Influence of substrate temperature on the properties of oxygen‐ion‐assisted deposited CeO2 films

Substrate temperature and ion bombardment during deposition have been observed to modify significantly the optical and structural properties of dielectric thin films. Single‐layer films of CeO2 have been deposited by electron beam evaporation with simultaneous oxygen‐ion bombardment using a Kaufman broad beam ion source and maintaining the substrates at elevated temperature. A systematic study has been made on the influence of (a) substrate temperature in the range ambient to 300 °C, (b) ion energy in the range 300–700 eV, and (c) ion current density 100–220 μA/cm2 on optical properties such as refractive index, extinction coefficient, inhomogeneity, packing density, and structural properties. The refractive index increased with in increase in substrate temperature: ion energy up to 600 eV and ion current density. Homogeneous, absorption free and high index (2.48) films have been obtained at 600 eV, 220 μA/cm2 and at substrate temperature of 300 °C. The packing density of the films was observed to be unity for the same deposition conditions. Substrate temperature with simultaneous ion bombardment modified the structure of the films from highly ordered to fine grain structure.

Effect of Oxygen Pressure on Structural and Magnetic Properties of YIG Thin Films

The effect of oxygen pressure (P-O2) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 degrees C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P-O2.

Evidence of collective relaxation behavior in the reentrant phase of oxygen-rich LaMnO3

The reentrant low temperature phase of the perovskite manganite LaMnO3+delta (delta=0.22) has been investigated with ac susceptibility and dc magnetization studies. A critical examination of the memory effects in ac susceptibility leads us to the conclusion that the slow dynamics in the system is a consequence of collective relaxation processes resulting from interactions between ferromagnetic clusters, whose presence was indicated in earlier studies. Here, we postulate that the collective behavior is due to the existence of long-range (dipolar) interactions between the large ferromagnetic `superspins'. This is also confirmed by an abnormally large microscopic spin-flip time (similar to 10(-9) s) compared to a canonical spin glass. (C) 2013 Elsevier B.V. All rights reserved.

Estimating the fraction of progeny virions that must incorporate APOBEC3G for suppression of productive HIV-1 infection

The contest between the host factor APOBEC3G (A3G) and the HIV-1 protein Vif presents an attractive target of intervention. The extent to which the A3G-Vif interaction must be suppressed to tilt the balance in favor of A3G remains unknown. We employed stochastic simulations and mathematical modeling of the within-host dynamics and evolution of HIV-1 to estimate the fraction of progeny virions that must incorporate A3G to render productive infection unsustainable. Using three different approaches, we found consistently that a transition from sustained infection to suppression of productive infection occurred when the latter fraction exceeded similar to 0.8. The transition was triggered by A3G-induced hypermutations that led to premature stop codons compromising viral production and was consistent with driving the basic reproductive number, R-o, below unity. The fraction identified may serve as a quantitative guideline for strategies targeting the A3G-Vif axis. (C) 2013 Elsevier Inc. All rights reserved.

First-principles DFT plus GW study of oxygen vacancies in rutile TiO2

We perform first-principles calculations of the quasiparticle defect states, charge transition levels, and formation energies of oxygen vacancies in rutile titanium dioxide. The calculations are done within the recently developed combined DFT + GW formalism, including the necessary electrostatic corrections for the supercells with charged defects. We find the oxygen vacancy to be a negative U defect, where U is the defect electron addition energy. For Fermi level values below similar to 2.8 eV (relative to the valence-band maximum), we find the +2 charge state of the vacancy to be the most stable, while above 2.8 eV we find that the neutral charge state is the most stable.

Effect of oxygen vacancies on the elastic properties of zinc oxide: A first-principles investigation

The effect of oxygen vacancies on the elastic properties of zinc oxide (ZnO) is examined using first-principles calculations based on density functional theory. Formation energies of vacancies in different types of oxygen deficient structures were analyzed to ascertain their stability. This analysis reveals that the doubly-charged oxygen vacancy under zinc-rich growth conditions is the most stable. Results show considerable degradation of some of the elastic moduli due to the presence of oxygen vacancies, which is in agreement with recent experiments. The decrease observed in elastic constants is more pronounced with increase in vacancy concentration. Further, the charge state of the defect structure was found to influence the shear elastic constants. Evaluation of elastic anisotropy of stoichiometric and oxygen deficient ZnO indicates the significant anisotropy in elastic properties and stiff c-axis orientation. (C) 2014 Elsevier B.V. All rights reserved.

