171,212 research outputs found
Systematic design approach for optimized resonantly enhanced Mach-Zehnder modulators
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
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
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
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
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
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
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
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
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
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 in
three different ways and find 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
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