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排序方式: 共有663条查询结果,搜索用时 0 毫秒
1.
S. Akhtar D. S. Bernstein 《International Journal of Adaptive Control and Signal Processing》2005,19(10):745-767
Discrete‐time model reference adaptive control (MRAC) is considered with both least squares and projection algorithm parameter identification. For both cases complete Lyapunov proofs are given for stability and convergence. The results extend the approach of Johansson (Int. J. Control 1989; 50 (3):859–869) to include Lyapunov stability for MRAC when the normalized projection algorithm is used for parameter identification. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
2.
3.
Aleena Kiran Majid Niaz Akhtar Muhammad Yousaf Khalid Mujassam Batoo Omar M.Aldossary Salman Naeem Khan 《中国稀土学报(英文版)》2021,39(10):1224-1231
Rare earths(REs) play a key role in distorting spinel structure by creating some defects at the lattice sites and make them suitable for magnetodielectric applications.In the present study,the nanoferrites of CuRE_(0.02)Fe_(1.98)O_4,where REs=Y~(3+),Yb~(3+),Gd~(3+),were prepared using one step sol-gel method.The prepared samples are copper ferrite(CFO),yttrium doped copper ferrite(Y-CFO),ytterbium doped copper ferrite(Yb-CFO) and gadolinium doped copper ferrite(Gd-CFO),respectively.The single-phase structure of all the REs doped nanoferrites was determined by X-ray diffraction(XRD) analysis.The porosity,agglomerations and grain size of the REs doped copper ferrite were examined using field emission scanning electron microscopy(FESEM) analysis.Fourier transform infrared spectroscopy(FTIR)elaborates the phase formation and environmental effects on the REs doped nanoparticles(NPs).The recorded room temperature M-H loops from a vibrating sample magnetometer(VSM) elucidate the magnetic properties of the REs doped spinel nanoferrites.The magnetic saturation(M_s) was calculated in the range of 23.08 to 51.78 emu/g.The calculated coercivity values(272.6 to 705.60 Oe) confirm the soft magnetic behavior of REs doped copper ferrites.Furthermore,the electromagnetic and dielectric properties were assessed using a Vector network analyzer(VNA) from 1 to 6 GHz.The permeability,permittivity,dielectric tangent loss and electric modulus of the REs doped spinel ferrites illustrate that the prepared NPs may be suitable for microwave and high frequency applications. 相似文献
4.
A novel method for the reconstruction of inhomogeneous permittivity profiles of spherical dielectric objects illuminated by higher order TE/sub mn/ and TM/sub mn/ spherical modes is presented. The overall technique is based on the derivation of Riccati-similar nonlinear differential equations in a spherical coordinate system for both TE and TM illuminations as a part of the direct problem formulation. These differential equations are then inverted using a quasi-linear approach to obtain a closed-form expression of the radially varying permittivity profile of spherical objects in terms of a spherical Fourier-Bessel transform of the measured spectral domain reflection coefficient data. To validate the proposed method, several examples with different mode illuminations and with different noise levels are considered for reconstructions. A good agreement between the actual and the reconstructed permittivity profiles even under high noisy conditions shows that our method is not much sensitive to the presence of noise in the reflection coefficient data. 相似文献
5.
Mohammad Akhtar 《电信科学》2010,26(11)
LTE是目前大部分电信运营商首选的下一代移动通信技术,已有100多家运营商承诺将于2010年开始部署LTE.不过,在非成对频段部署LTE的商机却常被忽略. 相似文献
6.
Imran Memon Qasim Ali Arain Muhammad Hammad Memon Farman Ali Mangi Rizwan Akhtar 《International Journal of Communication Systems》2017,30(16)
The mobile vehicle is gaining popularity nowadays using map services like Google Maps and other mapping services. However, map services users have to expose sensitive information like geographic locations (GPS coordinates) or address to personal privacy concerns as users share their locations and queries to obtain desired services. Existing mix zones location privacy protection methods are most general purposed and theoretical value while not applicable when applied to provide location privacy for map service users. In this paper, we present new (multiple mix zones location privacy protection) MMLPP method specially designed for map services on mobile vehicles over the road network. This method enables mobile vehicle users to query a route between 2 endpoints on the map, without revealing any confidential location and queries information. The basic idea is to strategically endpoints to nearby ones, such that (1) the semantic meanings encoded in these endpoints (eg, their GPS coordinates) change much, ie, location privacy is protected; (2) the routes returned by map services little change, ie, services usability are maintained. Specifically, a mobile client first privately retrieves point of interest close to the original endpoints, and then selects 2 points of interest as the shifted endpoints satisfying the property of geoindistinguishability. We evaluate our MMLPP approach road network application for GTMobiSim on different scales of map services and conduct experiments with real traces. Results show that MMLPP strikes a good balance between location privacy and service usability. 相似文献
7.
Ahmed Ouameur Messaoud Massicotte Daniel Akhtar Auon Muhammad Girard Reno 《Wireless Networks》2020,26(6):4079-4093
Wireless Networks - This paper discusses a framework for algorithm-architecture synergy for (1) performance evaluation and (2) FPGA implementation complexity analysis of linear massive MIMO... 相似文献
8.
Thin films of ZnS were deposited on soda lime glass substrates by a modified close-space sublimation technique. The change
in optical and structural properties of the films deposited at various substrate temperatures (150–450°C) was investigated.
X-ray diffraction spectra showed that films were polycrystalline in nature having cubic structure oriented only along (111)
plan. The crystallinity of films increased with the substrate temperature up to 250°C. However, crystallinity decreased with
further increase of substrate temperature and films became amorphous at 450°C. The atomic force microscopy data revealed that
the films become more uniform and dense with the increase of substrate temperature. Optical properties of the films were determined
from the transmittance data using Swanepoel model. It was observed that the energy band gap is increased from 3.52 to 3.65
eV and refractive index of the films are decreased with the increase of substrate temperature. Moreover, considerable improvement
in blue response of the films was noticed with increasing substrate temperature. 相似文献
9.
Akhtar S. Roblin P. Sunyoung Lee Xiaohui Ding Shuang Yu Kasick J. Strahler J. 《Microwave Theory and Techniques》2002,50(6):1561-1570
A new approach for the electro-thermal modeling of LDMOSFETs for power-amplifier design that bypasses pulsed-IVs and pulsed-RF measurements is presented in this paper. The existence of low-frequency dispersion in LDMOSFETs is demonstrated by comparing pulsed IVs with iso-thermal IVs. The modeling technique uses iso-thermal IV and microwave measurements to obtain the temperature dependence of small-signal parameters. Optimized tensor-product B-splines, which distribute knots to minimize fitting errors, are used to represent the small-signal parameters and extract the large-signal model as a function of voltages and temperature. The model is implemented on ADS and is verified by simulating and measuring the power harmonics and IMD large-signal performance of a power amplifier. The impact on the model of temperature-dependent drain and gate charge is investigated. The presented model is found to compare well and, in some cases, exceed the existing MET model for LDMOSFETs 相似文献
10.
During the last few years a number of space-time block codes have been proposed for use in multiple transmit antennas systems. We propose a method to extend any space-time code constructed for m transmit antennas to m p transmit antennas through group-coherent codes (GCCs). GCCs make use of very limited feedback from the receiver (as low as 1 bit). In particular the scheme can be used to extend any orthogonal code (e.g., Alamouti code) to more than two antennas while preserving low decoding complexity, full diversity benefits, and full data rate. 相似文献