8,257 research outputs found
Connectivity-Enforcing Hough Transform for the Robust Extraction of Line Segments
Global voting schemes based on the Hough transform (HT) have been widely used
to robustly detect lines in images. However, since the votes do not take line
connectivity into account, these methods do not deal well with cluttered
images. In opposition, the so-called local methods enforce connectivity but
lack robustness to deal with challenging situations that occur in many
realistic scenarios, e.g., when line segments cross or when long segments are
corrupted. In this paper, we address the critical limitations of the HT as a
line segment extractor by incorporating connectivity in the voting process.
This is done by only accounting for the contributions of edge points lying in
increasingly larger neighborhoods and whose position and directional content
agree with potential line segments. As a result, our method, which we call
STRAIGHT (Segment exTRAction by connectivity-enforcInG HT), extracts the
longest connected segments in each location of the image, thus also integrating
into the HT voting process the usually separate step of individual segment
extraction. The usage of the Hough space mapping and a corresponding
hierarchical implementation make our approach computationally feasible. We
present experiments that illustrate, with synthetic and real images, how
STRAIGHT succeeds in extracting complete segments in several situations where
current methods fail.Comment: Submitted for publicatio
Macroeconomic Volatility Trade-off and Monetary Policy Regime in the Euro Area
This research uncovers a well-defined monetary policy regime starting in 1986 in the aggregate Euro Area. Both alternative solution-estimation methods employed - optimal control cum GMM, and dynamic programming cum FIML - identify a regime of strict inflation targeting with interest rate smoothing. The unemployment gap, properly estimated as quasi real-time information, is a relevant element in the information set of the monetary authority, despite not being included in its preferences. The emergence of the regime relates to the improvement of the volatility trade-off between inflation and unemployment gap since the mid-80s. Additional improving factors have been milder supply shocks and better ability of policymakers to set the interest rate closer to optimum.Monetary Policy Regime, Euro Area, Optimal Control, Dynamic Programming, GMM, FIML.
Testing for Asymmetries in the Preferences of the Euro-Area Monetary Policymaker
This paper tests for asymmetries in the preferences of the Euro-Area monetary policymaker with 1995:I-2004:III data from the last update of the ECB's Area-wide database. Following the relevant literature, we distinguish between three types of asymmetry: precautionary demand for expansions, precautionary demand for price stability and interest rate smoothing asymmetry. Based on the joint GMM estimation of the Euler equation of optimal policy and the AS-AD structure of the macroeconomy, we find evidence of precautionary demand for price stability in the preferences revealed by the monetary policymaker. This type of asymmetry is consistent with the ECB’s definition of price stability and with the priority of credibility-building by a recently created monetary authority.Central Bank Preferences, Asymmetry, Euro Area, Optimal Control, GMM.
Growth Cycles in XXth Century European Industrial Productivity: Unbiased Variance Estimation in a Time-varying Parameter Model
This note applies the median unbiased estimation of coefficient variance, proposed by Stock and Watson (1998), to the extraction of the time-varying trend growth rate of industrial productivity in fifteen European countries, over most of the XXth Century, by means of an unobservable components univariate decomposition. In addition to the description of the procedure, this illustration is particularly useful in explaining why the method is especially appropriate for comparison of trends growth rates extracted from time series with diverse degrees of variability.unobservable components model; industrial productivity; growth cycles; Europe.
Rutherford scattering with radiation damping
We study the effect of radiation damping on the classical scattering of
charged particles. Using a perturbation method based on the Runge-Lenz vector,
we calculate radiative corrections to the Rutherford cross section, and the
corresponding energy and angular momentum losses.Comment: Latex, 11 pages, 4 eps figure
Revisiting Complex Moments For 2D Shape Representation and Image Normalization
When comparing 2D shapes, a key issue is their normalization. Translation and
scale are easily taken care of by removing the mean and normalizing the energy.
However, defining and computing the orientation of a 2D shape is not so simple.
In fact, although for elongated shapes the principal axis can be used to define
one of two possible orientations, there is no such tool for general shapes. As
we show in the paper, previous approaches fail to compute the orientation of
even noiseless observations of simple shapes. We address this problem. In the
paper, we show how to uniquely define the orientation of an arbitrary 2D shape,
in terms of what we call its Principal Moments. We show that a small subset of
these moments suffice to represent the underlying 2D shape and propose a new
method to efficiently compute the shape orientation: Principal Moment Analysis.
Finally, we discuss how this method can further be applied to normalize
grey-level images. Besides the theoretical proof of correctness, we describe
experiments demonstrating robustness to noise and illustrating the method with
real images.Comment: 69 pages, 20 figure
Backward stochastic differential equation approach to modeling of gene expression
In this article, we introduce a novel backward method to model stochastic
gene expression and protein level dynamics. The protein amount is regarded as a
diffusion process and is described by a backward stochastic differential
equation (BSDE). Unlike many other SDE techniques proposed in the literature,
the BSDE method is backward in time; that is, instead of initial conditions it
requires the specification of endpoint ("final") conditions, in addition to the
model parametrization. To validate our approach we employ Gillespie's
stochastic simulation algorithm (SSA) to generate (forward) benchmark data,
according to predefined gene network models. Numerical simulations show that
the BSDE method is able to correctly infer the protein level distributions that
preceded a known final condition, obtained originally from the forward SSA.
This makes the BSDE method a powerful systems biology tool for time reversed
simulations, allowing, for example, the assessment of the biological conditions
(e.g. protein concentrations) that preceded an experimentally measured event of
interest (e.g. mitosis, apoptosis, etc.).Comment: Accepted in Physical Review
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