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Emily S. Tepe Ellen S. Deutsch MD Quiana Sampson Stephen Lawless James S. Reilly Robert Thayer Sataloff 《Journal of voice》2002,16(2):244-250
The objective of this study was to determine the incidence of vocal problems in young choir singers and to correlate vocal problems with demographic and behavioral information. A questionnaire addressing vocal habits and hygiene was offered to 571 young choir singers, up to 25 years of age, who sing at least weekly; 129 (22.6%) responded. More than one-half of the respondents had experienced vocal difficulty, particularly older adolescents. Detrimental behaviors and circumstances surveyed were not reflective of the incidence of vocal difficulty, except for morning hoarseness, chronic fatigue, insomnia, and female gender after puberty. Voice care professionals should be aware that self-reported voice difficulties are common among young choral singers, especially postpubescent girls, and children with symptoms consistent with reflux (morning hoarseness) and emotional stress (insomnia). Laryngologists should communicate with choral conductors and singing teachers to enhance early identification and treatment of children with voice complaints, and to develop choral educational strategies that help decrease their incidence. 相似文献
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R. XuF.A. Davidson M.A.J. Chaplain 《Journal of Mathematical Analysis and Applications》2002,269(1):256-277
A two-species ratio-dependent predator-prey model with distributed time delay is investigated. It is shown that the system is persistent under some appropriate conditions, and sufficient conditions are obtained for both the local and global stability of the positive equilibrium of the system. 相似文献
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The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH2O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH2O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k1a = 5.0 × 1015 exp(‐308 kJ mol?1/RT) cm3 mol?1 s?1. The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M → H2 + CO + M, and the branching fraction β = k1a/(kA1a + k1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH2O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH2O molecules. At high initial CH2O mole fractions the reverse of reaction (6), CH2OH + HCO ? CH2O + CH2O becomes noticeable. The rate of the forward reaction was roughly measured to be k6 = 1.5 × 1013 cm3 mol?1 s?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004 相似文献
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In this work we display a numerical comparison, under statistical and computational point of view, between semi-analytical Eulerian and Lagrangian dispersion models to simulate the ground-level concentration values of a passive pollutant released from a low height source. The Eulerian approach is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian approach is based on solution of the Langevin equation through the Picard’s Iterative Method. Turbulence inputs are calculated according to a parameterization capable of generating continuous values in all stability conditions and in all heights of the Planetary Boundary Layer (PBL). Numerical simulations and comparisons show a good agreement between predicted and observed concentrations values. The comparison reveals the main advantages and disadvantages between the models. 相似文献
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