Vocal tract resonances and the sound of the Australian didjeridu (yidaki). III. Determinants of playing quality

Traditional didjeridus have a broad range of bore geometries with many details not immediately apparent to a player, and are therefore suitable for examining the relationship between perceived quality and physical properties. Seven experienced players assessed the overall playing quality of 38 didjeridus that spanned a wide range of quality, pitch, and geometry, as well as 11 plastic cylindrical pipes. The ranking of these instruments was correlated with detailed measurements of their acoustic input impedance spectra. Most significantly, the ranked quality of a didjeridu was found to be negatively correlated with the magnitude of its acoustic input impedance, particularly in the frequency range from 1 to 2 kHz. This is in accord with the fact that maxima in the impedance of the player's vocal tract can inhibit acoustic flow, and consequently sound production, once the magnitude of these impedance maxima becomes comparable with or greater than those of the instrument. This produces the varying spectral peaks or formants in the sound envelope that characterize this instrument. Thus an instrument with low impedance and relatively weak impedance maxima in this frequency range would allow players greater control of the formants in the output sound and thus lead to a higher perceived playing quality.     

Development of Enantioselective Palladium‐Catalyzed Alkene Carboalkoxylation Reactions for the Synthesis of Tetrahydrofurans

The Pd‐catalyzed coupling of γ‐hydroxyalkenes with aryl bromides affords enantiomerically enriched 2‐(arylmethyl)tetrahydrofuran derivatives in good yield and up to 96:4 e.r. This transformation was achieved through the development of a new TADDOL/2‐arylcyclohexanol‐derived chiral phosphite ligand. The transformations are effective with an array of different aryl bromides, and can be used for the preparation of products bearing quaternary stereocenters.     

On the structures of alpha-lithiated sulfoxide,sulfone and sulfonium systems. Implications for the stereochemistry of functionalization of carbon atoms adjacent to sulfur

The fully optimized geometries of C-S torsional isomers of LiCH₂SHO, LiCH₂SHO₂, and LiCH₂SH₂⁺ have been computed at the 3–21G^* level. The global minima of the sulfoxide and sulfone contain intramolecular LiO bonds. In the presence of Li⁺, intermolecular LiO bonding alters the structure of the alpha-lithiated sulfoxide, and the CLi bond is antiperiplanar to oxygen. The alpha-lithiated sulfonium cation exhibits no unusual conformational features, and a low barrier to CS torsion. The implications of these results upon the stereochemistry of functionalization of a carbon atom adjacent to sulfur by a lithiation-quenching sequence are discussed.     

Vibroacoustic characteristics of a gothic harp

The "gothic" style of harp was popular across most of Europe from the late medieval period to the Renaissance. These harps have a one-piece, longitudinally oriented hardwood soundboard, as opposed to the transverse-oriented bonded softwood structure on a modern instrument. In addition, the one-piece back is flexible, whereas the back of a modern instrument is a rigid molded shell. To study the gothic harp, one was constructed from plans created by the Boston Museum of Fine Arts from a late German model in their collection. The vibrational behaviors of the soundboard and soundbox were measured at various stages of construction. The completed instrument was subjected to modal analysis and radiativity measurements. The sound radiation is dominated by two breathing modes at 188 and 273 Hz, each with strong motion of the back, and modes around 350 Hz. Taken together, these modes function like the A0/T1 resonance pairs seen in the soundboxes of other instruments, and a comparison is made with the guitar. Also observed is that as the frequency increases, radiation is emitted from higher up the soundboard, and from higher soundholes. This feature has been observed in other harps, and is a consequence of the harp family's unique geometry.     

An existence-convergence theorem for a class of iterative methods

LetM ₀, characterized byx _k+1=G ₀(x _k),k?0,x ₀ prescribed, be an iterative method for the solution of the operator equationF(x)=0, whereF:X → X is a given operator andX is a Banach space. Let ω:X → X be a given operator, and let the methodM _mbe characterized byx _x+1,m =G _m(x _k,m),k?0,x _0,m prescribed, where $$G_i (x) = G_0 (x) - \sum\limits_{j = 0}^{i - 1} { F'(\omega (x))^{ - 1} F(G_j (x)), i = 1, . . . ,m,} $$ in whichG ₀:X → X is a given operator andF′:X → L(X) is the Fréchet derivative ofF. Sufficient conditions for the existence of a solutionx* _m ofF(x)=0 to which the sequence (x _k,m) generated from methodM _mconverges are given, together with a rate-of-convergence estimate.     

Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I. experiment

The didjeridu, or yidaki, is a simple tube about 1.5 m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers' vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1-3 kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player's lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of "circular breathing" and combined playing and vocalization are shown.     

Recombination radiation from landau states in impactionized GaAs

Recombination radiation from Landau states in impact ionized high-purity GaAs has been observed. The narrow band (～ 3 cm^?1) emission has been magnetically tuned from 80–120 cm^?1, and used to observe rotational transitions in water vapor.     

Vocal Parameters of Aerobic Instructors with and without Voice Problems

Aerobic instructors frequently experience vocal fatigue and are at risk for the development of vocal fold pathology. Six female aerobic instructors, three with self-reported voice problems and three without, served as subjects. Measures of vocal function (perturbation and EGG) were obtained before and after a 30-minute exercise session. Results showed that the group with self-reported voice problems had greater amounts of jitter, lower harmonic-to-noise ratios, and less periodicity in sustained vowels overall, but no significant differences in measures of perturbation and EGG were found before and immediately after instruction. Measures of vocal parameters showed that subjects with self-reported voice problems projected with relatively greater vocal intensity and phonated for a greater percentage of time across beginning, middle, and ending periods of aerobic instruction than subjects with no reported voice problems.