A new family of Routh approximants

Based on the combinatorial Routh- and- expansions of a stable transfer function, a new energy decomposition tree for linear systems is developed. The pertinent properties to the energy decomposition tree are investigated, and an algorithm is derived for synthesizing transfer functions from the tree. The synthesis process naturally leads to a new family of Routh approximants to the system. It is indicated that the selection of Routh approximants based on the values of impulse-response energy is often inadequate because there may be a number of different Routh approximants with the same order and the same impulse-response energy. In such cases, an additional performance criterion, such as the integral of squared error of impulse response or unit-step response, has to be used to select a suitable Routh approximant.This work was supported by the National Science Council of the Republic of China under Grant NSC80-0402-E006-12.     

Miniature aperture-coupled microstrip antenna of very highpermittivity

A miniature aperture-coupled microstrip antenna of very high permittivity designed at 1.66 GHz is described. Superstrates of appropriate thickness are added on the substrate for gain enhancement. Its size is dramatically reduced and the electrical performance remains almost the same as compared with the conventional microstrip antenna of low dielectric constant. Experimental data for the return loss, radiation pattern and measured antenna gain are presented to validate the design     

Fabrication of V-grooved inner stripe GaAs-AlGaAs quantum-wire lasers

V-grooved inner stripe (VIS) GaAs-AlGaAs quantum-wire (QWR) lasers were successfully fabricated by, combining two-step metalorganic chemical vapor deposition (MOCVD) growth with a wet-etching technique. In order to achieve low threshold current density and high reliability, a conductive stripe width (W), a thickness (t/sub p-CBL/), and a doping concentration (n/sub p-CBL/) of the p-GaAs current-blocking layer (CBL) were determined to be W=1.2 /spl mu/m, t/sub p-CBL/=2 /spl mu/m, and n/sub p-CBL/=1/spl times/10/sup 18/ cm/sup -3/. The leakage currents passing through the CBL were also estimated using a modified P-SPICE. Thus far, a threshold current of 45 mA and an output power of 4 mW at 51 mA have been achieved under room-temperature pulsed operation for some devices with uncoated facets.     

Polymeric 2/spl times/2 electrooptic switch consisting of asymmetric Y junctions and Mach-Zehnder interferometer

2/spl times/2 electrooptic switches consisting of a pair of asymmetric Y junctions and Mach-Zehnder interferometer have been demonstrated in polymeric waveguides. The switching voltage is 15 V with 1.5 cm long electrode for TM polarized light at 1.3 /spl mu/m. When the branching angle of the asymmetric Y junction is 0.2/spl deg/, crosstalk of -27 to -22 dB are obtained for both input arms. The measured insertion loss by the lens coupling is about 9-10 dB.     

客观的图象质量测度及其在分割评价中的应用

图象分割是图象分析中的关健步骤。对图象分割的评价是研究分割技术性能的有效手段,其中分割质量测度起着重要作用。本文介绍一类新的客观质量测度并对其性能进行了比较研究。另外为了验证新测度的有效性,本文提出了一种比较合理全面的分割技术分类法。在此基础上选取各类技术中有代表性的算法借助新的质量测度进行了实际评价比较并取得了有意义的结果。     

Integrated-Optic Polarization Controlling Devices Using Electro-Optic Polymers

Integrated-optic polarization controlling devices such as polarizers, polarization splitters, and polarization converters, are proposed and demonstrated in nonlinear optic polymers. Poling-induced birefringence in electro-optic polymers is exploited to fabricate the devices. The polymeric waveguide polarizers show low excess losses, and extinction ratios of 20.7 dB and 17.1 dB for TM-pass and TE-pass polarizers, respectively. The polymeric waveguide polarization splitters exhibit TE-TM mode splittings with crosstalk of 14.2 dB and 10.1 dB for TM and TE mode splittings, respectively. The polymeric waveguide polarization converters show successful TE/TM polarization mode conversion with conversion efficiencies of higher than 30 dB. The device employs poling-induced waveguides which have slowly rotating azimuth angle of optic axis along the light propagation direction. The novel polarization converter is insensitive to wavelength and easier to fabricate than the other polarization converters containing periodic structures.     

A location‐aware peer‐to‐peer overlay network

This work describes a novel location‐aware, self‐organizing, fault‐tolerant peer‐to‐peer (P2P) overlay network, referred to as Laptop. Network locality‐aware considerations are a very important metric for designing a P2P overlay network. Several network proximity schemes have been proposed to enhance the routing efficiency of existing DHT‐based overlay networks. However, these schemes have some drawbacks such as high overlay network and routing table maintenance overhead, or not being completely self‐organizing. As a result, they may result in poor scalability as the number of nodes in the system grows. Laptop constructs a location‐aware overlay network without pre‐determined landmarks and adopts a routing cache scheme to avoid maintaining the routing table periodically. In addition, Laptop significantly reduces the overlay maintenance overhead by making each node maintain only the connectivity between parent and itself. Mathematical analysis and simulations are conducted to evaluate the efficiency, scalability, and robustness of Laptop. Our mathematical analysis shows that the routing path length is bounded by log_d N, and the joining and leaving overhead is bounded by d log_d N, where N is the number of nodes in the system, and d is the maximum degree of each node on the overlay tree. Our simulation results show that the average latency stretch is 1.6 and the average routing path length is only about three in 10 000 Laptop nodes, and the maximum degree of a node is bounded by 32. Copyright © 2006 John Wiley & Sons, Ltd.     

Differential Game for Distributed Power Control in Device-to-Device Communications Underlaying Cellular Networks

Wireless Personal Communications - In the formulating of power control for wireless networks, the radio channel is commonly formulated using static models of optimization or game theory. In these...     

End-to-End Security Protocol for Mobile Communications with End-User Identification/Authentication

As great progress has been made in mobile communications, many related researches on this topic have been proposed. In most of the proposed protocols so far, it has been assumed that the person using the mobile station is the registrar of the SIM card; as a matter of, the previous protocols for authentication and session key distribution are built upon this assumption. This way, the mobile user can only verify the identity of the owner of the SIM card. This means that the mobile user can only know that who registers the SIM card with which he communicates. Note that the human voice can be forged. To make sure that the speaker at the other end is the right owner of the SIM card, concept of the password is involved to construct the end-to-end security authentication protocol. In the proposed protocol, each mobile user can choose a password. When two mobile users want to communicate with each other, either user can request to perform a end-user identification process. Only when both of the end users input the correct passwords can the correct common session key be established.     

Performance of GaAs-AlGaAs V-grooved inner stripe quantum-well wirelasers with different current blocking configurations

GaAs-AlGaAs V-grooved inner stripe (VIS) quantum-well wire (QWW) lasers grown by metalorganic chemical vapor deposition with different current blocking configurations, n-blocking on p-substrate (VIPS), p-n-p-n blocking on n-substrate (VI(PN)_nS) and p-blocking on n-substrate (VINS) have been fabricated and characterized. The VIPS QWW lasers show the most stable characteristics with effective current confinement: one of the lasers shows fundamental transverse mode, lasing up to 5 mW/facet, typical threshold current of 39.9 mA at 818.5 mm, an external differential quantum efficiency of 24%/facet, and characteristic temperature of 92 K. The current tuning rate was almost linear at 0.031 mm/mA, and the temperature tuning rate was measured to be 0.14 nm/°C. Comparison of the light output versus current characteristics of the lasers with different current blocking configurations is presented here