810 research outputs found
Spontaneous transition to a fast 3D turbulent reconnection regime
We show how the conversion of magnetic field energy via magnetic reconnection
can progress in a fully three-dimensional, fast, volume-filling regime. An
initial configuration representative of many laboratory, space and
astrophysical plasmas spontaneously evolves from the well-known regime of slow,
resistive reconnection to a new regime that allows to explain the rates of
energy transfer observed in jets emitted from accretion disks, in stellar/solar
flare processes as well as in laboratory plasmas. This process does not require
any pre-existing turbulence seed which often is not observed in the host
systems prior to the onset of the energy conversion. The dynamics critically
depends on the interplay of perturbations developing along the magnetic field
lines and across them, a process possible only in three-dimensions. The
simulations presented here are the first able to show this transition in a
fully three-dimensional configuration.Comment: 6 pages, 6 figure
Intermittent predictive control of an inverted pendulum
Intermittent predictive pole-placement control is successfully applied to the constrained-state control of a prestabilised experimental inverted pendulum
Residual stress measurement in thin films using the semi-destructive ring-core drilling method using Focused Ion Beam
In the present study, residual stress evaluation in thin films was achieved using a semi-destructive trench-cutting method. Focused Ion Beam (FIB) was employed to introduce the strain relief by ring-core milling, i.e. creating a trench around an "island". Either SEM or FIB imaging can be used to record sequences of images for strain change evaluation by Digital Image Correlation (DIC) analysis of micrographs. A regular array of shallow holes was drilled on a thin overlayer of Pt (∼100nm) deposited on to the film prior to patterning and trenching, in order to reduce the damage introduced by the ion beam during imaging and to assist the DIC strain evaluation by adding traceable markers. Finite Element (FE) simulation was also carried out to predict the curves for strain relief as a function of milling depth, and compared with the experimental measurements, which show good agreement with each other. An empirical mathematical description of the curves was proposed that allows efficient residual stress evaluation in thin solid films. © 2011 Published by Elsevier Ltd
Water demand forecasting for the optimal operation of large-scale drinking water networks: The Barcelona case study
Trabajo presentado al 19th IFAC World Congress celebrado del 24 al 29 de agosto de 2014 en Cape Town (Sudafrica).Drinking Water Networks (DWN) are large-scale multiple-input multiple-output systems with uncertain disturbances (such as the water demand from the consumers) and involve components of linear, non-linear and switching nature. Operating, safety and quality constraints deem it important for the state and the input of such systems to be constrained into a given domain. Moreover, DWNs' operation is driven by time-varying demands and involves an considerable consumption of electric energy and the exploitation of limited water resources. Hence, the management of these networks must be carried out optimally with respect to the use of available resources and infrastructure, whilst satisfying high service levels for the drinking water supply. To accomplish this task, this paper explores various methods for demand forecasting, such as Seasonal ARIMA, BATS and Support Vector Machine, and presents a set of statistically validated time series models. These models, integrated with a Model Predictive Control (MPC) strategy addressed in this paper, allow to account for an accurate on-line forecasting and flow management of a DWN.This work was financially supported by the EU FP7 research project EFFINET “Efficient Integrated Real-time monitoring and Control of Drinking Water Networks,” grant agreement no. 318556.Peer Reviewe
A Map-Reduce Parallel Approach to Automatic Synthesis of Control Software
Many Control Systems are indeed Software Based Control Systems, i.e. control
systems whose controller consists of control software running on a
microcontroller device. This motivates investigation on Formal Model Based
Design approaches for automatic synthesis of control software.
Available algorithms and tools (e.g., QKS) may require weeks or even months
of computation to synthesize control software for large-size systems. This
motivates search for parallel algorithms for control software synthesis.
In this paper, we present a Map-Reduce style parallel algorithm for control
software synthesis when the controlled system (plant) is modeled as discrete
time linear hybrid system. Furthermore we present an MPI-based implementation
PQKS of our algorithm. To the best of our knowledge, this is the first parallel
approach for control software synthesis.
