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71.
Critical stress and load conditions for pitting calculations of involute spur and helical gear teeth 总被引:1,自引:0,他引:1
Calculation methods of spur and helical gear drives for preliminary designs or standardization purposes available in technical literature, use the Hertz equation to evaluate the contact stress, assuming the load to be uniformly distributed along the line of contact. However, this model presents some discrepancies with experimental results because the changing rigidity of the pair of teeth along the path of contact produces a non-uniform load distribution, which implies that some load distribution factors are required to compute the contact stress. In this paper, a non-uniform model of load distribution along the line of contact, recently developed, obtained from the minimum elastic potential criterion, has been used. This model combined with the Hertz equation yields more accurate values of the contact stress. As the load per unit of length at any point of the line of contact and any position of the meshing cycle has been described by a very simple analytic equation, a complete study of the location and value of the critical contact stress has been carried out. From this study, a recommendation for the calculation of the pitting load capacity of spur and helical gears is proposed. 相似文献
72.
We report image blurring and energy broadening effects in energy-filtered XPEEM when illuminating the specimen with soft X-rays at high flux densities. With a flux of 2×1013 photons/s, the lateral resolution in XPEEM imaging with either core level or secondary electrons is degraded to more than 50 nm. Fermi level broadening up to several hundred meV and spectral shift to higher kinetic energies are also systematically observed. Simple considerations suggest that these artifacts result from Boersch and Loeffler effects, and that the electron-electron interactions are strongest in the initial part of the microscope optical path. Implications for aberration corrected instruments are discussed. 相似文献
73.
Jesús Gallardo Crescencio Bravo Miguel A. Redondo Juan de Lara 《Journal of Visual Languages and Computing》2013,24(1):10-23
Over the last two decades, Collaborative Systems have become increasingly popular thanks to the many advances made in networks, communications and software tools. Within this field, Collaborative Modeling Systems apply the collaborative paradigm to the construction of (often visual) models, where users build diagrams from building blocks and the relationships between them. In these kinds of applications, the work is usually arranged into sessions, with the definition of some kind of time organization between those sessions. This organization is known as a collaboration protocol. Unfortunately, it is not usually easy to define these protocols, and many applications do not allow users to make any use of them.In an effort to overcome these difficulties, in this paper we propose a visual language for defining collaboration protocols for these systems. As such, in our language, sessions, artifacts and the transformations between them can be specified visually, and different coordination relationships (such as fork and join) can be defined. The visual language is included in a development method for collaborative systems that take advantage of the Eclipse platform in order to develop model-driven graphical editors that are enhanced with collaboration capabilities. 相似文献
74.
Álvaro Rubio-Largo Miguel A. Vega-Rodríguez Juan A. Gómez-Pulido Juan M. Sánchez-Pérez 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2013,17(2):199-211
Nowadays, the most promising technology for designing optical networks is the wavelength division multiplexing. This technique divides the huge bandwidth of an optical fiber link into different wavelengths, providing different available channels per link. However, a problem comes up when it is necessary to interconnect a set of traffic demands. This problem is known as routing and wavelength assignment problem, and due to its complexity (NP-hard problem) it is very suitable for being solved using evolutionary computation. The selected heuristics is the artificial bee colony algorithm, an heuristics based on the behavior of honeybee foraging for nectar. Therefore, we have applied multiobjective optimization to solve the static routing and wavelength assignment problem, and adapted this algorithm to the multiobjective context. New results have been obtained that significantly improve those published in previous researches. 相似文献
75.
76.
Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst
case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with
a very large bound.
In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented. TLSF is designed and implemented to accommodate
real-time constraints. The proposed allocator exhibits time-bounded behaviour, O(1), and maintains a very good execution time. This paper describes in detail the data structures and functions provided by
TLSF. We also compare TLSF with a representative set of allocators regarding their temporal cost and fragmentation.
Although the paper is mainly focused on timing analysis, a brief study and comparative analysis of fragmentation incurred
by the allocators has been also included in order to provide a global view of the behaviour of the allocators.
The temporal and spatial results showed that TLSF is also a fast allocator and produces a fragmentation close to that caused
by the best existing allocators.
相似文献
Alfons Crespo (Corresponding author)Email: |
77.
