Fused-cast refractory materials are widely used in the glass industry, especially in the building of superstructures and side walls of fusion furnaces. The HZFC (High Zirconia Fused Cast) products are especially used as tank blocks for the fusion of highly corrosive glasses melted at very high temperature (such as LCD glass), due to their high corrosion resistance and their low generation of glass defects generation.The presence of this high amount of pure ZrO2 in the refractory can be responsible for microdamage occurrence during the cooling step after melt casting (annealing), associated to the martensitic transition of zirconia.Acoustic emission (AE) analysis is well known as a reliable tool to investigate microstuctural evolution at a very small scale. In this work, a fused-cast ZrO2 refractory has been investigated using a AE unsupervised pattern recognition procedure and a frequency-energy coupled analysis. Data gathering during thermal cycles at high temperature (typically 1500 degrees C) has been done thanks to an innovative self-developed testing device. The analysis of frequency and energy parameters makes it possible to detect and to characterize the occurrence and the chronology of microdamage in specific range of temperature. Hypothesis concerning different ways of microdamage formation below the temperature of the martensitic transformation of ZrO2 during the cooling stage can be proposed related to thermo-mechanical properties and the microstructure of the material. In particular, intergranular and intragranular microcracks due to CTE mismatches occurring in the material have been also investigated. (C) 2010 Elsevier Ltd. All rights reserved.

A non-destructive testing technique based on the time reversal principle is applied to cementitious materials. Preliminary results are presented showing the reversibility of wave propagation and that focusing by time reversal is feasible in cementitious materials. Then, the technique is implemented on a mechanical test in order to monitor the cracking process of a concrete specimen loaded under three point bending. The acoustic mirror permits qualitative monitoring of the propagation of a crack by analyzing the focusing of a reference signal on a sensor placed near the expected crack path. A decrease of energy and of amplitude of the focused signal is observed upon cracking. Then, the specimen made of a material with high capabilities of self healing, is immersed in water, and healing processes are monitored. The results show a recovery of signal focusing upon healing. Comparisons with mechanical test data indicate that the method is sensitive to the variation of stiffness of the structure due to crack propagation and crack healing.

Au cours de leur vie, les avions sont regulierement examines visuellement. D'autres visites plus poussees necessitent le demontage de certains elements de l'avion. Le controle reste principalement visuel. Certaines parties de l'avion demeurent cependant difficiles d'acces. De plus, tous ces controles immobilisent l'avion plus ou moins longtemps et de ce fait coutent cher. La signature des defauts typiques et representatifs de micro compression du bois a ete investiguee en laboratoire sur eprouvettes par deux techniques d'essais non destructifs: emission acoustique et acousto-ultrasons. Des essais sur sous structure (longeron) ont ete menes afin de caracteriser l'evolution de defauts reels. La troisieme etape consiste en un essai en taille reelle sur une aile en bois d'un avion CAP 10, testee jusqu'a rupture, suivi par Emission Acoustique (EA). Le cycle de sollicitation de la structure a ete decide dans le but de fournir un maximum de donnees EA et de permettre la prediction et la localisation de l'endommagement final en temps reel. Les resultats obtenus avec le systeme EA sont presentes dans cet article. L'idee d'installer un systeme qui verifierait en temps reel et en vol la sante structurelle de l'avion est envisagee ainsi que celle d'un controle periodique au sol. (Resume d'auteur)

This paper presents the first results obtained from the coupling of acoustic emission, ultrasonic testing and electrochemical noise measurements for the real-time monitoring of metal–electrolyte interfacial processes of stochastic nature. In this first paper, this combined approach is applied to gas-evolving electrodes (hydrogen and oxygen) to verify the ability of acoustic–ultrasonic measurements to complement the purely electrochemical information brought by conventional potential and current electrochemical noise measurements. Results have been treated both in the time and frequency domains indicating that acoustic–ultrasonic measurements actually sense the dynamic bubble evolution behaviour. It is hence shown that this new approach is a promising efficient tool that can be potentially extended to the study of other complex multiphase phenomena.

Consequences of 5-HT(1/2) systems blockade by methysergide on newborn rats respiratory drive were evaluated in vivo with unrestrained animals and in vitro using brainstem-spinal cord preparations. A decrease in respiratory frequency until a plateau level was observed under both in vivo (82.8 +/- 0.6% of control values) and in vitro (76.8 +/- 0.8% of control values) conditions whereas an increase in inspiratory amplitude (135.1 +/- 2.1% of control values) was only retrieved in vivo. By the use of the c-fos expression analysis, we correlated these effects with neuronal activity changes, particularly, in vivo in two key structures between the respiratory ponto-medullary network and the peripheral or suprapontine afferences, namely the commissural subnucleus of the nucleus of the solitary tract and the lateral parabrachial nucleus. Thus, peripheral and suprapontine inputs seem to be of a primeval importance in the respiratory influence of endogenous 5-HT. Besides, as 5-HT is involved in the respiratory perturbations that occur in sudden infant death syndrome (SIDS), our results suggest a participation of peripheral and suprapontine inputs in these disorders.

