Scaling properties of magnetic domain walls in Pt/Co/Pt trilayers on MgO (1 1 1)

We present a scaling analysis of the time evolution of domain walls in ultrathin magnetic films that are subject to different forms of uncorrelated and correlated disorder caused by the microstructure of the underlying template. The study is performed on ultrafine modulated Pt/Co/Pt trilayers grown on as-supplied and structured MgO (1 1 1) substrates employing polar Kerr microscopy for the imaging of the magnetic domains.     

Advanced simulations of spectroscopic signatures of charge exchange in laser-produced plasmas

We present an advanced theory of charge-exchange-caused dips (also called X-dips) in spectral lines from laser-produced plasmas. We compare predictions of this advanced theory with our previously published experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two X-dips in the L _γ line of Al XIII perturbed by fully stripped carbon. We show that our advanced theory is in excellent agreement with our experimental results. From the practical point of view, our results open up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because the X-dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively “low” densities of laser-produced plasmas. Received 25 March 2002 Published online 19 July 2002     

Reliability of semi-classical calculations for collisional lineshapes in thev 2 ammonia band

Summary Diode laser measurements, recently published for self- and N₂ broadening in thev ₂ ammonia band, are proved in agreement with predictions of the semi-classical ATC theory. Discrepancies for the self-shifts calculated by other authors are also discussed.     

Crystallization of low and high molecular materials

For a better understanding of the crystallization of high molecular materials the paper starts with detailed statements as to the crystallization of low molecular materials. In this way it can be shown that there exist more properties in common than supposed before. This fact becomes evident from the thermodynamical point of view if the polymer is formally considered as a 2-components-system. In this system the stable rotational isomers, viz., the trans- and the gauche-form, are the components. In that case the crystallization process of linear polyethylene (HDPE) can be regarded as a crystallization of the trans-form in a trans-gauche mixture.In the paper the critical nuclei, which build up at the beginning of the crystallization and which have so-called equilibrium shapes, as well as the complete crystals, which have so-called growth shapes influenced by the kinetics of formation, are discussed. Special attention is paid to the lamellar growth because it often occurs in polymers. It is shown that the lamellar growth can be attributed to an activated sorption of foreign substances. In many polymers the role of the foreign substance is played by the gauche-form (autogenous activated sorption).By means of electron micrographs and calorimetric measurements of HDPE samples with a bimodal distribution of the lamellar thicknesses it could be proved that the melting range of polymers is due to a distribution of the lamellar thicknesses and apparently not to a changing conformational parts _Lk of the melting entropy as supposed by other authors [1]. Values from the literature for the conformational entropys _Lk of different polymers confirm in a good approximation thats _Lk can be compared to a mean entropy of mixing of the 2-components-model for polymers. This result makes evident that Flory's model for a polymer melt of interpenetrating chain coils can indeed be replaced, in a good approximation, by an ideal mixture of independent trans and gauche units in the sense of the 2-components-model. There follows in conclusion thats _Lk is a function of the gauche-trans ratio.Dedicated to Professor Dr. F. H. Müller. Presented at the Festive Colloquium, 7 May, 1982, in Marburg/Lahn, on the occasion of the 75th birthday of Professor Dr. F. H. Müller.Presented at the 14th Europhysics Conference on Macromolecular Physics, 21–24 September, 1982, in Vilafranca del Penedès (Barcelona), Spain.     

Deriving correction functions to model the efficiency of noise barriers with complex shapes using boundary element simulations

The boundary element method (BEM) is a commonly used method to compute the insertion loss of noise barriers having arbitrary cross-sections. For large scale three-dimensional problems, however, the BEM is not feasible. On the other hand, standardized calculation methods for noise mapping are efficient, but shapes other than the straight barrier cannot be properly calculated. Attempts to merge these two approaches by using BEM to derive correction functions based on geometrical quantities such as source and target angle as well as the path length elongation between source and receiver caused by the barrier were usually focused on a small set of barrier types, dimensions, absorptive configurations, source or receiver positions. The main objective of this study is to investigate which functions based on the most common geometrical parameters are well suited for approximating the efficiency of different types of barriers, dimensions and absorptive configurations. To achieve this, numerous combinations of 7 different barrier types, different heights and widths as well as 3 different absorptive configurations were simulated using the 2D BEM for 8 different source positions. The octave-band-wise efficiency, i.e. the frequency-dependent gain in insertion loss compared to an equally high, fully reflective straight barrier was used as a basis for the correction functions. Linear as well as polynomial models were compared yielding a polynomial of third degree in the source and fourth degree in the target angle as the best model. Effects on the error using uniform sampling in the target angle instead of a uniform receiver grid as a basis for the correction functions are also investigated. Furthermore, wide-band efficiencies based on standardized traffic emission spectra are calculated showing small errors compared to single-band errors, in particular in the high-frequency range. A linear interpolation scheme is suggested to deal with barriers having dimensions not simulated in this work.     

薄膜横向振动的有限元分析

构造了一种3节点三角形膜单元,以适用于平面薄膜横向振动的有限元分析.在给出单元形函数的基础上,根据最小势能原理建立了薄膜自由振动方程,并推导了单元刚度矩阵和单元质量矩阵.研究结果表明,单元刚度矩阵和单元质量矩阵形式简单,且自由度少;通过两个典型算例,证明3节点三角形膜单元的计算结果非常接近理论解,同时可以达到很高的精度...     

复合材料板冲击损伤检测的二维间隔平滑法

本文发展了一种基于振动的复合材料板的损伤检测方法,将原有的一维间隔平滑法(1D GSM,one dimensional gapped smoothing method)发展至二维(2D GSM),并进一步提出二维间隔平滑法的标准化损伤指标.与其他多数基于振动分析的损伤检测方法不同,该方法只需分析含有损伤结构的检测数据,无需结构健康时的数据或理论、计算结果作为对比信号,即可判定缺陷的存在,并能准确定位.针对由冲击造成的准各向同性碳纤维增强复合材料板中的层裂损伤,本文采用压电片阵列组合激励的方式,得到了复合材料板多频率扭转振型的同时激励,可实现快速、高效的损伤检测.通过扫描式激光测振仪测得结构在不同固定频率下的结构响应ODS(operational deflection shapes),利用提出的二维间隔平滑法,分析得出损伤指标.实验结果表明,二维间隔平滑法可以准确地检测碳纤维增强复合材料板的冲击损伤,并具有较好的精度.     

Optimization of 3D wings based on Navier-Stokes solutions and genetic algorithms

The problem of the aerodynamic shape optimization to minimum drag, subject to geometrical and aerodynamic constraints, is considered. An accurate and computationally efficient approach to the multiobjective constrained design of 3D aerodynamic wings is proposed. The optimization is driven by full Navier-Stokes computations and Genetic Algorithms (GAs). The verification results include a variety of optimization cases for a classical test-case of ONERA M6 wing in transonic flight conditions. The method allows to significantly reduce the total drag of optimized wings, while exhibiting high robustness and keeping CFD computational volume to an acceptable level.