基于多普勒频谱特征的空中目标识别

分析了直升机和固定翼飞机两类空中目标的多普勒频谱测量能力，并在测量能力得到满足的前提下，对其目标的多普勒频谱特征进行了分析，找出了它们之间的不同之处，提出了对其目标进行分类识别的方法，通过对18种直升机和固定翼飞机的仿真数据以及现场实测数据的检验，证明该方法是有效的，并且适用于悬停直升机的探测与识别。     

Mechanistic understanding of CO2 Reduction Reaction Towards C1 products by molecular transition metal porphyrin catalysts

Designing low-cost, highly efficient, and durable electrocatalysts for carbon dioxide reduction reaction (eCO₂RR) to value-added chemicals is an appealing approach to balance the global carbon emission. Heterogeneous molecular catalysts is emerging as an important area for CO₂ utilization. Herein, a series of atomically isolated transition metal-N₄ sites anchored on porphyrin framework (TM/PRF) molecular catalysts are employed as electrocatalysts for eCO₂RR because of their well-defined structure, the versatility and relatively low cost, and remarkable activity, which allow the establishment of precise structural model for a better understanding of the CO₂ reduction mechanism. Based on density functional theory calculations and the computational hydrogen electrode model on 27 candidates, we propose a number of TM/PRF (TMs = Ni, Co, Mn, Cu, Ag, Au, Zn, Pd, Ti, V, Cr, Ta, W), which show promise of highly active and selective catalysts for carbon monoxide, formic acid, methane and methanol production, while simultaneously suppress competing hydrogen evolution reaction. Studies have shown that the TM center plays a crucial role in determining the catalytic performance of the material. And the TM/PRF molecule tends to stabilize different radical intermediates at the TM site. Thus, when reacted with a greater number of electrons, highly reduced products are formed. Among the different TM/PRF materials, Ta/PRF and W/PRF have been shown to produce CH₃OH selectively at low overpotentials (0.39 and 0.58 V), whereas Ti/PRF has been found as highly selective toward CH₄ production with low overpotential of 0.58 V, outperforming most known electrodes. The calulation of activation energy and the d-band center reveal that Cr/PRF shows higher catalystic activity in comparison with other TM/PRF. The advantages of the outstanding selectivity of products, the reduced overpotentials and the higher activity of catalyst allow these new systems TM/PRF (TMs = Ta, W, Ti, Cr) to be promising catalysts, which will motivate more fundamental mechanism studies and technological applications for eCO₂RR.     

逆合成孔径雷达多普勒质心跟踪法性能分析

 目标强散射中心的转动相位成分(RPC)是限制逆合成孔径雷达多普勒质心跟踪(DCT)法自聚焦性能的主要因素.基于统一的目标散射信号模型,本文提出扰动角的概念以衡量RPC的影响,并分析了决定扰动角的若干因素.据此,本文证明了提高雷达脉冲重复频率可改善DCT法的自聚焦性能,并证明了圆移位DCT(CS-DCT)和图像均衡DCT(IE-DCT)两类改进方法的原理等效性.最后,数值实验结果验证了本文性能分析的正确性.     

Multi-Factor Password-Authenticated Key Exchange via Pythia PRF Service

Multi-factor authentication (MFA) was proposed by Pointcheval et al. [Pointcheval and Zimmer (2008)] to improve the security of single-factor (and two-factor) authentication. As the backbone of multi-factor authentication, biometric data are widely observed. Especially, how to keep the privacy of biometric at the password database without impairing efficiency is still an open question. Using the vulnerability of encryption (or hash) algorithms, the attacker can still launch offline brute-force attacks on encrypted (or hashed) biometric data. To address the potential risk of biometric disclosure at the password database, in this paper, we propose a novel efficient and secure MFA key exchange (later denoted as MFAKE) protocol leveraging the Pythia PRF service and password-to-random (or PTR) protocol. Armed with the PTR protocol, a master password pwd can be translated by the user into independent pseudorandom passwords (or rwd) for each user account with the help of device (e.g., smart phone). Meanwhile, using the Pythia PRF service, the password database can avoid leakage of the local user’s password and biometric data. This is the first paper to achieve the password and biometric harden service simultaneously using the PTR protocol and Pythia PRF.     

超宽带脉冲对全球定位系统的潜在干扰

结合已有的超宽带(UWB)信号对全球定位系统(GPS)接收机的干扰实验,分析了不同脉冲重复频率(PRF)的超宽带脉冲信号对全球定位系统的潜在干扰.这些干扰主要是对中心频率为1176.45±12MHz的GPS接收机.     

用加速量热仪研究参比燃料的低温氧化特性(Ⅱ)

基于用加速量热仪(ARC)对参比燃料与空气的混合物在低温条件下的氧化特性的实验结果,对ARC实验结果进行了热力学和化学动力学分析．根据能量平衡方程,推导出在较小的样品质量下,考虑到密闭容器中各种基本反应物质的比热容随温度变化时,热惰性因子的准确表达式,算出参比燃料在反应过程中的实际自放热率,并根据化学动力学分析求出正庚烷和异辛烷低温氧化动力学参数．对正庚烷和异辛烷的自放热率分析发现,它们都出现双峰现象,并分别在589．4K和585．7K时有最大放热率,随后在598．5K和594．8K结束自放热．     

MRI Temperature Mapping and Determination of Liquid-particulate Heat Transfer Coefficient in an Ohmically Heated Food System

ABSTRACT: Real-time temperature maps of ohmically heated liquid-particulate mixtures were acquired using the Proton Resonance Frequency (PRF) shift method incorporated into a fast Magnetic Resonance Imaging (MRI). Noise in the MRI images induced by the electrical heating power was eliminated by a post-processing algorithm of the PRF shift method and correction phase images. The time-dependent interface heat transfer coefficients ( h_fp ) were determined during the holding period using the MRI temperature maps and numerical solutions to the Fourier's 2nd law. The calculated values of h_fp range from 30 to 105 W/m²K, consistent with literature values for natural convection. These results provide crucial data for understanding the ohmic heating process.     

基于伪文档的伪相关反馈方法

传统的伪相关反馈(Pseudo Relevance Feedback, PRF)方法通常是以文档作为扩展源单元提取扩展词,提取粒度过大造成扩展源质量下降,使得检索结果鲁棒性差。该文研究利用主题分析技术,尝试将文本语义内容作为扩展源单元,缓解扩展源质量不高的问题。提出并实现了对文本集中各文档内容的伪文档描述,通过对其进行隐式多样化处理,实现了从更细微的文本内容角度出发提取扩展词。通过在真实NTCIR8中文语料的检索结果表明,该方法可以有效地提升伪相关反馈的检索性能。     

用加速量热仪研究参比燃料的低温氧化特性（Ⅰ）

分析了两种参比燃料正庚烷和异辛烷氧化过程的化学动力学机理.在初始压力约1.5MPa和当量比为0.52左右的条件下,采用加速量热仪对两种基本参比燃料及其均匀燃/空混合物在450～650K之间的氧化特点进行了考察.实验结果表明两种参比燃料在450K时就有放热发生,并且随着自放热的发生正庚烷的压力逐渐升高,而异辛烷的压力在整个放热过程中基本保持不变,但当放热结束时却突然升高;正庚烷和异辛烷分别在598.5K和594.8K结束自放热,进入负温度系数区.