8,243 research outputs found
Enhanced goal-oriented error assessment and computational strategies in adaptive reduced basis solver for stochastic problems
This work focuses on providing accurate low-cost approximations of stochastic ¿nite elements simulations in the framework of linear elasticity. In a previous work, an adaptive strategy was introduced as an improved Monte-Carlo method for multi-dimensional large stochastic problems. We provide here a complete analysis of the method including a new enhanced goal-oriented error estimator and estimates of CPU (computational processing unit) cost gain. Technical insights of these two topics are presented in details, and numerical examples show the interest of these new developments.Postprint (author's final draft
DeepMatching: Hierarchical Deformable Dense Matching
We introduce a novel matching algorithm, called DeepMatching, to compute
dense correspondences between images. DeepMatching relies on a hierarchical,
multi-layer, correlational architecture designed for matching images and was
inspired by deep convolutional approaches. The proposed matching algorithm can
handle non-rigid deformations and repetitive textures and efficiently
determines dense correspondences in the presence of significant changes between
images. We evaluate the performance of DeepMatching, in comparison with
state-of-the-art matching algorithms, on the Mikolajczyk (Mikolajczyk et al
2005), the MPI-Sintel (Butler et al 2012) and the Kitti (Geiger et al 2013)
datasets. DeepMatching outperforms the state-of-the-art algorithms and shows
excellent results in particular for repetitive textures.We also propose a
method for estimating optical flow, called DeepFlow, by integrating
DeepMatching in the large displacement optical flow (LDOF) approach of Brox and
Malik (2011). Compared to existing matching algorithms, additional robustness
to large displacements and complex motion is obtained thanks to our matching
approach. DeepFlow obtains competitive performance on public benchmarks for
optical flow estimation
Greedy algorithms for high-dimensional eigenvalue problems
In this article, we present two new greedy algorithms for the computation of
the lowest eigenvalue (and an associated eigenvector) of a high-dimensional
eigenvalue problem, and prove some convergence results for these algorithms and
their orthogonalized versions. The performance of our algorithms is illustrated
on numerical test cases (including the computation of the buckling modes of a
microstructured plate), and compared with that of another greedy algorithm for
eigenvalue problems introduced by Ammar and Chinesta.Comment: 33 pages, 5 figure
Advanced Algorithms for 3D Medical Image Data Fusion in Specific Medical Problems
Fúze obrazu je dnes jednou z nejběžnějších avšak stále velmi diskutovanou oblastí v lékařském zobrazování a hraje důležitou roli ve všech oblastech lékařské péče jako je diagnóza, léčba a chirurgie. V této dizertační práci jsou představeny tři projekty, které jsou velmi úzce spojeny s oblastí fúze medicínských dat. První projekt pojednává o 3D CT subtrakční angiografii dolních končetin. V práci je využito kombinace kontrastních a nekontrastních dat pro získání kompletního cévního stromu. Druhý projekt se zabývá fúzí DTI a T1 váhovaných MRI dat mozku. Cílem tohoto projektu je zkombinovat stukturální a funkční informace, které umožňují zlepšit znalosti konektivity v mozkové tkáni. Třetí projekt se zabývá metastázemi v CT časových datech páteře. Tento projekt je zaměřen na studium vývoje metastáz uvnitř obratlů ve fúzované časové řadě snímků. Tato dizertační práce představuje novou metodologii pro klasifikaci těchto metastáz. Všechny projekty zmíněné v této dizertační práci byly řešeny v rámci pracovní skupiny zabývající se analýzou lékařských dat, kterou vedl pan Prof. Jiří Jan. Tato dizertační práce obsahuje registrační část prvního a klasifikační část třetího projektu. Druhý projekt je představen kompletně. Další část prvního a třetího projektu, obsahující specifické předzpracování dat, jsou obsaženy v disertační práci mého kolegy Ing. Romana Petera.Image fusion is one of today´s most common and still challenging tasks in medical imaging and it plays crucial role in all areas of medical care such as diagnosis, treatment and surgery. Three projects crucially dependent on image fusion are introduced in this thesis. The first project deals with the 3D CT subtraction angiography of lower limbs. It combines pre-contrast and contrast enhanced data to extract the blood vessel tree. The second project fuses the DTI and T1-weighted MRI brain data. The aim of this project is to combine the brain structural and functional information that purvey improved knowledge about intrinsic brain connectivity. The third project deals with the time series of CT spine data where the metastases occur. In this project the progression of metastases within the vertebrae is studied based on fusion of the successive elements of the image series. This thesis introduces new methodology of classifying metastatic tissue. All the projects mentioned in this thesis have been solved by the medical image analysis group led by Prof. Jiří Jan. This dissertation concerns primarily the registration part of the first project and the classification part of the third project. The second project is described completely. The other parts of the first and third project, including the specific preprocessing of the data, are introduced in detail in the dissertation thesis of my colleague Roman Peter, M.Sc.
Local states of free bose fields
These notes contain an extended version of lectures given at the ``Summer
School on Large Coulomb Systems'' in Nordfjordeid, Norway, in august 2003. They
furnish a short introduction to the theory of quantum harmonic systems, or free
bose fields. The main issue addressed is the one of local states. I will adopt
the definition of Knight of ``strictly local excitation of the vacuum'' and
will then state and prove a generalization of Knight's Theorem which asserts
that finite particle states cannot be perfectly localized. It will furthermore
be explained how Knight's a priori counterintuitive result can be readily
understood if one remembers the analogy between finite and infinite dimensional
harmonic systems alluded to above. I will also discuss the link between the
above result and the so-called Newton-Wigner position operator thereby
illuminating, I believe, the difficulties associated with the latter. I will in
particular argue that those difficulties do not find their origin in special
relativity or in any form of causality violation, as is usually claimed
Light trapping in high-density ultracold atomic gases for quantum memory applications
High-density and ultracold atomic gases have emerged as promising media for
storage of individual photons for quantum memory applications. In this paper we
provide an overview of our theoretical and experimental efforts in this
direction, with particular attention paid to manipulation of light storage (a)
through complex recurrent optical scattering processes in very high density
gases (b) by an external control field in a characteristic electromagnetically
induced transparency configuration.Comment: Submitted to Journal of Modern Optics, Special 2010 PQE Issu
- …