SN 2010LP - A type IA supernova from a violent merger of two carbon-oxygen white dwarfs

SN 2010lp is a subluminous Type Ia supernova (SN Ia) with slowly evolving lightcurves. Moreover, it is the only subluminous SN Ia observed so far that shows narrow emission lines of [O I] in late-time spectra, indicating unburned oxygen close to the center of the ejecta. Most explosion models for SNe Ia cannot explain the narrow [O I] emission. Here, we present hydrodynamic explosion and radiative transfer calculations showing that the violent merger of two carbon-oxygen white dwarfs of 0.9 and 0.76 M adequately reproduces the early-time observables of SN 2010lp. Moreover, our model predicts oxygen close to the center of the explosion ejecta, a pre-requisite for narrow [O I] emission in nebular spectra as observed in SN 2010lp. © 2013. The American Astronomical Society. All rights reserved.

Irradiation of oxygen and water ices at by 4 keV singly and doubly charged ions; sputtering and molecular synthesis

The icy surfaces of dust grains in the Interstellar Medium and those of comets, satellites and Kuiper Belt Objects are continuously exposed tophoton and charged particle irradiation. These energetic particles maysputter and induce chemical changes in the ices and the underlyingsurfaces.In the present work 258 nm thick O2 and H2O ices were deposited at 10 K with the thickness measured by a laser interferometer method. Asimple model fit to the reflected laser intensity as measured by aphotodiode detector enabled the refractive index of the ices to bedetermined. The ices were then irradiated with various singly and doublycharged ions such as He+, 13C+, N+, O+ , Ar+, 13C2+, N2+ and O2+ at 4keV. The decrease in ice thickness as a function of ion dose wasmonitored by a laser interferometer and the model used to determine thesputtering yield as shown in Figure 1.In the case of O2 ice thesputtering yields increased with increasing ion mass in good agreementwith a model calculation [Fama, J, Shi, R.A Baragiola, Surface Sci.,602, 156 (2007)]. In the case of O2 ice, O2+ has a significant lowersputtering yield when compared to O+. The sputtering yields for O2 icewere found to be at least 9 times larger compared to those for H2O ice.For H2O ice the sputter yields for C, N and O ions were found todecrease with increasing mass. Doubly charged C, N and O ions which werefound to have the same sputtering yield as the singly charged ionswithin the experimental errors. A preliminary TPD study was carried outusing a QMS to detect the desorbed species from water ice afterirradiation by 6 × 10^15 ions of 13C+ and 13C2+. The formation of13CO and 13CO2 was observed with the yield of 13CO almost of a factor of100 larger than of 13CO2. This is in contrast to our earlier work whereonly CO¬2 was observed.

Quantification of singlet oxygen generation from photodynamic hydrogels

Recently, we described a series of novel porphyrin-impregnated hydrogels capable of producing microbicidal singlet oxygen (1O2) on photoactivation. Indirect assessment of the efficacy of 1O2 production from such hydrogels has been previously described using microbiological techniques, but here we report a novel, direct method of quantification. Anthracene-9,10-dipropionic acid (ADPA) is known to irreversibly form an endoperoxide on reaction with 1O2, causing photobleaching of its absorbance band at approximately 378 nm. Here, the reaction of this probe is exploited in a novel way to provide a simple, inexpensive, and convenient measurement of 1O2 generation from the surface of porphyrin-incorporated photosensitising hydrogels, with the ability to account for effects due to hydrogel porosity. Ingress of the probe into the materials was observed, with rates of up to 3.83 x 103 s-1. This varied by up to 200-fold with material composition and surface modification. Rates of 1O2 generation in these porphyrin-incorporated hydrogels, after compensating for ADPA ingress, ranged from 1.86x103 – 5.86x103 s-1. This work demonstrates a simple and straightforward method for direct 1O2 quantification from porous materials, with general utility.

Small GTPase RhoA and its effector rho kinase mediate oxygen glucose deprivation-evoked in vitro cerebral barrier dysfunction

BACKGROUND AND PURPOSE: Enhanced vascular permeability attributable to disruption of blood-brain barrier results in the development of cerebral edema after stroke. Using an in vitro model of the brain barrier composed of human brain microvascular endothelial cells and human astrocytes, this study explored whether small GTPase RhoA and its effector protein Rho kinase were involved in permeability changes mediated by oxygen-glucose deprivation (OGD), key pathological phenomena during ischemic stroke.

