bluuebunny/crossref_metadata_2025 huggingface dataset:
Self‐tuning fuzzy logic control for ultrasound hyperthermia with reference temperature based on objective functions
Authors: Chen Yung‐Yaw , Lin Win‐Li , Liou Hau‐Li , Yen Jia‐Yush , Shieh Ming‐Jium
Published: July 2002

The purpose of this paper is to develop and evaluate a self‐tuning fuzzy logic controller for a scanned focused ultrasound hyperthermia system with the reference temperaturedetermined from objective functions. This work employs simulation programs to develop the power deposition for the scanned focused ultrasound system and to solve the responses of temperature profiles based on the transient bioheat transfer equation. A fuzzy logic control algorithm is employed to determine the output power level for the heating system and an observer for blood perfusion variation is used to enhance the capability of the controller to adjust the required output power level for the treatment due to the drastic change of the blood perfusion. The reference temperaturefor the controller is based on objective functions to tune its value during the heating process, while a control temperaturefrom the thermosensors located in the tumor region is used as the input for the controller. The objective function based on the entire temperature profile is used to evaluate the appropriateness of the heating temperature distribution for a time‐variational blood perfusion. Simulation results demonstrate that the tumor region can be rapidly heated to the desired temperature level and maintained at that level despite blood perfusion variation. The resulting temperature profile, the objective function, and the output power level are related to the magnitude of blood perfusion, but are almost independent of thelocation and the initial setting value ofThe fuzzy logic control algorithm withdetermined from objective functions can be used for controlling the entire temperature distribution through a single control temperature, and the combination of control and optimization allows appropriate temperature fields to be created during the entire heating process. The control algorithm does not require the accurate prior knowledge of the locations of the thermosensors and the appropriate setting value for.
A pattern classification approach to characterizing solitary pulmonary nodules imaged on high resolution CT: Preliminary results
Authors: McNitt‐Gray Michael F. , Hart Eric M. , Wyckoff Nathaniel , Sayre James W. , Goldin Jonathan G. , Aberle Denise R.
Published: July 2002

The purpose of this research is to characterize solitary pulmonary nodules as benign or malignant based on quantitative measures extracted from high resolution CT (HRCT) images. High resolution CT images of 31 patients with solitary pulmonary nodules and definitive diagnoses were obtained. The diagnoses of these 31 cases (14 benign and 17 malignant) were determined from either radiologic follow‐up or pathological specimens. Software tools were developed to perform the classification task. On the HRCT images, solitary nodules were identified using semiautomated contouring techniques. From the resulting contours, several quantitative measures were extracted related to each nodule's size, shape, attenuation, distribution of attenuation, and texture. A stepwise discriminant analysis was performed to determine which combination of measures were best able to discriminate between the benign and malignant nodules. A linear discriminant analysis was then performed using selected features to evaluate the ability of these features to predict the classification for each nodule. A jackknifed procedure was performed to provide a less biased estimate of the linear discriminator's performance. The preliminary discriminant analysis identified two different texture measures—correlation and difference entropy—as the top features in discriminating between benign and malignant nodules. The linear discriminant analysis using these features correctly classified 28/31 cases (90.3%) of the training set. A less biased estimate, using jackknifed training and testing, yielded the same results (90.3% correct). The preliminary results of this approach are very promising in characterizing solitary nodules using quantitative measures extracted from HRCT images. Future work involves including contrast enhancement and three‐dimensional measures extracted from volumetric CT scans, as well as the use of several pattern classifiers.
Classifier design for computer‐aided diagnosis: Effects of finite sample size on the mean performance of classical and neural network classifiers
Authors: Chan Heang‐Ping , Sahiner Berkman , Wagner Robert F. , Petrick Nicholas
Published: July 2002

