3,289 research outputs found
MRI Super-Resolution using Multi-Channel Total Variation
This paper presents a generative model for super-resolution in routine
clinical magnetic resonance images (MRI), of arbitrary orientation and
contrast. The model recasts the recovery of high resolution images as an
inverse problem, in which a forward model simulates the slice-select profile of
the MR scanner. The paper introduces a prior based on multi-channel total
variation for MRI super-resolution. Bias-variance trade-off is handled by
estimating hyper-parameters from the low resolution input scans. The model was
validated on a large database of brain images. The validation showed that the
model can improve brain segmentation, that it can recover anatomical
information between images of different MR contrasts, and that it generalises
well to the large variability present in MR images of different subjects. The
implementation is freely available at https://github.com/brudfors/spm_superre
QGP tomography with photon tagged jets in ALICE
jet events provide a tomographic measurement of the medium formed
in heavy ion collisions at LHC energies. Tagging events with a well identified
high direct photon and measuring the correlation distribution of
hadrons emitted oppositely to the photon, allows us to determine, with a good
approximation, both the jet fragmentation function and the back-to-back
azimuthal misalignement of the direct photon and the jet. Comparing these two
observables measured in collisions with the ones measured in
collisions will reveal the modifications of the jet structure induced by the
medium formed in collisions and consequently will infer the medium
properties.Comment: 3 pages, 3 figures, Proceedings for 5th International Conference on
Quarks and Nuclear Physic
Joint Total Variation ESTATICS for Robust Multi-Parameter Mapping
Quantitative magnetic resonance imaging (qMRI) derives tissue-specific
parameters -- such as the apparent transverse relaxation rate R2*, the
longitudinal relaxation rate R1 and the magnetisation transfer saturation --
that can be compared across sites and scanners and carry important information
about the underlying microstructure. The multi-parameter mapping (MPM) protocol
takes advantage of multi-echo acquisitions with variable flip angles to extract
these parameters in a clinically acceptable scan time. In this context,
ESTATICS performs a joint loglinear fit of multiple echo series to extract R2*
and multiple extrapolated intercepts, thereby improving robustness to motion
and decreasing the variance of the estimators. In this paper, we extend this
model in two ways: (1) by introducing a joint total variation (JTV) prior on
the intercepts and decay, and (2) by deriving a nonlinear maximum \emph{a
posteriori} estimate. We evaluated the proposed algorithm by predicting
left-out echoes in a rich single-subject dataset. In this validation, we
outperformed other state-of-the-art methods and additionally showed that the
proposed approach greatly reduces the variance of the estimated maps, without
introducing bias.Comment: 11 pages, 2 figures, 1 table, conference paper, accepted at MICCAI
202
Nietzsche : historia, cultura, estado
No hay abstract
The ALICE EMCal L1 trigger first year of operation experience
The ALICE experiment at the LHC is equipped with an electromagnetic
calorimeter (EMCal) designed to enhance its capabilities for jet, photon and
electron measurement. In addition, the EMCal enables triggering on jets and
photons with a centrality dependent energy threshold. After its commissioning
in 2010, the EMCal Level 1 (L1) trigger was officially approved for physics
data taking in 2011. After describing the L1 hardware and trigger algorithms,
the commissioning and the first year of running experience, both in proton and
heavy ion beams, are reviewed. Additionally, the upgrades to the original L1
trigger design are detailed.Comment: Proceedings of TWEPP-12, Oxford. 10 pages, 9 figure
Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE
Invariant cross sections for neutral pions and eta mesons in pp collisions at
sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large
Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations
describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured
cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent
with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling
were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions,
Quark Matter 2011, Annec
Evaluation and comparison of integer programming solvers for hard real-time scheduling
[EN] In order to obtain a feasible schedule of a hard real-time system, heuristic based techniques are the solution of choice. In the last few years, optimization solvers have gained attention from research communities due to their capability of handling large number of constraints. Recently, some works have used integer linear programming (ILP) for solving mono processor scheduling of real-time systems. In fact, ILP is commonly used for static scheduling of multiprocessor systems. However, two main solvers are used to solve the problem indistinctly. But, which one is the best for obtaining a schedulable system for hard real-time systems? This paper makes a comparison of two well-known optimization software packages (CPLEX and GUROBI) for the problem of finding a feasible schedule on monoprocessor hard real-time systems.This work was supported under Grant PLEC2021-007609 funded by MCIN/AEI/10.13039/501100011033 and by the "European Union NextGeneration EU/PRTR"Guasque Ortega, A.; Balbastre, P. (2022). Evaluation and comparison of integer programming solvers for hard real-time scheduling. IEICE Transactions on Information and Systems. E105-D(10):1726-1733. https://doi.org/10.1587/transinf.2022EDP707317261733E105-D1
Groupwise Multimodal Image Registration Using Joint Total Variation
In medical imaging it is common practice to acquire a wide range of modalities (MRI, CT, PET, etc.), to highlight different structures or pathologies. As patient movement between scans or scanning session is unavoidable, registration is often an essential step before any subsequent image analysis. In this paper, we introduce a cost function based on joint total variation for such multimodal image registration. This cost function has the advantage of enabling principled, groupwise alignment of multiple images, whilst being insensitive to strong intensity non-uniformities. We evaluate our algorithm on rigidly aligning both simulated and real 3D brain scans. This validation shows robustness to strong intensity non-uniformities and low registration errors for CT/PET to MRI alignment. Our implementation is publicly available at https://github.com/brudfors/coregistration-njtv
Modelling the propagation of electromagnetic waves across complex metamaterials in closed structures
[EN] Metamaterials are currently one of the most popular fields in microwave technology because their particular electromagnetic properties lead to a plenty of very relevant applications, both military and civilian. Additionally, the analysis and design of microwave components based on this kind of materials is one of the more challenging problems found by the applied electromagnetism community due to the complexity introduced in the mathematical formulation by their constitutive relationships. The most general case of metamaterial is the bi-anisotropic one, where both the electric field and the electric induction simultaneously depend on the magnetic field and the magnetic induction. In this paper, we present a new and powerful Finite Element Method scheme valid for the analysis of the most general waveguides, filled with lossy bi-anisotropic linear materials. Edge elements have been used in order to prevent the appearance of spurious solutions and the final eigensystems are very sparse, thus allowing a great memory and computing time saving.Balbastre Tejedor, JV.; Nuño Fernández, L. (2019). Modelling the propagation of electromagnetic waves across complex metamaterials in closed structures. Journal of Computational and Applied Mathematics. (352):40-49. https://doi.org/10.1016/j.cam.2018.11.004S404935
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