Université catholique de Louvain

About: Université catholique de Louvain is a education organization based out in Louvain-la-Neuve, Belgium. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 25319 authors who have published 57360 publications receiving 2172080 citations. The organization is also known as: University of Louvain & UCLouvain.

Semidefinite relaxation and nonconvex quadratic optimization

Abstract: In this paper we study the quality of semidefinite relaxation for a global quadratic optimization problem with diagonal quadratic consraints. We prove that such relaxation approximates the exact solution of the problem with relative accuracy mu = (pi/2)-1. We consider some applications of this result.

Liver fibrosis: non‐invasive assessment with MR elastography

Abstract: The aim of this study was to assess the feasibility of using non-invasive MR elastography for determining the stage of liver fibrosis. Twenty-five consecutive patients who had liver biopsy for suspicion of chronic liver disease were included in the study. The stage of fibrosis on the biopsies was assessed according to the METAVIR scoring system from F0, no fibrosis, to F4, cirrhosis. MR elastography was performed by transmitting low-frequency (65 Hz) mechanical waves into the liver with a transducer placed at the back of the patients. The MR pulse sequence was a motion-sensitized spin-echo sequence, phase-locked to the mechanical excitation. The phase maps were processed to obtain shear elasticity and shear viscosity maps. The mean hepatic shear elasticity increased with increasing stage of fibrosis. The mean elasticity was 2.24 +/- 0.23 kPa in the 11 patients without substantial fibrosis (F0-F1 grades), 2.56 +/- 0.24 kPa in the four patients with substantial fibrosis (F2-F3) and 4.68 +/- 1.61 kPa in the 10 patients with cirrhosis (F4). The differences between groups were statistically significant (p

Reference frames for representing visual and tactile locations in parietal cortex.

Abstract: The ventral intraparietal area (VIP) receives converging inputs from visual, somatosensory, auditory and vestibular systems that use diverse reference frames to encode sensory information. A key issue is how VIP combines those inputs together. We mapped the visual and tactile receptive fields of multimodal VIP neurons in macaque monkeys trained to gaze at three different stationary targets. Tactile receptive fields were found to be encoded into a single somatotopic, or head-centered, reference frame, whereas visual receptive fields were widely distributed between eye- to head-centered coordinates. These findings are inconsistent with a remapping of all sensory modalities in a common frame of reference. Instead, they support an alternative model of multisensory integration based on multidirectional sensory predictions (such as predicting the location of a visual stimulus given where it is felt on the skin and vice versa). This approach can also explain related findings in other multimodal areas.

Coalescence of Single-Walled Carbon Nanotubes

Abstract: The coalescence of single-walled nanotubes is studied in situ under electron irradiation at high temperature in a transmission electron microscope. The merging process is investigated at the atomic level, using tight-binding molecular dynamics and Monte Carlo simulations. Vacancies induce coalescence via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices along adjacent tubes. Other topological defects induce the polymerization of tubes. Coalescence seems to be restricted to tubes with the same chirality, explaining the low frequency of occurrence of this event.

Holistic Processing Is Finely Tuned for Faces of One's Own Race

Abstract: Recognizing individual faces outside one's race poses difficulty, a phenomenon known as the other-race effect. Most researchers agree that this effect results from differential experience with same-race (SR) and other-race (OR) faces. However, the specific processes that develop with visual experience and underlie the other-race effect remain to be clarified. We tested whether the integration of facial features into a whole representation-holistic processing-was larger for SR than OR faces in Caucasians and Asians without life experience with OR faces. For both classes of participants, recognition of the upper half of a composite-face stimulus was more disrupted by the bottom half (the composite-face effect) for SR than OR faces, demonstrating that SR faces are processed more holistically than OR faces. This differential holistic processing for faces of different races, probably a by-product of visual experience, may be a critical factor in the other-race effect.