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排序方式: 共有360条查询结果,搜索用时 15 毫秒
101.
The IEEE 802.15.4 protocol offers great potential in several application fields, such as industrial Wireless Sensor Networks (WSNs). An industrial automation cell (field level) is characterized mostly by periodic traffic flows. Using the IEEE 802.15.4 protocol, it is necessary to manage Guaranteed Time Slots (GTSs) allocation and at the same time ensure adequate performance both to other periodic traffic flows and network management/control flows. For these reasons, this paper shows a flexible approach in order to improve GTSs assignment and medium access performance. Analytical results are shown in order to demonstrate benefits introduced by deadline-aware algorithm (for guaranteed access to reserved slots) and CSMA-CA-priority based (for latencies reduction during medium access attempts). Otherwise, obtained results show that the proposed technique improves the number of deadlines met and the probability to find the channel free for transmissions. 相似文献
102.
103.
E. L. Schneider Sook P. Loke D. T. Hopkins 《Journal of the American Oil Chemists' Society》1968,45(9):585-590
A method is described for the analysis of cyclopropenoid fatty acids in oils. The method consists of reacting the methyl esters
of the cyclopropenoid fatty acids with silver nitrate in methanol to form ether and ketone derivatives. The derivatives formed
from the cyclopropenoid fatty acids are separated from the methyl esters of the normal fatty acids by gas-liquid chromatography
on a 15% diethylene glycol succinate column. The method is applicable to oils containing from 0.01% to 100% of cyclopropenoid
fatty acids. The derivatives of oils containing lew levels of cyclopropenoids are separated from the normal methyl esters
by alumina chromatography prior to gas-liquid chromatography. Studies on the quantitative aspects of the derivative formation,
alumina chromatography, and gas-liquid chromatography are reported. Analyses for total cyclopropenoid fatty acid content of
cottonseed oil andSterculia foetida oil by the gas-liquid chromatographic and hydrobromic acid titration procedures showed good agreement. Replicate analyses
of a sample ofSterculia foetida oil for malvalic and sterculic acid gave coefficients of variation of 6.04% and 1.17%, respectively. 相似文献
104.
The study aims to produce a design guide for the calculations of stresses and deflections of adhesively bonded beams fabricated from steel adherends using a structural epoxy adhesive. Such design calculations already exist for welded but not for bonded beams. Small models based on beams with a T-section profile, at various beam lengths, are formulated. A key to these calculations is the determination of the adhesive/adherend interface factors/coefficients, to correct the estimated values of stress and deflection from three-point bending conditions. This article presents the methodology for evaluating bonded beams in relation to equivalent welded (solid) beams. This includes mechanical testing, an analytical method based on beam and sandwich theory, and finite element techniques. Results from these techniques are presented and compared and values of the coefficients for T-section beams are determined. 相似文献
105.
Suan Khai Chong Mohamed Medhat Gaber Shonali Krishnaswamy Seng Wai Loke 《Knowledge and Information Systems》2011,28(3):579-614
The research reported in this paper addresses the problem of energy conservation in wireless sensor networks (WSNs). It proposes
concepts and techniques to extract environmental information that are useful for controlling sensor operations, in order to
enable sensor nodes to conserve their energy, and consequently prolong the network lifetime. These concepts and techniques
are consolidated in a generic framework we term CASE: Context Awareness in Sensing Environments framework. CASE targets energy
conservation at the network level. A subset framework of CASE, we term CASE Compact, targets energy conservation at the sensor
node level. In this paper, we elaborate on these two frameworks, elucidate the requirements for them to operate together within
a WSN and evaluate the applications they can be applied to for energy conservation. 相似文献
106.
