CiteULike: Author Albouy

One pot synthesis of hierarchical porous silica membrane material with dispersed Pt nanoparticles using a microwave-assisted sol-gel route

Christelle Yacou — 2008-08-05T23:10:27-00:00

J. Mater. Chem. (2008)

A versatile sol-gel route has been developed for the preparation of hierarchical porous silica membrane material with highly dispersed platinum nanoparticles (Pt-NPs). The outstanding feature of the "one pot" synthesis developed in this work lies in the successful preparation of a stable complex suspension made of silica sol, multi-scale porogens and Pt nanoparticles. The multi-scale porogens were based on non-ionic triblock copolymers and aqueous latex suspension to create mesopores and macropores, respectively, with finely tuned pore size and organization. For further functionalization of the membranes, Pt nanoparticles of about 4 nm in diameter were prepared by irradiating with microwaves (MW) the Pt precursors added in the starting suspension. This original path is suggested to enable a pre-organization of Pt nanoparticles in the ordered mesoporous structure. The suspensions were then deposited as thin films on either dense or macroporous supports, and further thermally treated at 450 [degree]C to remove the porogen units. Hierarchical porous layers composed of micropores (<2 nm), ordered mesopores ([similar]4 nm) and macropores ([similar]70 nm) with or without Pt were prepared and characterized. The resulting membranes are foreseen to exhibit great potential as multifunctional membranes for gas separation coupled with catalytic reaction.

Both the Hippocampus and Striatum Are Involved in Consolidation of Motor Sequence Memory

Geneviève Albouy — 2008-04-25T12:12:01-00:00

Neuron, Vol. 58, No. 2. (24 April 2008), pp. 261-272.

Summary Functional magnetic resonance imaging (fMRI) was used to investigate the cerebral correlates of motor sequence memory consolidation. Participants were scanned while training on an implicit oculomotor sequence learning task and during a single testing session taking place 30 min, 5 hr, or 24 hr later. During training, responses observed in hippocampus and striatum were linearly related to the gain in performance observed overnight, but not over the day. Responses in both structures were significantly larger at 24 hr than at 30 min or 5 hr. Additionally, the competitive interaction observed between these structures during training became cooperative overnight. These results stress the importance of both hippocampus and striatum in procedural memory consolidation. Responses in these areas during training seem to condition the overnight memory processing that is associated with a change in their functional interactions. These results show that both structures interact during motor sequence consolidation to optimize subsequent behavior.

Azobenzene-Containing Liquid Crystal Triblock Copolymers: Synthesis, Characterization, and Self-Assembly Behavior

Wei Deng — 2008-04-25T12:18:41-00:00

Macromolecules, Vol. 41, No. 7. (8 April 2008), pp. 2459-2466.

Abstract: A series of azobenzene-containing isotropic/nematic/isotropic liquid crystal (LC) triblock copolymers (PBMA-b-PMAazo444-b-PBMA) with different block ratios was synthesized by atom transfer radical polymerization (ATRP). The central block PMAazo444 is an azobenzene-containing side-on nematic liquid crystalline polymer and PBMA a coil polymer. These azo-triblock copolymers were prepared and studied with the aim of producing, in the future, photoresponsive elastomers with lamellar structure. Kinetic studies on the polymerization of the azobenzene-containing LC monomer demonstrate that its polymerization is a controlled process. A LC homopolymer with narrow molecular weight distribution (Mw/Mn = 1.13) was used as a difunctional macroinitiator to prepare the triblock copolymers by ATRP. The triblock copolymers were characterized by NMR, SEC, DSC, and POM. A triblock copolymer with 47 wt % of LC part self-assembles into a lamellar phase as evidenced both by SAXS and by TEM. The surface alignment of this lamellar phase on a silicon substrate was studied by AFM and compared with its nonphotosensitive triblock homologue (PBA-b-PA444-b-PBA). For this nonphotosensitive triblock copolymer the lamellas aligned parallel to the substrate, while for the azobenzene-containing triblock copolymer they organized perpendicular to the substrate.

Hemodynamic cerebral correlates of sleep spindles during human non-rapid eye movement sleep

M Schabus — 2007-08-07T17:37:19-00:00

PNAS, Vol. 104, No. 32. (7 August 2007), pp. 13164-13169.

