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排序方式: 共有930条查询结果,搜索用时 15 毫秒
101.
Leandro A. Villas Daniel L. Guidoni Guilherme Maia Richard W. Pazzi Jó Ueyama Antonio A. F. Loureiro 《Wireless Networks》2015,21(2):485-498
Localization and synchronization are fundamental services for many applications in wireless sensor networks (WSNs), since it is often required to know the sensor nodes’ position and global time to relate a given event detection to a specific location and time. However, the localization and synchronization tasks are often performed after the sensor nodes’ deployment on the sensor field. Since manual configuration of sensor nodes is usually an impractical activity, it is necessary to rely on specific algorithms to solve both localization and clock synchronization problems of sensor nodes. With this in mind, in this work we propose a joint solution for the problem of 3D localization and time synchronization in WSNs using an unmanned aerial vehicle (UAV). A UAV equipped with GPS flies over the sensor field broadcasting its geographical position. Therefore, sensor nodes are able to estimate their geographical position and global time without the need of equipping them with a GPS device. Through simulation experiments, we show that our proposed joint solution reduces time synchronization and localization errors as well as energy consumption when compared to solutions found in the literature. 相似文献
102.
Wislei R. Osório Leandro C. Peixoto Daniel J. Moutinho Laércio G. Gomes Ivaldo L. Ferreira Amauri Garcia 《Materials & Design》2011,32(7):3832-3837
The aim of this article is to compare the electrochemical corrosion resistance of two as-cast Al–6 wt.% Cu–1 wt.% Si and Al–8 wt.% Cu–3 wt.% Si alloys considering both the solutes macrosegregation profiles and the scale of the microstructure dendritic arrays. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) and potentiodynamic anodic polarization techniques were used to analyze the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that the Al–8Cu–3Si alloy has better electrochemical corrosion resistance than the Al–6Cu–1Si alloy for any position along the casting length. At the castings regions where the Cu inverse profile prevailed (up to about 10 mm from the castings surface) the corrosion current density decreased up to 2.5 times with the decrease in the secondary dendrite arm spacing. 相似文献
103.
Inflammatory processes are central to reproductive events including ovulation, menstruation, implantation and labour, while inflammatory dysregulation is a feature of numerous reproductive pathologies. In recent years, there has been much research into the endogenous mechanisms by which inflammatory reactions are terminated and tissue homoeostasis is restored, a process termed resolution. The identification and characterisation of naturally occurring pro-resolution mediators including lipoxins and annexin A1 has prompted a shift in the field of anti-inflammation whereby resolution is now observed as an active process, triggered as part of a normal inflammatory response. This review will address the process of resolution, discuss available evidence for expression of pro-resolution factors in the reproductive tract and explore possible roles for resolution in physiological reproductive processes and associated pathologies. 相似文献
104.
Leandro Ezequiel Di Persia Diego Humberto Milone Masuzo Yanagida 《Journal of Signal Processing Systems》2011,63(3):333-344
In a recent publication the pseudoanechoic mixing model for closely spaced microphones was proposed and a blind audio sources
separation algorithm based on this model was developed. This method uses frequency-domain independent component analysis to
identify the mixing parameters. These parameters are used to synthesize the separation matrices, and then a time-frequency
Wiener postfilter to improve the separation is applied. In this contribution, key aspects of the separation algorithm are
optimized with two novel methods. A deeper analysis of the working principles of the Wiener postfilter is presented, which
gives an insight in its reverberation reduction capabilities. Also a variation of this postfilter to improve the performance
using the information of previous frames is introduced. The basic method uses a fixed central frequency bin for the estimation
of the mixture parameters. In this contribution an automatic selection of the central bin, based in the information of the
separability of the sources, is introduced. The improvements obtained through these methods are evaluated in an automatic
speech recognition task and with the PESQ objective quality measure. The results show an increased robustness and stability
of the proposed method, enhancing the separation quality and improving the speech recognition rate of an automatic speech
recognition system. 相似文献
105.
Jorge L. B. Maciel Emerson A. Floriano Luis V. A. Scalvi Leandro P. Ravaro 《Journal of Materials Science》2011,46(20):6627-6632
Aiming for the investigation of insulating properties of aluminum oxide (Al2O3) layers, as well as the combination of this oxide with tin dioxide (SnO2) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of
SnO2 thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al2O3 are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that
tetragonal Al2O3 is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide
and the transport properties of SnO2 as well. Results indicate a fair insulation when four layers or Al2O3 are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the
insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO2 alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication
that this combination may be useful for transparent devices. 相似文献
106.
本文着重介绍了数码涡旋技术在商用办公楼的设计及应用,该工程能在一年四季提供稳定的制冷和制热,充分体现数码涡旋技术的广泛适用性、节能可靠性、控制便利及精确性,具有安装和后期维护简单方便等突出优点。 相似文献
107.
Mora J. Ortega B. Andres M.V. Capmany J. Pastor D. Cruz J.L. Sales S. 《Electronics letters》2002,38(3):118-119
A novel dynamic chirping fibre Bragg grating device based on a magnetic field applied to a magnetostrictive transducer capable of tuning its dispersion is presented. Chirping ranges up to 300 ps/nm have been demonstrated, which are suitable for several applications such as tunable transversal filtering and dynamic dispersion compensation 相似文献
108.
Bazil Taha Ahmed Miguel Calvo Ramón Leandro De Haro Ariet 《Wireless Personal Communications》2004,31(1):19-31
The uplink capacity and the interference statistics (mean and variance) of the sectors of the cigar-shaped W-CDMA microcell are studied. A model with eighteen sectors is used to analyze the uplink. The microcells are assumed to exist in a long tunnel with at least nine base stations. The hybrid model of propagation is used in the calculations. The capacity and the interference statistics of the sectors are studied in terms of the most important parameters: sector radius, specific attenuation factor, antenna sidelobe levels, bend losses and the power control standard deviation error. 相似文献
109.
Sarah JS Domingues Francislete R Melo Juliana M Aguiar Adriana G Affonso Juclia SA Giuli Juliana L Rose Maurício P Sales Lara F Machado Cassiana R Azevedo Patrícia C da Cunha Adriana Ferreira Uchoa Antnia Elenir Amncio de Oliveira Jos Xavier‐Filho Ktia VS Fernandes 《Journal of the science of food and agriculture》2006,86(12):1977-1985
We have investigated the survival of Callosobruchus maculatus larvae when reared on resistant IT81D 1045 Vigna unguiculata seeds, whose resistance has been associated with variant forms of vicilins. Here, we present data which show that larvae of C. maculatus feeding on embryonic axis of resistant cowpea reach a mass of around 28 times higher than those feeding on cotyledonary tissues. Additionally, incorporation of 5–10% of embryonic axis flour on artificial seeds made of resistant flour restores toxicity of seeds to the bruchid. Vicilins purified from both susceptible and resistant embryonic axis had no deleterious effects either on insect development or on insect survival until a level of 4% of incorporation. In contrast, vicilins from resistant cotyledons show an LD50 (50% lethal dose) and WD50 (half weight dose) of 2%. Total vicilin contents of embryonic axes were around two times lower than in cotyledonary tissues, while proteolytic activities of all four proteinase classes were always higher in the former tissues. By 2D‐PAGE we visualized eight protein spots, which seem to be exclusively found on resistant cotyledons. Copyright © 2006 Society of Chemical Industry 相似文献
110.