Simulation of high fluence fast neutron damage with heavy ion bombardment

316 stainless steel has been irradiated with 5 MeV Cu ions to a fluence of 2 × 10¹⁶ ions/cm² at 500°C. Transmission electron microscopy of this sample reveals that 6 × 10¹⁵ voids/cm² of average diameter equal to 180 Å were produced. A method for correlating the fluence of ions with equivalent neutron fluences is described. This method predicts that the Cu bombardment in this study should produce a microstructure similar to that found in steel irradiated with 2–5 × 11²² neutrons/cm². A comparison of the ion produced voids with those found after previous neutron irradiation experiments confirms this prediction.     

Zur Berechnung von Geometriefaktoren bei der Kernstrahlungsmessung

Der Geometriefaktor von radioaktiven umschlossenen oder offenen Strahlenquellen hängt bei der Messung mittels einer Kernstrahlungsmeßsonde von der räumlichen Anordnung der Strahlenquelle zu der strahlenexponierten wirksamen Fläche des Detektors und von der Geometrie der Strahlenquelle selbst ab. Fūr punktförmige Strahler in verschiedenen Positionen, Geraden, Kreisflächen und Zylinder wurde in möglichst einheitlicher Vorgehensweise die Berechnung der Geometriefaktoren bezüglich kreisförmiger ebener Detektionsflächen vorgenommen und rechentechnisch in Form von BESM 6-Algolprogrammen realisiert. Die Berechnungsergebnisse sind untereinander konsistent und wurden möglichst durch unabhängige Verfahren oder experimentelle Werte kontrolliert. Die Rechengenauigkeit kann gemäß den vorliegenden Anforderungen frei gewählt werden.     

Influence of the Coulomb forces on the thermodynamic and transport properties of non stoichiometric cerium dioxide

Abstract

In this study, it is demonstrated that the Coulomb interactions explains the essential of experimental thermodynamic and transport thermodynamic results.     

Point defect interaction in alkali halide crystals

Abstract

Molecular statics method is used to determine the energy and configuration peculiarities of vacancy-bivacancy interaction in alkali halide crystals. It is shown that high level of local vacancy supersaturation defines the possibility of cluster formation. The study of carrier traps by luminescence methods is used to reveal vacancy clusters.     

Accurate Measurement of a Small Defect in a Planar Waveguide

Abstract

A non-destructive test method of a small defect (a dust particle or an air bubble) in a strongly confined planar waveguide is demonstrated in this work. Based on strong resonances between the small defect and some special incident wavelengths, an accurate reconstruction of the defect parameters can quickly be obtained from our previous numerical method. An example is given to verify the validity of the present measurement method.     

Athermal migration of vacancies in iron and copper induced by electron irradiation

Abstract

Irradiation with high-energy particles induces athermal migration of point defects, which affects defect reactions at low temperatures where thermal migration is negligible. We conducted molecular dynamics simulations of vacancy migration in iron and copper driven by recoil energies under electron irradiation in a high-voltage electron microscope. Minimum kinetic energy required for migration was about 0.8 and 1.0 eV in iron and copper at 20 K, which was slightly higher than the activation energy for vacancy migration. Around the minimum energy, the migration succeeded only when a first nearest neighbour (1NN) atom received the kinetic energy towards the vacancy. The migration was induced by higher kinetic energies even with larger deflection angles. Above several electron-volts and a few 10s of electron-volts, vacancies migrated directly to 2NN and 3NN sites, respectively. Vacancy migration had complicated directional dependence at higher kinetic energies through multiple collisions and replacement of atoms. The probability of vacancy migration increased with the kinetic energy and remained around 0.3–0.5 jumps per recoil event for 20–100 eV. At higher temperatures, thermal energies slightly increased the probability for kinetic energies less than 1.5 eV. The cross section of vacancy migration was 3040 and 2940 barns for 1NN atoms in iron and copper under irradiation with 1.25 MV electrons at 20 K: the previous result was overestimated by about five times.     

A Goal Programming model of the reference point method

Real-life decision problems are usually so complex they cannot be modeled with a single objective function, thus creating a need for clear and efficient techniques of handling multiple criteria to support the decision process. The most commonly used technique is Goal Programming. It is clear and appealing, but in the case of multiobjective optimization problems strongly criticized due to its noncompliance with the efficiency (Pareto-optimality) principle. On the other hand, the reference point method, although using similar control parameters as Goal Programming, always generates efficient solutions. In this paper, we show how the reference point method can be modeled within the Goal Programming methodology. It allows us to simplify implementations of the reference point method as well as shows how Goal Programming with relaxation of some traditional assumptions can be extended to a multiobjective optimization technique meeting the efficiency principle.     

腔光子-自旋波量子耦合系统中各向异性奇异点的实验研究

通过耦合三维微波腔中光子和腔内钇铁石榴石单晶小球中的自旋波量子形成腔-自旋波量子的耦合系统,并通过精确调节系统参数在该实验系统中观测到各向异性奇异点.奇异点对应于非厄米系统中一种特殊状态,在奇异点处,耦合系统的本征值和本征矢均简并,并且往往伴随着非平庸的物理性质.以往大量研究主要集中在各向同性奇异点的范畴,它的特征是在系统参数空间中沿着不同参数坐标趋近该奇异点时具有相同的函数关系.在这篇文章中,主要介绍实验上在腔光子-自旋波量子耦合系统中通过调节系统的耦合强度和腔的耗散衰减系数两条趋近奇异点的路径而实现了各向异性奇异点,具体分别对应于在趋近奇异点时,本征值的虚部的变化与耦合强度和腔的衰减系数的变化会有线性和平方根不同的行为.各向异性奇异点的实现有助于基于腔光子-自旋波量子耦合系统的量子信息处理和精密探测器件的进一步研究.     

基于机器视觉的刀具轮廓在线检测方法的研究

超精密单点金刚石车削过程中需要对刀具参数进行检测。基于机器视觉原理,采用新型的机械结构设计了新型刀具在线检测系统。通过垂直放置的两组由同轴远心镜头和CMOS相机组成的光学系统来获取车刀刀尖正面及侧面的图像,再经图像处理系统来获取刀具的轮廓及位置信息,完成对刀具轮廓及位置的在线检测,实验验证可实现测量的重复性定位精度达1μm。在线检测的方式借助了超精密车床自身的高精度和运动机构,可以保证相机焦点和机床主轴之间的相对位置关系,弥补了目前刀具检测系统稳定性差和重复性精度低的不足,提高了加工的整体效率。     

激光雷达辅助驾驶道路参数计算方法研究

针对特定场景辅助驾驶的需求,构建道路场景车载激光雷达三维扫描系统,并设计基于三维激光点云的道路参数提取与计算方法,包括路面宽度、横杆或桥梁或隧道限高、拐弯半径等等,为辅助判断道路的可通过性提供决策依据。测试和对比实验表明,所设计算法效果稳定、精度良好,在效率和自动化程度上有一定优势,可为辅助驾驶提供非常有益的决策参数。