Towards sketch-based exploration of terrain : a feasibility study

CISRG discussion paper ; 1

Extraction of Airways with Probabilistic State-space Models and Bayesian Smoothing

Segmenting tree structures is common in several image processing applications. In medical image analysis, reliable segmentations of airways, vessels, neurons and other tree structures can enable important clinical applications. We present a framework for tracking tree structures comprising of elongated branches using probabilistic state-space models and Bayesian smoothing. Unlike most existing methods that proceed with sequential tracking of branches, we present an exploratory method, that is less sensitive to local anomalies in the data due to acquisition noise and/or interfering structures. The evolution of individual branches is modelled using a process model and the observed data is incorporated into the update step of the Bayesian smoother using a measurement model that is based on a multi-scale blob detector. Bayesian smoothing is performed using the RTS (Rauch-Tung-Striebel) smoother, which provides Gaussian density estimates of branch states at each tracking step. We select likely branch seed points automatically based on the response of the blob detection and track from all such seed points using the RTS smoother. We use covariance of the marginal posterior density estimated for each branch to discriminate false positive and true positive branches. The method is evaluated on 3D chest CT scans to track airways. We show that the presented method results in additional branches compared to a baseline method based on region growing on probability images.Comment: 10 pages. Pre-print of the paper accepted at Workshop on Graphs in Biomedical Image Analysis. MICCAI 2017. Quebec Cit

Avancée de Diabrotica virgifera virgifera [Coleoptera : Chrysomelidae] dans les champs de maïs au Québec et collecte dans le soja à Ottawa, Ontario

La chrysomèle des racines du maïs de l’Ouest, Diabrotica virgifera virgifera, a été trouvée au Québec en septembre 2000 dans la région de la Montérégie. Ceci constitue une extension vers le nord de son aire de répartition. De plus, à Ottawa, quelques individus se sont développés à partir du soja. Ceci constitue la première mention de développement de cet insecte sur du soja au Canada.The western corn rootworm, Diabrotica virgifera virgifera, was found in the Monteregie region in the province of Quebec in September 2000. This finding constitutes a northern extension of the species distribution. Moreover, at Ottawa, some specimens were found developing from soybean plants. This constitutes the first mention of development of this insect on soybean in Canada

Boundary interactions changing operators and dynamical correlations in quantum impurity problems

Recent developments have made possible the computation of equilibrium dynamical correlators in quantum impurity problems. In many situations however, one is rather interested in correlators subject to a non equilibrium initial preparation; this is the case for instance for the occupation probability $P(t)$ in the double well problem of dissipative quantum mechanics (DQM). We show in this paper how to handle this situation in the framework of integrable quantum field theories by introducing ``boundary interactions changing operators''. We determine the properties of these operators by using an axiomatic approach similar in spirit to what is done for form-factors. This allows us to obtain new exact results for $P(t)$; for instance, we find that that at large times (or small $g$), the leading behaviour for g < 1/2} is $P(t)\propto e^{-\Gamma t}\cos\Omega t$, with the universal ratio. $\Omega/\Gamma = \cot {\pi g}/{2(1-g)}$.Comment: 4 pages, revte

Exact Friedel oscillations in the g=1/2 Luttinger liquid

A single impurity in the 1D Luttinger model creates a local modification of the charge density analogous to the Friedel oscillations. In this paper, we present an exact solution of the case $g={1\over 2}$ (the equivalent of the Toulouse point) at any temperature $T$ and impurity coupling, expressing the charge density in terms of a hypergeometric function. We find in particular that at $T=0$, the oscillatory part of the density goes as $\ln x$ at small distance and $x^{-1/2}$ at large distance.Comment: 1 reference added. 13 pages, harvma

Colored noise in the fractional Hall effect: duality relations and exact results

We study noise in the problem of tunneling between fractional quantum Hall edge states within a four probe geometry. We explore the implications of the strong-weak coupling duality symmetry existent in this problem for relating the various density-density auto-correlations and cross-correlations between the four terminals. We identify correlations that transform as either ``odd'' or ``anti-symmetric'', or ``even'' or ``symmetric'' quantities under duality. We show that the low frequency noise is colored, and that the deviations from white noise are exactly related to the differential conductance. We show explicitly that the relationship between the slope of the low frequency noise spectrum and the differential conductance follows from an identity that holds to {\it all} orders in perturbation theory, supporting the results implied by the duality symmetry. This generalizes the results of quantum supression of the finite frequency noise spectrum to Luttinger liquids and fractional statistics quasiparticles.Comment: 14 pages, 3 figure

Anti-Reflection Coating for Nitrogen-Vacancy Optical Measurements in Diamond

We realize anti-reflection (AR) coatings for optical excitation and fluorescence measurements of nitrogen-vacancy (NV) color centers in bulk diamond by depositing quarter-wavelength thick silica layers on the diamondsurface. These AR coatings improve NV-diamond optical measurements by reducing optical reflection at the diamond-air interface from ≈17% to ≈2%, which allows more effective NV optical excitation and more efficient detection of NV fluorescence. We also show that diamondAR coatings eliminate standing-wave interference patterns of excitation laser intensity within bulk diamond, and thereby greatly reduce spatial variations in NV fluorescence, which can degrade spatially resolved magnetic field sensing using NV centers.Engineering and Applied SciencesPhysic

Hyperelliptic curves for multi-channel quantum wires and the multi-channel Kondo problem

We study the current in a multi-channel quantum wire and the magnetization in the multi-channel Kondo problem. We show that at zero temperature they can be written simply in terms of contour integrals over a (two-dimensional) hyperelliptic curve. This allows one to easily demonstrate the existence of weak-coupling to strong-coupling dualities. In the Kondo problem, the curve is the same for under- and over-screened cases; the only change is in the contour.Comment: 7 pages, 1 figure, revte

The Transition Between Quantum Coherence and Incoherence

We show that a transformed Caldeira-Leggett Hamltonian has two distinct families of fixed points, rather than a single unique fixed point as often conjectured based on its connection to the anisotropic Kondo model. The two families are distinguished by a sharp qualitative difference in their quantum coherence properties and we argue that this distinction is best understood as the result of a transition in the model between degeneracy and non-degeneracy in the spectral function of the ``spin-flip'' operator.Comment: some typos corrected and a reference adde

3D Geometric Analysis of Tubular Objects based on Surface Normal Accumulation

This paper proposes a simple and efficient method for the reconstruction and extraction of geometric parameters from 3D tubular objects. Our method constructs an image that accumulates surface normal information, then peaks within this image are located by tracking. Finally, the positions of these are optimized to lie precisely on the tubular shape centerline. This method is very versatile, and is able to process various input data types like full or partial mesh acquired from 3D laser scans, 3D height map or discrete volumetric images. The proposed algorithm is simple to implement, contains few parameters and can be computed in linear time with respect to the number of surface faces. Since the extracted tube centerline is accurate, we are able to decompose the tube into rectilinear parts and torus-like parts. This is done with a new linear time 3D torus detection algorithm, which follows the same principle of a previous work on 2D arc circle recognition. Detailed experiments show the versatility, accuracy and robustness of our new method.Comment: in 18th International Conference on Image Analysis and Processing, Sep 2015, Genova, Italy. 201