45,924 research outputs found
A New Approach to Probing Primordial Non-Gaussianity
We address the dual challenge of estimating deviations from Gaussianity
arising in models of the Early Universe, whilst retaining information necessary
to assess whether a detection of non-Gaussianity is primordial. We do this by
constructing a new statistic, the bispectrum-related power spectrum, which is
constructed from a map of the Cosmic Microwave Background. The estimator is
optimised for primordial non-Gaussianity detection, but can also be useful in
distinguishing primordial non-Gaussianity from secondary non-Gaussianity, such
as may arise from unsubtracted point sources, or residuals from component
separation. Extending earlier studies we present unbiased non-Gaussianity
estimators optimised for partial sky coverage and inhomogeneous noise
associated with realistic scan strategies, but which retain the ability to
assess foreground contamination.Comment: 13 pages, 1 figur
Preconditioned Bi-Conjugate Gradient Method for Radiative Transfer in Spherical Media
A robust numerical method called the Preconditioned Bi-Conjugate Gradient
(Pre-BiCG)method is proposed for the solution of radiative transfer equation in
spherical geometry.A variant of this method called Stabilized Preconditioned
Bi-Conjugate Gradient (Pre-BiCG-STAB) is also presented. These are iterative
methods based on the construction of a set of bi-orthogonal vectors. The
application of Pre-BiCG method in some benchmark tests show that the method is
quite versatile, and can handle hard problems that may arise in astrophysical
radiative transfer theory.Comment: 19 pages, 12 figure
Impact of Galactic polarized emission on B-mode detection at low multipoles
We use a model of polarized Galactic emission developed by the the Planck
collaboration to assess the impact of foregrounds on B-mode detection at low
multipoles. Our main interest is to applications of noisy polarization data and
in particular to assessing the feasibility of B-mode detection by Planck. This
limits the complexity of foreground subtraction techniques that can be applied
to the data. We analyze internal linear combination techniques and show that
the offset caused by the dominant E-mode polarization pattern leads to a
fundamental limit of r approximately 0.1 for the tensor-scalar ratio even in
the absence of instrumental noise. We devise a simple, robust, template fitting
technique using multi-frequency polarization maps. We show that template
fitting using Planck data alone offers a feasible way of recovering primordial
B-modes from dominant foreground contamination, even in the presence of noise
on the data and templates. We implement and test a pixel-based scheme for
computing the likelihood function of cosmological parameters at low multipoles
that incorporates foreground subtraction of noisy data.Comment: 20 pages, 10 figure
A Perturbation Scheme for Passivity Verification and Enforcement of Parameterized Macromodels
This paper presents an algorithm for checking and enforcing passivity of
behavioral reduced-order macromodels of LTI systems, whose frequency-domain
(scattering) responses depend on external parameters. Such models, which are
typically extracted from sampled input-output responses obtained from numerical
solution of first-principle physical models, usually expressed as Partial
Differential Equations, prove extremely useful in design flows, since they
allow optimization, what-if or sensitivity analyses, and design centering.
Starting from an implicit parameterization of both poles and residues of the
model, as resulting from well-known model identification schemes based on the
Generalized Sanathanan-Koerner iteration, we construct a parameter-dependent
Skew-Hamiltonian/Hamiltonian matrix pencil. The iterative extraction of purely
imaginary eigenvalues ot fhe pencil, combined with an adaptive sampling scheme
in the parameter space, is able to identify all regions in the
frequency-parameter plane where local passivity violations occur. Then, a
singular value perturbation scheme is setup to iteratively correct the model
coefficients, until all local passivity violations are eliminated. The final
result is a corrected model, which is uniformly passive throughout the
parameter range. Several numerical examples denomstrate the effectiveness of
the proposed approach.Comment: Submitted to the IEEE Transactions on Components, Packaging and
Manufacturing Technology on 13-Apr-201
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Integrated Dynamic Facade Control with an Agent-based Architecture for Commercial Buildings
Dynamic façades have significant technical potential to minimize heating, cooling, and lighting energy use and peak electric demand in the perimeter zone of commercial buildings, but the performance of these systems is reliant on being able to balance complex trade-offs between solar control, daylight admission, comfort, and view over the life of the installation. As the context for controllable energy-efficiency technologies grows more complex with the increased use of intermittent renewable energy resources on the grid, it has become increasingly important to look ahead towards more advanced approaches to integrated systems control in order to achieve optimum life-cycle performance at a lower cost. This study examines the feasibility of a model predictive control system for low-cost autonomous dynamic façades. A system architecture designed around lightweight, simple agents is proposed. The architecture accommodates whole building and grid level demands through its modular, hierarchical approach. Automatically-generated models for computing window heat gains, daylight illuminance, and discomfort glare are described. The open source Modelica and JModelica software tools were used to determine the optimum state of control given inputs of window heat gains and lighting loads for a 24-hour optimization horizon. Penalty functions for glare and view/ daylight quality were implemented as constraints. The control system was tested on a low-power controller (1.4 GHz single core with 2 GB of RAM) to evaluate feasibility. The target platform is a low-cost ($35/unit) embedded controller with 1.2 GHz dual-core cpu and 1 GB of RAM. Configuration and commissioning of the curtainwall unit was designed to be largely plug and play with minimal inputs required by the manufacturer through a web-based user interface. An example application was used to demonstrate optimal control of a three-zone electrochromic window for a south-facing zone. The overall approach was deemed to be promising. Further engineering is required to enable scalable, turnkey solutions
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