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81.
Axel Jahn 《International Journal of Satellite Communications and Networking》2001,19(2):169-203
Efficient resource management is mandatory to achieve maximum system capacity for next generation communications systems. Resource management deals with the available spectral band, time, power, and space for a transmission signal. It includes (i) the frequency planning, (ii) the selection of transmit power, and (iii) the assignment of the channels and access nodes to the users. The paper presents a generalized notation as well as graph algorithms for resource management problems. Impairment graphs can be used for frequency planning, whereas flow graphs are suitable for channel access problems. To evaluate the performance of the resource management, service criteria (such as blocking or the carrier to interference ratio C/I) or efficiency criteria (bandwidth requirements) can be derived from the graphs. The resource management techniques are applied to satellite networks with non‐geostationary orbits yielding time‐variant network topologies. As a simple example, the channel assignment and capacity optimization of the EuroSky Way system are shown. Furthermore, a comparison of fixed, dynamic and hybrid channel allocation schemes (FCA, DCA, HCA) for a typical MEO satellite scenario is given. Satellite diversity and its impact on bandwidth requirement and transmission quality is also examined. Finally, it is shown how spread spectrum systems can be investigated with the presented tools. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
82.
Fließkurven beschreiben das Formänderungsvermögen von Werkstoffen. Gleichzeitig liefern sie Informationen über die Wechselwirkung zwischen der Ver- und Entfestigung, wobei diese beiden Eigenschaften temperaturabhängig sind. Fließkurven wurden an Stählen aufgenommen, die sich im wesentlichen in ihrem Kohlenstoffgehalt unterscheiden. Die Bestimmung der Formänderungsfähigkeit erfolgte bei Temperaturen, die denen entsprechen, bei denen eine Austenitformhärtung vorgenommen wird. Die mathematische Beschreibung der Fließkurven läßt erkennen, daß zunächst mit steigender Umformtemperatur die Verfestigungsrate abnimmt. Der Kohlenstoffgehalt erhöht dagegen die Verfestigungsrate. Die dynamische Erholung wird mit wachsender Umformtemperatur beschleunigt, ebenso mit steigendem Kohlenstoffgehalt. 相似文献
83.
Axel Thallemer 《现代装饰》2009,(2):60-61
气膜建筑的外围结构采用了柔软的薄膜。想象一下未来建筑外围结构在这方面将如何发展?那真是其乐无穷!就目前来看,当今建筑的发展越来越强调提高能源、材料方面的利用效率。 相似文献
84.
Electron holography is a very powerful technique for mapping static electric and magnetic potentials down to atomic resolution. While electron holography is commonly considered synonymous with its off-axis variant in the high energy electron microscopy community, inline electron holography is widely applied in low-energy electron microscopy, where the realization of the off-axis setup is still an experimental challenge. This paper demonstrates that both inline and off-axis holography may be used to recover amplitude and phase shift of the very same object, in our example latex spheres of 90 and 200 nm in diameter, producing very similar results, provided the object does not charge under the electron beam. 相似文献
85.
Modular system-based engineering is the key to a quick, customized machine and plant configuration. This approach is seen as the best method to implement different functional requirements with a minimum amount of resources. The interdisciplinary configuration of control systems to automate machines has previously not been supported by engineering tools. This is partially due to the lack of standardized mechatronic information models. The machine manufacturer is required to create the necessary mechatronic information models uniquely for each control system independently. Thus, he does not comply with any modeling specifications. As a result, the mechatronic information models are not applicable for other control system architectures. The conventionally used mechatronic information models as well as the manufacturer-specific engineering tools define the control hardware components and their configurations. An abstraction of the logical and functional layers does not take place. Consequently, a mechatronic control architecture model is required. This architecture can serve as a modeling basis in modular system-based interdisciplinary engineering tools. Therefore, an approach to a manufacturer independent, mechatronic information model for control systems is the subject of this article. 相似文献
86.
The concern of this work is the influence of the thermal motion of the atoms on electron scattering simulations, used for quantitative interpretation of results in high-resolution electron microscopy. We distinguish between the influence of inelastic phonon excitation and the effect of a moving lattice on images generated by elastically scattered electrons. It is shown that, analog to aberrations, the impact of a moving lattice differs substantially with respect to different imaging conditions and cannot be described by the Debye–Waller damping applicable in XRD. We derive a new formalism, based on the frozen lattice and multislice approach, to incorporate the statistics of the thermal motion into elastic TEM imaging simulations, taking into account different imaging conditions. The averaging over different atom positions is generally performed within a density matrix framework, which can be linearized in the special case of off-axis electron holography. All findings are supported by explicit numerical simulations: molecular dynamics simulations are performed to get a realistic thermal motion and the electron scattering simulations are performed within the new multislice algorithm. 相似文献
87.
88.
Axel Kaiser 《今日印刷》2009,(1)
每台SPS STOP滚筒丝网印刷机都拥有一个独特的PEH(气压、电动、液压式)刮胶系统.该创新技术及精密结构一经问世,就成为诸多网印设备制造商竞相模仿的对象,但直到今天,仍没有一项其他技术可与之相媲美,也因此,SPS仍牢牢占据市场领导地位. 相似文献
89.
90.
Dr. Ralf Knackstedt Dipl.-Wirt.-Inform. Jens Pöppelbuß Dr. Axel Winkelmann 《WIRTSCHAFTSINFORMATIK》2008,50(3):235-247
The article presents results of an internet research on product-service systems. Web sites showing interesting practical examples and studies available online are presented to point out the practical relevance of innovative combinations of products and services. The multiplicity of research projects found on the internet shows that this phenomenon is also discussed intensively in research. These projects have been categorized by analyzing their web sites. Furthermore, the results of the internet research highlight a high diversity of terms for describing the concept of product-service systems. As a consequence, orientation in this subject area is hindered. 相似文献