A quasi-objective single-buoy approach for understanding Lagrangian coherent structures and sea ice dynamics

Sea ice drift and deformation, namely sea ice dynamics, play a significant role in atmosphere–ice–ocean coupling. Deformation patterns in sea ice can be observed over a wide range of spatial and temporal scales, though high-resolution objective quantification of these features remains difficult. In an effort to better understand local deformation of sea ice, we adapt the trajectory-stretching exponents (TSEs), quasi-objective measures of Lagrangian stretching in continuous media, to sea ice buoy data and develop a temporal analysis of TSE time series. Our work expands on previous ocean current studies that have shown TSEs provide an approximation of Lagrangian coherent structure diagnostics when only sparse trajectory data are available. As TSEs do not require multiple buoys, we find they have an expanded range of use when compared with traditional Eulerian buoy-array deformation metrics and provide local-stretching information below the length scales possible when averaging over buoy arrays. We verify the ability of TSEs to temporally and spatially identify dynamic features for three different sea ice datasets. The ability of TSEs to quantify trajectory stretching is verified by concurrent ice fracture in buoy neighborhoods ranging from tens to hundreds of kilometers in diameter, as well as the temporal concurrence of significant storm events.</p

Preconditioning of the 2007 sea-ice melt in the eastern Beaufort Sea, Arctic Ocean

During summer 2007, perennial sea ice in the Beaufort Sea, Arctic Ocean, experienced an unprecedented amount of basal melt. It has previously been shown that this basal melt was linked to an increase in open-water fraction, increasing absorption of solar radiation into the ocean. GPS ice drifters, deployed around the site where the unprecedented basal melt was observed, provide a coincident observation of local divergence. This divergence is used to drive a multi-thickness category thermodynamic sea-ice model. We demonstrate that ∼75% of the observed open-water fraction by midsummer 2007 can be attributed to ice pack divergence during the growth season, preconditioning the ice pack for early melt in summer. Divergence during the melt season explains the remaining 25% of open water. Enhanced ice pack divergence in spring and summer 2007, in response to the increased transport of ice out of the Beaufort Sea, was sufficient to explain the melt observed in summer 2007 and the heat stored in the upper ocean at the end of summer

Bicatalytic Multistep Reactions En Route to the One-Pot Total Synthesis of Complex Molecules: Easy Access to Chromene and 1,2-Dihydroquinoline Derivatives from Simple Substrates

By combining nanocatalysis and base-catalysis, a novel one-pot multistep process was found for the synthesis of substituted heterocycles of biological relevance from simple substrates. It is based on an initial Au/O2 oxidation of allylic alcohols followed by a base-catalysed tandem hetero-Michael/aldolisation/crotonisation with ortho-hydroxy or ortho-amino benzaldehydes. The flexibility of the reaction even allowed the benzaldehyde partner to be prepared in situ in an example of one-pot/5-steps process

Anomalous sea-ice reduction in the Eurasian Basin of the Arctic Ocean during summer 2010

Special Issue: The Second International Symposium on the Arctic Research (ISAR - 2

The direct synthesis of hydrogen peroxide from H₂ and O₂ using Pd-Ni/TiO₂ catalysts

The direct synthesis of hydrogen peroxide (H2O2) from molecular H2 and O2 offers an attractive solution to decentralised production compared to the anthraquinone process. Herein we evaluate the performance of a 0.5%Pd-4.5%Ni/TiO2 catalyst in batch and flow reactor systems using water as a solvent at ambient temperature which makes synthesising high H2O2 concentrations challenging. Catalyst activity was observed to be stable to prolonged use in multiple batch experiments or in a flow system, with selectivities towards H2O2 of 97% and 85% respectively. This study was carried out in the absence of halide or acid additives that are typically used to inhibit sequential H2O2 degradation reactions showing that this Pd-Ni catalyst has potential to produce H2O2 selectivel

Solid Acid Additives as Recoverable Promoters for the Direct Synthesis of Hydrogen Peroxide

The effectiveness of Cs-exchanged phosphotungstic acid as a recoverable solid acid additive for the direct synthesis of hydrogen peroxide (H2O2) using an Au-Pd / TiO2 catalyst is investigated and compared to the promotion effect of common oxides and non-halo acids. A clear improvement in catalytic activity towards H2O2 synthesis is reported when utilising Cs-containing heteropolyacids in addition to a standard H2O2 synthesising catalyst. The effect of Cs content on the promotion of H2O2 formation is investigated and the feasibility of a reusable heterogeneous additive has been explored revealing that the presence of the acid additive not only stabilises the H2O2 that is produced but also increases the H2O2 synthesis rate

Intrinsic Absorption in the Spectrum of NGC 7469: Simultaneous Chandra, FUSE, and STIS Observations

We present simultaneous X-ray, far-ultraviolet, and near-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 obtained with the Chandra X-Ray Observatory, the Far Ultraviolet Spectroscopic Explorer, and the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Previous non-simultaneous observations of this galaxy found two distinct UV absorption components, at -560 and -1900 km/s, with the former as the likely counterpart of the X-ray absorber. We confirm these two absorption components in our new UV observations, in which we detect prominent O VI, Ly alpha, N V, and C IV absorption. In our Chandra spectrum we detect O VIII emission, but no significant O VIII or O VII absorption. We also detect a prominent Fe K alpha emission line in the Chandra spectrum, as well as absorption due to hydrogen-like and helium-like neon, magnesium, and silicon at velocities consistent with the -560 km/s UV absorber. The FUSE and STIS data reveal that the H I and C IV column densities in this UV- and X-ray- absorbing component have increased over time, as the UV continuum flux decreased. We use measured H I, N V, C IV, and O VI column densities to model the photoionization state of both absorbers self-consistently. We confirm the general physical picture of the outflow in which the low velocity component is a highly ionized, high density absorber with a total column density of 10^20 cm^-2, located near the broad emission line region, although due to measurable columns of N V and C IV, we assign it a somewhat smaller ionization parameter than found previously, U~1. The high velocity UV component is of lower density, log N=18.6, and likely resides farther from the central engine as we find its ionization parameter to be U=0.08.Comment: Minor correction to abstract; STScI eprint #1683; 50 pages, incl. 19 figures, 4 tables; Accepted to Ap

Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst

The influence of reaction conditions on the oxidation of cyclohexane via the in-situ production of H2O2

The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), both key materials in the production of Nylon. Herein we demonstrate that through the in-situ production of H2O2 supported AuPd nanoparticles catalyse the formation of KA oil under conditions where activity is limited when using molecular O2, with no loss in catalytic activity observed upon re-use. The effect of key reaction parameters, including reaction temperature, catalyst mass and H2:O2 ratio are evaluated