Classifier design is one of the key steps in the development of computer‐aided diagnosis (CAD) algorithms. A classifier is designed with case samples drawn from the patient population. Generally, the sample size available for classifier design is limited, which introduces variance and bias into the performance of the trained classifier, relative to that obtained with an infinite sample size. For CAD applications, a commonly used performance index for a classifier is the area, under the receiver operating characteristic (ROC) curve. We have conducted a computer simulation study to investigate the dependence of the mean performance, in terms of on design sample size for a linear discriminant and two nonlinear classifiers, the quadratic discriminant and the backpropagation neural network (ANN). The performances of the classifiers were compared for four types of class distributions that have specific properties: multivariate normal distributions with equal covariance matrices and unequal means, unequal covariance matrices and unequal means, and unequal covariance matrices and equal means, and a feature space where the two classes were uniformly distributed in disjoint checkerboard regions. We evaluated the performances of the classifiers in feature spaces of dimensionality ranging from 3 to 15, and design sample sizes from 20 to 800 per class. The dependence of the resubstitution and hold‐out performance on design (training) sample size was investigated. For multivariate normal class distributions with equal covariance matrices, the linear discriminant is the optimal classifier. It was found that its curves can be closely approximated by linear dependences over the range of sample sizes studied. In the feature spaces with unequal covariance matrices where the quadratic discriminant is optimal, the linear discriminant is inferior to the quadratic discriminant or the ANN when the design sample size is large. However, when the design sample is small, a relatively simple classifier, such as the linear discriminant or an ANN with very few hidden nodes, may be preferred because performance bias increases with the complexity of the classifier. In the regime where the classifier performance is dominated by the term, the performance in the limit of infinite sample size can be estimated as the intercept of a linear regression of versus The understanding of the performance of the classifiers under the constraint of a finite design sample size is expected to facilitate the selection of a proper classifier for a given classification task and the design of an efficient resampling scheme.
Improved spatial resolution by MOSFET dosimetry of an x‐ray microbeam
Authors: Kaplan Greg I. , Rosenfeld Anatoly B. , Allen Barry J. , Booth Jeremy T. , Carolan Martin G. , Holmes‐Siedle Andrew
Published: July 2002

Measurement of the lateral profile of the dose distribution across a narrow x‐ray microbeam requires a dosimeter with a micron resolution. We investigated the use of a MOSFET dosimeter in an “edge‐on” orientation with the gate insulating oxide layer parallel to the direction of the beam. We compared results using this technique to Gafchromic film measurements of a 200 micrometer wide planar x‐ray microbeam. The microbeam was obtained by using a vernier micrometerdriven miniature collimator attached to a Therapax DXT300 x‐ray machine operated at 100The “edge‐on” application allows utilization of the ultra thin sensitive volume of the MOSFET detector. Spatial resolution of both the MOSFET and Gafchromic film dosimeters appeared to be of about 1 micrometer. The MOSFET dosimeter appeared to provide more uniform dose profiles with the advantage of on‐line measurements.
Feature selection and classifier performance in computer‐aided diagnosis: The effect of finite sample size
Authors: Sahiner Berkman , Chan Heang‐Ping , Petrick Nicholas , Wagner Robert F. , Hadjiiski Lubomir
Published: July 2002

In computer‐aided diagnosis (CAD), a frequently used approach for distinguishing normal and abnormal cases is first to extract potentially useful features for the classification task. Effective features are then selected from this entire pool of available features. Finally, a classifier is designed using the selected features. In this study, we investigated the effect of finite sample size on classification accuracy when classifier design involves stepwise feature selection in linear discriminant analysis, which is the most commonly used feature selection algorithm for linear classifiers. The feature selection and the classifier coefficient estimation steps were considered to be cascading stages in the classifier design process. We compared the performance of the classifier when feature selection was performed on the design samples alone and on the entire set of available samples, which consisted of design and test samples. The area under the receiver operating characteristic curve was used as our performance measure. After linear classifier coefficient estimation using the design samples, we studied the hold‐out and resubstitution performance estimates. The two classes were assumed to have multidimensional Gaussian distributions, with a large number of features available for feature selection. We investigated the dependence of feature selection performance on the covariance matrices and means for the two classes, and examined the effects of sample size, number of available features, and parameters of stepwise feature selection on classifier bias. Our results indicated that the resubstitution estimate was always optimistically biased, except in cases where the parameters of stepwise feature selection were chosen such that too few features were selected by the stepwise procedure. When feature selection was performed using only the design samples, the hold‐out estimate was always pessimistically biased. When feature selection was performed using the entire finite sample space, the hold‐out estimates could be pessimistically or optimistically biased, depending on the number of features available for selection, the number of available samples, and their statistical distribution. For our simulation conditions, these estimates were always pessimistically (conservatively) biased if the ratio of the total number of available samples per class to the number of available features was greater than five.
Insight into entropy
Authors: Styer Daniel F.
Published: July 2002

