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1.
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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Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献
5.
The activation of18O and19F by the reactions18O(γ, p)17N and19F(γ, 2p)17N was determined as a function of the maximum energy of the bremsstrahlung beam. By the use of this method it is possible
to measure oxygen or fluorine by counting the delayed neutrons emitted by17N with a half-life of 4.2 sec.
相似文献
6.
Alejandro R. Engelmann Mario A. Natiello Mikael Hghede Erik Engdahl Erkki Brndas 《International journal of quantum chemistry》1987,31(5):841-845
In the present article we show how the bound states of the Coulomb potential may be associated with resonances that occur when this potential is perturbed by a barrier potential. The main idea is to trace the bound states on successive switching on of the barrier perturbation. It is found that those bound states that are localized inside the barrier are highly sensitive to variation with respect to the barrier height, whereas those that are localized outside are less sensitive. However, there are certain intervals for the barrier height when the role of being “a state localized inside the barrier” is shifted from one bound state to another. The result can be pictured as a “relay race,” where the “deliveries of the baton” are carried out over corresponding avoided crossings. The baton is ultimately handed over to a shape-type resonance state. 相似文献
7.
Solid-phase micro extraction (SPME) and headspace derivatization of clenbuterol followed by GC–FID and GC–SIMMS quantification 总被引:1,自引:0,他引:1
Solid-phase micro extraction (SPME) and on-fiber derivatization followed by Gas Chromatography coupled with Flame Ionization Detection (GC-FID) or Selected Ion Monitoring Mass Spectrometry (GC-SIMMS) allows for simple yet sensitive quantification for the hexamethyldisilazane derivative of the beta-agonist clenbuterol. Using an 85- micro m polyacrylate fiber, the analysis method is optimized with respect to extraction time, derivatization time and temperature, and solution pH. In addition, the use of a rapid temperature ramping injection port allows for optimization of fiber desorption conditions. Under optimal conditions, the limits of detection for the hexamethyldisilazane derivative of clenbuterol are 1.1 ppb by FID and 0.20 ppb by SIMMS. 相似文献
8.
Zusammenfassung An einer polymerhomologen Reihe von linearen Polyisoprenen mit Molekulargewichten zwischen 40000 und > 107 wurde im Festzustand und in L?sung die Abh?ngigkeit der thermischen Stabilit?t von der jeweiligen Kettenl?nge untersucht.
Es zeigte sich, da? die zum Zerbrechen der Makromoleküle notwendigen Temperaturen mit steigendem Molekulargewicht deutlich
abnehmen und für Polyisoprene mit Molekulargewichten > 107 bei Raumtemperatur liegen.
Summary The dependence of thermal stability from the molecular weight of linear macromolecules was tested using polyisoprenes with m. w. between 40000 and > 107. We could demonstrate that the temperatures at which molecular fractures occur, decrease with increasing chain length and approach room temperature at molecular weights of about 107.相似文献
9.
The 837 keV resonance is used for the rapid and non-destructive determination of the gradient of fluorine on the surface of metallic samples. The precise yield curve of this resonance for thick target and the experimental sensitivity of the method have been determined. With this method less than 5·10?4 μg·cm?2 fluorine content can be measured. The resolution is of the order of 1000 Å in aluminium and the concentration profiles can be measured to the depth of 1 μm. The time requirement of a surface analysis is 15–30 min, and 2–3 hrs of a gradient measurement. In addition, this method is simpler and more sensitive than the detection of the 1350 keV alpha-particles from the19F(p, αo)16O reaction. 相似文献
10.
I. Golicheff M. Loeuillet Ch. Engelmann 《Journal of Radioanalytical and Nuclear Chemistry》1974,22(1-2):113-129
The experimental device used is described. Excitation functions are given for an angle of observation 150° with respect to
the incident beam. The possibilities of applying these reactions to the measurement of surface lithium and fluorine concentrations
are considered. The detection limits for these two elements are shown to be 5·10−3 μg·cm−2 with protons of energy between 1,350 and 1,500 keV. The method is compared with that based on the detection of prompt γ-rays
from the reactions7Li(p, γ)8Be and19F(p, α γ)16O.
相似文献