171,212 research outputs found

    Systematic design approach for optimized resonantly enhanced Mach-Zehnder modulators

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    A systematic design approach using the developed numerical model for the investigation of any arbitrary electrooptic modulator configuration is described, and its application to the simulation and synthesis of resonantly enhanced Mach-Zehnder modulators (RE-MZMs) is demonstrated. The tool is implemented using equivalent circuit model using transmission lines, lumped elements, and N-port S-parameters. The numerical tool is used to simulate the modulation enhancement factor and radio frequency (RF) return loss of a number of theoretically and experimentally demonstrated examples. Finally, the design tool is used to synthesize a new optimized RE-MZM. This RE-MZM is fabricated and measured, and predicted results are compared

    Load flow studies on stand alone microgrid system in Ranau, Sabah

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    This paper presents the power flow or load flow analysis of Ranau microgrid, a standalone microgrid in the district of Ranau,West Coast Division of Sabah. Power flow for IEEE 9 bus also performed and analyzed. Power flow is define as an important tool involving numerical analysis applied to power system. Power flow uses simplified notation such as one line diagram and per-unit system focusing on voltages, voltage angles, real power and reactive power. To achieved that purpose, this research is done by analyzing the power flow analysis and calculation of all the elements in the microgrid such as generators, buses, loads, transformers, transmission lines using the Power Factory DIGSilent 14 software to calculate the power flow. After the analysis and calculations, the results were analysed and compared

    Comparison of Field-To-Line Coupling Models: Coupled Transmission Lines Model versus Single-cell Corrected Taylor Model

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    International audienceModels for field-to-line coupling are interesting be- cause they help to predict the immunity of PCBs and explain the relation between routing and immunity. In this article a meandered PCB trace illuminated by EM field in a TEM cell is analysed. The near-end and far-end coupling is predicted using two models: a detailed and an approximative one. The detailed model is a circuit of coupled multi-conductor transmission lines evaluated with a circuit simulator. The approximative model consists of a single Taylor cell with an analytical modification evaluated using a numerical computing tool. Both predictions are compared with measurements and turn out to be equally precise. The advantage of the coupled lines model is its flexibility, the advantage of the modified Taylor model is its ease of use

    Multi-parametric Analysis for Mixed Integer Linear Programming: An Application to Transmission Planning and Congestion Control

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    Enhancing existing transmission lines is a useful tool to combat transmission congestion and guarantee transmission security with increasing demand and boosting the renewable energy source. This study concerns the selection of lines whose capacity should be expanded and by how much from the perspective of independent system operator (ISO) to minimize the system cost with the consideration of transmission line constraints and electricity generation and demand balance conditions, and incorporating ramp-up and startup ramp rates, shutdown ramp rates, ramp-down rate limits and minimum up and minimum down times. For that purpose, we develop the ISO unit commitment and economic dispatch model and show it as a right-hand side uncertainty multiple parametric analysis for the mixed integer linear programming (MILP) problem. We first relax the binary variable to continuous variables and employ the Lagrange method and Karush-Kuhn-Tucker conditions to obtain optimal solutions (optimal decision variables and objective function) and critical regions associated with active and inactive constraints. Further, we extend the traditional branch and bound method for the large-scale MILP problem by determining the upper bound of the problem at each node, then comparing the difference between the upper and lower bounds and reaching the approximate optimal solution within the decision makers' tolerated error range. In additional, the objective function's first derivative on the parameters of each line is used to inform the selection of lines to ease congestion and maximize social welfare. Finally, the amount of capacity upgrade will be chosen by balancing the cost-reduction rate of the objective function on parameters and the cost of the line upgrade. Our findings are supported by numerical simulation and provide transmission line planners with decision-making guidance

    Electromagnetic Bottom-Up Optimization for Automated Antenna Designs

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    This paper presents an automated design of antennas by using bottom-up optimization-oriented strategy in conjunction with a full-wave electromagnetic (EM) analysis. The proposed approach firstly set up a co-simulation environment between a commercial Electronic Design Automation (EDA) software and a numerical analyzer. Then bottom-up optimization method is applied by increasing the number of microstrip transmission lines (TLs) and examining various structures of TLs for modeling the antenna geometry. The optimization process is automated using ADS and MATLAB. ADS is preferred among other EDA tools as EM analysis criteria can be optimized well in this tool. In particular, the optimization method is applied for designing two single antennas in the operation bands of 16.3 GHz - 17.43 GHz (Ku band) and 10.1 GHz-10.9 GHz (X band), respectively. The optimized antennas exhibit gain performance between 5.57 dB-8.6 dB and 2.12 dB-4.1 dB, respectively. The simulated results have also been positively tested in Ansys HFSS tool

