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61.
We consider stochastic cellular networks where base stations locations form a homogeneous Poisson point process and each mobile is attached to the base station that provides the best mean signal power. The mobile is in outage if the signal-to-noise-plus-interference ratio falls below some threshold. The handover decision has to be made if the mobile is in outage during several time slots. The outage probability and the handover probabilities are evaluated taking into account the effect of path loss, shadowing, Rayleigh fast fading, frequency factor reuse and conventional beamforming. The main assumption is that the Rayleigh fast fading changes at each time slot while other network components remain static during the period of study. 相似文献
62.
ZnO structures were synthesised on the sapphire (112?0) substrate by a vapour transport method in a gas flowing furnace. The influence of the oxygen content in the gas mixture on the morphology and luminescent properties of ZnO structures grown on a strip-like substrate was investigated, with all other growth parameters being kept nominally identical. Integrated electron microscopy and cathodoluminescence analysis shows gradual variations of structural and optical emission properties for ZnO structures grown on the long substrate. Defect-related green luminescence of ZnO is found to be highly dependent on the oxygen vapour in the growth region of the furnace. Our findings demonstrate that the green luminescence is associated with oxygen deficiency in ZnO. 相似文献
63.
线路共享指的是,用户除了从自己归属的本地电话公司(ILEC)以外还能选择从其它运营公司(主要指CLEC)为自己提供数据业务,并且不必安装第二条电话线。线路共享为现有电话线路上开展数据业务竞争铺平了道路,它在美国被视作能否成功开放DSL市场的关键因素。本文对美国针对DSL发展问题出台线路共享政策以及线路共享政策出台后的实施状况加以报道。对于我国制定线路共享政策和实施管理提供参考。 相似文献
64.
The authors discuss ion-milled planar waveguide lenses in GaAs which exhibit a considerably higher efficiency than that previously reported for those lenses and near diffraction-limited spot size. The authors also report the performance characteristics of these latest lenses, including single lenses and lens array of analog Fresnel, chirp grating, and hybrid types as well as a collimation-Fourier transformation lens-pair, together with the detailed design and fabrication procedures. A simple theoretical model for the lens efficiency is also formulated to assist in the lens design. Ion milling has been shown to be a simple and versatile technique for fabrication of waveguide lenses in GaAs and applicable to any other substrate material. Such ion-milled waveguide lenses should facilitate realization of a variety of monolithically integrated optic device modules and circuits in GaAs and other related substrates with applications to communications, signal processing, and computing 相似文献
65.
B. Škipina D.Lj. Mirjani?S.M. Vu?enovi? J.P. Šetraj?i?I.J. Šetraj?i? A.J. Šetraj?i?-Tomi?S.S. Pelemiš B. Markoski 《Optical Materials》2011,33(11):1578-1584
We have formulated a microscopic theory of optical properties of ultrathin molecular films (nanofilms), i.e. quasi 2D systems parallel to XY planes bounded by two surfaces. Exposure of nanofilms to the external electromagnetic fields has result in creation of excitons - but different than bulk ones. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green’s functions. It has been shown that two types of optical excitations can occur: bulk and surface exciton states. Exciton energy dispersion law shows discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. In addition, permittivity shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of both resonance and quantum size effects. Influences of boundary conditions on optical characteristics (through analyses of dynamical absorption coefficient) of these nanostructures were specially and in details explored. 相似文献
66.
In this study, we report the electric transport of La0.7Ca0.3MnO3 prepared by various methods. Based on the fact that the metallic ferromagnetic and insulating paramagnetic clusters simultaneously exist at transition temperature, we applied phase-coexistence transport model to calculate the temperature dependence of the resistivity. This model can explain quantitatively the electrical conductivity of La0.7Ca0.3MnO3 for the whole temperature range studied. 相似文献
67.
Pattern nulling in difference pattern by amplitude control 总被引:2,自引:0,他引:2
A method of placing nulls in directions of any unwanted radio frequency interference (RFI) sources in the difference pattern of a phased array by controlling the current amplitudes is discussed. Thus one can now achieve pattern nulling in both the sum and difference patterns by amplitude control and can therefore carry out the minimization of RFI noise independently of the maximization of the desired signal. The method therefore provides an efficient alternative approach to the design of adaptive phased arrays. 相似文献
68.
The accuracy of the direction-of-arrival (DOA) estimation using a receiving phased array is degraded by the mutual coupling between the antenna elements. It is shown that by putting guard elements on each end of a linear array the DOA estimate error is reduced. 相似文献
69.
Optical add-drop multiplexers with low crosstalk 总被引:6,自引:0,他引:6
An Vu Tran Wen De Zhong Tucker R.C. Lauder R. 《Photonics Technology Letters, IEEE》2001,13(6):582-584
We propose and demonstrate three new optical add-drop multiplexer (OADM) architectures with simple and compact configuration and excellent crosstalk performance. The OADMs use a single multiport optical circulator and either one or two narrow-band fiber Bragg gratings, depending on the crosstalk requirement 相似文献
70.
Ahmad A. Hamid Harry G. Harris Vu N. Con Nilesh C. Chokshi 《Nuclear Engineering and Design》1986,91(1)
Concrete masonry walls have been used extensively in nuclear power plants as non-load bearing partitions serving as pipe supports, fire walls, radiation shielding barriers, and similar heavy construction separations. When subjected to earthquake loads, these walls should maintain their structural integrity. However, some of the walls do not meet design requirements based on working stress allowables. Consequently, utilities have used non-linear analysis techniques, such as the arching theory and the energy balance technique, to qualify such walls. This paper presents a critical review of the applicability of non-linear analysis techniques for both unreinforced and reinforced block masonry walls under seismic loading. These techniques are critically assessed in light of the performance of walls from limited available test data. It is concluded that additional test data are needed to justify the use of nonlinear analysis techniques to qualify block walls in nuclear power plants. 相似文献