In‐Situ Observation of the Formation of MnS during Solidification of High Sulphur Steels

A Confocal Scanning Laser Microscope equipped with a gold image furnace was used to directly observe the precipitation of MnS during solidification of high sulphur steels under isothermal conditions in the temperature region 1440 to 1480°C on the free surface of the steel melt. For the case of Al‐killed steels, below 1480°C MnS particles were found to precipitate with Fe forming simultaneously around them. This MnS containing structure continued to grow rapidly (264 μm/s) as a surface film. The film gradually changed, as the level of S in the melt decreased, into a eutectic structure (with lamella spacing of 2 μm) as predicted by thermodynamics. In Si‐ killed steels there was significantly lower tendency to form MnS both in terms of time until precipitation occurred and growth rate.     

Controlled undercooling of liquid iron in contact with ZrO2 and MgO substrates under varying oxygen partial pressures

The objective of this study is to determine the conditions under which the inclusions present in liquid steel can act as heterogeneous nucleants for solidification. In order to study the factors that define the undercooling of a given metal/oxide couple, the undercooling of a pure iron sessile droplet in contact with Al₂O₃, ZrO₂, and MgO substrates was measured under controlled oxygen partial pressures by observing droplet recalescence. The results showed that the undercooling of iron, in contact with a particular substrate, did not have a unique value, but was significantly affected by the oxygen content on the gas phase. For oxygen partial pressures between 10⁻²¹ and 10⁻¹⁹, the undercooling of iron on ZrO₂ substrates was stable and around 290 °C. In the same range of oxygen partial pressure, the undercooling of iron on MgO substrates remained below 100 °C due to the low stability of this oxide. At lower oxygen contents, substrate decomposition might be the cause for the observed drop in the undercooling of iron on ZrO₂ substrates to below 100 °C. The undercooling also decreased for increasing oxygen content as verified when the gas was changed from gettered Ar/Ar-H₂ to CO/CO₂ mixtures. The variation in undercooling was related to the wetting of the substrate by the liquid metal, where the deep undercooling observed in the ZrO₂ experiments occurred when the highest contact angle between the liquid metal and the substrate was achieved.     

选择正确的PFC解决方案

本文用一种创新的方法提出了四种功率因数校正(PFC)电路设计。两种临界导通模式(CRM)升压．一种连续导通模式(CCM)升压和一种CCM单段回扫，并且推荐了基于功率要求、效率、失真程度、电路板空间和成本限制的解决方案。     

Hepatitis G virus RNA is common in AIDS patients'' plasma but is not associated with abnormal liver function tests or other clinical syndromes

OBJECTIVE: To determine whether postmenopausal oestrogen replacement therapy affects carotid artery pulsatility index. DESIGN: A prospective double-blind placebo controlled trial. SETTING: University associated teaching hospital. PARTICIPANTS: Twenty-eight postmenopausal women who were more than 12 months postmenopausal and who had not taken exogenous oestrogen. INTERVENTIONS: Independent randomisation to receive oral oestradiol (2 mg daily) or placebo for 20 to 24 weeks. MAIN OUTCOME MEASURES: Internal carotid artery Doppler pulsatility index, measured within one centimetre of the carotid bifurcation. RESULTS: Replicate data were available from 27 women. The mean pulsatility index decreased by -0.11 in 15 women receiving oestradiol, compared with a mean rise of 0.05 in the 12 women who received placebo (P = 0.006, 95% CI for treatment difference 0.06-0.31). CONCLUSIONS: Oestrogen replacement decreases postmenopausal carotid artery pulsatility index, probably reflecting decreased peripheral vascular resistance. This is a further mechanism whereby hormone replacement therapy may impart cardiovascular protection.     

Drift and retention of pelagic spawning minnow eggs in a regulated river

Long‐distance drift of eggs and larvae has been identified as a possible cause of downstream displacement and poor recruitment of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Seven experiments were conducted using artificial eggs to estimate silvery minnow egg drift and retention in the Albuquerque and Isleta reaches of the regulated Middle Rio Grande, New Mexico, USA over a range of flows during expected spawning times. Bead retention varied by reach, discharge, and shape of the hydrograph. Highest retention (6.9 and 9.7% per km in the Albuquerque and Isleta reaches, respectively) occurred on the ascending limb of a high flow in areas where there was substantial floodplain inundation. Retention was maximized at different flows in each reach (97 and 140 m³/s, respectively), possibly associated with reach‐specific floodplain inundation thresholds. Lowest retention in each reach (2.1 and 1.7%, respectively) occurred on the descending limb of low and high flows, respectively. Of the silvery minnow eggs produced in the combined Albuquerque and Isleta reaches in 2005, 8–14% are predicted to have been retained in the Albuquerque Reach (67 km) and 49–83% in the Isleta Reach (86 km) based on the distribution of adult fish and measured bead retention rates. Although silvery minnow propagules are capable of drifting long distances, our study suggests that considerable retention occurs in the Middle Rio Grande. Habitat restoration to increase channel habitat complexity, and flow management to promote floodplain inundation should help to retain a greater proportion of propagules in upstream reaches. Copyright © 2010 John Wiley & Sons, Ltd.     

