Applied Mechanics and Materials Vols. 284-287

Abstract: With the development of the wireless internet, there are more and more mobile terminals. Without a mobility management protocol a mobile terminal could not communicate with other terminals when it is away from its home network. Mobile IPv6 is proposed which is host-based mobility management protocol. But it has several drawbacks, such as wireless link resource waste, load or consumption of power in mobile terminal is large. To overcome the weakness of host-based mobility management protocol, network-based mobility management protocol called Proxy Mobile IPv6 (PMIPv6) is standardized by the IETF NETLMM working group, and it is starting to attract considerable attentions. Although several proposals have been made for Route Optimization (RO), they still need too many communications and it may cause communication delay. In this paper we proposed a time-efficient RO in PMIPv6 by optimize the procedure of it. We use the characteristic of anycast to achieve the time efficiency. By the mathematical analysis we prove that the proposed protocol has shorter latency and supports faster mobility of the mobile terminals.

Abstract: With the increasing demand of wireless local area networks, the support of differentiated Quality of Service (QoS) has become one of the critical issues on IEEE 802.11 medium access control protocols. To support the differentiated QoS requirements, IEEE 802.11e has been standardized. IEEE 802.11e defines Enhanced Distributed Channel Access (EDCA) for access mechanism, which is a contention based channel access method and delivers traffic based on differentiated access categories for the support of QoS. This paper introduces a three dimensional Markov chain model to evaluate the performance of IEEE 802.11e EDCA mechanism with an arbitrary number of different access categories. The proposed analytical model captures the major QoS specific features in the IEEE 802.11e EDCA and hence can provide a numerical approach to pick the set of EDCA parameter values to meet the QoS requirements of each access category. The results of our proposed analytical model are verified using simulations.

Abstract: The yellow-ring (YR) is a chromatism phenomenon which is caused by the inhomogeneous phosphor layer of the white-light LED (WLED). The characterized lightspot with YR is that the yellow light appears in the periphery of white lightspot zone. The lightspot image of WLED can be acquired from two approaches; projective lightspot method (PLM) and transmissive lightspot method (TLM). By the PLM system, the lightspot could be projected on the spot screen (wall or others) and its image is acquired by a CCD camera. However, the working distance between camera and sample WLED must be larger (~ 2 m) to obtain the lightspot image without tilt aberration. For the convenience of automatic inspection, the working distance in the TLM system can be modified to 0.3 m. Since the light travels through the spot screen, such as copier paper or acrylic plate, etc., the camera cannot obtain the real lightspot image in the TLM system. In practice, the material of spot screen will absorb and scatter the WLED light, and in the image color would be a bit different between the real lightspot and the acquired lightspot. In order to improve the above disadvantages, the study presents the reflective lightspot method (RLM) that the camera acquires the reflective lightspot image from the 50/50 beam splitter at the same optical axis. The RLM system is not only able to capture the tilt-less lightspot image, but also obtain readily the non-saturated image. The experiment results show the RLM system has the better evaluation of YR index (YRI), and is more suitable for the automatic inspection of WLEDs.

Abstract: The telescope primary mirror Isostatic Mount (ISM) design is an important issue for optical performance. The ISM bonding position will affect the telescope performance. The primary mirror reflection surface is parallel with gravity force during telescope alignment process. Thus, the distance between ISM geometry center and primary mirror center of gravity will lead mirror surface deformation. The ISM mounting mainly aberration is astigmatism at mirror surface. This study is applied Finite Element (FEM) simulate mirror surface deformation and using Zernike polynomial fitting the mirror surface aberration. The simulation result show the ISM bonding at mirror neutral plane the aberration will minimum at 1G gravity. The ISM bonding position errors also affect aberration distribution.

