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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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| 33. |
- 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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| 34. |
- Ternström, Sten, 1956-
(author)
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Hearing myself with others : sound levels in choral performance measured with separation of one's own voice from the rest of the choir.
- 1994
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 8:4, s. 293-302
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Journal article (peer-reviewed)abstract
- The choir singer has two acoustic signals to attend to: the sound of his or her own voice (feedback), and the sound of the rest of the choir (reference). The balance in loudness between feedback and reference is governed mainly by the room acoustics. Although earlier experiments have shown that singers have a fairly large tolerance for imbalance, with references ranging from -23 to +5 dB, experience suggests that, when singers are given control over this parameter, their preferences are much narrower. A quantification of the optimum balance would be useful in the design of concert stages and rehearsal halls. A method is described for measuring the feedback and reference levels as experienced by singers under live performance conditions. Recordings were made using binaural microphones worn by choir singer subjects. With the given combination of choir and room, it was possible to achieve adequate separation of the feedback and reference signals with simple signal processing. The feedback-to-reference ratio averaged over the 12 singers was found to be +3.9 dB, with extremes of +1.5 and +7.3 dB.
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| 35. |
- Ternström, Sten, 1956-
(author)
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Perceptual evaluations of voice scatter in unison choir sounds.
- 1993
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 7:2, s. 129-135
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Journal article (peer-reviewed)abstract
- The preferences of experiences listerners for pitch and formant frequency dispersion in unison choir sounds were explored using synthesized stimuli. Two types of dispersion were investigated: (a) pitch scatter, which arises when voices in an ensemble exhibit small differences in mean fundamental frequency, and (b) spectral smear, defined as such dispersion of formants 3 to 5 as arises from differences in vocal tract length. Each stimulus represented a choir section of five bass, tenor, alto, or soprano voices, producing the vowel [u], [a], or [ae]. Subjects chose one dispersion level out of six available, selecting the "maximum tolerable" in a first run and the "preferred" in a second run. The listeners were very different in their tolerance for dispersion. Typical scatter choices were 14 cent standard deviation for "tolerable" and 0 or 5 cent for "preferred." The smear choices were less consistent; the standard deviations were 12 and 7%, respectively. In all modes of assessment, the largest dispersion was chosen for the vowel [u] on a bass tone. There was a vowel effect on the smear choices. The effects of voice category were not significant.
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| 36. |
- Gramming, Patricia, et al.
(author)
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Relationship between changes in voice pitch and loudness
- 1988
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 2:2, s. 118-126
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Journal article (peer-reviewed)abstract
- Summary Changes in mean fundamental frequency accompanying changes in loudness of phonation are analyzed in 9 professional singers, 9 nonsingers, and 10 male and 10 female patients suffering from vocal functional dysfunction. The subjects read discursive texts with noise in earphones, and some also at voluntarily varied vocal loudness. The healthy subjects phonated as softly and as loudly as possible at various fundamental frequencies throughout their pitch ranges, and the resulting mean phonetograms are compared. Mean pitch was found to increase by about half-semitones per decibel sound level. Grossly, the subject groups gave similar results, although the singers changed voice pitch more than the nonsingers. The voice pitch changes may be explained as passive results of changes of subglottal pressure required for the sound level variation.
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| 37. |
- Granqvist, Svante, 1963-, et al.
(author)
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Simultaneous analysis of vocal fold vibration and transglottal airflow : exploring a new experimental setup
- 2003
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 17, s. 319-330
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Journal article (peer-reviewed)abstract
- Summary: The purpose of this study was to develop an analysis system for studying the relationship between vocal fold vibration and the associated transglottal airflow. Recordings of airflow, electroglottography (EGG), oral air pressure, and acoustic signals were performed simultaneously with high-speed imaging at a rate of approximately 1900 frames/s. Inverse filtered airflow is compared with the simultaneous glottal area extracted from the high-speed image sequence. The accuracy of the synchronization between the camera images and the foot pedal synchronization pulse was examined, showing that potential synchronization errors increase with time distance to the synchronization pulse. Therefore, analysis was limited to material near the synchronization pulse. Results corroborate previous predictions that air flow lags behind area, but also they reveal that relationships between these two entities may be complex and apparently varying with phonation mode.
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| 44. |
- Lindestad, Per Å, et al.
(author)
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Voice source characteristics in mongolian throat singing studied with high-speed imaging technique, acoustic spectra, and inverse filtering
- 2001
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In: Journal of Voice. - 0892-1997 .- 1873-4588. ; 15:1, s. 78-85
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Journal article (peer-reviewed)abstract
- Mongolian “throat singing” can be performed in different modes. In Mongolia, the bass-type is called Kargyraa. The voice source in bass-type throat singing was studied in one male singer. The subject alternated between modal voice and the throat singing mode. Vocal fold vibrations were observed with high-speed photography, using a computerized recording system. The spectral characteristics of the sound signal were analyzed. Kymographic image data were compared to the sound signal and flow inverse filtering data from the same singer were obtained on a separate occasion. It was found that the vocal folds vibrated at the same frequency throughout both modes of singing. During throat singing the ventricular folds vibrated with complete but short closures at half the frequency of the true vocal folds, covering every second vocal fold closure. Kymographic data confirmed the findings. The spectrum contained added subharmonics compared to modal voice. In the inverse filtered signal the amplitude of every second airflow pulse was considerably lowered. The ventricular folds appeared to modulate the sound by reducing the glottal flow of every other vocal fold vibratory cycle.
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| 50. |
- Södersten, M., et al.
(author)
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Vocal behavior and vocal loading factors for preschool teachers at work studied with binaural DAT recordings
- 2002
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In: Journal of Voice. - : Mosby. - 0892-1997 .- 1873-4588. ; 16:3, s. 356-371
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Journal article (peer-reviewed)abstract
- Preschool teachers are at risk for developing voice problems such as vocal fatigue and vocal nodules. The purpose of this report was to study preschool teachers' voice use during work. Ten healthy female preschool teachers working at daycare centers (DCC) served as subjects. A binaural recording technique was used. Two microphones were placed on both sides of the subject's head, at equal distance from the mouth, and a portable DAT recorder was attached to the subject's waist. Recordings were made of a standard reading passage before work (baseline) and of spontaneous speech during work. The recording technique allowed separate analyses of the level of the background noise, and of the subjects' voice sound pressure level, mean fundamental frequency, and total phonation time. Among the results, mean background noise level for the ten DCCs was 76.1 dBA (range 73.0-78.2), which is more than 20 dB higher than what is recommended where speech communication is important (50-55 dBA). The subjects spoke on an average of 9.1 dB louder (p < 0.0001), and with higher mean fundamental frequency (247 Hz) during work as compared to the baseline (202 Hz) (p < 0.0001). Mean phonation time for the group was 17%, which was considered high. It was concluded that preschool teachers do have a highly vocally demanding profession. Important steps to reduce the vocal loading for this occupation would be to decrease the background noise levels and include pauses so that preschool teachers can rest their voices.
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