排序方式: 共有19条查询结果,搜索用时 15 毫秒
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分析了后门限位扣的冲压工艺,确定了排样方案,介绍了后门限位扣多工位级进模的整体结构和主要零部件设计,为保证条料的同步移动和送料顺畅,模具采用浮动顶料机构,解决了零件定位精度等问题。确定了级进模模具设计方案,该模具充分利用工件本身的结构特点,采用了自动卸料、出料、少废料冲裁,有效提高了材料利用率。成形工序中打薄圆角过渡处后,实现了在直壁上切断,解决了分离切断的问题。试冲结果表明,提出的排样方案和设计的10工位级进模是合理可行的,能满足座椅加强板零件的大批量生产需要。 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):299-303
AbstractThe vacuum analysis algorithm was developed to simulate the total system of high pressure die casting process including vacuum vent, cavity and plunger area. The various vacuum degrees (760, 650, 500, 250 and 60 mmHg) were artificially applied in cavity. The filling behaviours of molten metal under the applied vacuum conditions were simulated and compared with those of experiment. The filling amount in cavity was increased with the increase of applied vacuum pressure during partial shot experiments. The simulated filling behaviours of molten metal were relatively well agreed with those of experiment. Through the results of fluid flow simulation, the relationship of filling length and filling velocity with the variation of vacuum pressure was analysed respectively. And it applied to a real die casting product and the internal gas quantity of product was significantly reduced by modification of vacuum gate system. 相似文献
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采用Monte Carlo法仿真软件GATE,构建专用于乳腺成像的双平板正电子发射断层成像系统PEM并研究其性能。参考NEMA NU 4–2008标准,并在试验中略作改动。研究了PEM(positron emission mammography)的灵敏度、散射分数、晶体散射、计数率、固有空间分辨率等参数。结果表明,在350–650 keV能窗、6 cm平板间距下,系统灵敏度达14.17%,固有空间分辨率约1.2 mm;乳腺仿体活度为29.6 MBq时,噪声等效计数率NECR为1.508×105/s,满足PEM系统所需。 相似文献
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N. ZeraatkarM.R. Ay P. GhafarianS. Sarkar P. Geramifar A. Rahmim 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,659(1):508-514
While there is continuing demand for higher resolution in PET systems the technological improvements are still challenged by the presence of inter-crystal scatter (ICS) and inter-crystal penetration phenomena in PET detectors, which play an important role in deterioration of the spatial resolution. Both ICS and penetration have deteriorative impact on spatial resolution of PET scanners because they can lead to inaccurate incident crystal assignments. As such, an understanding of the quantitative behavior of ICS and penetration can be beneficial whether for design of a more optimized PET detection system or for more accurate modeling of ICS and penetration effects within the image reconstruction system matrix in order to enhance the quality of reconstructed images. In this work we analyzed the quantity of ICS and penetrated events in the form of coincidences, in contrast with the other studies that have assessed ICS and penetration in the form of single photons. This was performed in the PET subsystem of three GE whole-body PET/CT scanners: Discovery RX (DRX), Discovery ST (DST), and Discovery STE (DSTE). Furthermore, as a novel study, we discriminated between ICS vs. penetration events. In order to do this, we employed the GATE (Geant4 Application for Tomographic Emission) Monte Carlo (MC) toolkit for our simulations and used our previously validated GATE models of the scanners. Developing an algorithm, purely true coincidences were discriminated from ICS- and/or penetration-induced (ICS-P) coincidences. ICS-P coincidences were also categorized into three groups: group-1 consisted of coincidence event(s) only affected by penetration (one or both). Group-2 includes coincidences where one event is affected by ICS (possibly including penetration), while the other event is not affected by ICS (i.e. penetration or no mispositioning at all). Finally in group-3, both events are affected by ICS (possibly also including penetration). The results showed that the most magnificent quantitative variations of ICS-P occur along radial direction. In DRX, more than 55% of the true coincidences are mispositioned due to ICS and/or penetration when the source is located at the end of the transaxial field of view (FOV). This value for DST and DSTE is about 45%. Incidentally, the results revealed that the quantities of ICS-P coincidences in the DST and DSTE are almost equal, while there is much smaller ICS-P in the DRX. 相似文献
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《Advanced Robotics》2013,27(12):1341-1358
In order to construct truly autonomous mobile robots, the concept of 'packaging' is indispensable; in packaging, all parts such as controllers, power systems and batteries should be embedded inside a finite physical space, i.e., a robot's body. Therefore, implementing a controller on hardware is one of the most promising ways, since this contributes to low power consumption, miniaturization, etc. Another crucial requirement in the field of autonomous mobile robots is robustness, i.e., autonomous mobile robots have to cope with their unpredictably changing environment in real-time. In this study, to meet these requirements, the concept of a dynamically rearrangeable electrical circuit (DREC) is proposed and we implement this onto field progammable gate arrays as physical electronic circuits by borrowing the idea from neuromodulation widely observed in biological nervous systems through the diffusion-reaction mechanism of neuromodulators. We developed the DREC for the peg-pushing task as a practical example. We confirmed that the physical DREC can successfully regulate the behavior according to the situation encountered by changing its properties in real-time. 相似文献
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《钢铁冶炼》2013,40(5):360-368
AbstractThis paper is the second of a series of two describing abnormal transient phenomena observed during online monitoring of a billet continuous casting machine. Special attention is paid in Part 2 to in mould solidification. A mould heat flux drift phenomenon (HFD) has been detected, but only for mould powder basicities larger than 0·8. The HFD is related to a decrease of the heat flux in the lower part of the mould and an increase in both the billet-mould friction force and mould thermocouple variability. Results of tests changing the mould powder grade during casting have provided help in explaining the HFD. The probable reason for the HFD is crystallisation of the glassy slag layer. The heat flux ratio parameter (HFR), defined as the ratio between the heat flux in the lower part of the mould and the heat flux in the upper part of the mould, has proved to be a good tool for judging the casting performance of a mould powder. 相似文献
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GATE/Geant4 Monte Carlo simulations are computationally demanding applications, requiring thousands of processor hours to produce realistic results. The classical strategy of distributing the simulation of individual events does not apply efficiently for Positron Emission Tomography (PET) experiments, because it requires a centralized coincidence processing and large communication overheads. We propose a parallel computational model for GATE that handles event generation and coincidence processing in a simple and efficient way by decentralizing event generation and processing but maintaining a centralized event and time coordinator. The model is implemented with the inclusion of a new set of factory classes that can run the same executable in sequential or parallel mode. A Mann–Whitney test shows that the output produced by this parallel model in terms of number of tallies is equivalent (but not equal) to its sequential counterpart. Computational performance evaluation shows that the software is scalable and well balanced. 相似文献
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文章针对垂直搜索引擎技术进行了介绍,介绍了通用信息检索技术、信息抽取技术和信息抓取技术,例如Nutch和GATE。并利用当前流行的技术构建了一个垂直搜索引擎,最后描述了系统的架构和实现过程。 相似文献