Wavelet packet based digital watermarking

International audienceWe present a method for digital image watermarking based on the modification of certain subsets of the wavelet packet decomposition. These subsets are determined both from a secret key and an image dependent procedure that chooses a best basis from an energy criterion. The mark is set by imposing a parity constraint at each level of the decomposition. We elaborate on the choice of some of the parameters of the model, showing how they can be tuned so as to obtain good resistance to attacks. Examples are displayed to assess the validity of our approach

B-cell Zone Reticular Cell Microenvironments Shape CXCL13 Gradient Formation

Through the formation of concentration gradients, morphogens drive graded responses to extracellular signals, thereby fine-tuning cell behaviors in complex tissues. Here we show that the chemokine CXCL13 forms both soluble and immobilized gradients. Specifically, CXCL13+ follicular reticular cells form a small-world network of guidance structures, with computer simulations and optimization analysis predicting that immobilized gradients created by this network promote B-cell trafficking. Consistent with this prediction, imaging analysis show that CXCL13 binds to extracellular matrix components in situ, constraining its diffusion. CXCL13 solubilization requires the protease cathepsin B that cleaves CXCL13 into a stable product. Mice lacking cathepsin B display aberrant follicular architecture, a phenotype associated with effective B cell homing to but not within lymph nodes. Our data thus suggest that reticular cells of the B cell zone generate microenvironments that shape both immobilized and soluble CXCL13 gradient

Patterns, receptors and signals:regulation of phagosome maturation

Recognition of microbial pathogens and dead cells and their phagocytic uptake by specialized immune cells are essential to maintain host homeostasis. Phagosomes undergo fusion and fission events with endosomal and lysosomal compartments, a process called 'phagosome maturation', which leads to the degradation of the phagosomal content. However, many phagocytic cells also act as antigen-presenting cells and must balance degradation and peptide preservation. Emerging evidence indicates that receptor engagement by phagosomal cargo, as well as inflammatory mediators and cellular activation affect many aspects of phagosome maturation. Unsurprisingly, pathogens have developed strategies to hijack this machinery, thereby interfering with host immunity. Here, we highlight progress in this field, summarize findings on the impact of immune signals, and discuss consequences for pathogen elimination

Tatouage d'images numériques par paquets d'ondelettes

Digital image watermarking has attracted a lot of interest in recent years, due in particular to the development of Internet and the World Wide Web. The aim is to protect ownership by including in the image a copyright information. This information, or mark, has to be set in such a way that it is invisible: indeed, it must not alter the viewing content and, in addition, it should not be easy to remove. Furthermore, the mark must be resistant to attacks directed at erasing it. A number of methods have been proposed to insert robust and invisible watermarks. Some operate directly in pixel space, other in a transform domain, such as Fourier or DCT . We propose here to study a wavelet packet based watermarking procedure. Working in the wavelet domain yields a number of advantages: First, it allows to control in a precise way the location both in space and scale of the mark. Second,wavelet coefficients give a structured way of representing the information: as is well known for instance from studies in image compression, in most cases, only a few coefficients are large, indicating where the information lies in a given image in terms of scale and space. This is useful both for invisibility and robustness concerns. Using wavelet packets adds another degree of freedom because it allows to select frequency independently of scale. Finally, wavelet based algorithms are fast and allow to reconstruct the image. After an overview of the algorithms recently used, we recall some basics facts about wavelet packets decomposition and best bases selection criteria. Thirdly, we presented our watermarking algorithm. The part 4 gives amelioration of results under attacks and the last part presents an analysis of the proposed method.Avec l'apparition et le développement des nouvelles technologies numériques, les fraudes se sont multipliées, soulignant le manque de méthodes concernant la protection des données numériques. Ces données sont en effet très faciles à pirater : on peut les stocker, les copier, les modifier et enfin les diffuser illégalement sans qu'elles perdent de leur qualité et sans prise en compte des droits d'auteurs. Pour répondre à ces besoins, un nouvel axe de recherche se développe très rapidement : le tatouage. Le principe des techniques dites de tatouage est d'insérer une marque imperceptible dans les valeurs de la donnée. Dans le cadre de la protection des droits d'auteurs, la marque insérée, appelée watermarque correspond au code du copyright. Ce type de tatouage doit répondre à des contraintes fortes en termes de robustesse. En effet, quelles que soient les transformations (licites ou illicites) que la donnée tatouée subie, la marque doit rester présente tant que la donnée reste exploitable. De plus, la présence de la marque ne doit être détectée que par des personnes autorisées (possédant une clef de détection privée). De nombreux algorithmes ont étés présentés récemment et certains produits sont même commercialisés, cependant, aucun d'eux ne satisfait pleinement au cahier des charges idéal. Le travail présenté dans ce rapport a pour objectif de proposer une nouvelle méthode de tatouage des images digitales en vue de la protection du copyright. Dans un premier temps, nous présenterons les propriétés générales du processus de tatouage ainsi qu'un aperçu des méthodes utilisées actuellement. Puis nous présenterons la décomposition en paquets d'ondelettes d'un signal ainsi que la sélection de meilleures bases. Ces outils, très utilisés en traitement des images et du signal pour des applications variées tels que la compression, le débruitage , la classification ou la détection de rupture nous permettrons de définir le domaine sur lequel nous insérons la watermarque. Après avoir explicité l'algorithme de tatouage, nous donnerons diverses améliorations à cette méthode. Puis nous l'analyserons de façon conceptuelle

