On aerodynamic noises radiated by the pantograph system of high-speed trains

Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver （NLAS） and Ffowcs Williams-Hawkings （FW-H） acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level （OASPL） at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.

Effect of sintering temperature on structure and tribological properties of nanostructured Ti-15Mo alloy for biomedical applications

The effect of sintering temperature(1073?1373 K)on the structural and tribological properties of nanostructured ballmilledβ-type Ti?15Mo samples was investigated.The prepared samples were characterized using various apperatus such as X-ray diffractometer,scanning electron microscope(SEM)and ball-on-plate type oscillating tribometer.Wear tests were conducted under different applied loads(2,8 and 16 N).Structural results showed that the mean pore and crystallite size continuously decreased with increasing sintering temperature to reach the lowest values of 4 nm and 29 nm at 1373 K,respectively.The relative density of the sintered sample at 1373 K was as high as 97.0%.Moreover,a higher sintering temperature resulted in higher relative density,greater hardness and elastic modulus of the sample.It was observed that both the friction coefficient and wear rate were lower in the sample sintered at 1373 K which was attributed to the closed porosity.

Measurement of oil-water flow via the correlation of turbine flow meter, gamma ray densitometry and drift-flux model

The flow rate of the oil-water horizontal flow is measured by the combination of the turbine flow meter and the singlebeam gamma ray densitometry. The emphasis is placed on the effects of the pipe diameter, the oil viscosity and the slip velocity on the measurement accuracy. It is shown that the mixture flow rate measured by the turbine flow meter can meet the application requirement in the water continuous pattern（ o- w flow pattern）. In addition, by introducing the developed drift-flux model into the measurement system, the relative errors of measurements for component phase flow rates can be controlled within ±5%. Although more accurate methods for the flow rate measurement are available, the method suggested in this work is advantageous over other methods due to its simplicity for practical applications in the petroleum industry.

Can the occurrence of rare insertion/deletion polymor-phisms in human mtDNA be verified from phylogeny?

Due to its specific characteristics, such as ma-ternal inheritance and absence of recombination, each mtDNA belongs to certain monophyletic clade in the rooted mtDNA tree (haplogroup) according to the mutations it harbors. Rare mutation (excluding parallel mutation) occur-ring at multiple times in different haplogroups could thus be a potential reading error according to the mtDNA phylogeny. This experience has been widely used in double-checking the credibility of the rare mutations in human mtDNA sequences. However, no test has been performed so far for the feasibility of applying this strategy to the rare insertion/deletion (indel) events in mtDNA sequences. In this study, we attempted to relate the rare indels in mtDNAs to their haplogroup status in a total of 2352 individuals from 50 populations in China. Our results show that the insertion of A at position 16259 is restricted to a subclade of haplogroup C and can be verified. The other indel polymorphisms, which occur in the repeat of the deleted or inserted nucleotide(s), may not be distin-guished from phantom mutations from a phylogenetic point of view. Independently and multiply sequencing the frag-ment with the indel is the best and the most reliable way for confirmation.

瑞典乐美福餐盒

在2005年欧洲最大的德国户外商品展中。SNEWS（美国著名户外运动社团）发现了来自瑞典的LMF（乐美福）公司和其被称为“重新发明的套装餐盒”的标志性产品——Light My Fire瑞典乐美福餐盒。