基于随机虚拟环的WSNs源位置隐私保护算法

针对幻影路由算法中源节点距离基站节点较近时安全周期低的问题,提出基于随机虚拟环的无线传感器网络源位置隐私保护算法。初始时由源节点随机产生一个以基站为中心的虚拟环,利用源节点到基站的直线方程和虚拟环方程确定预期幻影源节点,为选择幻影源节点提供依据;通过数据包在虚拟环上转发随机的角度,确定第二个幻影源节点。理论分析表明算法安全周期与通信开销呈正相关。仿真结果表明,该算法能有效诱导攻击者偏离真实路径,提高安全周期。     

360°全息幻影系统的开发与实现

360°全息幻影系统能够在空间中显示具有真实立体感的3D影像,在了解该技术原理及问题的基础上,进行相关的软件研发及硬件制作。系统的软件部分基于C++与OpenGL,在一个窗体下渲染出4幅参数可控的影像,结合硬件,利用一个投影仪,完成一套可实时交互的360°全息幻影系统。实验结果表明,该系统能呈现较好的立体仿真效果,并具有良好的实时性与交互性。     

基于电刺激的上肢截肢者诱发手指幻肢感初步研究

目前商用假肢缺乏有效的感觉反馈机制,人们通过机械刺激可进行间接的感觉反馈,但仍不 能产生“自然”感觉。一些研究者们通过神经内植入式电刺激可以帮助使用者获取“自然”感觉,这种有创的方式需要进行手术且对电极材料的要求很严格。相比之下,经皮电刺激更易实现,然而目前的研究还缺乏有效的控制策略来主动调控电刺激参数。因此,该文对经皮电刺激诱发手指幻肢感进行了初步研究,并结合脑电信号(EEG)特征,探究了一种客观的方法来评价电刺激参数与所诱发的手指幻肢感觉的关系,使得实现电刺激参数的主动调控成为可能。结果初步表明了通过经皮电刺激可以诱 发上臂截肢患者幻肢手指收缩的感觉;并且,通过分析脑电地形分布可建立刺激的位置与所诱发感觉的位置之间的关系;通过提取事件相关电位并分析其曲线特征,可判断所施加的电刺激强度是否足够诱发明显的幻肢感觉。该研究有助于在电刺激诱发幻肢感的研究中实现刺激参数的自动调控。     

医用磁共振成像系统计量测试方法浅析

为确保医用磁共振成像系统的影像质量,采用美国模体实验室和Goodenough博士研制的magphan模体,根据美国医学物理学家协会(AAPM)的建议和美国电气制造商协会(NEMA)提出的标准方法,对影响图像质量的信噪比、均匀性、空间分辨率、密度分辨率、线性、层厚及纵横比等主要性能参数进行检测。结果表明,上述的国外标准比较符合我国的实际情况,测量结果能够比较全面地评价医用磁共振成像系统的各项性能参数,为医生准确诊断病情提供可靠保障。     

图像分割在肺部计数器虚拟刻度中的应用

基于边缘检测及阈值分割算法,采用Matlab编程对一物理体模的CT图片进行了自动分割,区分出肺、肌肉、骨骼3种组织,并对分割出的数据进行了三维重建,实现了体素模型的快速建立。将自动分割出的器官的体积与实际器官的比较,相对偏差小于2%。将体素模型用于肺部计数器的虚拟刻度,结果显示,虚拟刻度与实验结果的相对偏差小于10%。     

Estimating, testing, and comparing specific effects in structural equation models: The phantom model approach.