We experimentally show effectiveness of PQKS on two classical control
synthesis problems: the inverted pendulum and the multi-input buck DC/DC
converter. Experiments show that PQKS efficiency is above 65%. As an example,
PQKS requires about 16 hours to complete the synthesis of control software for
the pendulum on a cluster with 60 processors, instead of the 25 days needed by
the sequential algorithm in QKS.Comment: To be submitted to TACAS 2013. arXiv admin note: substantial text
overlap with arXiv:1207.4474, arXiv:1207.409
Magnetic Field Strength in the Upper Solar Corona Using White-light Shock Structures Surrounding Coronal Mass Ejections
To measure the magnetic field strength in the solar corona, we examined 10
fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO
images. By applying piston-shock relationship to the observed CME's standoff
distance and electron density compression ratio, we estimated the Mach number,
Alfven speed, and magnetic field strength in the height range 3 to 15 solar
radii (Rs). Main results from this study are: (1) the standoff distance
observed in solar corona is consistent with those from a magnetohydrodynamic
(MHD) model and near-Earth observations; (2) the Mach number as a shock
strength is in the range 1.49 to 3.43 from the standoff distance ratio, but
when we use the density compression ratio, the Mach number is in the range 1.47
to 1.90, implying that the measured density compression ratio is likely to be
underestimated due to observational limits; (3) the Alfven speed ranges from
259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG
when the standoff distance is used; (4) if we multiply the density compression
ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are
consistent in both methods; (5) the magnetic field strengths derived from the
shock parameters are similar to those of empirical models and previous
estimates.Comment: Accepted for publication in ApJ, 11 Figures, 1 Tabl
Composition Structure of Interplanetary Coronal Mass Ejections From Multispacecraft Observations, Modeling, and Comparison with Numerical Simulations
We present an analysis of the ionic composition of iron for two
interplanetary coronal mass ejections observed in May 21-23 2007 by the ACE and
STEREO spacecraft in the context of the magnetic structure of the ejecta flux
rope, sheath region, and surrounding solar wind flow. This analysis is made
possible due to recent advances in multispacecraft data interpolation,
reconstruction, and visualization as well as results from recent modeling of
ionic charge states in MHD simulations of magnetic breakout and flux
cancellation CME initiation. We use these advances to interpret specific
features of the ICME plasma composition resulting from the magnetic topology
and evolution of the CME. We find that in both the data and our MHD
simulations, the flux ropes centers are relatively cool, while charge state
enhancements surround and trail the flux ropes. The magnetic orientation of the
ICMEs are suggestive of magnetic breakout-like reconnection during the eruption
process, which could explain the spatial location of the observed iron
enhancements just outside the traditional flux rope magnetic signatures and
between the two ICMEs. Detailed comparisons between the simulations and data
were more complicated, but a sharp increase in high iron charge states in the
ACE and STEREO-A data during the second flux rope corresponds well to similar
features in the flux cancellation results. We discuss the prospects of this
integrated in-situ data analysis and modeling approach to advancing our
understanding of the unified CME-to-ICME evolution.Comment: Accepted for submission to The Astrophysical Journa
State Space Realization of Model Predictive Controllers Without Active Constraints
To enable the use of traditional tools for analysis of multivariable controllers such as model predictive control (MPC), we develop a state space formulation for the resulting controller for MPC without constraints or assuming that the constraints are not active. Such a derivation was not found in the literature. The formulation includes a state estimator. The MPC algorithm used is a receding horizon controller with infinite horizon based on a state space process model. When no constraints are active, we obtain a state feedback controller, which is modified to achieve either output tracking, or a combination of input and output tracking. When the states are not available, they need to be estimated from the measurements. It is often recommended to achieve integral action in a MPC by estimating input disturbances and include their effect in the model. We show that to obtain offset free steady state the number of estimated disturbances must equal the number of measurements. The estimator is included in the controller equation, and we obtain a formulation of the overall controller with the set-points and measurements as inputs, and the manipulated variables as outputs. One application of the state space formulation is in combination with the process model to obtain a closed loop model. This can for example be used to check the steady-state solution and see whether integral action is obtained or not
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