Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3

The microstructure and phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain to be one of the most puzzling issues of solid state science. In the present work we have investigated the evolution of the phase symmetry in PMN-xPT ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <= x <= 0.15) by means of high-resolution synchrotron x-ray diffraction. Structural analysis based on the experimental data reveals that the substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in the development of a clean rhombohedral phase at a PT-concentration as low as 5%. The results provide some new insight into the development of the ferroelectric order in PMN-PT, which has been discussed in light of the kinetics of polar nanoregions and the physical models of the relaxor ferroelectrics to illustrate the structural evolution from a relaxor to a ferroelectric state.Comment: Revised version with updated references; 9 pages, 4 figures embedde

A chimerical phagocytosis model reveals the recruitment by Sertoli cells of autophagy for the degradation of ingested illegitimate substrates

Phagocytosis and autophagy are typically dedicated to degradation of substrates of extrinsic and intrinsic origins respectively. Although overlaps between phagocytosis and autophagy were reported, the use of autophagy for ingested substrate degradation by nonprofessional phagocytes has not been described. Blood-separated tissues use their tissue-specific nonprofessional phagocytes for homeostatic phagocytosis. In the testis, Sertoli cells phagocytose spermatid residual bodies produced during germ cell differentiation. In the retina, pigmented epithelium phagocytoses shed photoreceptor tips produced during photoreceptor renewal. Spermatid residual bodies and shed photoreceptor tips are phosphatidylserine-exposing substrates. Activation of the tyrosine kinase receptor MERTK, which is implicated in phagocytosis of phosphatidylserine-exposing substrates, is a common feature of Sertoli and retinal pigmented epithelial cell phagocytosis. The major aim of our study was to investigate to what extent phagocytosis by Sertoli cells may be tissue specific. We analyzed in Sertoli cell cultures that were exposed to either spermatid residual bodies (legitimate substrates) or retina photoreceptor outer segments (illegitimate substrates) the course of the main phagocytosis stages. We show that whereas substrate binding and ingestion stages occur similarly for legitimate or illegitimate substrates, the degradation of illegitimate but not of legitimate substrates triggers autophagy as evidenced by the formation of double-membrane wrapping, MAP1LC3A-II/LC3-II clustering, SQSTM1/p62 degradation, and by marked changes in ATG5, ATG9 and BECN1/Beclin 1 protein expression profiles. The recruitment by nonprofessional phagocytes of autophagy for the degradation of ingested cell-derived substrates is a novel feature that may be of major importance for fundamentals of both apoptotic substrate clearance and tissue homeostasis

Epididymis Response Partly Compensates for Spermatozoa Oxidative Defects in snGPx4 and GPx5 Double Mutant Mice

We report here that spermatozoa of mice lacking both the sperm nucleaus glutathione peroxidase 4 (snGPx4) and the epididymal glutathione peroxidase 5 (GPx5) activities display sperm nucleus structural abnormalities including delayed and defective nuclear compaction, nuclear instability and DNA damage. We show that to counteract the GPx activity losses, the epididymis of the double KO animals mounted an antioxydant response resulting in a strong increase in the global H2O2-scavenger activity especially in the cauda epididymis. Quantitative RT-PCR data show that together with the up-regulation of epididymal scavengers (of the thioredoxin/peroxiredoxin system as well as glutathione-S-transferases) the epididymis of double mutant animals increased the expression of several disulfide isomerases in an attempt to recover normal disulfide-bridging activity. Despite these compensatory mechanisms cauda-stored spermatozoa of double mutant animals show high levels of DNA oxidation, increased fragmentation and greater susceptibility to nuclear decondensation. Nevertheless, the enzymatic epididymal salvage response is sufficient to maintain full fertility of double KO males whatever their age, crossed with young WT female mice

Quels outils pour une gestion des prélèvements individuels en nappe ? Application au cas de la plaine du Roussillon

La première partie de ce rapport est consacrée à la recherche des instruments économiques les mieux adaptés à la gestion des prélèvements agricoles diffus : la pénalité collective est l'instrument le plus rejeté, que ce soit par les agriculteurs sur le terrain qu'en laboratoire par les sujets. L'instrument mixte, dans la forme testée, semble peu acceptable : son mécanisme a été mal compris, il est rejeté par les individus non fraudeurs (même s'il peut permettre de faciliter les dénonciations) et il est difficile à instaurer si le niveau total prélevé n'est pas aisément mesurable. La taxe individuelle au volume semble l'instrument le plus efficace, à condition que son niveau soit suffisamment élevé. La deuxième partie de ce rapport s'intéresse à l'analyse des raisons qui expliquaient l'échec relatif de la politique de substitution de la ressource en eau souterraine par de l'eau de surface conduite dans la plaine du Roussillon cas étudié par la suite. Lorsque les agriculteurs ont le choix dans la ressource, ils prennent en effet en compte les éléments suivants : le coût d'accès, la disponibilité à la demande de l'eau, la garantie d'avoir de l'eau, le type d'accès à l'eau (sous pression ou gravitaire), la qualité de l'eau, la réglementation en vigueur et les contraintes des cahiers des charges de leurs clients. Il semble ainsi indispensable de réunir des conditions pour le succès de la politique de substitution : (1) une offre attractive en terme de coût et de qualité et (2) un engagement du monde agricole (qui rebouche les forages et/ou qui doive gérer de manière unique l'ensemble des ressources en eau). Mais la politique de substitution ne suffit pas et doit être souvent accompagnée d'une politique de gestion de la demande au moins pour limiter la croissance de cette dernière (partie 3). Un des instruments envisagés dans cet objectif par la loi sur l'eau de décembre 2006 est l'instauration d'organismes uniques chargés de la répartition des autorisations de prélèvement (article 21). Nous étudions donc, dans la partie 3 de ce rapport, la possibilité de transformer les associations de préleveurs en nappe existant dans le Roussillon en organismes uniques

Glutathione peroxidases (GPX) at work on epididymal spermatozoa: An example of the dual effect of reactive oxygen species on mammalian male fertilizing ability.

The mammalian glutathione peroxidase gene family encodes bi-functional enzymes that can work either as classical reactive oxygen species (ROS) scavengers or as thiol-peroxidases, thereby introducing disulfide bridges in thiol-containing proteins. These dual effects are nowhere better demonstrated than in epididymal maturing spermatozoa where the concomitant actions of several glutathione peroxidases ensure the achievement of the structural maturation of sperm cells as well as their protection against ROS-induced damage. We review here the roles played by the sperm-associated forms of GPx4 (mitochondrial GPx4 and nuclear GPx4), the secreted GPx5 protein as well as the epithelial proteins GPx1, GPx3 and cellular GPx4, all functioning in the mammalian epididymis at different stages of the sperm&#39;s epididymal journey, and in different epididymis compartments

High Performance 15-V Novel LDMOS Transistor Architecture in a 0.25µm BiCMOS Process for RF Power Applications.

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