Franco-Russian comparison of mixed neutron and gamma radiation field dosimeters at the Silène reactor

This paper gives the results of dosimetry measurements carried out in the Silène reactor at Valduc (France) with neutron and photon dosimeters in mixed neutron and gamma radiation fields, in the frame of a Franco-Russian comparison of dosimeters. Neutron dosimetry was supplied by passive semiconductors, activation detectors and nuclear track detectors. For photon dosimetry, thermoluminescent and passive semiconductor detectors were used. The experiments were located at 3 m from the reactor core, in free air and also at the front and back of a tissue-equivalent phantom. The pulse operating mode of the reactor was used to simulate a criticality accident with solid fissile material, while the free evolution mode simulated a criticality accident in a fissile solution. The photon absorbed dose showed a slight increase on entering the phantom compared to measurements in free air, probably due to backscattering by the phantom. At the rear of the phantom, the neutron kerma was four times lower than on the front, whereas the photon dose was only two times lower. The heterogeneity of dose inside the phantom was far greater for neutrons than for photons.     

DNS of a spatially developing turbulent boundary layer with passive scalar transport

A direct numerical simulation (DNS) of a spatially developing turbulent boundary layer over a flat plate under zero pressure gradient (ZPG) has been carried out. The evolution of several passive scalars with both isoscalar and isoflux wall boundary condition are computed during the simulation. The Navier–Stokes equations as well as the scalar transport equation are solved using a fully spectral method. The highest Reynolds number based on the free-stream velocity U_∞ and momentum thickness θ is Re_θ=830, and the molecular Prandtl numbers are 0.2, 0.71 and 2. To the authors’ knowledge, this Reynolds number is to date the highest with such a variety of scalars. A large number of turbulence statistics for both flow and scalar fields are obtained and compared when possible to existing experimental and numerical simulations at comparable Reynolds number. The main focus of the present paper is on the statistical behaviour of the scalars in the outer region of the boundary layer, distinctly different from the channel-flow simulations. Agreements as well as discrepancies are discussed while the influence of the molecular Prandtl number and wall boundary conditions is also highlighted. A Pr scaling for various quantities is proposed in outer scalings. In addition, spanwise two-point correlation and instantaneous fields are employed to investigate the near-wall streak spacing and the coherence between the velocity and the scalar fields. Probability density functions (PDF) and joint probability density functions (JPDF) are shown to identify the intermittency both near the wall and in the outer region of the boundary layer. The present simulation data will be available online for the research community.     

Numerical evaluation of passive control of shock wave/boundary layer interaction on NACA0012 airfoil using jagged wall

Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the prac-ticability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disinte-grates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17%occurs with a triangular shape, while the max-imum increase in aerodynamic efficiency (lift-to-drag ratio) of around 10%happens with a rectangular shape at an angle of attack of 2.26?.     

Surface characterisation and crevice corrosion behaviour of nickel-based alloys in the paper industry

Recycled water in the paper industry acts as a stronger electrolyte as its concentration and temperature are quite high. The lower pH that exists in these solutions enhances the corrosion and the high concentration of solids leads to leaching of metal ions from surface. Crevice corrosion is a form of localised attack, which can quickly induce metal perforation even with high grade stainless steels like 316L when the protective chromium oxide film is damaged. A specially designed crevice cell assembly was used to study the electrochemical aspects of nickel-based alloys with the commonly used 316L SS. The mounted specimen with its crevice was anodically polarised in a white water medium, which is normally encountered in the paper machine section. The nickel-based alloys show remarkable crevice corrosion resistance. X-ray photoelectron spectroscopy studies revealed that the enhanced corrosion resistance of these alloys is due to the contributing nature of the individual elements Cr, Ni and Mo and their presence in the form of various oxidised species on the passive films. Received: 22 February 1999 / Accepted: 6 June 1999     