METHODS: OGD increased RhoA and Rho kinase protein expressions in human brain microvascular endothelial cells and human astrocytes while increasing or unaffecting that of endothelial nitric oxide synthase in respective cells. Reperfusion attenuated the expression and activity of RhoA and Rho kinase in both cell types compared to their counterparts exposed to equal periods of OGD alone while selectively increasing human brain microvascular endothelial cells endothelial nitric oxide synthase protein levels. OGD compromised the barrier integrity as confirmed by decreases in transendothelial electric resistance and concomitant increases in flux of permeability markers sodium fluorescein and Evan's blue albumin across cocultures. Transfection of cells with constitutively active RhoA also increased flux and reduced transendothelial electric resistance, whereas inactivation of RhoA by anti-RhoA Ig electroporation exerted opposite effects. In vitro cerebral barrier dysfunction was accompanied by myosin light chain overphosphorylation and stress fiber formation. Reperfusion and treatments with a Rho kinase inhibitor Y-27632 significantly attenuated barrier breakdown without profoundly altering actin structure.

CONCLUSIONS: Increased RhoA/Rho kinase/myosin light chain pathway activity coupled with changes in actin cytoskeleton account for OGD-induced endothelial barrier breakdown.

Determining the Effect of Plasma Pre-Treatment on Antimony Tin Oxide to Support Pt@Pd and the Oxygen Reduction Reaction Activity

This article reveals the effect of plasma pre-treatment on antimony tin oxide (ATO) nanoparticles. The effect is to allow Pt@Pd to be deposited homogeneously on the ATO surface with high dispersion and narrow particle size distribution. The Pt@Pd core–shell catalyst was prepared using the polyol method and shows a dramatic improvement towards ORR activity and durability.

Sputtering of oxygen ice by low energy ions

Naturally occurring ices lie on both interstellar dust grains and on celestial objects, such as those in the outer Solar system. These ices are continuously subjected to irradiation by ions from the solar wind and/or cosmic rays, which modify their surfaces. As a result, new molecular species may form which can be sputtered off into space or planetary atmospheres. We determined the experimental values of sputtering yields for irradiation of oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2 +, N2 + and O2 +) charged ions with 4 keV kinetic energy. In these laboratory experiments, oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber at low temperature to simulate the environment of space. The number of molecules removed by sputtering was observed by measurement of the ice thickness using laser interferometry. Preliminary mass spectra were taken of sputtered species and of molecules formed in the ice by temperature programmed desorption (TPD). We find that the experimental sputtering yields increase approximately linearly with the projectile ion mass (or momentum squared) for all ions studied. No difference was found between the sputtering yields for singly and doubly charged ions of the same atom within the experimental uncertainty, as expected for a process dominated by momentum transfer. The experimental sputter yields are in good agreement with values calculated using a theoretical model except in the case of oxygen ions. Preliminary studies have shown molecular oxygen as the dominant species sputtered and TPD measurements indicate ozone formation.

Tailoring the nonlinear frequency coupling between odd harmonics for the optimisation of charged particle dynamics in capacitively coupled oxygen plasmas

The influence of nonlinear frequency coupling in an oxygen plasma excited by two odd harmonics at moderate pressure is investigated using a numerical model. Through variations in the voltage ratio and phase shift between the frequency components changes in ionization dynamics and sheath voltages are demonstrated. Furthermore, a regime in which the voltage drop across the plasma sheath is minimised is identified. This regime provides a significantly higher ion flux than a single frequency discharge driven by the lower of the two frequencies alone. These operating parameters have potential to be exploited for plasma processes requiring low ion bombardment energies but high ion fluxes. 

Density functional theory study on the activation of molecular oxygen on a stepped gold surface in an aqueous environment: a new approach for simulating reactions in solution

The activation of oxygen molecules is an important issue in the gold-catalyzed partial oxidation of alcohols in aqueous solution. The complexity of the solution arising from a large number of solvent molecules makes it difficult to study the reaction in the system. In this work, O-2 activation on an Au catalyst is investigated using an effective approach to estimate the reaction barriers in the presence of solvent. Our calculations show that O-2 can be activated, undergoing OOH* in the presence of water molecules. The OOH* can readily be formed on Au(211) via four possible pathways with almost equivalent free energy barriers at the aqueous-solid interface: the direct or indirect activation of O-2 by surface hydrogen or the hydrolysis of O-2 following a Langmuir-Hinshelwood mechanism or an Eley-Rideal mechanism. Among them, the Eley-Rideal mechanism may be slightly more favorable due to the restriction of the low coverage of surface H on Au(211) in the other mechanisms. The results shed light on the importance of water molecules on the activation of oxygen in gold-catalyzed systems. Solvent is found to facilitate the oxygen activation process mainly by offering extra electrons and stabilizing the transition states. A correlation between the energy barrier and the negative charge of the reaction center is found. The activation barrier is substantially reduced by the aqueous environment, in which the first solvation shell plays the most important role in the barrier reduction. Our approach may be useful for estimating the reaction barriers in aqueous systems.