What is the qualitative character of entropy? Several examples from statistical mechanics (including liquid crystal reentrant phases, two different lattice gas models, and the game of poker) demonstrate facets of this difficult question and point toward an answer. The common answer of “entropy as disorder” is regarded here as inadequate. An alternative but equally problematic analogy is “entropy as freedom.” Neither simile is perfect, but if both are used cautiously and not too literally, then the combination provides considerable insight.
Multistate flow devices for geophysical fluid dynamics and climate
Authors: Whitehead J. A. , Lawson W. Gregory , Salzig John
Published: July 2002

Two fluid devices exhibit simple aspects of nonlinear finite-amplitude instability in laminar fluid flow. The first shows multiequilibria; two steady flow regimes can be found within a certain range of the control parameter. The flow exhibits hysteresis as the control parameter is slowly increased and then decreased through this range of the control parameter. The second shows transition from steady flow to finite amplitude oscillations within a certain range. The two experiments share similar dynamics and only use different control parameters. A third experiment is described that exhibits either multiequilibria or oscillations, depending on which variable is selected to be the control parameter.
The pre-pharmacy major: A survey of physics requirements
Authors: McCall Richard P.
Published: July 2002

This paper presents the results of a survey of 81 colleges of pharmacy affiliated with the American Association of Colleges of Pharmacy regarding physics requirements for the pre-pharmacy major. Responses include number of semesters required, credit hours, student majors in the course, and mathematical basis. Strengths and weaknesses as reported by the college representatives are also presented. Their comments are used to point to needed changes in the pre-professional physics course.
Acoustic characteristics of English fricatives
Authors: Jongman Allard , Wayland Ratree , Wong Serena
Published: July 2002

This study constitutes a large-scale comparative analysis of acoustic cues for classification of place of articulation in fricatives. To date, no single metric has been found to classify fricative place of articulation with a high degree of accuracy. This study presents spectral, amplitudinal, and temporal measurements that involve both static properties (spectral peak location, spectral moments, noise duration, normalized amplitude, and F2 onset frequency) and dynamic properties (relative amplitude and locus equations). While all cues (except locus equations) consistently serve to distinguish sibilant from nonsibilant fricatives, the present results indicate that spectral peak location, spectral moments, and both normalized and relative amplitude serve to distinguish all four places of fricative articulation. These findings suggest that these static and dynamic acoustic properties can provide robust and unique information about all four places of articulation, despite variation in speaker, vowel context, and voicing.
Measured capacitance of a condenser microphone as a function of diaphragm displacement
Authors: Yan Xinche , Crocker Malcolm J. , Zeng Li Jun
Published: July 2002

This paper shows that the capacitance of a polarized condenser microphone measured with a sinusoidal electrical signal is quantitatively related to the displacement of the microphone diaphragm. In fact, the capacitance measured with an ac signal is the “input capacitance” of the microphone when it acts as a transmitter. The expressions for the diaphragm displacement and the input capacitance are derived with damping taken into account. The input capacitance differs from the static capacitance with bias by an additional term which varies with the polarization voltage and frequency. Therefore, in general, it is impossible to measure the static capacitance with bias using a low frequency ac signal without the diaphragm being blocked. In order to measure the true static capacitance with bias, a static method based on the dc voltage distribution is presented. The experimental results for the input capacitance and the static capacitance with bias, obtained with the abovementioned ac and dc methods, respectively, give a high level of confidence in the theory. The experimental results reported by some others also support the theory.
Some effects of duration on vowel recognition
Authors: Hillenbrand James M. , Clark Michael J. , Houde Robert A.
Published: July 2002

