10,000 publications from this institution
The effect of EDTA (ethylenediaminetetraacetic acid, added as ) on the electrochemical behavior of iron and on the semiconducting properties of passive films formed on this metal in borate buffer solution (pH 8.4) was studied. Electrochemical studies, including potentiodynamic and galvanostatic reduction experiments and capacitance measurements coupled with Mott‐Schottky analysis, were carried out over the entire passive range in borate buffer solutions in the presence and absence of 0.01 M EDTA. Passive films formed in the presence of EDTA were thinner and showed higher donor concentrations. EDTA present in the borate buffer solution effectively inhibited the formation of the Fe(III) outer layer, thereby rendering the defective inner layer to direct examination. The barrier layer is found to be an n‐type semiconductor, which is consistent with the oxide being a defective magnetite in which the principal defects are oxygen vacancies and cation interstitials. EDTA effectively competes with chloride ion for adsorption into oxygen vacancies at the barrier layer/solution interface, thereby suggesting that the chelating agent might be an effective inhibitor of passivity breakdown. © 2000 The Electrochemical Society. All rights reserved.
Chapter 6 reviews the literature on behavioural processes and draws conclusions about the extent to which they are transdiagnostic. Three behavioural processes considered are escape/avoidance, within-situation safety-seeking behaviours, and ineffective safety-signals. These processes are considered in the context of anxiety disorders and obsessive-compulsive disorder (OCD), somatoform disorders, eating disorders, sleep disorders, and substance-related disorders).
New direction: Changes in the ligand structure divert the reactivity of vanadium(V) oxo complexes from alcohol oxidation to a novel non-oxidative CO bond cleavage. Thus, highly functionalized aryl enones can be selectively generated from lignin model compounds by vanadium-catalyzed cleavage of the β-O-4 linkage (see scheme; N blue, O red).
Three metalorganic complex arrays (MOCAs) with a specific sequence of metal centers as well as that of amino acid units were synthesized. These MOCAs are also isomers exhibiting a gelation capability dependent on the location of the metal complexes in the arrays.
Several recently proposed techniques achieve latency reduction by trading it off for some amount of additional bandwidth usage. But how would one quantify whether the tradeoff is actually beneficial in a given system? We develop an economic cost vs. benefit analysis for answering this question. We use the analysis to derive a benchmark for wide-area client-server applications, and demonstrate how it can be applied to reason about a particular latency saving technique --- redundant DNS requests.
Rhodamine 6G-doped mesostructured silica is prepared by an acidic sol−gel route using poly-b-poly(propylene oxide)-b-poly(ethylene oxide) (EOx−POy−EOx) block copolymer surfactants. Using low-refractive-index (n ∼ 1.2) mesoporous SiO2 as a support, the synthesis is combined with soft lithography to produce high-quality waveguides. This enables efficient waveguiding in the line-patterned rhodamine 6G-doped mesostructured domains, which have a higher refractive index than both the mesoporous support and cladding. For the structure-directing block copolymer surfactants used, (EO)20(PO)70(EO)20 (P123) and (EO)106(PO)70(EO)106 (F127), X-ray diffraction patterns and transmission electron microscopy reveal hexagonal mesophases, whose longitudinal cylinder axes are aligned predominantly parallel to the substrate plane. For samples made by micromolding-in-capillaries (MIMIC), the longitudinal axes are also aligned along the longitudinal waveguide axes. Samples made by micromolding also possess a high mesostructural order, though in the absence of an aligning flow field, their long-range order (ca. several hundred nanometers) is lower than for samples processed using the MIMIC technique. When optically pumped, the rhodamine 6G-doped waveguides exhibit amplified spontaneous emission with thresholds as low as ∼6 kW cm-2, substantially lower than rhodamine 6G-doped sol−gel glasses. This is attributed to the ability of the polymeric surfactant to co-assemble with the dye molecules, thereby leading to high dye dispersions and reduced dye dimerization. Additionally, rhodamine 6G shows good photostablility in the mesostructured waveguides, similar to that of rhodamine 6G in organically modified silicates.
