Antioxidant deactivation on graphenic nanocarbon surfaces

This article reports a direct chemical pathway for antioxidant deactivation on the surfaces of carbon nanomaterials. In the absence of cells, carbon nanotubes are shown to deplete the key physiological antioxidant glutathione (GSH) in a reaction involving dissolved dioxygen that yields the oxidized dimer, GSSG, as the primary product. In both chemical and electrochemical experiments, oxygen is only consumed at a significant steady-state rate in the presence of both nanotubes and GSH. GSH deactivation occurs for single- and multi-walled nanotubes, graphene oxide, nanohorns, and carbon black at varying rates that are characteristic of the material. The GSH depletion rates can be partially unified by surface area normalization, are accelerated by nitrogen doping, and suppressed by defect annealing or addition of proteins or surfactants. It is proposed that dioxygen reacts with active sites on graphenic carbon surfaces to produce surface-bound oxygen intermediates that react heterogeneously with glutathione to restore the carbon surface and complete a catalytic cycle. The direct catalytic reaction between nanomaterial surfaces and antioxidants may contribute to oxidative stress pathways in nanotoxicity, and the dependence on surface area and structural defects suggest strategies for safe material design.     

Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation

Materials with high aspect ratio, such as carbon nanotubes and asbestos fibres, have been shown to cause length-dependent toxicity in certain cells because these long materials prevent complete ingestion and this frustrates the cell. Biophysical models have been proposed to explain how spheres and elliptical nanostructures enter cells, but one-dimensional nanomaterials have not been examined. Here, we show experimentally and theoretically that cylindrical one-dimensional nanomaterials such as carbon nanotubes enter cells through the tip first. For nanotubes with end caps or carbon shells at their tips, uptake involves tip recognition through receptor binding, rotation that is driven by asymmetric elastic strain at the tube-bilayer interface, and near-vertical entry. The precise angle of entry is governed by the relative timescales for tube rotation and receptor diffusion. Nanotubes without caps or shells on their tips show a different mode of membrane interaction, posing an interesting question as to whether modifying the tips of tubes may help avoid frustrated uptake by cells.     

Modelling recombination current in polysilicon solar cell grain boundaries

The recombination current in grain boundaries is theoretically investigated for a polycrystalline silicon solar cell n–p junction operating either in short-circuit or in open-circuit configurations. The analysis is carried out using results performed in earlier works, by means of numerical simulations including the presence of grain boundaries. The variation of grain boundary recombination current density with exciting light wavelength is reported for different cell parameters like grain boundary recombination velocity, base dopant density and base thickness.The objective of the present paper is to understand to what extend the light wavelength and the junction configuration allow an optimal measure of the grain boundary recombination parameter.     

Steam oxidation and microstructural evolution of rare earth silicate environmental barrier coatings

A primary failure mode for environmental barrier coatings (EBCs) on SiC ceramic matrix composites (CMCs) is the oxidation of the intermediate Si-bond coating, where the formation of SiO₂ at the bond coating–EBC interface results in debonding and spallation. This work compares the microstructure evolution and steam oxidation kinetics of the Si-bond coating beneath yttrium/ytterbium disilicate ((Y/Yb)DS) and ytterbium disilicate/monosilicate (YbDS/YbMS) EBCs to better understand the impact of EBC composition on oxidation kinetics. After 500 1-h cycles at 1350°C, (Y/Yb)DS displayed a decreasing concentration of the monosilicate minor phase and increasing concentration of porosity as furnace cycling time increased, whereas the YbDS/YbMS EBC displayed negligible microstructural evolution. For both EBC systems, thermally grown oxide growth rates in steam were found to increase by approximately an order magnitude compared to dry air oxidation. The (Y/Yb)DS EBC displayed a reduced steam oxidation rate compared to YbDS/YbMS.     

A novel follicle culture system markedly increases follicle volume, cell number and oestradiol secretion

This study reports a novel, simple method for culture of mouse follicles which results in follicles with cell numbers similar to in vivo fully grown follicles. Using this method, follicles (180-240 microm in diameter) were cultured in a 100 microl inverted drop of medium without oil and compared with culture in upright drops with and without a mineral oil overlay. Follicles, isolated from C57BL/6 x CBA/ca crossbred and MF1 inbred mice, were cultured individually at 37 degrees C in 96-well round-bottomed suspension cell tissue culture plates for 6 days. Follicles grown in the inverted drop culture system reached a markedly higher final diameter (means+/-s.e.m.; 471 +/- 6.0 microm) as compared with the upright with oil (363 +/- 2.7 microm) and without oil (358 +/- 4.0) systems. There was no significant effect of mouse strain on follicle diameter. Follicular secretion of oestradiol and lactate into the medium was measured on days 2, 4 and 6 of culture. Secretion of oestradiol per follicle on day 6 was 2.49 +/- 0.45 ng in the inverted and 0.90 +/- 0.17 ng in the upright without oil system (P < 0.001). Follicular secretion of lactate on a per unit of follicle volume basis remained constant in the inverted system over days 2, 4 and 6 and was less (P < 0.001) than secretion in both the upright with and without oil systems. Follicle cell proliferation was markedly increased in the inverted as compared with the upright with oil system; the increases in cell numbers were significant on day 3 (P < 0.01) and on all subsequent days (P < 0.001). These results are discussed in relation to the supply of oxygen to the follicle in culture.     