In humans, some evidence suggests that there are two different types of spindles during sleep, which differ by their scalp topography and possibly some aspects of their regulation. To test for the existence of two different spindle types, we characterized the activity associated with slow (1113 Hz) and fast (1315 Hz) spindles, identified as discrete events during non-rapid eye movement sleep, in non-sleep-deprived human volunteers, using simultaneous electroencephalography and functional MRI. An activation pattern common to both spindle types involved the thalami, paralimbic areas (anterior cingulate and insular cortices), and superior temporal gyri. No thalamic difference was detected in the direct comparison between slow and fast spindles although some thalamic areas were preferentially activated in relation to either spindle type. Beyond the common activation pattern, the increases in cortical activity differed significantly between the two spindle types. Slow spindles were associated with increased activity in the superior frontal gyrus. In contrast, fast spindles recruited a set of cortical regions involved in sensorimotor processing, as well as the mesial frontal cortex and hippocampus. The recruitment of partially segregated cortical networks for slow and fast spindles further supports the existence of two spindle types during human non-rapid eye movement sleep, with potentially different functional significance. 10.1073/pnas.0703084104

Sleep transforms the cerebral trace of declarative memories

Steffen Gais — 2007-11-18T21:18:23-00:00

Proceedings of the National Academy of Sciences (13 November 2007), 0705454104.

After encoding, memory traces are initially fragile and have to be reinforced to become permanent. The initial steps of this process occur at a cellular level within minutes or hours. Besides this rapid synaptic consolidation, systems consolidation occurs within a time frame of days to years. For declarative memory, the latter is presumed to rely on an interaction between different brain regions, in particular the hippocampus and the medial prefrontal cortex (mPFC). Specifically, sleep has been proposed to provide a setting that supports such systems consolidation processes, leading to a transfer and perhaps transformation of memories. Using functional MRI, we show that postlearning sleep enhances hippocampal responses during recall of word pairs 48 h after learning, indicating intrahippocampal memory processing during sleep. At the same time, sleep induces a memory-related functional connectivity between the hippocampus and the mPFC. Six months after learning, memories activated the mPFC more strongly when they were encoded before sleep, showing that sleep leads to long-lasting changes in the representation of memories on a systems level. 10.1073/pnas.0705454104

Daytime light exposure dynamically enhances brain responses.

G Vandewalle — 2006-08-23T12:52:17-00:00

Curr Biol, Vol. 16, No. 16. (22 August 2006), pp. 1616-1621.

In humans, light enhances both alertness and performance during nighttime and daytime and influences regional brain function . These effects do not correspond to classical visual responses but involve a non-image forming (NIF) system, which elicits greater endocrine, physiological, neurophysiological, and behavioral responses to shorter light wavelengths than to wavelengths geared toward the visual system . During daytime, the neural changes induced by light exposure, and their time courses, are largely unknown. With functional magnetic resonance imaging (fMRI), we characterized the neural correlates of the alerting effect of daytime light by assessing the responses to an auditory oddball task , before and after a short exposure to a bright white light. Light-induced improvement in subjective alertness was linearly related to responses in the posterior thalamus. In addition, light enhanced responses in a set of cortical areas supporting attentional oddball effects, and it prevented decreases of activity otherwise observed during continuous darkness. Responses to light were remarkably dynamic. They declined within minutes after the end of the light stimulus, following various region-specific time courses. These findings suggest that light can modulate activity of subcortical structures involved in alertness, thereby dynamically promoting cortical activity in networks involved in ongoing nonvisual cognitive processes.

Implicit oculomotor sequence learning in humans: Time course of offline processing.

G Albouy — 2006-07-02T02:40:04-00:00

Brain Res, Vol. 1090, No. 1. (23 May 2006), pp. 163-171.

Studies of manual and digital sequence learning indicate that motor memories continue to be processed after training has ended, following a succession of identifiable steps. However, it is not known whether this offline memory processing constitutes a basic feature of motor learning and generalizes to the implicit learning of a sequence of eye movements. To assess this hypothesis, we have created the serial oculomotor reaction time task (SORT). Participants were trained to the SORT then tested after either 30 min, 5 h or 24 h. During training, ocular reaction times decreased monotonically over practice of a repeated sequence, then increased when a different sequence was displayed, demonstrating oculomotor learning of the trained sequence. When tested 30 min after training, a significant gain in oculomotor performance was observed irrespective of the sequence learning. This gain was no longer present after 5 h. Remarkably, a gain in performance specific to the learned sequence emerged only 24 h after training. After testing, a generation task confirmed that most subjects learned implicitly the regularities of the sequence. Our results show that, as for manual or digital sequences, oculomotor sequences can be implicitly learned. The offline processing of oculomotor memories follows distinct stages in a way similar to those observed after manual or digital sequence learning.