This study was designed to examine the role of duration in vowel perception by testing listeners on the identification of CVC syllables generated at different durations. Test signals consisted of synthesized versions of 300 utterances selected from a large, multitalker database of /hVd/ syllables [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099–3111 (1995)]. Four versions of each utterance were synthesized: (1) an original duration set (vowel duration matched to the original utterance), (2) a neutral duration set (duration fixed at 272 ms, the grand mean across all vowels), (3) a short duration set (duration fixed at 144 ms, two standard deviations below the mean), and (4) a long duration set (duration fixed at 400 ms, two standard deviations above the mean). Experiment 1 used a formant synthesizer, while a second experiment was an exact replication using a sinusoidal synthesis method that represented the original vowel spectrum more precisely than the formant synthesizer. Findings included (1) duration had a small overall effect on vowel identity since the great majority of signals were identified correctly at their original durations and at all three altered durations; (2) despite the relatively small average effect of duration, some vowels, especially /ɑ/-/ɔ/-/ʌ/ and /æ/-/ɛ/, were significantly affected by duration; (3) some vowel contrasts that differ systematically in duration, such as /i/-/ɪ/, /u/-/ᴜ/, and /ɪ/-/e/-/ɛ/, were minimally affected by duration; (4) a simple pattern recognition model appears to be capable of accounting for several features of the listening test results, especially the greater influence of duration on some vowels than others; and (5) because a formant synthesizer does an imperfect job of representing the fine details of the original vowel spectrum, results using the formant-synthesized signals led to a slight overestimate of the role of duration in vowel recognition, especially for the shortened vowels.
Estimating source position accuracy of a large-aperture hydrophone array for bioacoustics
Authors: Wahlberg Magnus , Møhl Bertel , Teglberg Madsen Peter
Published: July 2002

A linear error propagation analysis was applied to a hydrophone array used to locate sperm whales [see Møhl et al., J. Acoust. Soc. Am. 107, 638–648 (2000)]. The accuracy of two-dimensional (2D) and three-dimensional (3D) array configurations was investigated. The precision in source location was estimated as a function of inaccuracies in measurements of sound velocity, time-of-arrival differences (TOADs), and receiver positions. The magnitude of additional errors caused by geometric simplification was also assessed. The receiver position uncertainty had the largest impact on the precision of source location. A supplementary vertical linear array consisting of three receivers gave information on the vertical bearing and distance to the sound sources. The TOAD data from an additional receiver as well as from surface reflections were used to form an overdetermined location system. This system rendered positions within two standard deviations of the estimated errors from the original 3D array.
On the feasibility of remote palpation using acoustic radiation force
Authors: Nightingale Kathryn R. , Palmeri Mark L. , Nightingale Roger W. , Trahey Gregg E.
Published: July 2002

A method of acoustic remote palpation, capable of imaging local variations in the mechanical properties of tissue, is under investigation. In this method, focused ultrasound is used to apply localized (on the order of 2 mm3) radiation force within tissue, and the resulting tissue displacements are mapped using ultrasonic correlation based methods. The tissue displacements are inversely proportional to the stiffness of the tissue, and thus a stiffer region of tissue exhibits smaller displacements than a more compliant region. In this paper, the feasibility of remote palpation is demonstrated experimentally using breast tissue phantoms with spherical lesion inclusions, and in vitro liver samples. A single diagnostic transducer and modified ultrasonic imaging system are used to perform remote palpation. The displacement images are directly correlated to local variations in tissue stiffness with higher contrast than the corresponding B-mode images. Relationships between acoustic beam parameters, lesion characteristics and radiation force induced tissue displacement patterns are investigated and discussed. The results show promise for the clinical implementation of remote palpation.
Quantifying the intelligibility of speech in noise for non-native listeners
Authors: van Wijngaarden Sander J. , Steeneken Herman J. M. , Houtgast Tammo
Published: July 2002

