173,106 research outputs found
Nonlinear mechanisms in passive microwave devices
Premi extraordinari doctorat curs 2010-2011, Ă mbit dâEnginyeria de les TICThe telecommunications industry follows a tendency towards smaller devices, higher power and higher frequency, which imply an increase on the complexity of the electronics involved. Moreover, there is a need for extended capabilities like frequency tunable devices, ultra-low losses or high power handling, which make use of advanced materials for these purposes. In addition, increasingly demanding communication standards and regulations push the limits of the acceptable performance degrading indicators. This is the case of nonlinearities, whose effects, like increased Adjacent Channel Power Ratio (ACPR), harmonics, or intermodulation distortion among others, are being included in the performance requirements, as maximum tolerable levels.
In this context, proper modeling of the devices at the design stage is of crucial importance in predicting not only the device performance but also the global system indicators and to make sure that the requirements are fulfilled. In accordance with that, this work proposes the necessary steps for circuit models implementation of different passive microwave devices, from the linear and nonlinear measurements to the simulations to validate them. Bulk acoustic wave resonators and transmission lines made of high temperature superconductors, ferroelectrics or regular metals and dielectrics are the subject of this work. Both phenomenological and physical approaches are considered and circuit models are proposed and compared with measurements. The nonlinear observables, being harmonics, intermodulation distortion, and saturation or detuning, are properly related to the material properties that originate them. The obtained models can be used in circuit simulators to predict the performance of these microwave devices under complex modulated signals, or even be used to predict their performance when integrated into more complex systems. A key step to achieve this goal is an accurate characterization of materials and devices, which is faced by making use of advanced measurement techniques. Therefore, considerations on special measurement setups are being made along this thesis.Award-winningPostprint (published version
Cascading Power Outages Propagate Locally in an Influence Graph that is not the Actual Grid Topology
In a cascading power transmission outage, component outages propagate
non-locally, after one component outages, the next failure may be very distant,
both topologically and geographically. As a result, simple models of
topological contagion do not accurately represent the propagation of cascades
in power systems. However, cascading power outages do follow patterns, some of
which are useful in understanding and reducing blackout risk. This paper
describes a method by which the data from many cascading failure simulations
can be transformed into a graph-based model of influences that provides
actionable information about the many ways that cascades propagate in a
particular system. The resulting "influence graph" model is Markovian, in that
component outage probabilities depend only on the outages that occurred in the
prior generation. To validate the model we compare the distribution of cascade
sizes resulting from contingencies in a branch test case to
cascade sizes in the influence graph. The two distributions are remarkably
similar. In addition, we derive an equation with which one can quickly identify
modifications to the proposed system that will substantially reduce cascade
propagation. With this equation one can quickly identify critical components
that can be improved to substantially reduce the risk of large cascading
blackouts.Comment: Accepted for publication at the IEEE Transactions on Power System
Exploring Interacting Quantum Many-Body Systems by Experimentally Creating Continuous Matrix Product States in Superconducting Circuits
Improving the understanding of strongly correlated quantum many body systems
such as gases of interacting atoms or electrons is one of the most important
challenges in modern condensed matter physics, materials research and
chemistry. Enormous progress has been made in the past decades in developing
both classical and quantum approaches to calculate, simulate and experimentally
probe the properties of such systems. In this work we use a combination of
classical and quantum methods to experimentally explore the properties of an
interacting quantum gas by creating experimental realizations of continuous
matrix product states - a class of states which has proven extremely powerful
as a variational ansatz for numerical simulations. By systematically preparing
and probing these states using a circuit quantum electrodynamics (cQED) system
we experimentally determine a good approximation to the ground-state wave
function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose
gas in one dimension. Since the simulated Hamiltonian is encoded in the
measurement observable rather than the controlled quantum system, this approach
has the potential to apply to exotic models involving multicomponent
interacting fields. Our findings also hint at the possibility of experimentally
exploring general properties of matrix product states and entanglement theory.
The scheme presented here is applicable to a broad range of systems exploiting
strong and tunable light-matter interactions.Comment: 11 pages, 9 figure
Efficient transient simulation of transmission lines
The paper focuses on revealing the salient structural aspects of a new transmission-line model with a view to exploiting them for gains in efficiency and accuracy. The new transmission-line model has as its basis the Telegraphers Equations but the manner of solution is what distinguishes the new approach from existing transmission-line simulation techniques. The technique is based on identifying natural modes of oscillation on the transmission line. The result is a model structure which can be tailored to the accuracy requirements of a simulation and which is amenable to tuning to fit measured admittance data
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Diagnostic Applications for Micro-Synchrophasor Measurements
This report articulates and justifies the preliminary selection of diagnostic applications for data from micro-synchrophasors (”PMUs) in electric power distribution systems that will be further studied and developed within the scope of the three-year ARPA-e award titled Micro-synchrophasors for Distribution Systems
Random walk with barriers: Diffusion restricted by permeable membranes
Restrictions to molecular motion by barriers (membranes) are ubiquitous in
biological tissues, porous media and composite materials. A major challenge is
to characterize the microstructure of a material or an organism
nondestructively using a bulk transport measurement. Here we demonstrate how
the long-range structural correlations introduced by permeable membranes give
rise to distinct features of transport. We consider Brownian motion restricted
by randomly placed and oriented permeable membranes and focus on the
disorder-averaged diffusion propagator using a scattering approach. The
renormalization group solution reveals a scaling behavior of the diffusion
coefficient for large times, with a characteristically slow inverse square root
time dependence. The predicted time dependence of the diffusion coefficient
agrees well with Monte Carlo simulations in two dimensions. Our results can be
used to identify permeable membranes as restrictions to transport in disordered
materials and in biological tissues, and to quantify their permeability and
surface area.Comment: 8 pages, 3 figures; origin of dispersion clarified, refs adde
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