Analysis of internal cracks in railway wheels under experimentally determined pressure distributions 总被引:2,自引:0,他引:2
In recent years much effort has been devoted to the definition of design approaches of railway systems based on the analysis of the system itself and on accurate knowledge of its effective working conditions. In this paper, the attention is focused on railway wheels. This latter component is subjected to different types of damage: sub-surface crack propagation is considered. The prediction of the evolution of this process depends on the knowledge of the stress intensity factors concerning modes I, II and III, which are dependant both on the total load acting on the wheel and on how the load is transmitted through the wheel/rail interface. However, until now the solutions commonly used consider a theoretical (Hertzian) pressure distribution, even if, due to wear or to the dynamic phenomena, the actual contact patch can be strongly different for most of the lifespan of the wheel. An approach is developed with the aim to solve the case of an internally cracked wheel subjected to an arbitrary contact patch and pressure distribution. It is based on Boussinesq's formulae and utilises a three-dimensional finite element model of the part of the wheel close to the crack to calculate the stress intensity factors along a curvilinear crack front. Pressure distributions experimentally determined by means of a technique based on the reflection of high-frequency ultrasonic waves from the wheel–rail interface were applied to internal cracks in wheels: the results were critically compared with the those obtained by considering Hertzian pressure distributions, the aim being the assessment of the influence of the contact conditions in respect of damage cause by internal crack propagation. 相似文献
107.
Loke YC Hofbauer W Lu P Ansari K Tang XS O'Shea SJ 《The Review of scientific instruments》2011,82(11):115002
A cantilever has been microfabricated for use in non-contact Atomic Force Microscopy (AFM) using a very thick magnetic film to actuate the cantilever motion. The thick magnetic block is deposited electrochemically over a defined area of the cantilever. This cantilever is particularly suitable for driving stiff AFM cantilevers in a liquid environment. Clean mechanical resonances are easily observed. Examples are given of a hard (CoPt) magnet of dimension 29 × 21 × 6 μm(3) electroplated on Silicon cantilevers of stiffness ~22 N/m, giving a static displacement of ~0.2 nm in an applied field of 10(-3) T. 相似文献
108.
Camilo Lozoya Pau Martí Manel Velasco Josep M. Fuertes Enrix X. Martin 《Real-Time Systems》2013,49(3):267-307
Embedded control systems are subject to conflicting demands: end-users ask for devices with better capabilities while strong industrial competition impose tight cost constrains that results in devices with limited resources. Current research in the multidisciplinary embedded systems discipline indicates that by combining real-time and control systems it is theoretically feasible to design resource-constrained embedded control systems capable of trading-off control performance and resource usage. This paper focuses on the implementation feasibility of recent state-of-the-art resource/performance-aware (RPA) policies that can be applied to a set of control loops that concurrently execute on a microprocessor. The objective of these policies is to improve control performance and/or to minimize resource utilization. The paper first reviews existing state-of-the-art RPA policies. Then it presents a performance evaluation framework (PEF) that permits to assess whether RPA policies can be implemented in practice. The PEF is designed using a modular approach and following the guidelines obtained by a taxonomic analysis performed on the state-of-the-art RPA policies. Finally, a case study is presented where the PEF is applied to a set of representative RPA policies. The case study reveals that the modularity of the PEF allows tailoring the framework to evaluate any specific RPA policy, which indicates that RPA policies can be implemented in practice. But it also reveals that the problem of assessing diverse RPA policies in fair conditions implies facing and solving conflicting demands by even taking decisions that may not favor equal all policies under evaluation. Nevertheless, the comparative analysis permits identifying potential benefits and drawbacks of each policy, as well as extracting design guidelines for future real-time embedded control systems theory and practice. 相似文献
109.
A light scanning device consisting of an electronically-driven mechanically-resonant cantilever spring-mirror system has been developed for innovative lighting applications. The repeated flexing of the cantilever spring during operation can lead to premature fatigue failure. A model was created to optimize the spring design. The optimized spring design can reduce stress by approximately one-third from the initial design. Fatigue testing showed that the optimized spring design can operate continuously for over 1 month without failure. Analysis of failures indicates surface cracks near the root of the spring are responsible for the failures. 相似文献
110.
Giovanni Condello Paolo Pasteris Danilo Pau Mariagiovanna Sami 《Signal Processing: Image Communication》2013,28(4):345-350
Nowadays visual search is one of the most active branches of computer vision. It relies on finding invariant points inside images, describing them into features and then matching these features against a reference database to identify objects in the scene or the entire photo (environment). In this paper, we discuss an approach to feature matching that exploits the capabilities of modern GPUs to speed up the aforementioned and that keeps low the number of false matches. 相似文献