Tatouage d'images numériques par paquets d'ondelettes

Aves l'apparition et le développement des nouvelles technologies numériques, les fraudes se sont multipliées, soulignant le manque de méthodes concernant la protection des données numériques. Ces données sont en effet très faciles à pirater : on peut les stocker, les copier, les modifier et enfin les diffuser illégalement sans qu'elles perdent de leur qualité et sans prise en compte des droits d'auteurs. Pour répondre à ces besoins, un nouvel axe de recherche se développe très rapidement : le tatouage. Le principe des techniques dites de tatouage est d'insérer une marque imperceptible dans les valeurs de la donnée. Dans le cadre de la protection des droits d'auteurs, la marque insérée, appelée watermarque correspond au code du copyright. Ce type de tatouage doit répondre à des contraintes fortes en termes de robustesse...NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Synthesis of Ferrocenyl Phosphorhydrazone Dendrimers

Article électroniqueThis entry is adapted from 10.3390/molecules25030447The discovery of ferrocene is often associated with the rapid growth of organometallic chemistry. Dendrimers are highly branched macromolecules that can be functionalized at will at all levels of their structure. The functionalization of dendrimers with ferrocene derivatives can be carried out easily as terminal functions on the surface, but also at the core, or at one or several layers inside the structure. Depending on the desired location of the ferrocenes in the structure of phosphorhydrazone dendrimers, the ferrocenes should be functionalized differently. For the grafting to the surface, the ferrocene should bear a phenol group, suitable to react in substitution reactions with the P(S)Cl2 terminal groups of the dendrimers. To be used as core, the ferrocene should have two aldehyde functions, from which the synthesis of the dendrimer will be carried out. To be introduced in the branches, at all layers or within a single layer, the ferrocene should replace hydroxybenzaldehyde; thus, it should bear both a phenol and an aldehyde

Ferrocenyl phosphorhydrazone dendrimers dynthesis, and electrochemical and catalytic properties

International audienceThe discovery of ferrocene is often associated with the rapid growth of organometallic chemistry. Dendrimers are highly branched macromolecules that can be functionalized at will at all levels of their structure. The functionalization of dendrimers with ferrocene derivatives can be carried out easily as terminal functions on the surface, but also at the core, or at one or several layers inside the structure. This review will focus on phosphorhydrazone dendrimers functionalized with ferrocene derivatives, on the surface, at the core, at all layers or within a single layer inside the structure. The first part will describe the synthesis; the second part will concern the electrochemical properties; and the last part will give several examples concerning catalysis, with complexes of ferrocenyl phosphines used as terminal functions of dendrimers

EXPERIMENTAROUNDATRAININGENGINE --- Revision: 1.15

We describe a teaching experiment where an introductory course to Computer Science is accompanied by a computerized training engine. This whole engine relies on the existence of an interpreter of the taught programming language that allows us to offer quizzes as well as exercises with some automatic marking facility. Students may then perform their homework with an immediate feedback without being connected to the Internet. However students' answers are eventually gathered in a central database where they may be analyzed thus providing the means for "personal coaching"