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61.
Famurewa Stephen M. Stenström Christer Asplund Matthias Galar Diego Kumar Uday 《铁道工程科学(英文)》2014,22(4):214-224
Railway Engineering Science - The assessment and analysis of railway infrastructure capacity is an essential task in railway infrastructure management carried out to meet the required quality and... 相似文献
62.
P. Johansson 《Thin solid films》2006,515(2):477-480
Bismuth iron garnet (Bi3Fe5O12, BIG) epitaxial thin films were grown on single crystal (Gd3Ga5O12, GGG) (111) and (001) substrates by rf-magnetron sputtering technique. Processing parameters have been optimized to obtain high deposition rate (2.74 μm/h) and the surface rms roughness less than 10 nm. X-ray diffraction reveals films epitaxial quality: exclusive (111) or (001) orientation with narrow rocking curves and strong in-plane texture. Films possess low optical loss and magneto-optical Faraday rotation (FR) as high as 5 deg/μm at 677 nm wavelength. Comparative analysis of films grown on (111) and (001) substrates clearly shows significant superiority of BIG/GGG(001) film. For this film, the coercive field ∼100 Oe appears to be 2.5 times lower while the optical transmission to be 10% higher than that for BIG/GGG(111) film. Enhanced magneto-optical performance of BIG/GGG(001) films relies upon better accommodation of the film-to-substrate mismatch strain through the tetragonal BIG lattice distortions compared to the rhombohedral one in BIG/GGG(111) films. 相似文献
63.
Lygeros J. Johansson K.H. Simic S.N. Jun Zhang Sastry S.S. 《Automatic Control, IEEE Transactions on》2003,48(1):2-17
Hybrid automata provide a language for modeling and analyzing digital and analogue computations in real-time systems. Hybrid automata are studied here from a dynamical systems perspective. Necessary and sufficient conditions for existence and uniqueness of solutions are derived and a class of hybrid automata whose solutions depend continuously on the initial state is characterized. The results on existence, uniqueness, and continuity serve as a starting point for stability analysis. Lyapunov's theorem on stability via linearization and LaSalle's invariance principle are generalized to hybrid automata. 相似文献
64.
Lin Xiao Johansson M. Hindi H. Boyd S. Goldsmith A. 《Automatic Control, IEEE Transactions on》2003,48(1):148-153
We consider a linear control system in which several signals are transmitted over communication channels with bit rate limitations. With the coding and medium access schemes of the communication system fixed, the achievable bit rates are determined by the allocation of communications resources such as transmit powers and bandwidths, to different communication channels. We model the effect of bit rate limited communication channels by uniform quantization and the quantization errors are modeled by additive white noises whose variances depend on the achievable bit rates. We optimize the stationary performance of the linear system by jointly allocating resources in the communication system and tuning parameters of the controller. 相似文献
65.
Computationally tractable planning problems reported in the literature so far have almost exclusively been defined by syntactical restrictions. To better exploit the inherent structure in problems, it is probably necessary to study also structural restrictions on the underlying state-transition graph. The exponential size of this graph, though, makes such restrictions costly to test. Hence, we propose an intermediate approach, using a state-variable model for planning and defining restrictions on the separate state-transition graphs for each state variable. We identify such restrictions which can tractably be tested and we present a planning algorithm which is correct and runs in polynomial time under these restrictions. The algorithm has been implemented and it outperforms Graphplan on a number of test instances. In addition, we present an exhaustive map of the complexity results for planning under all combinations of four previously studied syntactical restrictions and our five new structural restrictions. This complexity map considers both the optimal and non-optimal plan generation problem. 相似文献
66.
Peter Jonsson Christer Bäckström 《Annals of Mathematics and Artificial Intelligence》1998,22(3-4):281-296
We present a class, 3S, of planning instances such that the plan existence problem is tractable while plan generation is provably
intractable for instances of this class. The class is defined by simple structural restrictions, all of them testable in polynomial‐time.
Furthermore, we show that plan generation can be carried out in time bounded by a polynomial in the size of the input and
the size of the generated solution. For this class, we propose a provably sound and complete incremental planner, i.e., a
planner that can usually output an executable prefix of the final plan before it has generated the whole plan.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
67.
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69.
This study investigates associations between perceived micro-level urban design qualities, the affective experience of walking, and intention to walk specific routes in the neighbourhood. A total of 106 residents assessed on-site three routes planned for walking in semi-central neighbourhoods. In the prediction of the residents’ intention to choose to walk and intention to avoid walking the route, perceived urban design qualities were mediated by the affective experience of valence of the walk. The perceived complexity and aesthetic quality, upkeep and order, and the presence of well-maintained greenery, were identified as important. These perceived urban design qualities and affective experiences varied between the three routes, but also within the routes. It is proposed that understanding of site-specific affective experience of walking environments could serve as guidance for urban design practices. 相似文献
70.
Wireless sensor–actuator networks offer flexibility for control design. One novel element which may arise in networks with multiple nodes is that the role of some nodes does not need to be fixed. In particular, there is no need to pre-allocate which nodes assume controller functions and which ones merely relay data. We present a flexible architecture for networked control using multiple nodes connected in series over analog erasure channels without acknowledgments. The control architecture proposed adapts to changes in network conditions, by allowing the role played by individual nodes to depend upon transmission outcomes. We adopt stochastic models for transmission outcomes and characterize the distribution of controller location and the covariance of system states. Simulation results illustrate that the proposed architecture has the potential to give better performance than limiting control calculations to be carried out at a fixed node. 相似文献