Poly(L‐lactic acid) with added α‐tocopherol and resveratrol: optical,physical, thermal and mechanical properties

Poly(L ‐lactic acid) (PLLA) films containing various concentrations of two natural antioxidants, α‐tocopherol and resveratrol, were fabricated by a melt compounding and compression molding process. The influence of the antioxidants on the optical properties such as color and UV‐visible light transmission was analyzed. The thermal, mechanical, rheological and physical properties of PLLA films with added antioxidants were assessed. PLLA films with added α‐tocopherol and resveratrol showed a yellowish brown color and the lightness was influenced by the presence of the antioxidants. The glass transition and melting temperatures were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed, which could be a benefit and important for processing and production. PLLA films with added antioxidants were slightly more hydrophobic than neat PLLA. The combination effect of plasticizing and enhancement of the elastic modulus with differing concentrations of two antioxidants played a critical role in the mechanical and thermomechanical properties of PLLA films. The melt viscosity of the PLLA films with added antioxidants was substantially higher than that of neat PLLA. The higher melt viscosity and G′(ω) could be an indication of formation of entanglement between PLLA and the two antioxidants. Copyright © 2012 Society of Chemical Industry     

Highly selective CuO/γ–Al2O3 catalyst promoted with hematite for efficient methanol dehydration to dimethyl ether

A recent alternative for replacing traditional hydrocarbons like gasoline, diesel, and natural gas, is the use of dimethyl ether (DME), which is more environmentally friendly. One of the ongoing challenges is to catalyze methanol dehydration for selectively producing the DME (2CH₃OH → CH₃OCH₃ + H₂O). It is established that the CuO catalyst over alumina performs the methanol dehydration, but the formation of by-products is the main drawback. For these reasons, we synthesized a CuO/γ–Al₂O₃ catalyst promoted with hematite aiming to enhance the activity toward DME at atmospheric conditions. The resulting bimetallic catalyst (CuO-Fe₂O₃/Al₂O₃) performed a 70% conversion at 290 °C, which is similar to other catalysts recently reported in the literature but done in harsh conditions. In addition, this bimetallic catalyst exhibited a 100% in selectivity toward the DME production. XPS spectra of the fresh and used catalyst suggested that the chemical oxidation states of Cu and Fe remain without change. After regenerating the catalyst at 600 °C for 2 h in air, it performed at a similar catalytic conversion, confirming the reusability of the as-synthesized material and reducing the environmental impact.     

Oxidation Behavior of Aerospace Materials in High Enthalpy Flows Using an Oxyacetylene Torch Facility

The oxyacetylene torch facility is used to measure the ablation rates of graphite and the surface temperatures of different aerospace materials. The free‐stream flame environment is characterized as a function of flame chemistry for heat flux, pO₂, and flow velocity. Measured ablation rates for graphite increase as a function of increasing heat flux and pO₂, which are validated by applying an oxygen diffusion based model. The model uses experimentally measured values for temperature, pO₂, and gas velocity in order to confirm torch testing results are reliable and reproducible. Surface temperatures of ultra‐high temperature ceramic composites are measured as a function of increasing heat flux and show an enthalpic cooling effect on the flame during oxidation testing.     

CARBON FROM PERIPHYTON SUPPORTS FISH BIOMASS IN WATERHOLES OF A WET–DRY TROPICAL RIVER

The identification of the dominant sources of carbon supporting consumer biomass in aquatic food webs is often difficult but essential to understanding the limits to aquatic secondary production. Stable isotope analysis (SIA) is a powerful tool to estimate the contribution of different sources to consumers, but most food web studies using this approach limit analyses to a few key consumer taxa rather than measuring biomass‐weighted contribution of sources to the entire community. Here we combined stable isotope analysis with standardized measurements of abundance and biomass of fishes and invertebrates in seven waterholes of a wet–dry tropical river sampled early and late in the dry season. We showed that periphyton (as opposed to phytoplankton and terrestrial C3 plant detritus) was responsible for most standing fish biomass (range 42%–97%), whereas benthic invertebrates were reliant on a mixture of the three sources (range 26%–100%). Furthermore, larger, older fishes at high trophic levels (catfish Neoarius spp., sleepy cod Oxyeleotris lineaolatus and barramundi Lates calcarifer) were supported almost exclusively by periphyton. Phytoplankton and detritus supported a considerable biomass of benthic and pelagic invertebrates, but only in taxa that occupied low trophic levels (e.g. snails). These measurements provide further evidence that although periphyton is relatively inconspicuous relative to other sources, it contributes disproportionately to metazoan biomass in wet–dry tropical rivers. Copyright © 2012 John Wiley & Sons, Ltd.