http://hdl.handle.net/10397/23 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5704 Title: Applications of complex network science<br/><br/>Authors: Liu, Xiaofan<br/><br/>Abstract: Systems of inter-connected components can be modeled by networks. A network is a collection of "nodes" linked by "edges". The network models of large scale complex systems, e.g., social networks, transportation systems, engineering infrastructures, etc., have shown some non-trivial universal structural properties compared to regular graphs such as lattices or random graphs. These network models are hence referred to as complex networks. In this thesis the author analyzes the structure and dynamics of the complex networks abstracted from different systems, including arts, finance and social systems, in order to describe the functioning mechanisms and to optimize the functionalities of the systems. In Chapter 3, music compositions are analyzed from a complex network perspective. By abstracting music notes to network nodes and the co-occurrence of notes to edges between nodes, it is shown that different genres of music, ranging from pop to classic, western to oriental, all display universal network properties. It is shown that the theme of music is also embedded in the underlying complex networks of music compositions. Computer algorithms for automatic music generation are proposed based on a random walk process in the musical networks. Applying some additional rudimentary rhythmic constraints on the computer algorithms, appealing music can be generated.; In Chapter 4, global stock markets are analyzed from a complex network perspective. The dynamical complex network model considers each stock market as a node and connects each pair of nodes by an edge. Each edge is assigned by a time varying weight which equals the dynamic conditional correlation of the market index return values. The network properties reveal that the global stock market integration exhibits a periodic behavior, and that developed markets show stronger integration than emerging and frontier markets. The network also exhibits strong synchronization when the markets experience volatility. Unlike in the market integration, this volatility spillover phenomenon is more obvious in frontier markets than in developed markets. In Chapter 5, scientific collaborations are analyzed from a complex network perspective. With scientists abstracted by network nodes and the coauthorship of academic papers by edges between nodes, the collaboration network has been found to be intensively evolving in a local scale, where most coauthorships are one time collaboration. The structure of the collaboration network of a scientist depicts his/her influence in the peer collaborators. By examining the impact of unforeseen deaths of active eminent scientists to their collaboration networks, it is found that the fast evolving scientific collaboration networks are very robust to attacks on the hub nodes. It is suggested that future design of engineering systems should imitate the evolution mechanism of human social interactions to create robust systems. In Chapter 5, the consensus process in online social networks is analyzed from a complex network perspective. Users of online social websites form social communities by indicating friendship or interacting with each other. The resulting networks of online social relationship can be considered snapshots of the entire human social communities. By studying the consensus process in an online social network, it is found that a few users with very large number of connections can shift the final consensus decision of the community. Moreover,the compartmental structure of social networks can actually slow down the consensus rate.<br/><br/>Description: xviii, 163 p. : ill. (some col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P EIE 2012 Liu http://hdl.handle.net/10397/5659 Title: Salinity sensor based on polyimide-coated photonic crystal fiber<br/><br/>Authors: Wu, Chuang; Guan, Bai-Ou; Lu, Chao; Tam, Hwa-yaw<br/><br/>Abstract: We proposed and experimentally demonstrated a highly sensitive salinity sensor using a polyimide-coated Hi-Bi photonic crystal fiber Sagnac interferometer based on the coating swelling induced radial pressure. This is the first time to exploit fiber coating induced pressure effect for salinity sensing. The achieved salinity sensitivity is 0.742 nm/(mol/L), which is 45 times more sensitive than that of a polyimide-coated fiber Bragg grating. A bare fiber Bragg grating is incorporated into the fiber loop for temperature compensation.<br/><br/>Description: DOI: 10.1364/OE.19.020003 http://hdl.handle.net/10397/5658 Title: OSNR monitoring for QPSK and 16-QAM systems in presence of fiber nonlinearities for digital coherent receivers<br/><br/>Authors: Dong, Zhenhua; Lau, Alan Pak Tao; Lu, Chao<br/><br/>Abstract: OSNR monitoring is indispensable for coherent systems to ensure robustreliable network operation and potentially enable impairment-aware routing for future dynamic optical networks. In a longhaul transmission link with chromatic dispersion (CD) and fiber nonlinearityit is difficult to distinguish between amplifier noise and fiber nonlinearity induced distortions from received signal distributions even after various transmission impairment compensation techniquesthus resulting in grossly inaccurate OSNR estimates. Based on the received signal distributions after carrier phase estimation (CPE)we propose to characterize the nonlinearity-induced amplitude noise correlation across neighboring symbols and incorporate such information into error vector magnitude (EVM) calculation to realize fiber nonlinearity-insensitive OSNR monitoring. For a transmission link up to 1600 km and signal launched power up to 2 dBmexperimental results for 112 Gb/s polarization-multiplexed quadrature phase-shift keying (PM-QPSK) demonstrate an OSNR monitoring range of 10-24 dB with a maximum estimation error below 1 dB. For 224 Gb/s PM-16-quadrature amplitude modulation (PM-16-QAM) systemssimulation results demonstrate an OSNR monitoring range of 18-28 dB with a maximum estimation error below 1 dB. Tolerance of the proposed OSNR monitoring technique to different pulse shapestiming phase offsetspolarization dependent loss (PDL)polarization-mode dispersion (PMD) and WDM effects are also investigated through simulations.<br/><br/>Description: DOI: 10.1364/OE.20.019520 http://hdl.handle.net/10397/5656 Title: Single tilted Bragg reflector fiber laser for simultaneous sensing of refractive index and temperature<br/><br/>Authors: Wong, Allan C. L.; Chung, Wenghong; Tam, Hwa-yaw; Lu, Chao<br/><br/>Abstract: A type of fiber laser, called tilted Bragg reflector fiber laser (TBR-FL), is proposed and its application in simultaneous sensing of surrounding refractive index (SRI) and temperature is demonstrated. This FL is formed by a pair of wavelength and tilt-angle matched tilted fiber Bragg gratings (TFBGs) that acted both as a resonant cavity and sensing element. A unique spectral feature of the TBR-FL is the presence of grating tilt-induced cladding modes spectrum that does not appear in other type of FL, which provides an extra sensing mechanism. By employing a simple experimental setup with the discrete wavelet transform as the demodulation technique, simultaneously sensing of SRI and temperature are achieved by measuring and analyzing the wavelet coefficients shifts of the laser output and averaged cladding modes.<br/><br/>Description: DOI: 10.1364/OE.19.000409