对多普勒天气雷达的欺骗干扰方法分析

多普勒天气雷达是利用云雨等散射体中的粒子与雷达之间的相对运动所形成的多普勒效应而进行气象探测的一种PD雷达.本文首先对多普勒天气雷达的多假目标欺骗干扰进行了仿真分析;然后从多普勒天气雷达探测气象目标的基本原理出发,提出了一种针对多普勒天气雷达实施假目标欺骗的新方法.     

宽带雷达回波的高频电磁散射快速算法

提出一种将射弹跳射线法和等效边缘电磁流法与线性调频信号雷达信号处理过程相结合的高频电磁散射算法,该算法能够快速准确计算复杂电大尺寸目标的大时宽带宽雷达回波信号.利用宽带雷达回波计算结果,获得了目标的一维距离像和二维ISAR成像,验证了方法的正确性.     

Knowledge work and practices of seeing: Epistemologies of the eye,gaze, and professional vision

Much practice within organizations is to some extent embodied in and centered on the visual capacities of the agent, the acting subject. Distinguishing between ‘epistemologies of the eye’, i.e. theories of how knowledge is acquired through visual practices, and ‘practices of seeing’, i.e. theories and studies of how vision and visuality are actually used in everyday working life, the paper points to the need to understand vision and visuality in organizational practice. Using the case of functional magnetic resonance imaging (fMRI), it is suggested that professional vision, i.e. practices of seeing that are shared within epistemic communities, is firstly technologically mediated and, secondly, based on the ability to combine vision, speech, gesture, and other embodied and cognitive resources in order to make sense of the images produced by fMRI technology. The paper concludes that organization theory should examine practices of seeing in greater detail and as part of the project in order to understand how knowledge is constituted and used as a collectively constituted resource within organizations.     

The toxicology report audit

In a study of volunteers in medical research we found contrasting readings of “being comfortable” by the volunteer research subjects and the researchers. Although the experimental process (testing a new kind of diagnostic technology) involved some physical discomfort—and the researchers focused on this—the volunteers’ concerns centred on feeling socially comfortable and managing feelings of embarrassment or isolation, and they generally made light of the physical aspects. The bias of volunteer concerns, which is understandable in terms of the different situations of researchers and volunteers and the different tensions they create, has potential implications for the engagement of researchers with their research subjects and prevailing standards for the ethical and accountable conduct of research.     

Safety First: Recognizing and Managing the Risks to Child Participants in Magnetic Resonance Imaging Research

Specialized and up-to-date knowledge is required to identify and manage the risks associated with advanced biomedical research. Additional complexities need to be considered when the research involves infants or young children. In this article, we focus on recent information about the physical risks of pediatric magnetic resonance imaging research and highlight information gaps. With an eye to assisting institutional review boards and researchers, we consider strategies for the management of these risks and formulate key questions aimed at exposing hidden hazards. Institutional review boards should ask these questions, and researchers should bear them in mind as they develop research protocols.     

Disclosure of Unknown Harms in Magnetic Resonance Imaging Research

Unknown harms are by their nature difficult to communicate. While magnetic resonance imaging (MRI) has known risks (e.g., metal projectiles, dislodgement of medical implants), this imaging modality also has potential unknown long-term negative health effects associated with its static magnetic fields. We carried out a research ethics board (REB) file review of previously approved MRI research studies and found that unknown risks were either left undisclosed or were inadequately disclosed to research participants and REBs. This article outlines issues raised by our REB file review and suggests steps that should be taken in order to satisfactorily communicate information about potential unknown harms of MRI.     

Multivariate functional response low‐rank regression with an application to brain imaging data

We propose a multivariate functional response low‐rank regression model with possible high‐dimensional functional responses and scalar covariates. By expanding the slope functions on a set of sieve bases, we reconstruct the basis coefficients as a matrix. To estimate these coefficients, we propose an efficient procedure using nuclear norm regularization. We also derive error bounds for our estimates and evaluate our method using simulations. We further apply our method to the Human Connectome Project neuroimaging data to predict cortical surface motor task‐evoked functional magnetic resonance imaging signals using various clinical covariates to illustrate the usefulness of our results.     

A spatial Bayesian semiparametric mixture model for positive definite matrices with applications in diffusion tensor imaging

Studies on diffusion tensor imaging (DTI) quantify the diffusion of water molecules in a brain voxel using an estimated 3 × 3 symmetric positive definite (p.d.) diffusion tensor matrix. Due to the challenges associated with modelling matrix‐variate responses, the voxel‐level DTI data are usually summarized by univariate quantities, such as fractional anisotropy. This approach leads to evident loss of information. Furthermore, DTI analyses often ignore the spatial association among neighbouring voxels, leading to imprecise estimates. Although the spatial modelling literature is rich, modelling spatially dependent p.d. matrices is challenging. To mitigate these issues, we propose a matrix‐variate Bayesian semiparametric mixture model, where the p.d. matrices are distributed as a mixture of inverse Wishart distributions, with the spatial dependence captured by a Markov model for the mixture component labels. Related Bayesian computing is facilitated by conjugacy results and use of the double Metropolis–Hastings algorithm. Our simulation study shows that the proposed method is more powerful than competing non‐spatial methods. We also apply our method to investigate the effect of cocaine use on brain microstructure. By extending spatial statistics to matrix‐variate data, we contribute to providing a novel and computationally tractable inferential tool for DTI analysis.     

临床X射线相衬成像研究进展

X射线相衬成像在提高人体软组织成像的衬度分辨率及空间分辨率研究中具有潜在优势,是一项有着广阔发展前景的技术。它利用空间相干X射线投过物体后携带的相位信息进行成像,在临床上适用于软组织物体,可以减少吸收剂量,进而减轻病人的辐射损伤。本文详述了当今几种典型的X射线相衬成像方法,包括X射线干涉相衬,衍射增强相衬以及类同轴相衬的成像原理以及发展历程。通过对比表明了几种成像方法的优缺点。最后对临床X射线相衬成像有待解决的问题作了分析。     

不同小波基下的SAR图像相干斑抑制性能分析

分析了合成孔径雷达(SAR)图像中相干斑(Speckle)的统计特性。基于小波变换(WT),给出了一种多尺度的Speckle滤波方法,该方法利用小波分解后的HH分量(低频分量)作Speckle抑制,得到图像Speckle的相当大的改进。文中还对不同的小波基进行了理论分析,并利用实验数据,从等效视数(ENL)角度进行了比较,证实了不同小波基下该方法对Speckle具有较好的抑制性能。