Steps on vicinal Si(001) are either one or two atomic layers high. When the tilt of the surface about [11̄0] is 2°, alternating type-A and type-B single steps dominate. When the tilt angle is increased to 4°, the steps combine to form straight, evenly spaced type-B double steps. Type-A double steps do not occur. At kinks the double steps split into single steps. Tunneling images of the double steps reveal the rebonded atoms described by the Chadi model.
A novel, noninvasive experiment is proposed that reliably shows the strength of glottal oscillations. The quasi-glottogram (QGG) signal is generated from a microphone array that is trained to approximate the electroglottogram signal. The QGG may be useful to improve estimates of whether speech is voiced, to quantify partial voicing, and to reduce the phoneme effect when measuring the amplitude of speech signals. The technique is well adapted to the generation of text-to-speech systems, as it allows an estimate of the glottal flow during undisturbed, natural speech. For prosody studies, it can be used to provide an estimate of amplitude which is relatively unaffected by changes in phonemes, and is at least as reliable as standard estimators of amplitude.
Prosodic differences between dysarthric and healthy speakers were studied. Six acoustic properties that are plausibly more influenced by suprasegmental aspects of speech (e.g., emphasis) than the segmental details of the words were measured. The time course of these properties were analyzed over each utterance by fitting Legendre Polynomials. The resultant Legendre coefficients were then fed to linear- and quadratic-discriminant classifiers. All of the six properties were individually capable of distinguishing dysarthric speech from healthy speech. Based on one acoustic property measured over a single short sentence, we could correctly classify a speaker as healthy or dysarthric 55–75% of the time, depending on the acoustic property used. More complex classifiers that used all the acoustic properties correctly classified the speaker 97% of the time based on nine utterances. The strongest difference between normal and dysarthric speech was in loudness. Dysarthric speakers did not reliably produce the loudness patterns associated with stressed syllables. They also had a wider range in amplitude, greater voicing variability, smaller excursions of fundamental frequency, and less final lengthening compared to healthy speakers. The classification we demonstrated may be extended to a become a graduated measurement of severity, thereby contributing to diagnostics and intervention in dysarthria.
Diamond has recently emerged as a desirable material for field emitters due to its negative electron affinity and robust mechanical and chemical properties. This study identifies structural properties which govern the electron field emission process from undoped diamond. Desirable low-voltage diamond field emitters with such properties have been synthesized by controlling various CVD process parameters.
We have confined over 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ atoms of hydrogen in a static magnetic trap. The atoms are loaded into the trap by precooling with a dilution refrigerator. At operating densities near 1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ the gas is observed to be electron and nuclear polarized in the uppermost hyperfine state. The long lifetime of the trapped gas (over 20 min) suggests that it is thermally decoupled from the wall and has evaporatively cooled to a temperature of about 40 mK. The residual decay of the gas density is consistent with spin relaxation induced by dipolar interactions between atoms.
Although the pitch of the human voice is continuously variable, some linguists contend that intonation in speech is restricted to a small, limited set of patterns. This claim is tested by asking subjects to mimic a block of 100 randomly generated intonation contours and then to imitate themselves in several successive sessions. The produced f0 contours gradually converge towards a limited set of distinct, previously recognized basic English intonation patterns. These patterns are “attractors” in the space of possible intonation English contours. The convergence does not occur immediately. Seven of the ten participants show continued convergence toward their attractors after the first iteration. Subjects retain and use information beyond phonological contrasts, suggesting that intonational phonology is not a complete description of their mental representation of intonation.
Despite the apparent simplicity, measuring the position of peaks in speech fundamental frequency (f0) can produce unexpected results in a model where f0 is the superposition of a supersegmental component and a segmental component. In these models, the measured f0 peak position can be as much as an entire syllable different from the peak of the intonation component. This difference can be large enough so that the measured peak positions could falsely suggest a phonological distinction in the intonation where none really exists. This paper then discusses measurement techniques that are less sensitive to segmental effects than directly measuring the position of the f0 maximum. A algorithm, called the “bracketed maximum,” is presented. The performance of these techniques is compared on a corpus of speech data where the intonation is expected to be in a stable position. The bracketed maximum can reduce the variance of peak position measurements by at least 15%, in the presence of changing segmental structure, thereby presumably yielding a more accurate measurement of the intonation peak position.
Seven British English dialects were studied to see what prosodic distinctions are made between statements and questions in read speech. A set of Bayesian classifiers was built upon feature vectors obtained from a spectral analysis of measures of (1) f0, (2) loudness, (3) spectral slope and (4) voicing periodicity. It was found that the prosodic information useful for the question/statement distinction is distributed broadly across the utterance, and that loudness and spectral slope can be nearly as informative as f0 (voicing is less informative). The three important acoustic features carry somewhat less than one bit of information each, so prosodic information could be valuable to the listener, and the listener may be able to make the question/statement decision early in the utterance. The contrast differs from one acoustic property to the next: f0 is marked primarily by slow variations. Conversely, the spectral slope and loudness measurements primarily use shorter-wavelength features, corresponding to structures that are a syllable or two long. We also find substantial differences in the prosodic information that different dialects use, and substantial differences between speakers of the same dialect. [Research supported by the UK Economic and Social Research Council, Grant RES 00-23-1049.]
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