The phantom model approach for estimating, testing, and comparing specific effects within structural equation models (SEMs) is presented. The rationale underlying this novel method consists in representing the specific effect to be assessed as a total effect within a separate latent variable model, the phantom model that is added to the main model. The following favorable features characterize the method: (a) It enables the estimation, testing, and comparison of arbitrary specific effects for recursive and nonrecursive models with latent and manifest variables; (b) it enables the bootstrapping of confidence intervals; and (c) it can be applied with all standard SEM programs permitting latent variables, the specification of equality constraints, and the bootstrapping of total effects. These features along with the fact that no manipulation of matrices and formulas is required make the approach particularly suitable for applied researchers. The method is illustrated by means of 3 examples with real data sets. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Simulation of transmission electron microscope images of biological specimens

We present a new approach to simulate electron cryo‐microscope images of biological specimens. The framework for simulation consists of two parts; the first is a phantom generator that generates a model of a specimen suitable for simulation, the second is a transmission electron microscope simulator. The phantom generator calculates the scattering potential of an atomic structure in aqueous buffer and allows the user to define the distribution of molecules in the simulated image. The simulator includes a well defined electron–specimen interaction model based on the scalar Schrödinger equation, the contrast transfer function for optics, and a noise model that includes shot noise as well as detector noise including detector blurring. To enable optimal performance, the simulation framework also includes a calibration protocol for setting simulation parameters. To test the accuracy of the new framework for simulation, we compare simulated images to experimental images recorded of the Tobacco Mosaic Virus (TMV) in vitreous ice. The simulated and experimental images show good agreement with respect to contrast variations depending on dose and defocus. Furthermore, random fluctuations present in experimental and simulated images exhibit similar statistical properties. The simulator has been designed to provide a platform for development of new instrumentation and image processing procedures in single particle electron microscopy, two‐dimensional crystallography and electron tomography with well documented protocols and an open source code into which new improvements and extensions are easily incorporated.     

Robust Recollection Rejection in the Memory Conjunction Paradigm.

The present research provides compelling evidence for recollection rejection in the memory conjunction paradigm. In Experiment 1, warnings provided at time of test were shown to reduce memory conjunction errors. Moreover, the authors found substantial evidence of recollection rejection and phantom recollection. In Experiment 2, the authors manipulated how often study items were presented. Participants were told that they could earn a cash payoff for being accurate. Recognition of conjunction lures was lower in the multiple presentation condition. However, the payoff manipulation did not significantly interact with item type. The authors obtained evidence of robust recollection rejection from 3 different dependent measures. Consistent with Experiment 1, they also found evidence of phantom recollection. These findings provide evidence that recollection rejection can be quite robust in the memory conjunction paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Poly(vinyl alcohol) tissue phantoms as a robust in vitro model for heat transfer

Glutaraldehyde-crosslinked poly(vinyl alcohol) (PVA) was used to create pourable, volume-stable hydrogel tissue phantoms that demonstrate several advantages over traditional poly(acrylamide) phantoms. The crosslinker concentration, curing time, and curing temperature were tuned to produce a tissue phantom whose volume varied by <0.2% over a 25-day span. The thermal conductivity of the PVA phantoms was tuned across the physiological range from 0.475 to 0.795 W m^?1°C^?1 by incorporating inert particle fillers. Experimental thermal diffusivity trials demonstrated the method’s utility for creating reliable, versatile tissue phantoms for the in vitro study of heat transfer in biologically relevant scenarios.     

女性蹲姿曲面模型光子外照射剂量研究

基于中国女性参考人曲面模型建立女性蹲姿曲面模型,采用蒙特卡罗方法,针对6种标准光子外照射几何,计算光子能量0.01～10 MeV范围内21个能量点的器官吸收剂量转换系数和有效剂量转换系数,并与直立姿势的剂量数据进行了对比。结果表明:两种姿势中某些器官的吸收剂量转换系数在前后、后前以及侧向照射方式下差异较大。其中,后前照射方式下,光子能量为0.03 MeV时,乳腺的吸收剂量转换系数比直立姿势高115.1%。在不同照射方式下,大部分能量点的有效剂量转换系数的差异在10%范围内。转换系数的差异主要是由于胳膊和腿位置的改变,以及蹲姿时因身体前倾造成器官在照射方向上厚度发生改变而产生的。