979 research outputs found
Dynamics of ionization wave splitting and merging of atmospheric-pressure plasmas in branched dielectric tubes and channels
Atmospheric-pressure fast ionization waves (FIWs) generated by nanosecond, high voltage pulses are able to propagate long distances through small diameter dielectric tubes or channels, and so deliver UV fluxes, electric fields, charged and excited species to remote locations. In this paper, the dynamics of FIW splitting and merging in a branched dielectric channel are numerically investigated using a two-dimensional plasma hydrodynamics model with radiation transport, and the results are compared with experiments. The channel consists of a straight inlet section branching 90ĂÂŹĂąËĆŸ into a circular loop which terminates to form a second straight outlet section aligned with the inlet section. The plasma is sustained in neon gas with a trace amount of xenon at atmospheric pressure. The FIW generated at the inlet approaches the first branch point with speeds of ĂąâŹĆĄĂ¹à10 8ĂÂŹĂąâŹÂ cmĂÂŹĂąâŹÂ s ĂąâŹĆĄĂ ĂÂ1 , and produces a streamer at the inletĂąâŹĆĄĂâĂÂŹloop junction. The induced streamer then splits into two FIW fronts, each propagating in opposite directions through half of the loop channel. The FIWs slow as they traverse the circular sections due to a shorting of the electric field by the other FIW. Approaching the loopĂąâŹĆĄĂâĂÂŹoutlet junction, the two FIW fronts nearly come to a halt, induce another streamer which goes through further splitting and finally develops into a new FIW front. The new FIW increases in speed and plasma density propagating in the straight outlet channel. The electrical structure of the FIWs and the induced streamers during the splitting and merging processes are discussed with an emphasis on their mutual influence and their interaction with the channel wall. The FIW propagation pattern is in good agreement with experimental observations. Based on numerical and experimental investigations, a model for the splitting and merging FIWs in the branched loop channel is proposed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98591/1/0022-3727_45_27_275201.pd
Le gisement de méga-fossiles ligneux de Bourret (moyenne vallée de la Garonne) : processus de formation et signification climatique
International audienceLe gisement de mĂ©gafossiles ligneux de Bourret est le plus important identifiĂ© Ă ce jour en vallĂ©e de Garonne. La datation14C de 8 des 17 troncs subfossiles de Quercus extraits sâĂ©chelonne entre 8 300 et 4 200 ans cal. BP. Elles attestent du caractĂšrepartiellement remaniĂ© du gisement. Certains de ces bois ont subi une ou des phases de stockage temporaire dâune durĂ©e compriseentre 4 100 et 1 000 ans avant dâĂȘtre incorporĂ©s dĂ©finitivement dans la basse plaine. Les bois les plus anciens ont donc connu unehistoire complexe comportant une phase dâinjection dans le chenal, de stockage dans des unitĂ©s intermĂ©diaires, puis une Ă©rosion etune nouvelle phase de dĂ©pĂŽt avec la charge de fond. Les bois les plus jeunes rĂ©sultent quant Ă eux dâune injection directe depuis laripisylve dans le systĂšme fluvial. LâagrĂ©gation des dates obtenues sur ce site et sur les sites dĂ©couverts antĂ©rieurement sâorganisent en3 agrĂ©gats (env. 8 200, 5 200 et 4 200 ans cal. BP). Ceci suggĂšre que lâinjection des bois dans le systĂšme fluvial est liĂ©e Ă des phasesde forte activitĂ© hydrosĂ©dimentaire. Le synchronisme avec les Rapid Climate Changes (RCC) suggĂšre un contrĂŽle climatique sur ceprocessus, ce qui nous amĂšne Ă proposer un schĂ©ma conceptuel de formation des gisements de bois fossiles
The Immunogenicity of the Tumor-Associated Antigen α-Fetoprotein Is Enhanced by a Fusion with a Transmembrane Domain
Aim. To investigate the ability of recombinant modified vaccinia virus Ankara (rMVA) vector to induce an immune response against a well-tolerated self-antigen. Methods. rMVA vectors expressing different form of α-fetoprotein (AFP) were produced and characterized. Naïve mice were vaccinated with MVA vectors expressing the AFP antigen in either a secreted, or a membrane-bound, or an intracellular form. The immune response was monitored by an IFNΠELISpot assay and antibody detection. Results. Vaccination with the membrane-associated form of AFP induced a stronger CD8+ T-cell response compared to the ones obtained with the MVA encoding the secreted or the intracellular forms of AFP. Moreover, the vaccination with the membrane-bound AFP elicited the production of AFP-specific antibodies. Conclusions. The AFP transmembrane form is more immunogenic. Expressing a membrane-bound form in the context of an MVA vaccination could enhance the immunogenicity of a self-antigen
Synapto-protective drugs evaluation in reconstructed neuronal network
Chronic neurodegenerative syndromes such as Alzheimerâs and Parkinsonâs diseases, or acute syndromes such as ischemic stroke or traumatic brain injuries are characterized by early synaptic collapse which precedes axonal and neuronal cell body degeneration and promotes early cognitive impairment in patients. Until now, neuroprotective strategies have failed to impede the progression of neurodegenerative syndromes. Drugs preventing the loss of cell body do not prevent the cognitive decline, probably because they lack synapto-protective effects. The absence of physiologically realistic neuronal network models which can be easily handled has hindered the development of synapto-protective drugs suitable for therapies. Here we describe a new microfluidic platform which makes it possible to study the consequences of axonal trauma of reconstructed oriented mouse neuronal networks. Each neuronal population and sub-compartment can be chemically addressed individually. The somatic, mid axon, presynaptic and postsynaptic effects of local pathological stresses or putative protective molecules can thus be evaluated with the help of this versatile âbrain on chipâ platform. We show that presynaptic loss is the earliest event observed following axotomy of cortical fibers, before any sign of axonal fragmentation or post-synaptic spine alteration. This platform can be used to screen and evaluate the synapto-protective potential of several drugs. For instance, NAD+ and the Rho-kinase inhibitor Y27632 can efficiently prevent synaptic disconnection, whereas the broad-spectrum caspase inhibitor zVAD-fmk and the stilbenoid resveratrol do not prevent presynaptic degeneration. Hence, this platform is a promising tool for fundamental research in the field of developmental and neurodegenerative neurosciences, and also offers the opportunity to set up pharmacological screening of axon-protective and synapto-protective drugs
Functional polylactide via ring-opening copolymerisation with allyl, benzyl and propargyl glycidyl ethers.
