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71.
72.
J.R. Barber 《Wear》1975,35(2):283-289
An approximate solution is given for the thermoelastic contact problem in which a rotating sphere is loaded against a half-space. Frictional heating causes a redistribution of contact pressure away from the axis of rotation. The contact radius falls with increasing rotational speed, whilst for a given speed there is a limiting value which the radius cannot exceed, no matter how high the load. 相似文献
73.
André Rodrigues Tiago Camilo Jorge Sá Silva Fernando Boavida 《Journal of Network and Systems Management》2013,21(3):408-452
The availability of tools to diagnose Wireless Sensor Network (WSN) failures is a key success factor for this type of networks as already demonstrated by several long-running deployments. By nature, WSNs are resource-constrained, fragile, complex to analyse, and failure-prone. Naturally, with the growing number of installations, it is becoming fundamental to efficiently diagnose failures as soon as possible, in order to deal with the underlying causes. In accordance with this, from 2005 onwards, the offer of diagnostic tools has been increasing, as the other base technologies (e.g. networking, operating system, localisation, synchronisation) become reasonably stable. The purpose of this survey is to provide an overview of existing post-deployment WSN diagnostic tools, by briefly presenting their functionality, architecture and constraints, in order to enable a basic understating of each tool. The survey also includes a multi-dimensional comparative analysis of the various tools, based on a proposed classification scheme and evaluation criteria, as well as an identification of the main open research issues. Although the number of diagnostic tools is high and considerable work has been done in this area, we conclude that there are still several challenges concerning post-deployment WSN diagnostic tools, regarding scope, flexibility, generality, mobility and security. Moreover, there is a need for mature, native diagnostic-oriented functionality in WSN platforms and operating systems. 相似文献
74.
Connectivism, which has been argued to be a new learning theory, has emerged in the field of online learning during the last decade. On the World Wide Web at least, connectivism promises to establish learning spaces similar to those that Ivan Illich imagined in ‘Deschooling Society’, through so‐called massive online open courses (MOOCs). In this paper, we critically examine the theoretical postulates of connectivism and identify three important psychological and epistemological problems, namely the lack of a solution to the learning paradox, the underconceptualization of interaction and the inability to explain concept development. Some of the theoretical deficiencies in question may explain certain learning problems experienced by participants in MOOCs. The paper concludes that, although MOOCs are a worthwhile experience and ought to be continued, connectivism as a learning theory has significant theoretical problems and should be profoundly revised if it is to explain and foster learning in such environments. 相似文献
75.
Ana Dolores Santiago de Freitas Everardo Valadares Sá Barretto de Sampaio Bárbara Laine Ribeiro da Silva Jarcilene Silva de Almeida Cortez R?mulo Sim?es Cezar Menezes 《Nutrient Cycling in Agroecosystems》2012,94(2-3):181-192
Although biological nitrogen fixation (BNF) is considered the main input of N in mature and regenerating native tropical vegetation, it has seldom been quantified. Biomass and N accumulation and fixation were determined for spontaneously occurring herbaceous species in caatinga areas in four regeneration stages (2, 17, 39 and >50?years after abandonment from agricultural use). BNF was estimated using the 15N natural-abundance method. The 2-year regeneration area had the highest total herb (6,355?kg?ha?1) and legume (262?kg?ha?1) biomass production, N stocks (82?kg?ha?1) and fixed N (5.0?kg?ha?1). N2-fixing legumes (nine species in the sampled area) contributed over 97?% of legume biomass in all areas. Macroptilium gracile added the largest amount of N (3.9?kg?ha?1 in the 2-year regeneration area) because of its large biomass production (205?kg?ha?1), although it was not the species with the highest proportion of fixed N (76?%). All of the N2-fixing species obtained large proportions of their N from symbiosis, most of them more than 50?%.However, the amounts of fixed N per unit area were relatively low (0.22?C5.00?kg?ha?1) because the biomass of N2-fixing species was always less than 5?% of the total herb biomass. 相似文献
76.
I. Tortajada Montañana J. Montalvá Colomer M. Aguilar Rico 《Color research and application》2012,37(5):336-342
The aim of this article is to study the influence of an achromatic Ronchi grating (white and black stripes) used as a background, over a periodic chromatic test (red or green). Depending on the grating frequency, two parameters were used to study this influence: modulation ratio and grating contrast. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2012 相似文献
77.
Marko J. Tadjer Michael A. Mastro José M. Rojo Alberto Boscá Mojena Fernando Calle Francis J. Kub Charles R. Eddy Jr. 《Journal of Electronic Materials》2014,43(4):1188-1193
Manganese dioxide films were grown on large area flexible carbon aerogel substrates. Characterization by x-ray diffraction confirmed α-MnO2 growth. Three types of films were compared as a function of hexamethylenetetramine (HMTA) concentration during growth. The highest concentration of HM TA produced MnO2 flower-like films, as observed by scanning electron microscopy, whose thickness and surface coverage lead to both a higher specific capacitance and higher series resistance. Specific capacitance was measured to be 64 F/g using a galvanostatic setup, compared to the 47 F/g-specific capacitance of the carbon aerogel substrate. Such supercapacitor devices can be fabricated on large area sheets of carbon aerogel to achieve high total capacitance. 相似文献
78.
Antler bone displays considerable toughness through the use of a complex nanofibrous structure of mineralized collagen fibrils (MCFs) bound together by non-collagenous proteins (NCPs). While the NCP regions represent a small volume fraction relative to the MCFs, significant surface area is evolved upon failure of the nanointerfaces formed at NCP–collagen fibril boundaries. The mechanical properties of nanointerfaces between the MCFs are investigated directly in this work using an in situ atomic force microscopy technique to pull out individual fibrils from the NCP. Results show that the NCP–fibril interfaces in antler bone are weak, which highlights the propensity for interface failure at the nanoscale in antler bone and extensive fibril pullout observed at antler fracture surfaces. The adhesion between fibrils and NCP is additionally suggested as being rate dependent, with increasing interfacial strength and fracture energy observed when pullout velocity decreases. 相似文献
79.
80.
Daisuke Yamamoto Takeshi Ozaki Carlos A. R. Sá de Melo Ippei Danshita 《Journal of Low Temperature Physics》2014,175(1-2):258-264
We study a first-order phase transition between superfluid and Mott insulator phases in binary Bose mixtures loaded into a hypercubic optical lattice. The system is described by a two-component Bose-Hubbard model. Considering the difference between the two kinds of bosons in the intra-component interaction strength, we discuss the metastability of the system and the hysteresis associated with the first-order superfluid-Mott insulator transition. It is found that the sweeping of hopping amplitude induces a conventional hysteresis-loop behavior. We also find an anomalous hysteresis behavior when the chemical potential is varied. In the anomalous hysteresis, the phase transition occurs in a unidirectional way and a hysteresis loop does not form. 相似文献