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- Sun, Zhongxi, et al.
(author)
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Degradation kinetics of ethyl-xanthate as a function of pH in aqueous solution
- 1997
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In: Minerals Engineering. - 0892-6875 .- 1872-9444. ; 10:4, s. 389-400
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Journal article (peer-reviewed)abstract
- Xanthate degradation kinetics plays an important role in sulfide mineral flotation and in the treatment of flotation tailings. Increasing environmental concern about consequences of flotation tailings makes this information even more important. In this paper, the degradation kinetics of xanthate in homogeneous solution as a function of pH at 5 °C, 20 °C and 40 °C is systematically studied by UV-Visible spectrophotometric measurements. The results indicate that the degradation of ethyl xanthate is rapidly increased with decreasing pH at pH<7. At pH 7-8, the maximum half-life of the xanthate appears. The degradation was faster at pH 9-10, but at pHgt;10 the half-lives of xanthate once again increase. The investigations are also extended to different media other than pure water, such as, 0.1 M NaClO4, 0.1 M NaNO3 0.1 M NaCl as well as in the supernatants of flotation tailings of sulfide minerals.The rate constants of xanthate degradation are calculated and presented together with half-lives and activation energies of xanthate degradation. The degradation products and reaction mechanisms are discussed based on experimental results.
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- Evertsson, Magnus, 1967, et al.
(author)
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Investigation of Interparticle Breakage as Applied to Cone Crushing
- 1997
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In: Minerals Engineering. - 0892-6875. ; 10, s. 199-214
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Journal article (peer-reviewed)abstract
- The breakage of material in cone type gyratory crushers is traditionally regarded as relying upon single particle breakage. In the last ten years the emphasis has shifted with manufacturers trying to generate higher degrees of interparticle breakage. Increasing the degree of interparticle crushing is claimed to improve crushing efficiency and product shape. The current study uses form conditioned crushing tests (geometry controlled compression) to investigate how multiple particles respond to crushing loads. By variation of test parameters the breakage characteristics of a rock material can be determined and compared to traditional single particle crushing. The selection function, S (probability of crushing a single particle), seems to be related to the ratio between stroke and bed height, s/b, with a second order polynomial in s/b. An analysis of a given crusher chamber gives selection values in the range 0.05
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- Saunders, Carol D., et al.
(author)
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Summative Evaluation of "The Swamp": : A Conservation Exhibit with a Big Idea
- 1997
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In: Visitor Behavior. - Jacksonville, FL, USA. - 0892-4996. ; XII:1 & 2, s. 4-7
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Journal article (peer-reviewed)abstract
- In this article, Carol D. Saunders and H. Elizabeth Stuart Perry of the Brookfield Zoo provide findings from the summative evaluation of "The Swamp." This immersive wetlands exhibit was designed to encourage people to appreciate the benefits of ecosystems and features animals and plants of a cypress swamp and of an Illinois riverine wetland.
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- McAllister, Anita, et al.
(author)
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Perturbation and hoarseness : a pilot study of six children's voices.
- 1996
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 10:3
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Journal article (peer-reviewed)abstract
- Fundamental frequency (FO) perturbation has been found to be useful as an acoustic correlate of the perception of dysphonia in adult voices. In a previous investigation, we showed that hoarseness in children's voices is a stable concept composed mainly of three predictors: hyperfunction, breathiness, and roughness. In the present investigation, the relation between FO perturbation and hoarseness as well as its predictors was analyzed in running speech of six children representing different degrees of hoarseness. Two perturbation measures were used: the standard deviation of the distribution of perturbation data and the mean of the absolute value of perturbation. The results revealed no clear relation.
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- White, Peta, 1961-
(author)
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Formant frequency analysis of children's spoken and sung vowels using sweeping fundamental frequency production
- 1999
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In: Journal of Voice. - : Singular Publishing Group. - 0892-1997 .- 1873-4588. ; 13:4, s. 570-582
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Journal article (peer-reviewed)abstract
- High-pitched productions present difficulties in formant frequency analysis due to wide harmonic spacing and poorly defined formants. As a consequence, there is little reliable data regarding children's spoken or sung vowel formants. Twenty-nine 11-year-old Swedish children were asked to produce 4 sustained spoken and sung vowels. In order to circumvent the problem of wide harmonic spacing, F-1 and F-2 measurements were taken from vowels produced with a sweeping F-0. Experienced choir singers were selected as subjects in order to minimize the larynx height adjustments associated with pitch variation in less skilled subjects. Results showed significantly higher formant frequencies for speech than for singing. Formants were consistently higher in girls than in boys suggesting longer vocal tracts in these preadolescent bays. Furthermore, formant scaling demonstrated vowel dependent differences between boys and girls suggesting non-uniform differences in male and female vocal tract dimensions. These vowel-dependent sex differences were not consistent with adult data.
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