Abstract: Metal nanostructures can be used to control light transmission on the nanometer scale. In this paper, we propose a ladder-type comb-like metal nano-grating structure, based on optical filtering properties of the comb-like nanostructures and surface plasmon resonance effect of the metal nano-structures. The comb part of the structure is the silver nano-grating with the width of 20nm and a depth difference of 5nm between the adjacent gratings. We use the 532nm CW laser as the incident light source to study the reflective properties of the P polarized light and calculate the reflected power spectrum of the structure in three different parameters, which are the silver nano-grating, the silver-air nano-grating (silver grating are separated by air) and silver-SiO2 nano-grating. The experimental results show that the light wave oscillation modes are closely related to the comb-like structure parameters (including the depth and width) on the power spectrum. Meanwhile, we also draw conclusions that different intervention media does not change the position of the light wave oscillation modes, but only a significant effect on the reflection intensity of the different modes. Furthermore, we also noted that the depth of silver nano-gratings can affect the position of the resonance peak. As the waveguide depth of the silver nano-gratings increasing, the spacing of different modes’ oscillation peak is becoming larger. Based on the finding, we can modulate the light wave oscillation modes in a very wide spectral range. The results of this paper will promote the development of the optical filter, light wave mode selection and random laser excitation.

Abstract: In this work, we successfully developed a process to fabricate dual-channel polymeric waveguide filters based on an asymmetric Bragg coupler using holographic interference techniques, soft lithography, and micro molding. At the cross- and self-reflection Bragg wavelengths, the transmission dips of approximately –16.5 and –11.7dB relative to the 3dB background insertion loss and the 3dB transmission bandwidths of approximately 0.6 and 0.5nm were obtained from an ABC-based filter. The transmission spectrum overlaps when the effective index difference between two single waveguides is less than 0.0025.

Abstract: One of the major factors that affects the distributed network utility maximization(NUM) is the exchange message delay which leads to oscillations due to imperfect response to time-variant channel. In this paper, a novel technique is presented to solve the reverse impact control delay in distributed NUM of wireless mesh networks. Simulation results illustrate better performance.

Abstract: We present our experimental results on the measurements of excited state dynamics in 2, 9, 16, 23-phenoxy-phthalocyanine (Pc1) and 2, 9, 16, 23-phenoxy-phthalocyanine-zinc (Pc2) using the pump-probe experiment. The results show that the All-Optical Switching (A-OS) response time of Pc2 longer than that of Pc1, and switch-off and -on times of A-OS for Pc2 are 1.2 and 11.6 μs and for Pc1 are 2.3 and 7.8 μs at the same intensity. Moreover, analysis of modulation characteristics of A-OS shows that the stronger the light intensity of the pump light is, the smaller the normalized transmittance is and the shorter the response time of A-OS is. The consequences of such short lifetimes are also discussed in view of the strong A-OS properties of these molecules.

Abstract: Although the integration of SIP-based systems with a network address translation (NAT) environment has been investigated extensively, SIP-based system operation in symmetric model NAT remains relatively unexplored. This paper studies the application of symmetric NAT traversal techniques to SIP-based systems. This study focuses on following the SIP process, a non-additive service server, and employs standard SIP commands such as “REGISTER,” “INVITE,” and “200 OK” to predict and deliver the IP addresses and port numbers of the local NAT. This study also implements RTP streaming in the client-to-client (C2C) mode. The symmetric NAT traversal method for the SIP increases the direct peer-to-peer connection rate. This approach also avoids the STUN and RTP-Relay server. Experimental results with 50 types of NAT indicate that symmetric NAT traversal performs better than the STUN solution. The RTP-Relay server bandwidth cost is likewise superior to the TURN solution. These finding have important implications for SIP-based system developers and carrier providers.

Abstract: This study presents an integrated opto-mechanical analysis of a PMMA Fresnel lens used in solar concentrators for concentrated photovoltaic systems. The temperature dependence of refractive index of the PMMA lens was analyzed based on its temperature coefficient of refractive index dn/dT. In addition, the thermal distortion of the Fresnel lens under various temperature rises was computed by finite element analysis (FEA). Then, the temperature induced effects, variation of refractive index and the deformed lens geometry, were imported into ray tracing simulation simultaneously. Finally, the thermal-optical effects on the optical performance of a flat Fresnel lens were successfully investigated and discussed, including the maximum irradiances on the receiver and the optical efficiencies under different temperature rises.