    The semiclassical tool in mesoscopic physics

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    Semiclassical methods are extremely valuable in the study of transport and thermodynamical properties of ballistic microstructures. By expressing the conductance in terms of classical trajectories, we demonstrate that quantum interference phenomena depend on the underlying classical dynamics of non-interacting electrons. In particular, we are able to calculate the characteristic length of the ballistic conductance fluctuations and the weak localization peak in the case of chaotic dynamics. Integrable cavities are not governed by single scales, but their non-generic behavior can also be obtained from semiclassical expansions (over isolated trajectories or families of trajectories, depending on the system). The magnetic response of a microstructure is enhanced with respect to the bulk (Landau) susceptibility, and the semiclassical approach shows that this enhancement is the largest for integrable geometries, due to the existence of families of periodic orbits. We show how the semiclassical tool can be adapted to describe weak residual disorder, as well as the effects of electron-electron interactions. The interaction contribution to the magnetic susceptibility also depends on the nature of the classical dynamics of non-interacting electrons, and is parametrically larger in the case of integrable systems.Comment: Latex, Cimento-varenna style, 82 pages, 21 postscript figures; lectures given in the CXLIII Course "New Directions in Quantum Chaos" on the International School of Physics "Enrico Fermi"; Varenna, Italy, July 1999; to be published in Proceeding

    Soliton Propagation in Chains with Simple Nonlocal Defects

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    We study the propagation of solitons on complex chains built by inserting finite graphs at two sites of an unbranched chain. We compare numerical findings with the results of an analytical linear approximation scheme describing the interaction of large-fast solitons with non-local topological defects on a chain. We show that the transmission properties of the solitons strongly depend on the structure of the inserted graph, giving a tool to control the soliton propagation through the choice of pertinent graphs to be attached to the chain.Comment: Published in the special issue of Physica D from a conference on 'Nonlinear Physics: Condensed Matter, Dynamical Systems and Biophysics' held in honour of Serge Aubr

    Design of metallic nanoparticles gratings for filtering properties in the visible spectrum

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    Plasmonic resonances in metallic nanoparticles are exploited to create efficient optical filtering functions. A Finite Element Method is used to model metallic nanoparticles gratings. The accuracy of this method is shown by comparing numerical results with measurements on a two-dimensional grating of gold nanocylinders with elliptic cross section. Then a parametric analysis is performed in order to design efficient filters with polarization dependent properties together with high transparency over the visible range. The behavior of nanoparticle gratings is also modelled using the Maxwell-Garnett homogenization theory and analyzed by comparison with the diffraction by a single nanoparticle. The proposed structures are intended to be included in optical systems which could find innovative applications.Comment: submitted to Applied Optic

    Planar compact array with parasitic elements for MIMO systems

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    A compact planar array with parasitic elements is studied to be used in MIMO systems. Classical compact arrays suffer from high coupling which makes correlation and matching efficiency to be worse. A proper matching network improves these lacks although its bandwidth is low and may increase the antenna size. The proposed antenna makes use of parasitic elements to improve both correlation and efficiency. A specific software based on MoM has been developed to analyze radiating structures with several feed points. The array is optimized through a Genetic Algorithm to determine parasitic elements position in order to fulfill different figures of merit. The proposed design provides the required correlation and matching efficiency to have a good performance over a significant bandwidth

    Topological delocalization in the completely disordered two-dimensional quantum walk

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    We investigate numerically and theoretically the effect of spatial disorder on two-dimensional split-step discrete-time quantum walks with two internal "coin" states. Spatial disorder can lead to Anderson localization, inhibiting the spread of quantum walks, putting them at a disadvantage against their diffusively spreading classical counterparts. We find that spatial disorder of the most general type, i.e., position-dependent Haar random coin operators, does not lead to Anderson localization but to a diffusive spread instead. This is a delocalization, which happens because disorder places the quantum walk to a critical point between different anomalous Floquet-Anderson insulating topological phases. We base this explanation on the relationship of this general quantum walk to a simpler case more studied in the literature and for which disorder-induced delocalization of a topological origin has been observed. We review topological delocalization for the simpler quantum walk, using time evolution of the wave functions and level spacing statistics. We apply scattering theory to two-dimensional quantum walks and thus calculate the topological invariants of disordered quantum walks, substantiating the topological interpretation of the delocalization and finding signatures of the delocalization in the finite-size scaling of transmission. We show criticality of the Haar random quantum walk by calculating the critical exponent η\eta in three different ways and find η\eta ≈\approx 0.52 as in the integer quantum Hall effect. Our results showcase how theoretical ideas and numerical tools from solid-state physics can help us understand spatially random quantum walks.Comment: 18 pages, 18 figures. Similar to the published version. Comments are welcom
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