Fractal and topological characterization of branching patterns on the fracture surface of cross-linked dimethacrylate resins     

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   

Coded-orthogonal frequency division multiplexing in hybrid optical networks     

Djordjevic  I.B. 《Optoelectronics, IET》2010,4(1):17-28

Future Internet should be able to support a wide range of services containing large amount of multimedia over different network types at a high speed. The future optical networks will therefore be hybrid, composed of different single-mode fibre (SMF), multi-mode fibre (MMF) and free-space optical (FSO) links. In these networks, novel modulation and coding techniques are needed that are capable of dealing with different channel impairments, be it in SMF, MMF or FSO links. The authors propose a coded-modulation scheme suitable for use in hybrid FSO - fibre-optics networks. The proposed scheme is based on polarization-multiplexing and coded - orthogonal frequency division multiplexing (OFDM) with large girth quasi-cyclic low-density parity-check (LDPC) codes as channel codes. The proposed scheme is able to simultaneously deal with atmospheric turbulence, chromatic dispersion and polarisation mode dispersion (PMD). With a proper design for 16-quadrature amplitude modulation (QAM)-based polarisation-multiplexed coded-OFDM, the aggregate data rate of 100 Gb/s can be achieved for OFDM signal bandwidth of only 12.5 GHz, which represents a scheme compatible with 100 Gb/s per wavelength channel transmission and 100 Gb/s Ethernet.  相似文献   

Electrical properties of mechanochemically activated cordierite ceramics     

N. G. Djordjevic  N. Obradovic  S. Filipovic 《Powder Metallurgy and Metal Ceramics》2012,51(1-2):83-86

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Outage performance of dual‐hop relaying systems over extended generalized‐K fading channels     

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   

Cotton Yarn Sizing by Acrylamide Grafted Starch Copolymer     

S. Djordjevic  S. Kovacevic  LJ. Nikolic  M. Miljkovic  D. Djordjevic 《Journal of Natural Fibers》2014,11(3):212-224

Synthesis and characterization of copolymer obtained by grafting acrylamide onto hydrolyzed potato starch and its application in cotton yarn sizing were presented in this work. Some process parameters of starch hydrolysis and grafting, like as hydrolysis yield, grafting yield, grafting percentage, graft efficiency, and monomer to polymer conversion were determinated. Molar mass values of hydrolyzed starch and copolymer samples are located in a narrow range of 1 × 10⁵ to 1 × 10⁷ and 1 × 10² to 1 × 10⁴. Grafted hydrolyzed starch, as a sizing agent, gives better results than nongrafted, particularly in terms of sizing uniformity, yarn mechanical parameters, and easier removal in subsequent desizing process.  相似文献   

Time-domain measurements with the Hewlett-Packard network analyzerHP 8510 using the matrix pencil method     

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   

LDPC-Coded $M$ -ary PSK Optical Coherent State Quantum Communication     

Djordjevic  I.B. 《Lightwave Technology, Journal of》2009,27(5):494-499

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   

Detecting Regular Visit Patterns     

Bojan Djordjevic  Joachim Gudmundsson  Anh Pham  Thomas Wolle 《Algorithmica》2011,60(4):829-852

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   

Grounding effects of HV and MV underground cables associated withurban distribution substations     

Nahman  J.M. Djordjevic  V.B. Salamon  D.D. 《Power Delivery, IEEE Transactions on》2002,17(1):111-116

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   

Sensitivity of point- and line-source laser-generated acoustic wave to surface flaws     

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