The effects of Zr promotion on the structure and performance of Co-based Fischer-Tropsch synthesis (FTS) catalysts were investigated. Inclusion of Zr in the catalysts was found to increase the FTS turnover frequency and the selectivity to C<sub>5+</sub> hydrocarbons and to decrease the selectivity to methane under most operating conditions. These improvements to the catalytic performance are a function of Zr loading up to an atomic ratio of Zr/Co = 1.0, above which the product selectivity is insensitive to higher concentrations of the promoter. Characterization of the Co nanoparticles by different methods demonstrated that the optimal Zr loading corresponds to half monolayer coverage of the Co surface by the promoter. Measurements of the rate of FTS at different pressures and temperatures established that the kinetics data for both the Zr-promoted and unpromoted catalysts are described by a two-parameter Langmuir-Hinshelwood expression. The parameters used to fit this rate law to the experimental data indicate that the apparent rate coefficient and the CO adsorption constant for the Zr-promoted catalysts are higher than those for the unpromoted catalyst. Elemental mapping by means of STEM-EDS provided evidence that Zr is highly dispersed over the catalyst surface and has limited preference for association with the Co nanoparticles. In situ X-ray absorption spectroscopy confirmed the absence of mixing between the Zr and Co in the nanoparticles. Here, these results suggest that Zr exists as a partial layer of ZrO<sub>2</sub> on the surface of the Co metal nanoparticles. Accordingly, it is proposed that Zr promotion effects originate from sites of enhanced activity at the interface between Co and ZrO<sub>2</sub>. The possibility that ZrO<sub>2</sub> acts as a Lewis acid to assist in CO dissociation as well as to increase the ratio of CO to H adsorbed on the catalyst surface is discussed.
We present the mean-field phase diagram of electrons in a kagome flat band with repulsive interactions. In addition to flat-band ferromagnetism, the Hartree-Fock analysis yields cascades of unconventional magnetic orders driven by onsite repulsion as filling changes. These include a series of antiferromagnetic (AFM) spin-charge stripe orders, as well as an evolution from $120^\circ$AFM to intriguing noncoplanar spin orders with tetrahedral structures. We also map out the phase diagram under extended repulsion at half and empty fillings of the flat band. To examine the possibilities beyond the mean-field level, we conduct a projective symmetry group analysis and identify the feasible $\mathbb Z_2$ spin liquids and the magnetic orders derivable from them. The theoretical phase diagrams are compared with recent experiments on FeSn and FeGe, enabling a determination of the most likely magnetic instabilities in these and similar flat-band kagome materials.
We present an analysis of the central cusp slopes and core parameters of early-type galaxies using a large database of surface brightness profiles obtained from Hubble Space Telescope observations. We examine the relation between the central cusp slopes, core parameters, and black hole masses in early-type galaxies, in light of two models that attempt to explain the formation of cores and density cusps via the dynamical influence of black holes. Contrary to the expectations from adiabatic-growth models, we find that the cusp slopes do not steepen with increasing black hole mass fraction. Moreover, a comparison of kinematic black hole mass measurements with the masses predicted by the adiabatic models shows that they overpredict the masses by a factor of approximately 3. Simulations involving binary black hole mergers predict that both the size of the core and the central mass deficit correlate with the final black hole mass. These relations are qualitatively supported by the present data.
The warm season (mid‐June through late August) partitioning between sensible ( H ) and latent ( LE ) heat flux, or the Bowen ratio (β = H / LE ), was investigated at 27 sites over 66 site years within the international network of eddy covariance sites (FLUXNET). Variability in β across ecosystems and climates was analyzed by quantifying general climatic and surface characteristics that control flux partitioning. The climatic control on β was quantified using the climatological resistance ( R i ), which is proportional to the ratio of vapor pressure deficit (difference between saturation vapor pressure and atmospheric vapor pressure) to net radiation (large values of R i decrease β). The control of flux partitioning by the vegetation and underlying surface was quantified by computing the surface resistance to water vapor transport ( R c , with large values tending to increase β). There was a considerable range in flux partitioning characteristics ( R c , R i and β) among sites, but it was possible to define some general differences between vegetation types and climates. Deciduous forest sites and the agricultural site had the lowest values of R c and β (0.25–0.50). Coniferous forests typically had a larger R c and higher β (typically between 0.50 and 1.00 but also much larger). However, there was notable variability in R c and R i between coniferous site years, most notably differences between oceanic and continental climates and sites with a distinct dry summer season (Mediterranean climate). Sites with Mediterranean climates generally had the highest net radiation, R c , R i , and β. There was considerable variability in β between grassland site years, primarily the result of interannual differences in soil water content and R c .