A versatile and simple strategy is presented to synthesize reactive polylactide derivatives and
their block copolymers with polyethylene glycol. Commercially available glycidyl ethers with an
allyl, benzyl or propargyl functional group were copolymerised with D,L-lactide. Tin(II)-2-
ethylhexanoate-catalysis produced polymers with up to 4.6, 5.9 and 2.3 allyl, benzyl or propargyl
groups per chain, respectively. In contrast, less than one reactive group per chain was obtained
with the organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene. By increasing the polymerisation
feed ratio in glycidyl ether polymers with a higher number of reactive groups per chain were
obtained, however a decrease in molar mass was observed. An azidocoumarin was conjugated to
the propargylated polymers via copper-catalysed azide-alkyne cycloaddition. These dye-labelled
polymers produced nanospheres with fluorescent properties and diameters in the 100-nm sizerange,
as characterised by asymmetric flow field flow fractionation hyphenated with fluorescence,
static and dynamic light scattering detection. The functionalised polymers were obtained
at gram-scale in one step from commercially available reagents; therefore providing a robust and
easy to implement approach for the production of multifunctional nanomaterials
Vers une fédération de Cloud Académique dans France Grilles
Vers une fédération de Cloud Académique dans France Grille
The subfossil tree deposits from the Garonne Valley and their implications on Holocene alluvial plain dynamics
International audienceSubfossil tree trunks deposits are common in large rivers, but their status as a source for dating alluvial sequences and palaeoenvironmental studies is still discussed. Particularly their origin and the process(es) of deposition as well as a possible remobilization were pointed as a limit to their use to document river alluvial changes. In this work we report the discovery of the largest subfossil trunks deposits in the Garonne valley. These new data are compared to the previous ones. A set of 17 tree trunks and more than 300 smaller wood fragments were collected. The xylologic study shows the prevalence of Quercus and a single occurrence of Ulmus. These two hardwood species are commonly associated with riparian forest. The 14C dating carried out on seven trunks and a single branch of Quercus on the outermost identified growth rings, indicates age ranging from 8400-8000 cal. BP for the oldest fragment (bough) to 4300-4000 cal. BP for the most recent tree trunk. Radiocarbon ages of the trunks are aggregated into two main periods: 5300-5600 cal. BP (four trunks) and 4300-4000 cal. BP (three trunks). The radiocarbon (charcoal) dating of the top of the alluvial sequence overlaying the trunks gives an age between 1965-1820 and 1570-1810 cal. BP, i.e. between the 2nd and the 5th c. AD. In addition, the discovery of two unpublished subfossil tree trunks deposits in Finhan are reported (six trunks). At the light of these results, we discuss previously proposed models for the Garonne floodplain building
Toward the sustainable use of groundwater springs: A case study from Namibia
-The water supply in drylands mainly relies on groundwater, making it a crucial resource. Springs in southern Africa are often underutilized, and are neither protected nor monitored. Thus, the aim of this study was to evaluate their quality in a sample area in northwestern Namibia and to propose solutions for the sustainable use of springs. In total, 35 springs and hot springs were evaluated in the study area located in the drier part of Namibia (Pmean = 150â400 mm/year), an area highly impacted by ongoing climate change with longer and more frequent drought seasons. The springs there are mostly uncaptured and the discharge is in the form of surface runoff, which is mainly lost to the atmosphere by evaporation. Most of the studied springs were perennial, despite a severe drought period. Local communities rely on the springs mainly for livestock and human consumption, as well as for irrigation. However, 71% of the springs do not have any protective measures. The temperature, pH, conductivity and alkalinity were tested in situ. In total, 20 samples were collected and analyzed for major ions (boron, fluoride, silica and strontium) and total dissolved solids (TDS). The physical and inorganic results mostly indicated good and excellent quality water for human consumption, while the hot springs tended to have poor water quality in terms of Namibian standards, indicating that the water was not fit for human consumption
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