基于ATM的无源光网络媒质接入控制协议的设计

针对基于ＡＴＭ的无源光网络（ＡＴＭ－ＰＯＮ）设计了一种媒质接入控制（ＭＡＣ）协议。该协议的设计遵照ＩＴＵ－Ｔ有关ＡＴＭ－ＰＯＮ的建议Ｇ．９８３．１（１９９８年１０月）中所定义的帧结构。该协议能够支持ＣＢＲ／ＶＢＲ、ＡＢＲ和ＵＢＲ等多种业务,并能够保证用户公平地接入和充分地利用网络的资源。其中ＣＢＲ／ＶＢＲ业务的优先级最高,同时也确保ＡＢＲ业务至少能以最小信元通信。系统的剩余带宽资源被分配给ＵＢＲ业     

无源波分在5G前传接入中的应用研究

5G基站的大规模建设将消耗大量的前传光纤基础资源,给运营商带来建网成本、能耗的压力.通过比较各种前传方案,从技术、建设周期及成本效益等方面进行分析,提出在纤芯不足的区域采用无源波分方案,可大大节省建设成本、缩短建设周期、减少机房动力改造投资、降低运营成本.该方案能使综合TCO最优,高效解决5G前传难题,提高网络竞争力.     

一种星载天线金属网PIM性能的波导测试方法

金属网的无源互调(PIM)是大功率星载网状天线的一项重要性能参数。传统的金属网无源互调测试主要采用空间辐射法,但空间辐射法需要的金属网样件尺寸大,测试效率低。对此,提出一种基于三端口模块波导测试系统的金属网无源互调性能测试方法。为验证测试方法的有效性,搭建了基于三端口模块的金属网PIM性能测试系统,并对传统型和改进型2个金属网样件进行了PIM性能测试。测试结果表明,改进后的金属网PIM性能提升了50 dB以上。本文提出的金属网PIM性能测试方法使用的三端口测试系统集成度高,性能稳定,系统搭建效率高。相比传统的空间辐射测试法,本文方法的测试样件尺寸减小了一个数量级,为快速研究新型低PIM金属网提供了有力支持。     

一种相位可调的多载波无源互调测试方法

随着多波束卫星通信技术的发展,收发共用技术被广泛应用,微波无源器件大功率引发的无源互调(PIM)效应面临着挑战。本文根据多波束卫星通信工作模式,在双载波测试PIM的基础上设计了一种相位可调的多输入多输出多载波PIM测试方法。考虑多载波叠加效应,开展了多载波PIM理论分析。组建的7路测试系统通过了-60～60℃天线馈源PIM试验,PIM电平稳定在-155 dBm以下。此测试系统已用于星载部件多载波无源互调性能检测。     

DEM analysis of passive arching in a shallow trapdoor under eccentric loading

This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models. The numerical models were validated by comparison with laboratory test results. The deformation pattern, soil arching ratio, force chain distribution, and coordination number under various surcharge magnitudes and deviation distances were analyzed. The numerical results showed that the deformation diagram of soil particles can be divided into three zones: principal displacement zone, transition zone, and static zone. With an increase in the surcharge magnitude, the range of the principal displacement zone decreased, but the range of the transition region increased. The curve of the soil arching ratio on the trapdoor can be divided into three phases, which can be well characterized by the tangent modulus. The passive arching effect is degraded by a surcharge. The ultimate soil arching ratio could be approximated as a W-shaped distribution along the +x-direction. With an increase in the trapdoor displacement, the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape. The most powerful force on the trapdoor was mainly distributed on its edge. The average coordination number decreased gradually as the trapdoor moved upward.     

基于SERS探针技术的细胞识别、成像与诊疗

表面增强拉曼散射(surface-enhanced Raman scattering, SERS),是指吸附在粗糙的金属纳米结构表面的被分析物,在光照射下其拉曼光谱获得显著增强的异常表面光学现象。近年来,SERS技术已广泛地用于物质检测和生物传感等研究,在生物医学领域表现出巨大的应用潜力并取得了令人瞩目的研究成果。本文回顾了SERS探针技术在细胞识别、成像与诊疗等方面的应用及最新研究进展,重点介绍了SERS细胞探针的构建方法与原理,以及基于SERS探针的细胞检测应用策略,并讨论了SERS探针技术在细胞检测中仍有待解决的关键问题。