Synthesis of nanopowders and obtaining of composite ceramics with magnetic and dielectric phase for microelectronic application

U ovom radu sintetisani su kompozitni nanoprahovi i nanoprahovi tipa jezgro– omotač sa dielektričnom i magnetnom fazom, kao pogodan polazni materijal za procesiranje kompozitne keramike za primenu u mikroelektronici. Osnovni cilj ove doktorske disertacije je bio utvrđivanje veza između uslova sinteze, morfologije čestica, uslova procesiranja i mikrostrukture kompozitne keramike. Nanoprahovi su sintetisani hemijskim metodama sinteze u tečnoj fazi (sol-gel i koprecipitacija) i gasnoj fazi (CVS), pri čemu je vršena optimizacija procesnih uslova u cilju sinteze čestica željene strukture i hemijskog sastava. Istraživanja su vršena na nekoliko modelnih sistema sa feritima kao magnetnom fazom i titanatima ili silikom kao dielektričnom fazom: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 i BaTiO3Fe3O4. Hemijska sinteza u tečnoj fazi se pokazala pogodnom zato što pruža mogućnost kontrolisanja morfologije kompozitnih čestica ne samo podešavanjem procesnih parametara sinteze već i funkcionalizacijom faza kojom se uzrokuje njihovo elektrostatičko privlačenje i formiranje strukture jezgro–omotač. Ipak, zbog velikog stepena aglomeracije prisutnog tokom sinteze u tečnoj fazi, dobijanje omotača uniformne debljine i izbegavanje homogene nukleacije faza se pokazalo teško. Hemijskom sintezom u gasnoj fazi (CVS) je po prvi put sintetisan kompozitni nanoprah na bazi kompleksnih oksida titanata i ferita. Utvrđeno je da i pored velikog potencijala CVS metode u smislu sinteze ultrafinih prahova na bazi titanata i ferita u jednom koraku, ova metoda nudi relativno slabu kontrolu morfologije kompozitnih čestica pri visokim procesnim temperaturama koje su neophodne za kristalizaciju dve faze. Sintetisani nanoprahovi na bazi titanata i ferita (SrTiO3NiFe2O4 i BaTiO3NiFe2O4) procesirani su u gustu kompozitnu keramiku visokotemperaturnim sinterovanjem, u cilju ispitivanja veze morfologije čestica i mikrostrukture kompozita, optimizacije režima sinterovanja i funkcionalne karakterizacije dobijene keramike sa različitim masenim odnosom faza. Prahovi su sinterovani putem konvencionalnog sinterovanja u atmosferi vazduha, spark plazma sinterovanja (SPS) ili kombinacijom ove dve metode. Utvrđeno je da prahovi strukture jezgro–omotač densifikuju u značajno gušću i homogeniju keramiku u odnosu na kompozitne prahove istog sastava na istim procesnim temperaturama. Pored toga, pH vrednost sinteze čestica i atmosfera visokotemperaturnog sinterovanja su se pokazali veoma značajnim u smislu održavanja željenog faznog sastava dobijenih kompozita. U pogledu režima sinterovanja dobijenih prahova, kombinacija niskotemperaturnog konvencionalnog i SPS sinterovanja (1000 °C) je dala najbolje rezultate u smislu postizanja zadovoljavajuće gustine kompozita (>95% teorijske gustine), održavanja željenog faznog sastava i homogene distribucije faza. Funkcionalna karakterizacija sinterovane keramike sa različitim masenim odnosom faza (BaTiO3 : NiFe2O4 = 1,2,8) potvrdila je očekivano dielektrično, feroelektrično i ferimagnetno ponašanje dobijenih kompozita.Composite and core–shell nanopowders with dielectric and magnetic phase have been synthesized in this work, as a suitable starting material for processing of composite ceramics for microelectronic application. The main goal of this doctoral dissertation was the determination of the link between synthesis conditions, particle morphology, processing conditions and microstructure of composite ceramics. Nanopowders have been synthesized by chemical synthesis methods in wet phase (sol–gel and coprecipitation) and gas phase (CVS), whereas the optimization of processing parameters was conducted with the goal to synthesize particles of desired structure and chemical composition. Studies were conducted on the few model systems with ferrites as a magnetic and titanates as a dielectric phase: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 and BaTiO3Fe3O4. Chemical wet synthesis has proven suitable because it offers composite particle morphology control not only by adjustment of synthesis parameters but also by phase functionalization causing their mutual electrostatic attraction and thus core–shell structure formation. However, due to the high degree of agglomeration present during the wet phase synthesis, formation of the shell with uniform thickness and avoidance of homogeneous nucleation has proven difficult. For the first time, composite ferrite and titanate-based nanopowder has been synthesized by means of Chemical Vapor Synthesis (CVS). It has been found that beside high potential of CVS method for one-step synthesis of ultrafine titanate and ferrite-based nanopowders, this method offers relatively low control of composite particle morphology at high processing temperatures which are necessary for crystallization of both phases. Synthesized titanate and ferrite-based nanopowders (SrTiO3NiFe2O4 and BaTiO3NiFe2O4) were processed into dense ceramics by high-temperature sintering, in order to find the link between particle morphology and composite microstructure, optimize the sintering regime and conduct the functional characterization of obtained ceramics with different phase mass ratio. The powders were sintered by conventional sintering in air, spark plasma sintering (SPS) or combination of these two methods. It was found that core–shell powders densify in ceramics with considerably higher density and homogeneity at the same processing temperature, than the composite powders with the same composition. Moreover, synthesis pH value and sintering temperature was found to be very important in terms of phase composition preservation of obtained composites. Regarding the sintering regime of obtained powders, combination of low-temperature conventional and SPS sintering (1000 °C) has given the best results in terms of achieving adequate composite density (>95% theoretical density), phase preservation and homogeneous phase distribution. Functional characterization of sintered ceramics with different phase mass ratio (BaTiO3 : NiFe2O4 = 1,2,8) confirmed the expected dielectric, ferroelectric and ferromagnetic behaviour of obtained composites