So far, most of the applications of robotic technology to education have mainly focused on supporting the teaching of subjects
that are closely related to the Robotics field, such as robot programming, robot construction, or mechatronics. Moreover,
most of the applications have used the robot as an end or a passive tool of the learning activity, where the robot has been
constructed or programmed. In this paper, we present a novel application of robotic technologies to education, where we use
the real world situatedness of a robot to teach non-robotic related subjects, such as math and physics. Furthermore, we also
provide the robot with a suitable degree of autonomy to actively guide and mediate in the development of the educational activity.
We present our approach as an educational framework based on a collaborative and constructivist learning environment, where
the robot is able to act as an interaction mediator capable of managing the interactions occurring among the working students.
We illustrate the use of this framework by a 4-step methodology that is used to implement two educational activities. These
activities were tested at local schools with encouraging results. Accordingly, the main contributions of this work are: i) A
novel use of a mobile robot to illustrate and teach relevant concepts and properties of the real world; ii) A novel use of
robots as mediators that autonomously guide an educational activity using a collaborative and constructivist learning approach;
iii) The implementation and testing of these ideas in a real scenario, working with students at local schools.
相似文献
Alvaro Soto (Corresponding author)Email: |
78.
Andrew Grayland Chris Jefferson Ian Miguel Colva M. Roney-Dougal 《Annals of Mathematics and Artificial Intelligence》2009,57(1):75-102
Variable symmetries in a constraint satisfaction problem can be broken by adding lexicographic ordering constraints. Existing general methods of generating such sets of ordering constraints can require a huge number of constraints. This adds an unacceptable overhead to the solving process. Methods exist by which this large set of ordering constraints can be reduced to a much smaller set automatically, but their application is also prohibitively costly. In contrast, this paper takes a bottom-up approach. It examines some commonly-occurring families of groups and derives a minimal set of ordering constraints sufficient to break the symmetry each group describes. These minimal sets are then used as building blocks to generate minimal sets of ordering constraints for groups constructed via direct and imprimitive wreath products. Experimental results confirm the value of minimal sets of ordering constraints, which can now be generated much more cheaply than with previous methods. 相似文献
79.
J García Marco A Miguel Sosa J García Conde A Miguel García C Arbona V Escrig I Benet I Navarro A Ruiz F Carbonell 《Canadian Metallurgical Quarterly》1994,39(4):241-244
PURPOSE: To assess the "in vivo" effect of 13-cis-retinoic acid and low dose Ara-C in MDS as well as to establish "in vitro" advantage of retinoid dose-related growth pattern on bone marrow cultures as defined by culture timing and CFU-GM proliferative response. PATIENTS AND METHODS: We evaluated 28 patients diagnosed of MDS according to FAB classification, of whom 4 cases had RA, 8 cases SRA, 14 cases RAEB and 2 cases RAEB-T. Patients who had RA and SRA were treated with oral 13-cis-retinoic acid at doses of 20-40 mg daily for 4 months and those cases with RAEB and RAEB-T had subcutaneous Ara-C at doses of 3 mg/m2 twice a day for 21 days. The "in vivo" and "in vitro" effect of retinoic acid on the haemopoietic differentiation was evaluated by the growth CFU-GM in semisolid cell culture methods. RESULTS: Increasing in vitro concentrations of 13-cis retinoic acid did not enhance the growth of myelodysplastic progenitors. Nevertheless, our study did not find any beneficial therapeutic effect of retinoic compounds in MDS patients. In this study, low-dose Ara-C (3 mg/m2) showed similar effects when compared with higher doses reported by others. Furthermore, in terms of CFU-GM proliferation the concentration of colonies before and after treatment were fairly similar in all but two patients. CONCLUSIONS: The results drawn from our study demonstrated that there is no beneficial advantage of 13-cis-retinoic acid as a differentiation inducing agent on myelodysplastic patients. In contrast, lower doses of Ara-C showed similar effects on haemopoiesis of MDS patients than standard doses of 10-20 mg/m2 but with less side effects. 相似文献
80.
Fouto Ana R. Nunes Rita G. Pinto Joana Alves Luísa Calado Sofia Gonçalves Carina Rebolo Margarida Viana-Baptista Miguel Vilela Pedro Figueiredo Patrícia 《Magma (New York, N.Y.)》2022,35(5):779-790
Magnetic Resonance Materials in Physics, Biology and Medicine - Histogram-based metrics extracted from diffusion-tensor imaging (DTI) have been suggested as potential biomarkers for cerebral small... 相似文献