It has been a long‐standing debate on the nature of Elsässer variable z− observed in the solar wind fluctuations. It is widely believed that z− represents inward propagating Alfvén waves and interacts nonlinearly with z+ (outward propagating Alfvén waves) to generate energy cascade. However, z− variations sometimes show a feature of convective structures. Here we present a new data analysis on autocorrelation functions of z− in order to get some definite information on its nature. We find that there is usually a large drop on the z− autocorrelation function when the solar wind fluctuations are highly Alfvénic. The large drop observed by Helios 2 spacecraft near 0.3 AU appears at the first nonzero time lag τ = 81 s, where the value of the autocorrelation coefficient drops to 25%–65% of that at τ = 0 s. Beyond the first nonzero time lag, the autocorrelation coefficient decreases gradually to zero. The drop of z− correlation function also appears in the Wind observations near 1 AU. These features of the z− correlation function may suggest that z− fluctuations consist of two components: high‐frequency white noise and low‐frequency pseudo structures, which correspond to flat and steep parts of z− power spectrum, respectively. This explanation is confirmed by doing a simple test on an artificial time series, which is obtained from the superposition of a random data series on its smoothed sequence. Our results suggest that in highly Alfvénic fluctuations, z− may not contribute importantly to the interactions with z+ to produce energy cascade.
In this work, a new technique of modified-alkali leaching−dilute acid washing for extracting synthetic rutile from high-titanium slag is proposed. Most of the Ti components are enriched into the rutile phase during the modification, and rutile can be separated by alkali leaching−dilute acid washing. Thermodynamic analyses of the reactions occurring during the alkali leaching−dilute acid washing process were performed to provide a theoretical basis for rutile extraction from the modified slag. The calculated thermodynamic results suggest that it is possible to use the alkali leaching−acid washing process to separate rutile from the impurities in the modified slag. The structure of the glass phase, which contains almost all of the impurities, requires relatively high alkalinity to be destroyed, and the impurities of the slag, including Fe 2 O 3 , CaO, MgO, and MnO, can be removed easily with dilute acid after the alkali leaching stage. The technique is low in cost and obtains synthetic rutile for the chlorination process.
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