Effect of Cattail (Typha domingensis) Extracts, Leachates, and Selected Phenolic Compounds on Rates of Oxygen Production by Salvinia (Salvinia minima)

Salvinia (Salvinia minima Willd.) is a water fern found in Florida waters, usually associated with Lemna and other small free-floating species. Due to its buoyancy and mat-forming abilities, it is spread by moving waters. In 1994, salvinia was reported to be present in 247 water bodies in the state (out of 451 surveyed public waters, Schardt 1997). It is a small, rapidly growing species that can become a nuisance due to its explosive growth rates and its ability to shade underwater life (Oliver 1993). Any efforts toward management of salvinia populations must consider that, in reasonable amounts, its presence is desirable since it plays an important role in the overall ecosystem balance. New management alternatives need to be explored besides the conventional herbicide treatments; for example, it has been shown that the growth of S. molesta can be inhibited by extracts of the tropical weed parthenium (Parthenium hysterophorus) and its purified toxin parthenin (Pande 1994, 1996). We believe that cattail, Typha spp. may be a candidate for control of S. minima infestations. Cattail is an aggressive aquatic plant, and has the ability to expand over areas that weren't previously occupied by other species (Gallardo et al. 1998a and references cited there). In South Florida, T. domingensis is a natural component of the Everglades ecosystem, but in many cases it has become the dominant marsh species, outcompeting other native plants. In Florida public waters, this cattail species is the most dominant emergent species of aquatic plants (Schardt 1997). Several factors enable it to accomplish opportunistic expansion, including size, growth habits, adaptability to changes in the surroundings, and the release of compounds that can prevent the growth and development of other species. We have been concerned in the past with the inhibitory effects of the T. domingensis extracts, and the phenolic compounds mentioned before, towards the growth and propagation of S. minima (Gallardo et al. 1998b). This investigation deals with the impact of cattail materials on the rates of oxygen production of salvinia, as determined through a series of Warburg experiments (Martin et al. 1987, Prindle and Martin 1996).

A Simple Model For Predicting The Void Fraction Of Gas/Non-Newtonian Fluid Intermittent Flows In Upward Inclined Pipes

In this work, a simple correlation, which incorporates the mixture velocity, drift velocity, and the correction factor of Farooqi and Richardson, was proposed to predict the void fraction of gas/non-Newtonian intermittent flow in upward inclined pipes. The correlation was based on 352 data points covering a wide range of flow rates for different CMC solutions at diverse angles. A good agreement was obtained between the predicted and experimental results. These results substantiated the general validity of the model presented for gas/non-Newtonian two-phase intermittent flows.

Reactions of oxygen containing ligands in the coordination sphere of permethylhafnocene and permethyltantalocene

A series of terl-butylperoxide complexes of hafnium, Cp*₂Hf(R)(OOCMe₃) (Cp* = ((η⁵-C₅Me₅); R = Cl, H, CH₃, CH₂CH₃, CH₂CH₂CH₃, CH₂CH₂CH₂CH₃, CH₂CHMe₂, CH=CHCMe₃, C₆H₅, meta-C₆H₃(CH₂)2) and Cp*(η⁵-C₅(CH₃)₄CH₂CH₂CH₂)Hf(OOCMe₃), has been synthesized. One example has been structurally characterized, Cp*₂Hf(OOCMe₃)CH₂CH₃ crystallizes in space group P2₁/c, with a = 19.890(7)Å, b = 8.746(4)Å, c = 17.532(6)Å, β = 124.987(24)°, V = 2498(2)ų, Z = 4 and R_F = 0.054 (2222 reflections, I > 0). Despite the coordinative unsaturation of the hafnium center, the terl-butylperoxide ligand is coordinated in a mono-dentate ligand. The mode of decomposition of these species is highly dependent on the substituent R. For R = H, CH₂CH₃, CH₂CH₂CH₃, CH₂CH₂CH₂CH₃, CH₂CHMe₂ a clean first order conversion to Cp*₂Hf(OCMe₃)(OR) is observed (for R CH₂CH₃, ΔHǂ = 19.6 kcal•mol^-1, ΔSǂ = -13 e.u.). These results are discussed in terms of a two step mechanism involving η²-coordination of the terl-butylperoxide ligand. Homolytic O-O bond cleavage is observed upon heating of Cp*₂Hf(OOCMe₃) R (R = C₆H₆, meta-C₆H₃(CH₃)₂). In the presence of excess 9,10-dihydroanthracene thermolysis of Cp*₂Hf(OOCMe₃)C₆H₆ cleanly affords Cp*₂Hf(C₆H₆)OH and HOCMe₃ (ΔHǂ = 22.6 kcal•mol^-1, ΔSǂ = -9 e.u.). The O-O bond strength in these complexes is thus estimated to be 22 kcal•mol^-1.

Cp*₂Ta(CH₂)H, Cp*₂Ta(CHC₆H₅)H, Cp*₂Ta(C₆H₄)H, Cp*₂Ta(CH₂=CH₂)H and Cp*₂Ta(CH₂=CHMe)H react, presumably through Cp*₂Ta-R intermediates, with H₂O to give Cp*₂Ta(O)H and alkane. Cp*₂Ta(O)H was structurally characterized: space group P2₁/n, a= 13.073(3)Å, b = 19.337(4)Å, c = 16.002(3)Å, β = 108.66(2)°, V = 3832(1)ų, Z = 8 and R_F = 0.0672 (6730 reflections). Reaction of terlbutylhydroperoxide with these same starting materials ultimately yields Cp*₂Ta(O)R and HOCMe₃. Cp*₂Ta(CH₂=CHR)OH species are proposed as intermediates in the olefin hydride reactions. Cp*₂Ta(O₂)R species can be generated from the reaction of the same starting materials and O₂. Lewis acids have been shown to promote oxygen insertion in these complexes.

