1,369 research outputs found
Shear-induced fractures and three-dimensional motions in an organogel
The flow behavior of a viscoelastic organogel is investigated using
ultrasonic velocimetry combined with rheometry. Our gel presents a decreasing
flow curve, i.e., the measured stress decreases as a function of the applied
shear rate. Strikingly, we note that the local flow curve calculated from the
velocity profiles also exhibits a decreasing part. We attribute this regime to
the presence of a fracturing process and three-dimensional motions in the bulk
of the sample.Comment: 13 pages, 19 figure
Perineuronal Nets Suppress Plasticity of Excitatory Synapses on CA2 Pyramidal Neurons
Long-term potentiation of excitatory synapses on pyramidal neurons in the stratum radiatum rarely occurs in hippocampal area CA2. Here, we present evidence that perineuronal nets (PNNs), a specialized extracellular matrix typically localized around inhibitory neurons, also surround mouse CA2 pyramidal neurons and envelop their excitatory synapses. CA2 pyramidal neurons express mRNA transcripts for the major PNN component aggrecan, identifying these neurons as a novel source for PNNs in the hippocampus. We also found that disruption of PNNs allows synaptic potentiation of normally plasticity-resistant excitatory CA2 synapses; thus, PNNs play a role in restricting synaptic plasticity in area CA2. Finally, we found that postnatal development of PNNs on CA2 pyramidal neurons is modified by early-life enrichment, suggesting that the development of circuits containing CA2 excitatory synapses are sensitive to manipulations of the rearing environment
Carers' perceptions of harm and the protective measures taken to safeguard children's health against inhalation of volcanic ash: A comparative study across Indonesia, Japan and Mexico
Volcanic ash contains potentially toxic elements which could affect human health. There is a paucity of research focusing on the impact of airborne volcanic emissions on the health of children, and on their exposure reduction. Children's carers (parents/guardians) are critical to their protection, so documenting their perceptions of the health risk and their knowledge of how to reduce their children's exposure is an important first step to increase our understanding of how risks are acted upon. This article reports the findings of a survey of 411 residents with caring responsibilities for children aged 12 and under in communities near the active volcanoes of Sakurajima in Japan, Merapi in Indonesia, and Popocatépetl in Mexico. Informed by the Protective Action Decision Model (PADM) and Protection Motivation Theory (PMT), we investigated their perceptions of the health effects and harmful consequences of the ash on their children, how important they thought it was to protect them, and the protective actions taken. The Indonesian carers were the most concerned and motivated to protect their children, although, in all three countries, the large majority of carers had adopted protective measures that they perceived to be most effective, such as keeping windows and doors closed. Path analysis illustrated how the connection between perceptions of harm/worry and importance of protection could partially account for higher motivation levels to protect children, in the Indonesian carers. We discuss the key messages conveyed through the findings that are of relevance for policy, practice and training in all three countries
Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af
We present results based on Spitzer Space Telescope mid-infrared (3.6-30
micron) observations of the nearby IIP supernova 2005af. We report the first
ever detection of the SiO molecule in a Type IIP supernova. Together with the
detection of the CO fundamental, this is an exciting finding as it may signal
the onset of dust condensation in the ejecta. From a wealth of fine-structure
lines we provide abundance estimates for stable Ni, Ar, and Ne which, via
spectral synthesis, may be used to constrain nucleosynthesis models.Comment: ApJ Letters (accepted
Structure of nanoparticles embedded in micellar polycrystals
We investigate by scattering techniques the structure of water-based soft
composite materials comprising a crystal made of Pluronic block-copolymer
micelles arranged in a face-centered cubic lattice and a small amount (at most
2% by volume) of silica nanoparticles, of size comparable to that of the
micelles. The copolymer is thermosensitive: it is hydrophilic and fully
dissolved in water at low temperature (T ~ 0{\deg}C), and self-assembles into
micelles at room temperature, where the block-copolymer is amphiphilic. We use
contrast matching small-angle neuron scattering experiments to probe
independently the structure of the nanoparticles and that of the polymer. We