Role of immigrant males and muzzle contacts in the uptake of a novel food by wild vervet monkeys.

The entry into and uptake of information in social groups is critical for behavioral adaptation by long-lived species in rapidly changing environments. We exposed five groups of wild vervet monkeys to a novel food to investigate the innovation of processing and consuming it. We report that immigrant males innovated in two groups, and an infant innovated in one group. In two other groups, immigrant males imported the innovation from their previous groups. We compared uptake between groups with respect to the initial innovator to examine the extent to which dispersing males could introduce an innovation into groups. Uptake of the novel food was faster in groups where immigrant males ate first rather than the infants. Younger individuals were more likely overall, and faster, to subsequently acquire the novel food. We also investigated the role of muzzle contact behavior in information seeking around the novel food. Muzzle contacts decreased in frequency over repeated exposures to the novel food. Muzzle contacts were initiated the most by naïve individuals, high rankers, and juveniles; and were targeted most towards knowledgeable individuals and high rankers, and the least towards infants. We highlight the potential importance of dispersers in rapidly exploiting novel resources among populations

Alix is required for activity-dependent bulk endocytosis at brain synapses

In chemical synapses undergoing high frequency stimulation, vesicle components can be retrieved from the plasma membrane via a clathrin-independent process called activitydependent bulk endocytosis (ADBE). Alix (ALG-2-interacting protein X/PDCD6IP) is an adaptor protein binding to ESCRT and endophilin-A proteins which is required for clathrinindependent endocytosis in fibroblasts. Alix is expressed in neurons and concentrates at synapses during epileptic seizures. Here, we used cultured neurons to show that Alix is recruited to presynapses where it interacts with and concentrates endophilin-A during conditions triggering ADBE. Using Alix knockout (ko) neurons, we showed that this recruitment, which requires interaction with the calcium-binding protein ALG-2, is necessary for ADBE. We also found that presynaptic compartments of Alix ko hippocampi display subtle morphological defects compatible with flawed synaptic activity and plasticity detected electrophysiologically. Furthermore, mice lacking Alix in the forebrain undergo less seizures during kainate-induced status epilepticus and reduced propagation of the epileptiform activity. These results thus show that impairment of ADBE due to the lack of neuronal Alix leads to abnormal synaptic recovery during physiological or pathological repeated stimulations

