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1.
A novel method for transient analysis of electromagnetic systems with multiple lumped nonlinear loads is presented. The uniqueness of this approach is that we develop time-domain Green's functions for the multiport linear part of the electromagnetic system by suitably terminating the ports. This ensures a short duration of Green's functions. Hence the amount of frequency-domain data necessary to obtain the time-domain Green's functions is modest. The application of this technique to an arbitrary excitation is just a straightforward convolution. With this technique one can analyze responses of systems with arbitrary nonlinear loads (even with memory) as we have at any time instant Thevenin's equivalent of the linear portion of the electromagnetic system. Examples are presented to illustrate the application of this technique to multiport nonlinearly loaded antennas. 相似文献
2.
Maricevic Z.A. Sarkar T.K. Hua Y. Djordjevic A.R. 《Microwave Theory and Techniques》1991,39(3):538-547
The generalized pencil of function (GPOF) method, also known as the matrix pencil method, is used to improve the resolution of HP 8510B network analyzer data in the time domain. This method provides for much higher resolution than the Fourier techniques. A comparison of the two methods is given for the example of the Beatty standard. The examples show that a parametric technique such as the GPOF can provide accurate and reliable results with a high degree of resolution even when the fast Fourier transform (FFT)-based technique fails 相似文献
3.
Z. V. Djordjevic X. Feng Li Won Soo Shin S. L. Wunder G. R. Baran 《Journal of Materials Science》1995,30(11):2968-2980
The branching patterns formed as a result of crack growth in dimethacrylate resins below their glass transition temperatures looked similar to fractal trees. The skeletons of the patterns were analysed numerically for their topological and geometrical properties. The number of branches, N
i
, mean branch lengths, N
i
, and branch angles of a particular order, defined according to the Strahler and inverted Weibel schemes, followed exponential scaling behaviour: N
i
(R
b
)–i
and L
i
(R
l
)
i
. Using the relationship for the fractal dimension D=In R
B
/In R
L
, a value of D=1.4 was obtained for the fracture pattern. Fractal behaviour was also examined by the box-counting method which indicated a power-law dependence of the mass on the box size with fractal dimension exponent D=1.4 in the case of the fracture pattern. However, the mass-shell method for both the fracture pattern and the fractal trees gave an exponential increase of mass with distance from the origin, rather than the power-law behaviour expected for fractals. This was attributed to the fact that branches of different sizes were distributed in restricted regions of space closer to the periphery, rather than uniformly over the whole pattern. 相似文献
4.
Potkonjak V. Tzafestas S. Kostic D. Djordjevic G. Rasic M. 《Robotics & Automation Magazine, IEEE》2003,10(1):35-46
Two approaches are proposed to model and control a human-like motion of robot arms. The first, which is based on the concept of distributed positioning (DP), is suggested as a good model of arm motion in the phase where fatigue does not appear. The prescribed motion of the end-effector is distributed to a redundant number of arm joints in accordance to their acceleration capabilities. For the phase where fatigue appears, the concept of virtual fatigue is proposed. This artificial variable, which is based on robot dynamics, emulates the progress of biological fatigue. The human handwriting task is chosen for the simulation. The DP concept is tested first by modeling nonfatigued motion. The justification of the usual inclination of letters is presented, and the relation between the inclination, legibility, and a secondary objective (finger involvement, energy consumption, motor thermal load) is discussed. It is found that, for some prescribed level of legibility, the individual optima of all the secondary cost functions are quite near to each other. Writing in the presence of fatigue is also analyzed, applying the method of the so-called "virtual fatigue". 相似文献
5.
6.
Mihajlo C. Stefanovic Jelena A. Anastasov Aleksandra M. Cvetkovic Goran T. Djordjevic 《Wireless Communications and Mobile Computing》2015,15(18):2141-2149
The outage performance of the amplify‐and‐forward relaying strategies over mutually uncorrelated extended generalized‐K fading channels is addressed in this paper. The attention is dedicated to the analyses of the noise‐limited and also interference‐limited environment. The new analytical expression for outage probability of observed relaying system in the presence of thermal noise is derived using the method for approximating equivalent signal‐to‐noise ratio. In addition, the outage performance is studied for the dual‐hop system when only the single dominant co‐channel interference is inherent at the relay and destination node. The correctness of the proposed mathematical derivations is verified by simulations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
This paper addresses two important problems of interest for deep-space optical communications, quantum inter-chip/intra-chip optical communications and quantum-key distribution: 1) the problem of coded M-ary phase-shift keying optical coherent-state quantum communication in the absence of background radiation, and 2) the problem of coded binary coherent state communication in the presence of background radiation. In both cases large girth low-density parity-check (LDPC) codes are used as channel codes. With girth-10 LDPC-code of rate 0.8 and BPSK, the bit-error ratio of 10- 8 can be achieved for average number of signal photons of 0.73, resulting in net-effective coding gain of 7.63 dB. 相似文献
8.
We are given a trajectory
T\mathcal{T}
and an area
A\mathcal{A}
.
T\mathcal{T}
might intersect
A\mathcal{A}
several times, and our aim is to detect whether
T\mathcal{T}
visits
A\mathcal{A}
with some regularity, e.g. what is the longest time span that a GPS-GSM equipped elephant visited a specific lake on a daily
(weekly or yearly) basis, where the elephant has to visit the lake most of the days (weeks or years), but not necessarily on every day (week or year). 相似文献
9.
This paper derives a model for the evaluation of the performances of composite grounding systems of urban main distribution substations and associated power cable networks. The effects of the cables upon the dangerous voltages, transferred potentials and ground fault current distribution are encompassed including the conductive and magnetic coupling among grounding system elements, as well as the nonlinearity of cables sheaths impedances. An application example is presented, as are some experimental data 相似文献
10.
Kenderian S Djordjevic BB Green RE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(8):1057-1064
Laser generation and air-coupled detection were combined as a hybrid ultrasonic technique for the inspection of surface flaws in rails. Narrowband acoustic signals were generated using a formed laser source by focusing the laser light to a point and to a line on the surface of the rail. The pulse energy, and therefore the intensity of the laser source, varied such that the generated signal transitioned from the weak thermoelastic to the strong ablative regime. The detection of flaws using a laser-generated surface acoustic wave, in the presence of surface flaws, was compared between both point and line laser sources operating under different pulse energy levels. The line source was found to be more sensitive to the presence of surface flaws than a point source. The sensitivity of the laser-generated acoustic signal appeared to be independent of the severity of the flaw and, within the ablative regime, independent of the laser-pulse energy. Theoretical analysis is provided to explain the underlying cause that influences the interaction of a formed laser-generated surface acoustic wave to surface flaws and how this sensitivity may vary between the thermoelastic and ablative regimes. 相似文献