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排序方式: 共有83条查询结果,搜索用时 315 毫秒
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Resilience: An Evolutionary Approach to Spatial Economic Systems 总被引:5,自引:0,他引:5
The concept of resilience has received a great deal of attention in the past decades. Starting from the first fundamental definitions offered by Holling, Pimms and Perrings in an economic-ecological modeling context, the present paper explores the evolution of the resilience concept—as well as related different measures—in both a continuous and discrete time setting.From this perspective, the paper explores the relevance of the resilience concept in socio-economic systems, by focussing the attention on the relationships among resilience, transition dynamics and lock-in effects, in particular in the light of the dynamics of technological innovation diffusion and adaptive behaviour of firms. In this framework we will describe an empirical application, in which the resilience and dynamics of the West-German labour market will be investigated. This empirical illustration is offered by making use of an algorithm constructed for detecting Lyapunov exponents, so as to classify the resilience among employment sectors in our case study. 相似文献
3.
Roberto Patuelli Aura Reggiani Sean P. Gorman Peter Nijkamp Franz-Josef Bade 《Networks and Spatial Economics》2007,7(4):315-331
The analysis of complex networks has recently received considerable attention. The work by Albert and Barabási presented a
research challenge to network analysis, that is, growth of the network. The present paper offers a network analysis of the
spatial commuting network in Germany. First, we study the spatial evolution of the commuting network over time. Secondly,
we compare two spatial interaction model (SIM) specifications, in order to replicate the actual network structure. Our findings
suggest that the commuting network appeared to become more dense and clustered, while the SIMs seem to require more sophisticated
specifications, in order to replicate such a connectivity structure. 相似文献
4.
Information, communication and transport networks have always been in a state of flux, while they also influence each other. Extensive research efforts have been made to investigate the dynamics in the structure and use of networks, for example, by means of network geometries, Small-World effects and Scale-Free phenomena. We will illustrate these new developments on the basis of airline network evolution. Using Lufthansa's networks as an example, this paper aims to show the empirical relevance of various network indicators – such as connectivity and concentration – for understanding changing patterns in airline network configurations. After an extensive discussion of various statistical results, a decision-aid method, viz. multi-criteria analysis, is used to investigate the robustness of our findings. The results highlight the actual strategic choices made by Lufthansa for its own network, as well in combination with its partners in Star Alliance. 相似文献
5.
Aura Angelica Popa Eugenia Comăniţă Luminiţ Cianga C. I. Simionescu 《Polymer-Plastics Technology and Engineering》2013,52(9-10):871-884
The paper discusses the synthesis of the N,N,′-azobis(formamidopropionic) acid (AFP), along with some characteristics determined from NMR spectrum, differential thermal analysis, and DSC. The behavior of AFP acid—as well as of its analogue, N,N′-azobis(formamidoacetic) acid (AFA)—has been studied in the reaction with aromatic diamine and with bis(glycol)terephthalate, leading to azopolymers of the azopolyamide, or azopolyester, type. On employing N,N′-bis(β-hydroxyethyl) azobis-formamide (HEAF) as the azo bifunctional compound in the reaction with diphenylmethane diisocyanate, a polyurethane possessing azo groups was obtained. The structure of the azopolymers has been spectroscopically confirmed. 相似文献
6.
Tinca Buruiana Violeta Melinte Emil C Buruiana Aura Mihai 《Polymer International》2009,58(10):1181-1189
BACKGROUND: The development of polymeric nanocomposites incorporating intercalated or exfoliated layered silicate clays into the organic matrix has been substantially motivated by the significant improvements induced by the presence of the inorganic component. Moreover, understanding and controlling the dispersion of inorganic layers into segmented polyurethane matrices by means of ionic interactions, and exploiting these interactions to enhance physicomechanical behaviour, could be of great interest in the field of polymer nanocomposites. RESULTS: New cationic polyurethane elastomers were prepared starting from poly(butylene adipate)diol (Mn = 1000 g mol?1), 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol and N‐methyldiethanolamine or N,N′‐β‐hydroxyethylpiperazine, used as potential quaternizable moieties. The characterization of the polymers was achieved using specific analyses employed for the macromolecular samples (Fourier transform infrared and 1H NMR spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography). An extension of our research on polymers reinforced with organically modified montmorillonite (OM‐MMT) in order to prepare hybrid composites with improved properties was performed and the resulting materials were characterized using TGA, X‐ray diffraction, atomic force microscopy and scanning electron microscopy. Also, the mechanical properties of the cationic polyurethane/OM‐MMT composites were investigated in comparison with the pristine ionic/non‐ionic polymers and their composites containing non‐ionic polymer blended with OM‐MMT or ionic polymer and unmodified MMT. CONCLUSION: The insertion of the organically modified clay into the polymeric matrix gave an improvement of the mechanical properties of the polyurethane composites, especially the tensile strength and stiffness of the hybrid materials. Copyright © 2009 Society of Chemical Industry 相似文献
7.
In this paper, we present a collision free MAC protocol for wireless networks with smart antennas that provides proportional
service differentiation to various classes of traffic based on their respective bandwidth demand. The proposed protocol works
for diverse physical parameters such as number of interfaces at each node, number of communication frequencies, and antenna
beamwidth. To the best of our knowledge, this is the first work that provides link layer differentiated services for wireless
networks with smart antennas and explores the influence of the physical parameters and network topology on the performance
of the MAC layer.
Ashish Deopura received his B.Tech degree in Electrical Engineering from the Indian Institute of Technology Delhi, India, in 2003, and he
received his M.S. degree in Computer Systems Engineering from the University of Massachusetts Amherst, in 2005. He currently
works as a Modeling Engineer for OPNET Technologies located in Bethesda, MD
Professor Aura Ganz is the director of the Multimedia Networking Laboratory at the University of Massachusetts at Amherst. She has authored more
than 170 journal and conference papers in the areas of multimedia wireless networks, ubiquitous computing, telemedicine, and
security. She is a co-author of the book: “Multimedia Wireless Networks”, Prentice Hall, 2003. Some of her recent assignments
include: general co-chair of the IEEE UWBNETS workshop, general co-chair of the IEEE BROADMED workshop, general co-chair of
the Massachusetts 3rd Annual R&D Conference, keynote speaker at the NSF sponsored workshop in Mobile Computing, and invited
speaker at Personal and Local Wireless Network Solutions conference, and Motorola’s Wireless Communications Futures Forum,
Wireless Local Area Networks Conference. She has a PhD, MSc and BSc in Computer Science from the Technion in Israel. More
details can be found at: dvd1.ecs.umass.edu/wireless. 相似文献
8.
Cesar D. Fermin Ellis Diaz Aura Maldonado Dale Martin Zuzana Hruska 《Microscopy research and technique》1990,16(1):85-86
Kodak black and while film emulsions 4489, 4162, 2415, TMAX-100, TMAX-400, MPD-4 and RPC-651 can be developed in less than 10 minutes on a film processor, quickly printed on resin coated paper and dried with auto-processor and dryer. Adjustments to the ASA (ISO) to compensate for increased contrast with auto-processing are described. 相似文献
9.
10.
Mobile IPv6 is a network-layer mobility protocol for the IPv6 Internet. The protocol includes several security mechanisms, such as the return-routability tests for the mobile’s home address and care-of addresses. This paper explains the threat model and design principles that motivated the Mobile IPv6 security features. While many of the ideas have become parts of the standard toolkit for designing Internet mobility protocols, some details of the reasoning have not been previously documented. 相似文献