Tubulin tyrosination regulates synaptic function and is disrupted in Alzheimer's disease

: Microtubules play fundamental roles in the maintenance of neuronal processes and in synaptic function and plasticity. While dynamic microtubules are mainly composed of tyrosinated tubulin, long-lived microtubules contain detyrosinated tubulin, suggesting that the tubulin tyrosination/detyrosination cycle is a key player in the maintenance of microtubule dynamics and neuronal homeostasis, conditions which go awry in neurodegenerative diseases. In the tyrosination/detyrosination cycle, the C-terminal tyrosine of α-tubulin is removed by tubulin carboxypeptidases and re-added by tubulin tyrosine ligase. Here we show that tubulin tyrosine ligase hemizygous mice exhibit decreased tyrosinated microtubules, reduced dendritic spine density, and both synaptic plasticity and memory deficits. We further report decreased tubulin tyrosine ligase expression in sporadic and familial Alzheimer's disease, and reduced microtubule dynamics in human neurons harboring the familial APP-V717I mutation. Finally, we show that synapses visited by dynamic microtubules are more resistant to oligomeric amyloid β peptide toxicity and that expression of tubulin tyrosine ligase, by restoring microtubule entry into spines, suppresses the loss of synapses induced by amyloid β peptide. Together, our results demonstrate that a balanced tyrosination/detyrosination tubulin cycle is necessary for the maintenance of synaptic plasticity, is protective against amyloid β peptide-induced synaptic damage, and that this balance is lost in Alzheimer's disease, providing evidence that defective tubulin retyrosination may contribute to circuit dysfunction during neurodegeneration in Alzheimer's disease

Physiological and pathophysiological control of synaptic GluN2B-NMDA receptors by the C-terminal domain of amyloid precursor protein

The amyloid precursor protein (APP) harbors physiological roles at synapses and is central to Alzheimer's disease (AD) pathogenesis. Evidence suggests that APP intracellular domain (AICD) could regulate synapse function, but the underlying molecular mechanisms remain unknown. We addressed AICD actions at synapses, per se, combining in vivo AICD expression, ex vivo AICD delivery or APP knock-down by in utero electroporation of shRNAs with whole-cell electrophysiology. We report a critical physiological role of AICD in controlling GIuN2B-containing NMDA receptors (NMDARs) at immature excitatory synapses, via a transcription-dependent mechanism. We further show that AICD increase in mature neurons, as reported in AD, alters synaptic NMDAR composition to an immature-like GIuN2B-rich profile. This disrupts synaptic signal integration, via over-activation of SK channels, and synapse plasticity, phenotypes rescued by GIuN2B antagonism. We provide a new physiological role for AICD, which becomes pathological upon AICD increase in mature neurons. Thus, AICD could contribute to AD synaptic failure

Jeune fille du Canton de Zuric, en Suisse

Weibliche Ganzfigur stehend mit RegenschirmLanté del. ; Gatine sculpErschienen in: Cost.[umes] de Div.[ers] Pays, Paris (1817?

Unveiling novel forms of hippocampal synaptic plasticity with microelectrode arrays.

International audienceIn this report, we elucidate by use of microelectrode arrays novel forms of long-term depression and potentiation in the hippocampus which are triggered by low frequency afferent stimulation and which rely on the activation of metabotropic glutamate receptor of the fifth subtype (mGlu5 receptor)