The periodicity in the consumption of oxygen in Asellus aquaticus [Translation from: Vestnik ceskoslovenske zoologicke Spolecnosti, 15, 1, 89-97, 1951]

The consumption of oxygen in Asellus aquaticus was measured to find if there existed a periodicity in the consumption of oxygen and how this showed itself during the course of the day, year and in various experimental conditions. From the figures obtained comparative values were calculated and from these curves were plotted of the changes in the consumption of oxygen during the day and year.

The effect of oxygen concentration in water on the growth and nitrogen metabolism in the fry of rainbow trout [Translation from: Rybnoe Khoziaistvo,V.33, 74-75, 1957]

To ascertain the effect of various concentrations of oxygen in water on the fry of rainbow trout experiments were made with aquaria at various concentrations of oxygen. The food supplied was chironomid larvae (Chironomus plumosus). A surplus of food was supplied to the fry. Indices are given of the reaction of the fry to different temperatures.

Hypoxic and low pH water in the nearshore marine environments of Monterey Bay, California: characterizing a decade of oxygen and pH, and drivers of variability.

A decade-long time series recorded in southern Monterey Bay, California demonstrates that the shallow, near-shore environment (17 m depth) is regularly inundated with pulses of cold, hypoxic and low pH water. During these episodes, oxygen can drop to biologically threatening levels, and pH levels were lower than expected. Weekly water chemistry monitoring revealed that the saturation state of aragonite (the more soluble form of calcium carbonate) was often below saturation and had a moderate positive relationship with pH, however, analytical and human error could be high. Pulses of hypoxia and low pH water with the greatest intensity arise at the onset of the spring upwelling season, and fluctuations are strongly semidurnal (tidal) and diurnal. Arrival of cold, hypoxic water on the inner shelf typically occurs 3 days after the arrival of a strong upwelling event and appears to be driven by upwelling modulated by internal tidal fluctuations. I found no relationship between the timing of low-oxygen events and the diel solar cycle nor with terrestrial nutrient input. These observations are consistent with advection of hypoxic water from the deep, offshore environment where water masses experience a general decline of temperature, oxygen and pH with depth, and inconsistent with biochemical forcing. Comparisons with concurrent temperature and oxygen time series taken ~20 km away at the head of the Monterey Canyon show similar patterns but even more intense hypoxic events due to stronger semidiurnal forcing there. Analysis of the durations of exposure to low oxygen levels establishes a framework for assessing the ecological relevance of these events. Increasing oceanic hypoxia and acidification of both surface and deep waters may increase the number, intensity, duration and spatial extent of future intrusions along the Pacific coast. Evaluation of the resiliency of nearshore ecosystems such as kelp forests, rocky reefs and sandy habitats, will require consideration of these events.

Effect of oxygen substitution by halide ions on structure, thermal stability and upconversion fluorescence in Er3(+)/Yb3(+)-codoped germanium-bismuth glasses

For the first time. effect of halide ions (F-, Cl-, Br-, and I-) introduction on structure, thermal stability, and upconversion fluorescence in Er3+/Yb3+-codoped oxide-halide germanium-bismuth glasses has been systematically investigated. The results show that halide ions modified germanium-bismuth glasses have lower maximum phonon energy and phonon density, worse thermal stability. longer measured lifetimes of I-4(l1/2) level, and stronger upconversion emission than germanium-bismuth glass. All these results indicate that halide ions play an important role in the formation of glass network, and have an important influence on the upconversion luminescence. The possible upconversion mechanisms of Er3+ ion are also evaluated. © 2005 Elsevier Ltd. All rights reserved.

Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films

The effects of oxygen partial pressure on the structure and photoluminescence (PL) of ZnO films were studied. The films were prepared by direct current (DC) reactive magnetron sputtering with various oxygen concentrations at room temperature. With increasing oxygen ratio, the structure of films changes from zinc and zinc oxide phases, single-phase ZnO, to the (002) orientation, and the mechanical stresses exhibit from tensile stress to compressive stress. Films deposited at higher oxygen pressure show weaker emission intensities, which may result from the decrease of the oxygen vacancies and zinc interstitials in the film. This indicates that the emission in ZnO film originates from the oxygen vacancy and zinc interstitial-related defects. From optical transmittance spectra of ZnO films, the plasma edge shifts towards the shorter wavelength with the improvement of film stoichiometry. (C) 2004 Elsevier B.V. All rights reserved.