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排序方式: 共有98条查询结果,搜索用时 15 毫秒
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
2.
Summary We investigate the transition from two-frequency quasiperiodicity to chaotic behavior in a model for a quasiperiodically driven
magnetoelastic ribbon. The model system is a two-frequency parametrically driven Duffing oscillator. As a driving parameter
is increased, the route to chaos takes place in four distinct stages. The first stage is a torus-doubling bifurcation. The
second stage is a transition from the doubled torus to a strange nonchaotic attractor. The third stage is a transition from
the strange nonchaotic attractor to a geometrically similar chaotic attractor. The final stage is a hard transition to a much
larger chaotic attractor. This latter transition arises as the result of acrisis, the characterization of which is one of our primary concerns. Numerical evidence is given to indicate that the crisis arises
from the collision of the chaotic attractor with the stable manifold of a saddle torus. Intermittent bursting behavior is
present after the crisis with the mean time between bursts scaling as a power law in the distance from the critical control
parameter; τ ∼ (A-Ac)-α. The critical exponent is computed numerically, yielding the value α=1.03±0.01. Theoretical justification is given for the
computed critical exponent. Finally, a Melnikov analysis is performed, yielding an expression for transverse crossings of
the stable and unstable manifolds of the crisis-initiating saddle torus. 相似文献
3.
4.
Abe K Ahrens LA Amako K Aronson SH Beier EW Callas JL Cutts D Diwan M Durkin LS Gibbard BG Heagy SM Hedin D Hoftun JS Hurley M Kabe S Kurihara Y Lanou RE Mann AK Marx MD Murtagh MJ Nagashima Y Newcomer FM Shinkawa T Stern E Suzuki Y Terada S White DH Williams HH Yamaguchi Y 《Physical review letters》1987,58(7):636-639
5.
Substituent effects on monoboronic acid sensors for saccharides based on N-phenyl-1,8-naphthalenedicarboximides 总被引:4,自引:0,他引:4
In the course of our investigations on new monoboronic acid saccharide sensors with C(0) spacers, a series of probes 1-6 based on 1,8-naphthalenedicarboximide were synthesized. Sensor 1 displays features typical of PET monoboronic acid sensors and shows high selectivity to fructose. Sensor 2 exhibits a novel dual emission and remarkable sensitivity for glucose relative to fructose and galactose through subtle changes in pH. Sensor 3 displays significantly enhanced fluorescence in the presence of galactose at low pH. Although probes 4-6 exhibit unique properties such as high quantum yield (Phi(F) = 0.407) and excellent solubility in water, they did not show significant change in fluorescence intensity in the presence of monosaccharides. The effects of substituent on all six probes lend support to the proposed photoelectrochemical model. 相似文献
6.
7.
Chloroacetaldehyde reacts with viral M13mp18 single and double stranded DNA to form the highly fluorescent adducts, etheno-AMP and etheno-CMP. Absorbance and fluorescence spectroscopy can be used to monitor and characterize these reactions. Both single and double stranded DNA showed increases in the absorbance following reaction with the aldehyde. The fluorescence also increased in these two groups and continued to rise with increasing time of incubation until a point of saturation was reached. The fluorescence of the double stranded moiety was considerably enhanced following reaction with the aldehyde while that of the single stranded population was not, making this method appropriate for the separation of small quantities of the two populations of DNA. 相似文献
8.
Reza MD. Sultanur Taniguchi Rihito Kaneko Jyunya Oura Yasuji 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(6):2609-2619
Journal of Radioanalytical and Nuclear Chemistry - Instrumental photon activation analysis (IPAA) is nondestructive and multi-elemental analysis method like instrumental neutron activation... 相似文献
9.
Dr. Rebecca Walker Dr. Magdalena Majewska Dr. Damian Pociecha Dr. Anna Makal Prof. John MD Storey Prof. Ewa Gorecka Prof. Corrie T. Imrie 《Chemphyschem》2021,22(5):461-470
A selection of pyrene-based liquid crystal dimers have been prepared, containing either methylene-ether or diether linked spacers of varying length and parity. All the diether linked materials, CBOnO.Py (n=5, 6, 11, 12), exhibit conventional nematic and smectic A phases, with the exception of CBO11O.Py which is exclusively nematic. The methylene-ether linked dimer, CBnO.Py, with an even-membered spacer (n=5) was solely nematogenic, but odd-members (n=6, 8, 10) exhibited both nematic and twist-bend nematic phases. Replacement of the cyanobiphenyl fragment by cyanoterphenyl giving CT6O.Py, gave elevated melting and nematic-isotropic transition temperatures, and SmA and SmCA phases were observed on cooling the nematic phase. Intermolecular face-to-face associations of the pyrene moieties drive glass formation, and all these materials have a glass transition temperature at or above room temperature. The stability of the glassy twist-bend nematic phase allowed for its study using AFM, and the helical pitch length, PTB, was measured as 6.3 and 6.7 nm for CB6O.Py and CB8O.Py, respectively. These values are comparable to the shortest pitch of a twist-bend nematic phase measured to date. 相似文献
10.
Shozo Kawamura Makoto Suzuki Hossain MD. Zahid Hirofumi Minamoto 《Applied Acoustics》2009,70(11-12):1393-1399
Machine condition monitoring and fault diagnosis of rotating machinery are very important because of the wide use of rotating machinery in industry. Couplings and gears are used in many mechanical systems to connect elements and transmit power. The system is usually modeled as a single-degree-of-freedom system with a piecewise linear spring property, where the mass of main machine is only considered. In the present study, the dynamic behavior of a system with an unsymmetrical nonlinearity and a significant mass of the connecting part was investigated both experimentally and by numerical simulation. In the experiment, a 1/3 sub-harmonic oscillation was observed, but this oscillation was not found in the simulation using a single-degree-of-freedom system, in which the mass of the connecting part was ignored. However, when a two-degrees-of-freedom system was used that considered both the mass of the connecting part and the impact property, the 1/3 sub-harmonic oscillation was observed. Thus it is recognized that an adequate mathematical model for diagnosis in the early stage of abnormality must be selected on the basis of the mass ratio between the connecting part and the main body. 相似文献