Acoustic Emission (AE) is a non destructive testing method allowing to detect in real time growing defects. Many damaging processes can be in the scope of the technique such as crack propagation, delamination, corrosion of reinforced bar,... The AE signature of each phenomenon under interest can be characterised in order first to discriminate genuuine AE from noise but moreover to identify the damaging process and to evaluate the severity of the damage for the integrity of the structure, with often the help of the analysis of the AE signals with statistic tools and pattern recognition processing, to provide a good diagnosis. Intrinsic mechanical properties of concrete give raised high signal to noise emission when damage propagates. The high attenuation coefficient of elastic wave in concrete material was a limitation to apply AE on a large civil structure. The development of specific AE sensors has contributed to overcome this difficulty and nowadays AE can be applied on full scale structures. In real time, AF monitoring detects the occurring of growing damage versus the loading level, displays the trend of its AE activity and locates it. AE is applied during proof test in order to investigate the fitness for service or repair validation, during service to detect a problem of fatigue or corrosion. AE continuous monitoring allows to maintain a damaged structure in service. This paper covers applications from laboratory scale experiments to actual civil structures. For the covering abstract see ITRD E123168.

The retrotrapezoid nucleus (RTN), a part of the rostral ventrolateral medulla, is involved in the control of breathing. A recent immunohistological study suggested a possible involvement of the RTN in hypoxic chemoreflex loop. The present electrophysiological study performed in the cat demonstrates that 23 out of 24 RTN neurons were stimulated during the biphasic respiratory response to hypoxia, which consists of a reinforcement followed by a depression of respiratory activity. This confirms the previous immunohistological study. While 15 RTN neurons might integrate either phase I (n = 7) or phase II (n = 8) O2-chemosensitive inputs, the remaining eight RTN neurons stimulated by hypoxia are susceptible to integrate both phase I and phase II O2-chemosensitive inputs. In conclusion, our results suggest that the different subsets of RTN neurons may influence respiratory output by conveying signals originating from peripheral and/or central chemoreceptors stimulated during hypoxia.

The retrotrapezoid nucleus (RTN), a part of the rostral ventrolateral medulla, is involved in the control of breathing. The mechanisms by which the RTN modulate the activity of respiratory neurons during chemoreceptor stimulation are not fully understood. This electrophysiological study performed in the cat demonstrates that 18 out of 22 RTN neurons receive inputs from the commissural subnucleus of the solitary tract (cNTS), the peripheral chemoreceptor afferents projection site. Moreover, six RTN neurons are found to present interconnection between RTN and the ventrolateral subnucleus of the solitary tract, an area containing mainly bulbo-spinal respiratory neurons. The present data suggest that RTN play a key role by concomitantly integrating chemosensitive informations relayed by the cNTS and providing an influence on the respiratory network.

Extracellular recordings were made in the dorsal respiratory group (DRG) and adjacent reticular formation following single-shock stimulation of the anterior ethmoidal nerve (AEN) and during sneeze evoked by repetitive stimulation of the AEN in nembutal-anaesthetized, curarized and ventilated cats. These neurones were characterised according to (i) their activity during the respiratory cycle (as inspiratory augmenting or decrementing (I Aug or I Dec), expiratory augmenting or decrementing (E Aug or E Dec), silent or tonic), and (ii) their axonal projection (bulbospinal or non-bulbospinal-non-vagal (BS or NBS-NV)). Following single-shock stimulation of the AEN, most of the inspiratory neurones were transiently inhibited, whereas E Aug neurones were activated and E Dec neurones were activated and then inhibited. Silent neurones responded with a multispike or a paucispike pattern. Following repetitive stimulation of the AEN and during the resulting sneeze reflex, I Aug neurones increased their activity in parallel with the phrenic activity, I Dec neurones fired at the onset and at the end of the inspiration, E Dec and some silent neurones fired either during the compressive phase or after the expulsive phase, whereas E Aug and some silent neurones fired during the expulsive phase. We conclude that sneeze involves a reconfiguration of the central respiratory drive which uses, at least partly, the respiratory network to trigger a non-ventilatory defensive motor act.

Rat cerebellar RNA injected into Xenopus oocytes leads to the expression of putative P-type voltage-dependent Ca2+ channels (VDCCs). The monitoring of intracellular Ca2+ variations by recording the Ca2+ dependent chloride current in voltage clamped oocytes indicates that activation of these Ca2+ channels by depolarization gives rise to two distinct components of cytosolic Ca2+ elevation. If the early component (T1) can be directly attributed to the Ca2+ entry through VDCCs, the second delayed one (T2) is related to a Ca2+ release from InsP3 sensitive stores activated following Ca2+ entry. Modifications of cytosolic Ca2+ by direct injection of Ca2+ into oocytes or by increasing the Ca2+ influx through VDCCs suggest that the Ca2+ release from intracellular InsP3 sensitive stores can be modulated in a differential manner. Namely, discrete elevations of cytosolic Ca2+ switch on the Ca2+ release whereas higher Ca2+ concentrations dampen the release. These results suggest a functional coupling between P-type VDCCs and InsP3 receptors.

