Influence of turbulence on train noise

The subject of this paper is the long distance propagation of train noise. The sound exposure level of train noise L_AE was measured. To describe the results of measurements, a semi-analytical model was used. It takes into account the wave-front divergence, air absorption, ground effect, and the turbulence destroying the coherent nature of the ground effect. The model contains three adjustable parameters that must be estimated at the site. To verify the model, we performed measurements of L_AE at the distance D = 450 m from the train track center. The difference between the calculated and measured mean values of L_AE equals 1.3 dB.     

旋转对称非球面自动加工控制算法研究

介绍了计算机控制光学表面成型（ＣＣＯＳ） 技术的基本原理,对双旋转磨头的去除函数进行研究,研究了不同形状的磨头的去除函数特性,并在多次实验的基础上得到了最优的加工参数,在去除函数的基础上提出了模板函数的概念及算法。根据加工旋转对称非球面光学表面的特点,结合模板函数提出了一种基于同心圆磨头运动轨迹的控制算法。运用该算法对神光Ⅲ号打靶非球面透镜的一种工艺试样（ Φ３００ｍ ｍ ,Ｆ５－９ ,最大非球面度为４６μｍ） 进行自动加工,面型精度达到１λ（ＲＭＳ,λ＝ ６３２－８ｎｍ）,取得了满意的结果。     

Detection threshold in muscovite mica: Influence of the observation tool

For the observation of nuclear tracks, Atomic Force Microscopy (AFM) is a useful technique. In our study, we have irradiated a muscovite mica sample using 600 keV oxygen ions. This ion's energy is well below the detection threshold predicted by the existing models. The samples were visualized at high resolution with an AFM device. Before chemical etching no tracks were visualized on the surface at an atomic level. However, defects must have been initiated because tracks became observable after a brief etching time. Our results confirm that the detection threshold is influenced by the observation tool. In this article we provide information concerning the “observability” and “etchability” of latent tracks.     

Investigations of heavy ion tracks in polyethylene naphthalate films

The heavy ion beam (with fluence 3x10⁸ ion/cm²) from a cyclotron has been used for irradiation of thin polyethylene naphthalate (PEN) films. Latent tracks in these polymeric films have been sensitized by UV radiation and then chemically etched in NaOH solution. The etching process parameters have been controlled by the electroconductivity method. After etching, parameters of samples have been examined by SEM and bubble point methods (Coulter® Porometer II instrument). Results have shown good quality of PEN track membranes with pore sizes in the range: 0.1 – 0.5 μm. The described procedure is known for thin polythylene terephthalate (PET) films. Taking into consideration that PEN films have got better mechanical, thermal, gas barrier as well as better chemical resistance properties in comparison with PET films, the possibility of application of such membranes is much wider.     

Study of latent and etched tracks by a charged particle transmission technique

A recently suggested technique for non-destructive investigation of inhomogeneities in thin objects, which is based on the measurement of the energy spectra of charged particles transmitted through the object, is used for the study of thermal annealing of 10–20 μm thick polyethylene terephtalate, polypropylene and polycarbonate foils irradiated with 1–10 MeV/amu heavy ions. At elevated temperature a foil linear contraction is observed on pristine and irradiated material. Also the foil roughness increases with increasing temperature. On the same foils with etched pores 0.5–1.0 μm in diameter, the thermal annealing results in gradual closing of the pores up to about 30% of their initial diameter at the temperatures of 150–175°C. At higher temperatures the pore diameter increases and achieves its initial value.     

Study of pore formation during etching of latent tracks of accelerated heavy ions in poly(ethylene terephthalate) by atomic force microscopy

The process of transformation of latent tacks of accelerated heavy ions of poly(ethylene terephthalate) into pores and the formation of a porous structure of track membranes was studied by atomic force microscopy. It was shown that on initial etching, 10-nm high knolls with an average diameter of 800–1000 Å are formed in place of tracks. Based on the knolls, through channels are formed, which emerge on the surface as conical cavities. It was shown that further etching gives first cylindrical channels of diameter 800–1000 Å, which then undergo radial etching.     

Investigating cross-wind stability of high-speed trains with large-scale parallel CFD

ABSTRACT

The side-wind loading on a simplified train model at scale 1:25 is investigated by parallel large eddy simulation (LES) with incompressible solvers from the OpenFOAM package and a novel dynamically adaptive, parallel LES-type lattice Boltzmann method (LBM) implemented in our own AMROC framework. It is found that the new LBM code provides more accurate time-averaged force predictions, while compute times are reduced.     

Ionizing particles may create shockwaves

To find a model that describes the gas diffusion on irradiated polymers (Makrofol KG polycarbonate) the diffusion constants have been measured with argon as diffusion gas. The polymers were irradiated with uranium, gold and lead ions of about 10 MeV/u and ion fluences between 1×10¹⁰ and 4×10¹¹ ions/cm². The ion irradiated probes show two quite different dependencies of the diffusion constant on the ion energy loss. These effects are strongly related to the fluence of the irradiation. In case of low ion fluences, the diffusion constant is up to 8 times higher than that of pristine material. In the probes with high ion fluences we observe a decrease of diffusion constant to half the value of the pristine material. To understand the dependence of the diffusion constant on ion fluences we apply a model of compacting. This model describes the compacting ability of shockwaves arising from latent tracks. A track formation model is suggested. When an ion penetrates the foil it creates shockwaves around its path. These shockwaves put compacting forces on earlier created latent tracks in the same foil.     

Materials parameters and ion-induced track formation

ABSTRACT

The role of various materials parameters in track formation is discussed. Experimental information is utilized showing a direct quantitative relationship in different solids between the melting points T_m and the ion-induced track radii R_e without involving other materials parameters. It is shown for Θ?=?T_m???T_ir (T_ir – irradiation temperature) that Θ～exp{?R_e²/w²} for S_e/N?=?constant, where S_e and N are the electronic stopping power and the number density of atoms and w?=?4.5?nm. The validity of this universal-type relation is demonstrated for 14 different insulators including LiNbO₃ and BaFe₁₂O₁₉. It is shown that the thermal diffusivity D, the heat of fusion L the band gap energy E_g and the absorption radius α_e of the electron distribution must not affect the track sizes as this would not be coherent with this identical behavior. Original reports on LiNbO₃ and BaFe₁₂O₁₉ with opposite conclusions are critically analyzed. It is shown that an arbitrary value of the ion energy was used in the analysis that modified substantially the results leading to an undue justification of the contribution of L and E_g in apparent agreement with the experimental data.     

Annealing of heavy ion tracks in cellulose nitrate plastic track detectors

The effect of heat treatment on the latent tracks in cellulose nitrate plastic track detectors has been studied. The bulk etch rate increases with annealing temperature while the track diameters of different ions in cellulose nitrate decrease with increase in annealing time and temperature. Experimental results show that for heavier ions higher temperatures are needed for their complete erasure. The track length and track etch rate are decreased by the application of heat. Experiments reveal that annealing reduces track density. The vertical tracks are more stable than the oblique tracks and require higher temperature for their complete erasure.