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Extreme climate events over northern China during the last 50 years 被引量:19
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作者 hanhui GONGDaoyi 《Journal of Geographical Sciences》 SCIE CSCD 2003年第4期469-479,共11页
Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season f... Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season for precipitation is May-September, i.e., the rainy season. For temperature is the hottest three months, i.e., June through August. Heavy rain events, defined as those with daily precipitation equal to or larger than 50 mm, show no significant secular trend. A jump-like change, however, is found occurring in about 1980. For the period 1980-1993, the frequency of heavy rain events is significantly lower than the previous periods. Simultaneously, the occurring time of heavy rains expanded, commencing about one month early and ending one month later. Long dry spells are defined as those with longer than 10 days without rainfall. The frequency of long dry spells displays a significant (at the 99% confidence level) trend at the value of +8.3% /10a. That may be one of the major causes of the frequent droughts emerging over northern China during the last decades. Extremely hot and low temperature events are defined as the uppermost 10% daily temperatures and the lowest 10% daily temperatures, respectively. There is a weak and non-significant upward trend in frequency of extremely high temperatures from the 1950s to the mid-1990s. But the number of hot events increases as much as twice since 1997. That coincides well with the sudden rise in mean summer temperature for the same period. Contrary to that, the frequency of low temperature events have been decreasing steadily since the 1950s, with a significant linear trend of-15%/10a. 展开更多
关键词 agriculture-pasture transitional zone climate extremes TRENDS
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Yttrium aluminum garnet (Y_3A_(l5)O_(12)) nanopowders synthesized by the chemical method 被引量:6
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作者 ZHANGHuasha SUChunhui +2 位作者 hanhui HOUZhaoxia WANGGuangzhao 《Rare Metals》 SCIE EI CAS CSCD 2005年第2期166-169,184,共5页
The homogeneously dispersed, less agglomerated YAG nanopowders are synthesized by the citrate-gel method followed by low-temperature self-propagating combustion reaction, using Y2O3, Al(NO3)3?9H2O and citric acid as s... The homogeneously dispersed, less agglomerated YAG nanopowders are synthesized by the citrate-gel method followed by low-temperature self-propagating combustion reaction, using Y2O3, Al(NO3)3?9H2O and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and the hard ag-glomerates brought by the chemical precipitation method. The powders are characterized by TG-DTA, XRD, FT-IR and TEM respectively. The experiments show that the forming temperature of YAG crystal phase is 850°C and the pseudo-YAG crystalline appears during the calcination and transforms to pure YAG at 1050°C. The powders with sizes less than 50 nm are observed by TEM micrography, which is consistent with the result calculated by Scherrer's formula. The powders consist of single grains. 展开更多
关键词 inorganic materials yttrium aluminum garnet nanopowders citrate-gel method low temperature self-propagating combustion reaction
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风电机塔架连接螺栓超声波探伤系统发射技术 被引量:1
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作者 张华鹏 韩辉 +2 位作者 马野 张天添 王曦 《一重技术》 2021年第3期58-61,共4页
风力发电机塔架的连接螺栓是风电机组的重要连接零件,为防止发生灾难性事故,定期对其进行检测是必要的。超声检测(UT)是一种无损检测方法,具有非破坏性、全面性、全程性的特点,。超声波探伤系统包括发射、接收、AD采集、STM32主控等模块... 风力发电机塔架的连接螺栓是风电机组的重要连接零件,为防止发生灾难性事故,定期对其进行检测是必要的。超声检测(UT)是一种无损检测方法,具有非破坏性、全面性、全程性的特点,。超声波探伤系统包括发射、接收、AD采集、STM32主控等模块,发射模块是探伤系统中的关键部分,对风电机塔架连接螺栓超声波探伤系统发射技术进行研究具有重要意义。 展开更多
关键词 风力发电机 接螺栓 超声波探伤系统 发射模块
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