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- Chen, Fuqiang, et al.
(författare)
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减压阀噪声研究进展
- 2019
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Ingår i: Paiguan Jixie Gongcheng Xuebao/Journal of Drainage and Irrigation Machinery Engineering. - 1674-8530. ; 37:1, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- In order to comprehensively understand the specific noise generation process inside pressure reducing valves (PRV) and its existing research outcomes, the generation of noise in PRV with its research methods in China and abroad was summarized. Then, the current research status of noise reduction technologies was reviewed from two aspects: source and propagation. Based on analysis and summarization, the major existing problems in current noise reduction technologies were discussed, including complex flow situation in PRV, ambiguity of vortex location and uncertain of interaction between high-velocity jet flows and so on. In the future investigation of noise reduction in PRV, it is advised that the position of noise source in valve should be determined firstly through combination of theoretical analysis, experiment and numerical analysis. Then, the directivity of noise in the valve can be clarified. Thereby, a further study of noise reduction mechanism and technology can be launched. Finally, noise in PRV can be reduced to the utmost extent. In the future, control of noise inside PRV should start with flow mechanism and structural innovation, and then a universal valve design theory with low noise will be put forward. Investigation into noise characteristics in pressure reducing valve can provide a reliable basis for reducing noise effectively.
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| 2. |
- Lin, Jing, et al.
(författare)
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Semi-parametric Shared Frailty Model Based on MCMC Method and its Application in Reliability
- 2008
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Ingår i: Chinese Journal of Electronic Product Reliability and Environmental Testing. - 1672-5468. ; 26:153, s. 51-57
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Tidskriftsartikel (refereegranskat)abstract
- To mitigate the limitation of the traditional hypothesis that the lifetimes of the individuals obey the independent identically distribution, the semi-parametric shared frailty model based on the developmental proportional hazards model with frailty was constructed, which can reflect the influence caused by the random effect . In this model, the baseline hazard was supposed to be piecewise constant hazard. Then the MCMC method based on Gibbs sampling to simulate dynamically the Markov Chain of the parameters’ posterior distribution was brought forward. By that the parameters’ Bayesian estimations under the condition of the random truncated test and the prior distribution of the frailty belongs to the Gamma distribution were given out. Also the martingale process of the baseline hazard was introduced , as well as the precision of the numeration was improved. What’s more, an application of these techniques was illustrated by an example.
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| 3. |
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| 4. |
- Qian, Li-Bing, et al.
(författare)
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Transmission of electrons through the conical glass capillary with the grounded conducting outer surface
- 2017
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Ingår i: Wuli xuebao. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 66:12
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Tidskriftsartikel (refereegranskat)abstract
- The transmission of 1.5 keV-electrons through a conical glass capillary is reported. This study aims to understand the so-called guiding effect for the negatively charged particles (e.g. electrons). The guiding mechanism is understood quite well with positively charged particles in particular highly charged ions, but not clear with electrons, i. e., even the basic scheme mediated by the existence of negative charge patches to guide the electrons is still somewhat controversial.. The study of the charging-up dynamics causing the electrons transport inside the capillary will shed light on this issue. In order to perform this, a data acquisition system has been setup to follow the time evolution of the two-dimensional angular distribution of the transmitted electrons. The electrons are detected by the multi-channel plate (MCP) detector with a phosphor screen. The image from the phosphor screen is recorded by a charge-coupled device camera. The timing signals for the detected events are extracted from the back stack of the MCP detector and recorded by the data acquisition system, synchronized with the acquired images. The electron beam has a size of 0.5 mm x 0.5 mm and a divergence of less than 0.35.. The inner diameter of the straight part of the capillary is 1.2 mm and the exit diameter is 225 mu m. A small conducting aperture of 0.3 mm in diameter is placed at the entrance of the capillary. Two-dimensional angular distribution of the transmitted electrons through conical glass capillary and its time evolution are measured. The results show that the transmission rate decreases and reaches to a constant value for the completely discharged glass capillary with time going by. The centroid of the angular distribution moves to an asymptotic value while the width remains unchanged. These transmission characteristics are different from those indicated in our previous work (2016 Acta Phys: Si n: 65 204103). The difference originates from the different manipulations of the capillary outer surface. A conducting layer is coated on the outer surface of the capillary and grounded in this work. This isolates various discharge/charge channels and forms a new stable discharge channel. The transmission rate as a function of the tilt angle shows that the allowed transmission occurs at the tilt angle limited by the geometrical factors, i. e., the geometrical opening angle given by the aspect ratio as well as the beam divergence. The transmission characteristics suggest that most likely there are formed no negative patches to facilitate the electron transmission through the glass capillary at this selected beam energy. It is different from that of highly charged ions, where the formation of the charge patches prohibits the close collisions between the following ions and guides them out of the capillary.
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