612 research outputs found
Multifractional processes with random exponent
Multifractional Processes with Random Exponent (MPRE) are obtained by replacing the Hurst parameter of Fractional Brownian Motion (FBM) with a stochastic process. This process need not be independent of the white noise generating the FBM. MPREs can be conveniently represented as random wavelet series. We will use this type of representation to study their Hölder regularity and their self-similarity
A process very similar to multifractional Brownian motion
In Ayache and Taqqu (2005), the multifractional Brownian (mBm) motion is
obtained by replacing the constant parameter of the fractional Brownian
motion (fBm) by a smooth enough functional parameter depending on the
time . Here, we consider the process obtained by replacing in the
wavelet expansion of the fBm the index by a function depending on
the dyadic point . This process was introduced in Benassi et al (2000)
to model fBm with piece-wise constant Hurst index and continuous paths. In this
work, we investigate the case where the functional parameter satisfies an
uniform H\"older condition of order \beta>\sup_{t\in \rit} H(t) and ones
shows that, in this case, the process is very similar to the mBm in the
following senses: i) the difference between and a mBm satisfies an uniform
H\"older condition of order ; ii) as a by product, one
deduces that at each point the pointwise H\"older exponent of is
and that is tangent to a fBm with Hurst parameter .Comment: 18 page
Asymptotic normality for a modified quadratic variation of the Hermite process
We consider a modified quadratic variation of the Hermite process based on
some well-chosen increments of this process. These special increments have the
very useful property to be independent and identically distributed up to
asymptotically negligible remainders. We prove that this modified quadratic
variation satisfies a Central Limit Theorem and we derive its rate of
convergence under the Wasserstein distance via Stein-Malliavin calculus. As a
consequence, we construct, for the first time in the literature related to
Hermite processes, a strongly consistent and asymptotically normal estimator
for the Hurst parameter
Radiotherapy planning for glioblastoma based on a tumor growth model: Improving target volume delineation
Glioblastoma are known to infiltrate the brain parenchyma instead of forming
a solid tumor mass with a defined boundary. Only the part of the tumor with
high tumor cell density can be localized through imaging directly. In contrast,
brain tissue infiltrated by tumor cells at low density appears normal on
current imaging modalities. In clinical practice, a uniform margin is applied
to account for microscopic spread of disease.
The current treatment planning procedure can potentially be improved by
accounting for the anisotropy of tumor growth: Anatomical barriers such as the
falx cerebri represent boundaries for migrating tumor cells. In addition, tumor
cells primarily spread in white matter and infiltrate gray matter at lower
rate. We investigate the use of a phenomenological tumor growth model for
treatment planning. The model is based on the Fisher-Kolmogorov equation, which
formalizes these growth characteristics and estimates the spatial distribution
of tumor cells in normal appearing regions of the brain. The target volume for
radiotherapy planning can be defined as an isoline of the simulated tumor cell
density.
A retrospective study involving 10 glioblastoma patients has been performed.
To illustrate the main findings of the study, a detailed case study is
presented for a glioblastoma located close to the falx. In this situation, the
falx represents a boundary for migrating tumor cells, whereas the corpus
callosum provides a route for the tumor to spread to the contralateral
hemisphere. We further discuss the sensitivity of the model with respect to the
input parameters. Correct segmentation of the brain appears to be the most
crucial model input.
We conclude that the tumor growth model provides a method to account for
anisotropic growth patterns of glioblastoma, and may therefore provide a tool
to make target delineation more objective and automated
Information-Theoretic Active Learning for Content-Based Image Retrieval
We propose Information-Theoretic Active Learning (ITAL), a novel batch-mode
active learning method for binary classification, and apply it for acquiring
meaningful user feedback in the context of content-based image retrieval.
