确定QR系统的自激频率

准方波开关电源具有很多优点，例如软EMI特性，以及在很大的输出负载范围内保持稳定的效率。然而，由其特性决定，准谐振(QR)电源的开关频率在很大程度上受到输入/输出工作状态的影响。本文详细介绍了如何计算某一给定工作点上的开关频率，为设计人员计算其系统提供必要的知 识。     

损耗模型提供更实际的平均仿真

标准的平均模型不包含各种损耗,这些损耗不仅降低转换器效率,而且也影响小信号交流响应。当得到一个与给定拓扑结构相对应的方程(例如降压BUCK,升压BOOST等)时,通常在电路图中给人的是理想的元件,并且在计算中忽略各种损耗。这样做能够简化分析,同时也会改变直流工作点和交流响应。图1a和1b显示了一个BUCK转换器,包括如下损耗:a)电感的导线电阻、Rlf,b)功率开关的RDS(ON),Ron,c)二极管的正向压降、Vf,以及它的动态电阻:     

An Ogden-like iteration lemma for rational power series

Summary An Ogden-like iteration lemma for languages that are support of rational power series is proved; it is a generalization of Jacob's iteration lemma. The new bound we obtain is much smaller than the one of Jacob and does no more depend on the cardinality of the alphabet. The proof consists in studying how pseudo-regular matrices appear as subproducts of long products of square matrices.     

Integration and enhancement of low-level signals from air-pollution monitoring sensors

In this paper, we have demonstrated how signal enhancement techniques would be advantageous in the low-level analysis of air pollutants. We have further shown what type of signal-to-noise gain may be expected from an off-the-shelf, inexpensive run-of-the-mill mercury monitor. As long as an evoked response time constant is introduced into the measuring system, noise of a random nature may be reduced to such an extent that trace signals, buried deep in the electrical background, may be reliably measured. If we couple this type of analysis to a multi-parameter mercury analyzer, contributing factors may be evaluated⁸. This will result in a more efficient system application.We have also reported a manner in which evoked response time is related to instrument onset time. However, there are other methods for obtaining an evoked response. Of note is the use of wavelength in the enhancement of spectrophotometric signals.⁹ In additional work now being carried out in our laboratory, there are indications that it is possible to relate this type of processing to SO₂ analyzing systems using conductometry.     

Factors affecting the concentrations of cadmium, zinc, copper and lead in the sediments of the Vesdre River

The main factors influencing Cd, Zn, Cu and Pb concentrations in the sediments of the highly polluted Vesdre River (eastern Belgium) have been investigated. Only negative correlations were demonstrated between the clay content and heavy metals. The composition of the clay minerals could partially explain this paradox. However, the pretreatment of the minerals might influence the geochemical data obtained from analysis. Iron-hydroxides and phosphates seem to be the main sinks for Pb, Cd and Zn whereas organic components might play a less important role.