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任何企业在经营活动中都面临风险,然而,对于处在国内外双重环境下的外贸企业来说,它们面临的风险种类更多,防范起来更加困难,形势也更为紧迫。那么,外贸企业应该怎样防范这些风险呢? 相似文献
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把别人卖100元的毛绒玩具卖到500元,你相信吗?一场大雨将损失100万,你能承受吗?不到两个月要收回上亿的投资,你敢干吗?环球嘉年华做的就是这样的事情。 相似文献
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Power supply for generating frequency-variable resonant magnetic perturbations on the J-TEXT tokamak
To further research the response of the tearing mode(TM) to dynamic resonant magnetic perturbation(DRMP) on the J-TEXT tokamak, a modified series resonant inverter power supply(MSRIPS) with a function of discrete variable frequency is designed for DRMP coils in this study. The MSRIPS is an AC–DC–AC converter, including a phase-controlled rectifier, an LC filter, an insulated gate bipolar transistor(IGBT) full bridge, a matching transformer, three resonant capacitors with different capacitance values, and three corresponding silicon controlled rectifier(SCR) switches. The function of discrete variable frequency is realized by switching over different resonant capacitors with corresponding SCR switches while matching the corresponding driving frequency of the IGBT full bridge. A detailed switching strategy of the SCR switch is put forward to obtain sinusoidal current waveform and realize current waveform smooth transition during frequency conversion. In addition, a resistor and thyristor bleeder is designed to protect the SCR switch from overvoltage. Manufacturing of the MSRIPS is completed, and the MSRIPS equipment can output current with an amplitude of 1.5 kA when its working frequency jumps among different frequencies. Moreover, the current waveform is sinusoidal and can smoothly transition during frequency conversion. Furthermore, the transition time when the current amplitude rises from zero to a steady state is less than 2 ms during frequency conversion. By using the MSRIPS, the expected discrete variable frequency DRMP is generated, and the phenomenon of the TM being locked to the discrete variable frequency DRMP is observed on the J-TEXT tokamak. 相似文献
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多用户大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统能够有效提升系统和速率,但是导频资源有限情况下,用户数增加时,非正交导频引起的导频污染会严重降低系统容量。针对导频资源不足引起的干扰问题,提出了用户测向信息辅助的导频分配策略。先介绍了用户到达角估计算法,分析了角度域信道与用户间非正交导频干扰之间的关系;再提出了一种角度域用户分组方法,并对用户导频进行优化,从角度域和导频空间两个维度降低用户间导频干扰,提高了系统和速率;最后,将信道估计归一化均方误差作为性能指标进行比较,以验证算法的有效性。仿真结果表明,该算法在导频资源受限的多用户场景中,能够有效减小用户间导频污染,验证了所提算法的有效性和可靠性。 相似文献
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随着乳业、饮料、调味品等热门食品行业的快速发展,一批全国性品牌已经形成,并且占据相当的市场份额,垄断的态势已经初见端倪。但是,巨大的市场空间依然存在。资本的触角不会放过一丝机会。于是,无论是跨国公司还是国内资本巨头,都在探索一条驶向成功彼岸的航道。在众多的失败和离去之后,我们发现,兼并适当的中小企业不失为一条捷径。 相似文献
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1 概述新世纪已经来临。如何规划21世纪初有线电视的发展方向、目标及发展速度?这是我台领导和同志们极为关注的课题。众所周知,随着我国的改革开放,社会经济的发展和科学技术的进步,我国的有线电视事业得到了飞速发展。据统计,1998年底有线电视用户达7700万户,成为全国最大的用户接入网。1995年,全国有线电视联网规划制定之后,大多数省、区、直辖市加快了光纤骨干网的建设。到目前,光纤骨干网总长度达20万千米,广播电视网络已成为我国技术先进、规模最大的网络之一,从而确立了它在国家信息化结构框架中,“三网一平台”的基础网络地位。党… 相似文献
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