的改进推力模型,并与最新的多项式拟合改进推力模型进行了对比.对比结果显示两种改进推力模型数值结果很接近,但本文的解析改进推力模型形式更简单.为了重新评估电动帆在深空探测中的性能,以地球至火星的飞行任务为算例,分别采用传统推力模型和解析改进推力模型进行了电动帆轨迹优化仿真.仿真结果显示,在相同特征加速度情况下,采用改进解析推力模型完成任务所需时间,大于采用传统推力模型所用时间.上述现象的原因在于传统推力模型中忽略了姿态改变对推力加速度大小的影响,并高估了电动帆所能产生的最大推进角.     

多样化实时刚体破碎模拟

目的 现有刚体破碎仿真模拟中,基于物理受力分析的方法往往难以应用在对实时性要求较高的场景中;而基于非物理方法的破碎模拟,破碎效果大多缺乏多样性。为了使得破碎模拟同时满足实时性和破碎效果多样化,提出了一种多样化实时刚体破碎模拟方法。方法 进行破碎模拟时首先由选定的种子点生成类型得到种子点集,采用Sweep Plane算法生成Voronoi图后基于Voronoi图信息对模型进行空间剖分;然后选择破碎时行为模拟方式,对物体破碎时所受外力进行模拟;最后对破碎时碰撞检测及碰撞后碎片的运动过程进行模拟并渲染显示。结果 通过组合不同的种子点生成类型和破碎时行为模拟方式,得到了多样化的刚体破碎效果。对单个刚体进行破碎模拟时,碎片数目不超过200个时帧率可以达到75帧/s,满足实时性的需求;对多个可破碎目标同时存在的复杂场景,破碎仿真模拟的平均帧率可以达到50帧/s,同样满足实时性要求;与现有方法对比的结果也验证了本文方法在计算效率和破碎效果多样性两方面达到了较好的平衡。结论 本文方法在满足实时性要求的同时,丰富了刚体破碎的效果,不同种子点生成类型和破碎时行为模拟方式的组合可以实现破碎效果多样性。     

A decomposition technique of generalized degrees of freedom for mixedmode crack problems

The numerical manifold method (NMM) builds up a unified framework that is used to describe continuous and discontinuous problems; it is an attractive method for simulating a cracking phenomenon. Taking into account the differences between the generalized degrees of freedom of the physical patch and nodal displacement of the element in the NMM, a decomposition technique of generalized degrees of freedom is deduced for mixed mode crack problems. An analytic expression of the energy release rate, which is caused by a virtual crack extension technique, is proposed. The necessity of using a symmetric mesh is demonstrated in detail by analysing an additional error that had previously been overlooked. Because of this necessity, the local mathematical cover refinement is further applied. Finally, four comparison tests are given to illustrate the validity and practicality of the proposed method. The aforementioned aspects are all implemented in the high‐order NMM, so this study can be regarded as the development of the virtual crack extension technique and can also be seen as a prelude to an h‐version high‐order NMM. Copyright © 2017 John Wiley & Sons, Ltd.