Search results for "CONTRAST"

Figuration/Figure/Form

2020

It is still Weizsäcker to show that rather than a clear contrast (usually already referring to the names of Plato and Aristotle and to the competition between the concepts of eidos and morphé) it is a necessary correlation and a way through which the fundamental problem of unity of knowledge is placed.

Porphyrines et tétraazamacrocycles dérivés du DOTA : association de deux ligands pour la chélation de métaux d'intérêt en imagerie médicale multimoda…

2012

The goal of my PhD thesis was to synthesize new molecules, which give access to heterobimetallic complexes with interesting properties for multimodal imaging. In this manuscript, several main points have been studied. The first part of this work concerns the synthesis and characterization of ligands. We describe here the synthesis of five new ligands based on the association of one porphyrin and one or several cyclen derivatives. Those ligands are water-soluble. During the synthesis, we have targeted improvements to our work and developed a new synthetic pathway, which allowed us to obtain one ligand incorporating a porphyrin, a cyclen derivative and a free amine function. This function cou…

The classical concept of mass: theoretical difficulties and students’ definitions

1993

An analysis of the concepts of mass in classical physics on the basis of their historical, philosophical and semantic connotations is given. A classification of the most current definitions of mass is proposed from its physical representation and topic area. The definitions of mass, and some related issues, given by several groups of secondary school students are analysed. The results seem to confirm a generalized qualitative‐teleological view of scientific concepts in contrast to the more orthodox formal‐quantitative formulation of physics.

RUOLO DELL'ANGIO-TC NELLA DIAGNOSI DI URGENZA DI ANGIODISPLASIA INTESTINALE ILEALE: UNA RARA CAUSA DI SANGUINAMENTO

2018

RUOLO DELLA TC CON MEZZO DI CONTRASTO NELLA DIAGNOSI DELLE COMPLICANZE DELLA PANCREATITE ACUTA NECROTIZZANTE

2018

Sequence Learning in a Single Trial: A Spiking Neurons Model Based on Hippocampal Circuitry.

2020

ABSTRACTIn contrast with our everyday experience using brain circuits, it can take a prohibitively long time to train a computational system to produce the correct sequence of outputs in the presence of a series of inputs. This suggests that something important is missing in the way in which models are trying to reproduce basic cognitive functions. In this work, we introduce a new neuronal network architecture that is able to learn, in a single trial, an arbitrary long sequence of any known objects. The key point of the model is the explicit use of mechanisms and circuitry observed in the hippocampus, which allow the model to reach a level of efficiency and accuracy that, to the best of our…

Power estimation for non-standardized multisite studies

2016

A concern for researchers planning multisite studies is that scanner and T1-weighted sequence-related biases on regional volumes could overshadow true effects, especially for studies with a heterogeneous set of scanners and sequences. Current approaches attempt to harmonize data by standardizing hardware, pulse sequences, and protocols, or by calibrating across sites using phantom-based corrections to ensure the same raw image intensities. We propose to avoid harmonization and phantom-based correction entirely. We hypothesized that the bias of estimated regional volumes is scaled between sites due to the contrast and gradient distortion differences between scanners and sequences. Given this…

First-order visual interneurons distribute distinct contrast and luminance information across ON and OFF pathways to achieve stable behavior

2022

The accurate processing of contrast is the basis for all visually guided behaviors. Visual scenes with rapidly changing illumination challenge contrast computation because photoreceptor adaptation is not fast enough to compensate for such changes. Yet, human perception of contrast is stable even when the visual environment is quickly changing, suggesting rapid post receptor luminance gain control. Similarly, in the fruit fly Drosophila, such gain control leads to luminance invariant behavior for moving OFF stimuli. Here, we show that behavioral responses to moving ON stimuli also utilize a luminance gain, and that ON-motion guided behavior depends on inputs from three first-order interneuro…

Image quality metric based on multidimensional contrast perception models

1999

Abstract The procedure to compute the subjective difference between two input images should be equivalent to a straightforward difference between their perceived versions, hence reliable subjective difference metrics must be founded on a proper perception model. For image distortion evaluation purposes, perception can be considered as a set of signal transforms that successively map the original image in the spatial domain into a feature and a response space. The properties of the spatial pattern analyzers involved in these transforms determine the geometry of these different signal representation domains. In this work the general relations between the sensitivity of the human visual system…

Tactile input of the hand and the control of reaching to grasp movements

1997

The role of tactile information of the hand in the control of reaching to grasp movements was investigated. The kinematics of both reaching (or transport) and grasp components were studied in healthy subjects in two experimental conditions. In one condition (control condition) subjects were required to reach and grasp an object that could have two sizes and that could be located at two distances from the viewer. In the other condition (anaesthesia condition) the same movements were executed, but anaesthesia was provided to the subjects' fingertips. In both conditions vision of the hand was prevented during movement. Anaesthesia affected mainly the kinematics of the first phase of grasping, …