Inositol transport in mouse oocytes and preimplantation embryos: effects of mouse strain,embryo stage,sodium and the hexose transport inhibitor,phloridzin

The uptake of myo-inositol by mouse oocytes and preimplantation embryos of a crossbred (DBA x C57BL/6) and a purebred outbred strain (MF1) was measured using [2-(3)H]myo-inositol. Uptake in crossbred embryos increased about 15-fold between the one- and two-cell stages and increased again by about sixfold at the blastocyst stage compared with the morula stage. Uptake in purebred embryos increased about 42-fold between the one- and two-cell stages and increased more than threefold at the blastocyst stage compared with the morula stage. In all stages examined, except two-cell crossbred embryos, inositol uptake was, depending on the stage, either largely or partly sodium dependent and could be inhibited by the sodium-dependent hexose transport inhibitor, phloridzin. This is consistent with the hypothesis that transport occurs via a sodium myo-inositol transporter (SMIT) protein. In addition, there was strong evidence that a sodium-independent mechanism of uptake, possibly a channel, was switched on at the two-cell stage coincident with zygotic gene activation which resulted in 141-fold and 71-fold increases in sodium-independent uptake from the one-cell to two-cell stages in crossbred and purebred embryos, respectively. This mechanism was either abolished or drastically downregulated at the blastocyst stage, whereas sodium-dependent uptake was markedly upregulated. In two-cell crossbred embryos, there was a complete abolition of sodium-dependent uptake, again possibly regulated by zygotic gene activation. The hypothesis that the changes in mechanism of inositol uptake at about the two-cell stage are due to zygotic gene activation was supported by the finding that these changes did not occur in parthenogenetic two-cell embryos.     

Developmental change in judging important and critical elements of stories.

Conducted 2 experiments with 54 2nd, 4th, and 6th graders and 15 undergraduates (Exp I) and 45 2nd and 4th graders (Exp II) to examine children's understanding (metacognitive awareness) that in a simple story the following parts are most important or essential for comprehending it: what precipitates the character's action (initiating event), what the character did (action), and what follows the character's action (consequence). Ss' judgments of simple stories showed that 2nd graders seldom selected this sequence, but 4th, 5th, and 6th graders and adults did so under a variety of conditions. In addition there was a modest relation between recall of the stories and older children's (5th graders) judgments of them. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Raman spectroscopic characterization of SiO2 phase transformation and Si substrate stress relevant to EBC performance

To accurately model the long-term durability of environmental barrier coatings (EBCs), a more complete understanding of the phase composition and transformations of the thermally grown oxide SiO₂ (TGO) is desired. For the TGO formed during thermal cycling in steam, cristobalite formation and the subsequent β- to α-cristobalite transformation has been identified as a potentially life-limiting mechanism. In this study, Raman micro-spectroscopy was used to quantify the cristobalite transformation on a polycrystalline Si coupon that was exposed to steam at 1350°C for 100 h. The phase transformation was mapped at 200–260°C on the TGO surface at different ramp rates using a heating stage and a micro-positioning stage. The stress in the Si substrate was also determined using Raman spectroscopy by measuring the stress induced peak shift. The α→β phase transformation produced a 300–500 MPa tensile stress in the Si substrate, which compared well to the stress predicted from the volumetric expansion of the cristobalite. Quantifying the phase transformation and residual stress are critical tools in developing the next generation of high performance EBCs.     

A New Class of Proton Conductors with Dramatically Enhanced Stability and High Conductivity for Reversible Solid Oxide Cells

Reversible solid oxide cells based on proton conductors (P-ReSOCs) have potential to be the most efficient and low-cost option for large-scale energy storage and power generation, holding promise as an enabler for the implementation of intermittent renewable energy technologies and the widespread utilization of hydrogen. Here, the rational design of a new class of hexavalent Mo/W-doped proton-conducting electrolytes with excellent durability while maintaining high conductivity is reported. Specifically, BaMo(W)_0.03Ce_0.71Yb_0.26O_3-δ exhibits dramatically enhanced chemical stability against high concentrations of steam and carbon dioxide than the state-of-the-art electrolyte materials while retaining similar ionic conductivity. In addition, P-ReSOCs based on BaW_0.03Ce_0.71Yb_0.26O_3-δ demonstrate high peak power densities of 1.54, 1.03, 0.72, and 0.48 W cm⁻² at 650, 600, 550, and 500 °C, respectively, in the fuel cell mode. During steam electrolysis, a high current density of 2.28 A cm⁻² is achieved at a cell voltage of 1.3 V at 600 °C, and the electrolysis cell can operate stably with no noticeable degradation when exposed to high humidity of 30% H₂O at −0.5 A cm⁻² and 600 °C for over 300 h. Overall, this work demonstrates the promise of donor doping for obtaining proton conductors with both high conductivity and chemical stability for P-ReSOCs.