Imaging and structural feature decomposition of a complex target using multi-aspect polarimetric scattering

Based on the Huynen parametric decomposition of target scattering matrix, the polarimetric ellipse parameters are transformed and applied to decomposition of scattering mechanisms of a complex target in VHR POL-SAR images (very high resolution, polarimetric synthetic aperture radar). Making use of multi-aspect (or circle-aspect) and wideband VHR POL-SAR images, scattering mechanisms of a volumetric target and its structural components are recognized over image pixels. Utilizing the layover features, the target height profile is also estimated from two-dimensional image. As example, polarimetric scattering data of some vehicles on ground, including multi-aspect simulated data and experimental measurements, are applied to validations of scattering mechanism decompositions and target structural feature recognition.     

分形下的河道演变初探——以尼洋河为例

以尼洋河为例运用分形算法探讨了河道演变的机理,初步认为:在河道演变分类的基础上,河道演变是河道外部条件和河道内部条件不断协调的结果,即演变主要依靠水力和携砂两个关键因素。具体到尼洋河来说是渐进式演变与急剧式演变相结合的河道演变,其渐进式演变主要由于携砂带来河势演变,其急剧式演变主要是由于水位落差或流量增大引起的纵向和横向演变。     

Nano functional neural interfaces

Engineered functional neural interfaces (fNIs) serve as essential abiotic–biotic transducers between an engineered system and the nervous system. They convert external physical stimuli to cellular signals in stimulation mode or read out biological processes in recording mode. Information can be exchanged using electricity, light, magnetic fields, mechanical forces, heat, or chemical signals. fNIs have found applications for studying processes in neural circuits from cell cultures to organs to whole organisms. fNI-facilitated signal transduction schemes, coupled with easily manipulable and observable external physical signals, have attracted considerable attention in recent years. This enticing field is rapidly evolving toward miniaturization and biomimicry to achieve long-term interface stability with great signal transduction efficiency. Not only has a new generation of neuroelectrodes been invented, but the use of advanced fNIs that explore other physical modalities of neuromodulation and recording has begun to increase. This review covers these exciting developments and applications of fNIs that rely on nanoelectrodes, nanotransducers, or bionanotransducers to establish an interface with the nervous system. These nano fNIs are promising in offering a high spatial resolution, high target specificity, and high communication bandwidth by allowing for a high density and count of signal channels with minimum material volume and area to dramatically improve the chronic integration of the fNI to the target neural tissue. Such demanding advances in nano fNIs will greatly facilitate new opportunities not only for studying basic neuroscience but also for diagnosing and treating various neurological diseases.     

CO2 sequestration in depleted methane hydrate deposits with excess water

The recent increase in atmospheric CO₂ concentration makes it necessary to investigate new ways to reduce CO₂ emissions. Simultaneously, natural gas hydrate mining technology is developing rapidly. The use of depleted methane hydrate (MH) deposits as potential sites for CO₂ storage is relatively safe and economical. This method can alleviate the shortage of hydrate displacement gas with CO₂. The purpose of this study was to investigate CO₂ hydrate formation characteristics during the seepage process—in reservoirs with excess water—and their effect on CO₂ storage. The experimental process can be divided into 5 parts: MH formation, water injection, MH dissociation, CO₂ hydrate formation, and CO₂ hydrate dissociation. Magnetic resonance imaging was employed to monitor the distribution of liquid water, and the effects of different parameters on the formation and dissociation of CO₂ hydrates were analyzed. It was found that a state of initial water saturation can effectively control hydrate saturation in artificial MH reservoirs for hydrate reservoirs with excess gas. In the process of CO₂ flow, initial water saturation was not the main controlling factor for CO₂ hydrate formation. Increasing the flow pressure and reducing the flow rate were beneficial for CO₂ hydrate formation. This study is of great significance for advancing the science of CO₂ geological storage in the form of deep‐sea hydrates.     

乙烯装置裂解气压缩机开车过程动态模拟

裂解气压缩机作为乙烯装置的核心设备,其顺利启动对乙烯装置开车过程有着重要影响.传统的乙烯装置开车流程大多使用裂解气启动压缩机,近年来已经逐步被氮气、天然气和混合烃等开车工质取代.由于无法利用实际压缩机装置进行测试,因此化工模拟技术成为了解决上述问题的重要工具.本文根据"稳态-动态-开车"的研究方法,建立了某裂解气压缩机的稳态模拟模型,确定了氮气、混合烃和裂解气运行时的稳态运行参数.之后,将稳态模型转换为动态模型,通过动态模拟验证了各工况之间转换过程的安全性和可行性.     

Yb:YAG absorption at ambient and cryogenic temperatures

We have performed absorption measurements and generated absorption cross sections as a function of wavelength for the laser material YAG doped with ytterbium at 300, 175, and 75 K. This data was generated to enable a direct comparison of the absorption intensity and linewidths at room and cryogenic temperatures, and in particular near the temperature of liquid nitrogen at 77 K. The data have been used to compute universal absorption contour plots that display absorption as a function of the incident light center wavelength and optical thickness (doping density times penetration depth) for a number of bandwidths, and assuming that the spectrum of the incident light can be described as a Gaussian. Curves are presented for both 300 and 75 K, and may be used to optimize the absorption and laser efficiency.     

梯形齿同步带齿向载荷分布系数K_β的计算方法的研究

本文把带齿受载情况处理成由许多薄片叠成的力学模型,根据带齿失准度f_β、刚度C、平均载荷F_m/b及带传动基本参数计算出齿向载荷分布系数K_β。文中还简要介绍了带齿失准度f_β的确定方法。     

我国蔬菜种业发展战略研究

我国是世界第一大蔬菜生产国与消费国,蔬菜种业是确保现代蔬菜产业发展和蔬菜周年均衡供应的重要物质基础。实现蔬菜种业的可持续发展要靠科技创新。我国蔬菜种业发展进入了一个关键的时期。本文分析了我国蔬菜种业与种业科技的现状,对比了国外蔬菜种业发展的情况,针对我国蔬菜种业的主要问题,提出了我国蔬菜种业的发展战略、目标、任务、保障措施和政策建议。     

机床工作台的动力学分析

在考虑丝杠与螺母之间的接触关系以及轴承支承刚度的情况下,利用拉格朗日方程建立了滚珠丝杠传动系统的动力学方程,用振型叠加原理和隆格一库塔法进行求解,研究了滚珠丝杠传动系统的瞬态响应,按正交试验计算分析了系统参数对工作台轴向振动的影响,优化组合了系统参数,为滚珠丝杠传动系统参数的选择以及装配调整提供了理论依据,为提高工作台轴向定位精度奠定了基础.     

湍流模型对钝体燃烧器流场模拟的影响

湍流燃烧过程涉及燃烧反应和湍流在微小时间和空间尺度上的耦合,因此湍流模型的有效性对燃烧器流场CFD模拟的准确性有重要影响。采用5种k-ε类和k-ω类两方程模型和雷诺应力模型模拟了钝体燃烧器内冷流流场,并采用PIV测量方法进行了实验验证。比较和分析数值模拟和PIV实验结果发现,不同湍流模型的模拟结果在诸如速度分布和涡结构上存在较大差别,标准k-ε模型和RNGk-ε的模拟流场最接近本文的实验结果。