Home About us Contact
|
Home About us Contact | ||
|
|
||
Many Degrees (many + degree)
Selected AbstractsDesign of a Multistage Optical Packet SwitchEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2000Carla Raffaelli Optical packet switching is considered as a means to achieve high speed networking in future optical multi-service networks, Optical switches of limited size are feasible with present-day photonic technology, so solutions for the design and implementation of large switches are proposed here. They are based on a multistage architecture built using small switching modules with output queuing, organised according to a Clos topology. Many degrees of freedom are available for switch design and they are exploited to achieve performance optimisation in relation to packet loss. Simulation and analytical tools are developed to evaluate switch architecture performance. Results and application examples are given to show the feasibility of the multistage architecture for optical networking. [source] Closed-form solution for seismic response of adjacent buildings with linear quadratic Gaussian controllersEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2002Y. L. Xu Abstract Closed-form solution for seismic response of adjacent buildings connected by hydraulic actuators with linear quadratic Gaussian (LQG) controllers is presented in this paper. The equations of motion of actively controlled adjacent buildings against earthquake are first established. The complex modal superposition method is then used to determine dynamic characteristics, including modal damping ratio, of actively controlled adjacent buildings. The closed-form solution for seismic response of the system is finally derived in terms of the complex dynamic characteristics, the pseudo-excitation method and the residue theorem. By using the closed-form solution, extensive parametric studies can be carried out for the system of many degrees of freedom. The beneficial parameters of LQG controllers for achieving the maximum response reduction of both buildings using reasonable control forces can be identified. The effectiveness of LQG controllers for this particular application is evaluated in this study. The results show that for the adjacent buildings of different dynamic properties, if the parameters of LQG controllers are selected appropriately, the modal damping ratios of the system can be significantly increased and the seismic responses of both buildings can be considerably reduced. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the Design of High-Efficiency Thermoelectric Clathrates through a Systematic Cross-Substitution of Framework ElementsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Xun Shi Abstract Type I clathrates have recently been identified as prospective thermoelectric materials for power generation purposes due to their very low lattice thermal conductivity values. The maximum thermoelectric figure of merit of almost all type I clathrates is, however, less than 1 and occurs at, or above, 1000,K, making them unfavorable especially for intermediate temperature applications. In this report, the Zintl,Klemm rule is demonstrated to be valid for Ni, Cu, and Zn transition metal substitution in the framework of type I clathrates and offers many degrees of freedom for material modification, design, and optimization. The cross-substitution of framework elements introduces ionized impurities and lattice defects into these materials, which optimize the scattering of charge carriers by the substitution-induced ionized impurities and the scattering of heat-carrying lattice phonons by point defects, respectively, leading to an enhanced power factor, reduced lattice thermal conductivity, and therefore improved thermoelectric figure of merit. Most importantly, the bandgap of these materials can be tuned between 0.1 and 0.5,eV by adjusting the cross-substitution ratio of framework elements, making it possible to design clathrates with excellent thermoelectric properties between 500 and 1000,K. [source] Empirical orthogonal functions and related techniques in atmospheric science: A reviewINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2007A. Hannachi Abstract Climate and weather constitute a typical example where high dimensional and complex phenomena meet. The atmospheric system is the result of highly complex interactions between many degrees of freedom or modes. In order to gain insight in understanding the dynamical/physical behaviour involved it is useful to attempt to understand their interactions in terms of a much smaller number of prominent modes of variability. This has led to the development by atmospheric researchers of methods that give a space display and a time display of large space-time atmospheric data. Empirical orthogonal functions (EOFs) were first used in meteorology in the late 1940s. The method, which decomposes a space-time field into spatial patterns and associated time indices, contributed much in advancing our knowledge of the atmosphere. However, since the atmosphere contains all sorts of features, e.g. stationary and propagating, EOFs are unable to provide a full picture. For example, EOFs tend, in general, to be difficult to interpret because of their geometric properties, such as their global feature, and their orthogonality in space and time. To obtain more localised features, modifications, e.g. rotated EOFs (REOFs), have been introduced. At the same time, because these methods cannot deal with propagating features, since they only use spatial correlation of the field, it was necessary to use both spatial and time information in order to identify such features. Extended and complex EOFs were introduced to serve that purpose. Because of the importance of EOFs and closely related methods in atmospheric science, and because the existing reviews of the subject are slightly out of date, there seems to be a need to update our knowledge by including new developments that could not be presented in previous reviews. This review proposes to achieve precisely this goal. The basic theory of the main types of EOFs is reviewed, and a wide range of applications using various data sets are also provided. Copyright © 2007 Royal Meteorological Society [source] Empirical Challenges and Concept Formation in the History of HydrodynamicsCENTAURUS, Issue 3 2008Olivier Darrigol Abstract Although the fundamental equations of hydrodynamics were known at an early stage of its history, this theory long remained irrelevant to most of the practical problems of flow. The advent of a more efficient fluid mechanics in the early twentieth century depended on conceptual schemes that could not be read directly from the basic equations. Attention to concrete problems of flow, rather than purely mathematical deduction or purely intuitive guessing, permitted the gradual introduction of relevant substructures and their ultimate combination in powerful approximation schemes. This history is in part singular, owing to the extreme difficulty of dealing with non-linear systems with infinitely many degrees of freedom. But it is also typical as an illustration of the futility of reducing a physico-mathematical theory to its fundamental equations. Any advanced theory of physics must include an evolving modular structure that plays an essential role in melding the formal with the empirical. [source] | ||||||||||