find that the nanoparticles do not perturb the crystalline order. In addition,
a structure peak is measured for the silica nanoparticles dispersed in the
polycrystalline samples. This implies that the samples are spatially
heterogeneous and comprise, without macroscopic phase separation, silica-poor
and silica-rich regions. We show that the nanoparticle concentration in the
silica-rich regions is about tenfold the average concentration. These regions
are grain boundaries between crystallites, where nanoparticles concentrate, as
shown by static light scattering and by light microscopy imaging of the
samples. We show that the temperature rate at which the sample is prepared
strongly influence the segregation of the nanoparticles in the
grain-boundaries.Comment: accepted for publication in Langmui
Solvent contribution to the stability of a physical gel characterized by quasi-elastic neutron scattering
The dynamics of a physical gel, namely the Low Molecular Mass Organic Gelator
{\textit Methyl-4,6-O-benzylidene- -D-mannopyranoside (-manno)}
in water and toluene are probed by neutron scattering. Using high gelator
concentrations, we were able to determine, on a timescale from a few ps to 1
ns, the number of solvent molecules that are immobilised by the rigid network
formed by the gelators. We found that only few toluene molecules per gelator
participate to the network which is formed by hydrogen bonding between the
gelators' sugar moieties. In water, however, the interactions leading to the
gel formations are weaker, involving dipolar, hydrophobic or
interactions and hydrogen bonds are formed between the gelators and the
surrounding water. Therefore, around 10 to 14 water molecules per gelator are
immobilised by the presence of the network. This study shows that neutron
scattering can give valuable information about the behaviour of solvent
confined in a molecular gel.Comment: Langmuir (2015
A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova
We present late-time (590-994 d) mid-IR photometry of the normal, but
highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading
emission is detected from the direction of the supernova. Most of this flux
appears not to be driven by the supernova event but instead probably originates
in a cool, obscured star-formation region or molecular cloud along the
line-of-sight. We also show, however, that the declining component of the flux
is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR
emission could also be coming from newly-condensed dust and/or an ejecta/CSM
impact but their contributions are likely to be small. For the case of a CSM-IR
echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding
CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.
Such a CSM would have resulted from episodic mass loss whose rate declined
significantly about 28,000 years ago. Alternatively, an IR echo from a
surrounding, dense, dusty molecular cloud might also have been responsible for
the fading component. Either way, this is the first time that an IR echo has
been clearly identified in a Type IIP supernova. We find no evidence for or
against the proposal that Type IIP supernovae produce large amounts of dust via
grain condensation in the ejecta. However, within the CSM-IR echo scenario, the
mass of dust derived implies that the progenitors of the most common of
core-collapse supernovae may make an important contribution to the universal
dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in
Astrophysical Journal (References corrected
13 metastable states arising from a simple multifunctional unimolecular system
A diarylethene core decorated with two benzooxazolidine side-arms through ethylenic spacers represents a smart example of multi-addressable system whose reversible responses could be selectively activated on demand. UVâVisible and NMR spectroscopies and electrochemical studies allow to overview its performances when stimulated by light, acid/base and electrons, then underlining its photochromic, acidochromic and electrochromic properties. The multichromophoric combination could be considered as multifunctional and multistate systems, as interconversions can be performed by different stimuli whereas each stimulus provides a specific metastable state
Dithienylethene-Based Gated Ambichromic Dyads
A set of dithienylethene (DTE)-based ambichromic dyads containing an acido-, photo-, and electrosensitive indolino[2,1-b]oxazolidine (BOX) unit displays gated photochromism. Ring opening of BOX prevents photoinduced electrocylization between open and closed forms of DTE. The photochromic performances are regenerated by two different pathways. NMR and electrochemical studies evidence interactions between indolenium and phenylâthienyl sidearms
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