Instead of combining different heuristics such as uncertainty, diversity, or
density, our method is based on maximizing the mutual information between the
predicted relevance of the images and the expected user feedback regarding the
selected batch. We propose suitable approximations to this computationally
demanding problem and also integrate an explicit model of user behavior that
accounts for possible incorrect labels and unnameable instances. Furthermore,
our approach does not only take the structure of the data but also the expected
model output change caused by the user feedback into account. In contrast to
other methods, ITAL turns out to be highly flexible and provides
state-of-the-art performance across various datasets, such as MIRFLICKR and
ImageNet.Comment: GCPR 2018 paper (14 pages text + 2 pages references + 6 pages
appendix
Hydrographic network extraction and watersheds delimitation software of the South Oran (North Wester Algeria)
The development of space technology has allowed a better understanding and effective use of water resources through the use of Digital Terrain Models (DTM) Mapping the river system from DTM has two objectives, namely identifying first topography descriptors like hills, ridges and valleys of watersheds and second hydrological parameters to map areas of runoff recovery for a more efficient development and also a better representation of the actual land occupation. Our work is part of a methodological approach to satellite imagery processing and mapping of topographic and hydrographic parameters of watersheds. Thus, from DTM one was able to extract the full river system of the region. The results show a remarkable evolution of human activities and especially in areas of high water recovery capacity.Keywords: remote sensing, DTM, network hydrology, geographic, steppe, west of Algeria
Magnetic properties and phase diagrams of a bilayer spin-3/2 Ising model
The magnetic properties and phase diagrams of a bilayer spin-3/2 Ising model is studied, under the effect of crystal field, using the mean field (MF) theory and the Monte Carlo (MC) simulations. The ground state phase diagrams in the (Js1 / J, ∆s1 / J) and (Js2 / J, ∆s1 / J) planes are determined analytically. On the other hand, the magnetization and critical temperature is studied. The results found by the two methods are in good agreement with the ground state phase diagram. It was found that the critical temperature calculated by Monte Carlo simulations is less than that one obtained by the mean field method, for both positive and negative crystal field acting on each layer of the film.The magnetic properties and phase diagrams of a bilayer spin-3/2 Ising model is studied, under the effect of crystal field, using the mean field (MF) theory and the Monte Carlo (MC) simulations. The ground state phase diagrams in the (Js1 / J, ∆s1 / J) and (Js2 / J, ∆s1 / J) planes are determined analytically. On the other hand, the magnetization and critical temperature is studied. The results found by the two methods are in good agreement with the ground state phase diagram. It was found that the critical temperature calculated by Monte Carlo simulations is less than that one obtained by the mean field method, for both positive and negative crystal field acting on each layer of the film
Axial stereovision: modeling and calibration of the optical system, 3D reconstruction of natural objects
In passive binocular stereovision, we generally discern two approaches : the lateral
stereovision and the axial stereovision . We present here a study relating more
particularly to axial stereovision .
The axial systems have been studied by numerous research teams because of
their relative geometrical plainness which makes them interesting for industrial
applications, by simplifying the matching phase . Among the optical systems
previously studied, and able to be axial, we find
- a camera with a zoom,
- a camera moving along its optical axis .
In this paper we first present the geometrical model of an axial stereovision system .
Then, we describe a robust calibration method of such a system . This method takes
into account the fact that the optical systems described above are not strictly axial
because there always remain mechanical problems that do not allow a perfect
motion of the optical center along the optical axis .
Finally, we present a matching algorithm allowing to match characteristic points
present in the images and making thus possible the reconstruction ofnon polyhedral
objects .En stéréovision binoculaire passive, on distingue généralement deux approches: la stéréovision latérale et la stéréovision axiale. Nous présentons ici une étude portant plus particulièrement sur la stéréovision axiale. Les systèmes axiaux ont été étudiés par de nombreuses équipes de recherche, en raison de leur relative simplicité géométrique qui les rend intéressants pour des applications industrielles, en simplifiant la phase de mise en correspondance. Parmi les systèmes optiques étudiés antérieurement et pouvant être axiaux, nous trouvons: - une caméra munie d'un zoom, - une caméra se déplaçant le long de son axe optique. Dans cet article, nous présentons tout d'abord le modèle géométrique d'un système de stéréovision axiale. Puis nous décrivons une méthode robuste de calibrage d'un tel système de stéréovision. Cette méthode prend en compte le fait que les systèmes optiques décrits ci-dessus ne sont pas strictement des systèmes axiaux: en effet, il subsiste toujours des problèmes mécaniques ne permettant pas un mouvement parfait du centre optique le long de l'axe optique. En conclusion, nous présentons un algorithme d'appariement permettant de mettre en correspondance des points caractéristiques présents dans les images et rendant ainsi possible la reconstruction d'objets non polyédrique
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