Ultralow-temperature CO oxidation on an In2O3-Co3O4 catalyst: a strategy to tune CO adsorption strength and oxygen activation simultaneously

Highly efficient In2O3-Co3O4 catalysts were prepared for ultralow-temperature CO oxidation by simultaneously tuning the CO adsorption strength and oxygen activation over a Co3O4 surface, which could completely convert CO to CO2 at temperatures as low as -105 degrees C compared to -40 degrees C over pure Co3O4, with enhanced stability.

Oxygen vacancy formation in CeO2 and Ce1-xZrxO2 solid solutions:electron localization, electrostatic potential and structural relaxation

Ceria (CeO2) and ceria-based composite materials, especially Ce1-xZrxO2 solid solutions, possess a wide range of applications in many important catalytic processes, such as three-way catalysts, owing to their excellent oxygen storage capacity (OSC) through the oxygen vacancy formation and refilling. Much of this activity has focused on the understanding of the electronic and structural properties of defective CeO2 with and without doping, and comprehending the determining factor for oxygen vacancy formation and the rule to tune the formation energy by doping has constituted a central issue in material chemistry related to ceria. However, the calculation on electronic structures and the corresponding relaxation patterns in defective CeO2-x oxides remains at present a challenge in the DFT framework. A pragmatic approach based on density functional theory with the inclusion of on-site Coulomb correction, i.e. the so-called DFT + U technique, has been extensively applied in the majority of recent theoretical investigations. Firstly, we review briefly the latest electronic structure calculations of defective CeO2(111), focusing on the phenomenon of multiple configurations of the localized 4f electrons, as well as the discussions of its formation mechanism and the catalytic role in activating the O-2 molecule. Secondly, aiming at shedding light on the doping effect on tuning the oxygen vacancy formation in ceria-based solid solutions, we summarize the recent theoretical results of Ce1-xZrxO2 solid solutions in terms of the effect of dopant concentrations and crystal phases. A general model on O vacancy formation is also discussed; it consists of electrostatic and structural relaxation terms, and the vital role of the later is emphasized. Particularly, we discuss the crucial role of the localized structural relaxation patterns in determining the superb oxygen storage capacity in kappa-phase Ce1-xZr1-xO2. Thirdly, we briefly discuss some interesting findings for the oxygen vacancy formation in pure ceria nanoparticles (NPs) uncovered by DFT calculations and compare those with the bulk or extended surfaces of ceria as well as different particle sizes, emphasizing the role of the electrostatic field in determining the O vacancy formation.

Oxygen reduction reaction mechanism on nitrogen-doped graphene:A density functional theory study

Nitrogen-doped graphene (N-graphene) was reported to exhibit a good activity experimentally as an electrocatalyst of oxygen reduction reaction (ORR) on the cathode of fuel cells under the condition of electropotential of similar to 0.04 V (vs. NNE) and pH of 14. This material is promising to replace or partially replace the conventionally used Pt. In order to understand the experimental results. ORR catalyzed by N-graphene is studied using density functional theory (DFT) calculations under experimental conditions taking the solvent, surface adsorbates, and coverages into consideration. Two mechanisms, i.e., dissociative and associative mechanisms, over different N-doping configurations are investigated. The results show that N-graphene surface is covered by O with 1/6 monolayer, which is used for reactions in this work. The transition state of each elementary step was identified using four different approaches, which give rise to a similar chemistry. A full energy profile including all the reaction barriers shows that the associative mechanism is more energetically favored than the dissociative one and the removal of O species from the surface is the rate-determining step. (C) 2011 Elsevier Inc. All rights reserved.

Oxygen Reduction Reaction on Metal-Terminated MnCr2O4 Nano-octahedron Catalyzing MnS Dissolution in an Austenitic Stainless Steel

To understand pitting corrosion in stainless steel is very important, and a recent work showed that the MnS dissolution catalyzed by MnCr2O4{111} is a starting point of pit g. This demonstrates the need to understand the oxygen reduction reaction (ORR) on MnCr2O4{111}, which is the other half-reaction to complete pitting corrosion. In this study, the adsorption behaviors of all oxygen-containing species on MnCr2O4{111}, which has several possible terminations, are explored via density functional theory calculations. It is found that O-2 adsorbs on MnCr2O4{111) surfaces very strongly. Many possible reactions are investigated and the favored reaction mechanism of ORR is determined. The interactions between O-2 and H2O on the two metal-terminated MriCr(2)O(4){111} are found to be different according to the atomic configurations of the two surfaces. All the calculated results suggest that ORR can readily occur on the MnCr2O4{111} surfaces.

Size effect of graphene on electrocatalytic activation of oxygen

Crystals of graphite nanosheets, achieved via a simple ball milling approach, show a significant size effect in electrocatalytic activation of oxygen.