Endogenous calcium channels of Xenopus oocyte membrane do not fit with pharmacological classification of calcium channels. The present study demonstrates that the saccharidic derivate, OC8-MAGlu-MAGlu, has potent inhibitory effect on this channel activity.

The Ca++antagonist effects of new drugs derived from monosaccharides were tested in the rat duodenal muscle preparation in vitro.The structure-activity relationship shows that:1. The monoacetonide products (nR-O-MAG and nR-S-MAG) with alkyl chain from 8 to 9 C atoms induce a maximal reduction of muscular tonus and contraction.2. The inhibitory effect rapidly decreases when the alkyl chain has a number of C atoms smaller than 7 or larger than 9.3. The diacetonide (DAG) and acetonide (G) products induce an inhibition of less extent.4. The Ca++antagonist effect is very slightly changed by the type of heteroatom (O or S) linking the alkyl chain to the monosaccharide.5. The type of monosaccharide affects the Ca++ antagonist activity.Key Words: Calcium-antagonistmonosaccharides derivativesduodenal musclerat

The slow inward Na current observed during sustained depolarization of the Xenopus oocyte membrane is due to a complex mechanism described as the induction of the channels. The present work investigates the role of protein phosphorylation in Na channel function. Injection of alkaline phosphatase in the oocytes decreased inward current. Therefore, the possible involvement of protein kinase in Na channel induction was explored. Treatment of oocytes with two activators of protein kinase C (PKC) resulted in enhanced Na current amplitude, whereas the treatment of oocytes with two potent PKC inhibitors decreased the inward current. These results imply that PKC phosphorylation is a fundamental step of Na channel induction. The possibility that the depolarization of the oocyte membrane may be the factor involved in PKC activation is discussed.

Xenopus oocytes injected with rat cerebellar mRNA expressed functional voltage-dependent Ca channels detected as an inward Ba current (I(Ba)). The pharmacological resistance to dihydropyridines and omega-conotoxin together with the blockade obtained with Agelenopsis aperta venom suggest that these channels could be somehow assimilated to P-type Ca channels. The precise nature of the transplanted Ca channels was assessed by hybrid-arrest experiments using a specific oligonucleotide antisense-derivated from the recently cloned alpha1-subunit of P channels (BI-1 clone). In addition, we demonstrate that exogenous Ca channel activity was enhanced by two different PKC activators (a phorbol ester and a structural analog to diacylglycerol). The general electrophysiological and pharmacological properties of the stimulated Ca channels remain unchanged. This potentiation induced by PKC activators is antagonized by a PKC inhibitor (staurosporine) and by a monoclonal antibody directed against PKC. It is concluded that P-type Ca channels are potentially regulated by PKC phosphorylation and the functional relevance of this intracellular pathway is discussed.

The Ca++antagonist effects of new drugs derived from monosaccharides were tested in the rat duodenal muscle preparation in vitro.The structure-activity relationship shows that: 1. The monoacetonide products (nR-O-MAG and nR-S-MAG) with alkyl chain from 8 to 9 C atoms induce a maximal reduction of muscular tonus and contraction. 2. The inhibitory effect rapidly decreases when the alkyl chain has a number of C atoms smaller than 7 or larger than 9. 3. The diacetonide (DAG) and acetonide (G) products induce an inhibition of less extent. 4. The Ca++antagonist effect is very slightly changed by the type of heteroatom (O or S) linking the alkyl chain to the monosaccharide. 5. The type of monosaccharide affects the Ca++ antagonist activity.

P-type calcium channels are expressed in Xenopus oocytes after injection of rat cerebellar mRNA. The FTX and omega-Aga-IVa toxins extracted from Agelenopsis aperta venom are known to inhibit the activity of this channel. The present results demonstrate that 8RN-DAGal is also a antagonist of P-type calcium channels. The inhibition of the current, obtained with Ba2+, as charge carrier, is voltage dependent.

Cortical and spinal somatosensory evoked potentials (SEPs) have been recorded after median and tibial nerve stimulation in healthy newborns. Spinal SEPs were readily obtained and recorded in all but one neonates after stimulation of both nerves. Cortical SEPs were more frequently recorded after median nerve (87%) than after tibial nerve stimulation (73%) but the shape of cortical SEPs obtained after tibial nerve stimulation was less variable. The mean feature of cortical SEPs was a negative wave (N27) for median nerve and a positive wave (P32) for tibial nerve. The present results demonstrate the feasibility of obtaining in the same baby, spinal and cortical SEPs after stimulation of median and tibial nerve, giving information on the functional integrity of central and peripheral somatosensory pathways which supply upper and lower limbs.

In decerebrate, C2-spinalized cats, stimulation of the C6-phrenic root produces a weak activation of phrenic motoneurons in the adjacent C5 segment in a few animals (23%). When phrenic motoneurons are electrically excited by testing stimulation applied to the spinal cord or internal intercostal nerve, the evoked responses recorded in a cervical phrenic root are partly inhibited by conditioning stimulation applied to another ipsilateral or contralateral cervical phrenic root. We therefore conclude that phrenic fibers exert both inhibitory and excitatory effects on adjacent phrenic motoneurons in the cervical spinal cord.