When listening to languages learned at a later age, speech intelligibility is generally lower than when listening to one’s native language. The main purpose of this study is to quantify speech intelligibility in noise for specific populations of non-native listeners, only broadly addressing the underlying perceptual and linguistic processing. An easy method is sought to extend these quantitative findings to other listener populations. Dutch subjects listening to Germans and English speech, ranging from reasonable to excellent proficiency in these languages, were found to require a 1–7 dB better speech-to-noise ratio to obtain 50% sentence intelligibility than native listeners. Also, the psychometric function for sentence recognition in noise was found to be shallower for non-native than for native listeners (worst-case slope around the 50% point of 7.5%/dB, compared to 12.6%/dB for native listeners). Differences between native and non-native speech intelligibility are largely predicted by linguistic entropy estimates as derived from a letter guessing task. Less effective use of context effects (especially semantic redundancy) explains the reduced speech intelligibility for non-native listeners. While measuring speech intelligibility for many different populations of listeners (languages, linguistic experience) may be prohibitively time consuming, obtaining predictions of non-native intelligibility from linguistic entropy may help to extend the results of this study to other listener populations.
A model of lingual coarticulation based on articulatory constraints
Authors: Recasens Daniel , Pallarès Maria Dolors , Fontdevila Jordi
Published: July 2002

The magnitude and temporal extent of consonantal and vocalic coarticulation are reported for VCV sequences with two vowels (/i/, /a/) and seven consonants (/p/, /n/, dark /l/, /s/, /∫/, /ɲ/,/k/). Different degrees of articulatory constraint, or DAC values, are assigned to the consonants and vowels based on knowledge of their articulatory properties, in particular, the degree of involvement of the tongue dorsum in closure or constriction formation. Mean results on dorsopalatal contact and F2 frequency for five speakers of the Catalan language are presented. Predictions based on the DAC value for consonants and vowels account satisfactorily for the C-to-V effects (e.g., those for /ɲa/ are more prominent that those for /pi/); moreover, vowel-dependent effects tend to be negatively correlated with the DAC value for the consonant (e.g., they are more prominent when the intervocalic consonant is /p/ than when it is dark /l/). V-to-C effects are also conditioned by the tongue-dorsum position for the consonantal gesture. Coarticulatory directionality trends reveal that the extent to which the vowel-dependent tongue-dorsum activity may be anticipated is closely linked to the mechanico-inertial constraints associated with the tongue dorsum during consonantal production; this observation explains the salience of the vowel-dependent anticipatory effects in VCV sequences favoring C-to-V anticipation and of the vowel-dependent carryover effects in VCV sequences giving special weight to C-to-V carryover.
A perturbation method for the modes of cylindrical acoustic waveguides in the presence of temperature gradients
Authors: McCartin Brian J.
Published: July 2002

This paper concerns itself with how the cut-off frequencies and modal shapes of cylindrical acoustic waveguides are altered by the presence of temperature gradients induced by an applied temperature distribution along the duct walls. A physical model is first formulated which incorporates an inhomogeneous sound speed as well as a density gradient. The associated mathematical model is then a generalized eigenproblem. This is then discretized via the control region approximation (a finite difference scheme) yielding a generalized matrix eigenproblem. Under the assumption that the boundary temperature distribution is nearly constant, we apply a procedure of Schrödinger to express the propagation constants and modal functions as perturbation series whose successive terms can be generated recursively. The case of a rectangular duct with temperature variations in the cross section is considered in detail. All numerical computations are performed using MATLAB©.
Propagation of Love waves in a transversely isotropic fluid-saturated porous layered half-space
Authors: Wang Yue-Sheng , Zhang Zi-Mao
Published: July 2002

The dispersion equation for Love wave propagation in a layer lying over a half-space is derived. Both media are assumed to be transversely isotropic fluid-saturated poroelastic solids with principal axes perpendicular to the surface. The analysis is based on the Biot’s theory. The dissipation due to fluid viscosity is considered and therefore the dispersion equation is complex and intractable analytically. An iterative procedure is developed to solve this equation. Two situations are discussed in detail: (i) an elastic layer overlying a poroelastic half-space and (ii) a poroelastic layer lying over an elastic half-space. Dispersion curves and attenuation curves of Love waves are plotted for these two cases. In addition, the upper and lower bounds of Love wave speeds are also explored.
Modeling of pulsed finite-amplitude focused sound beams in time domain
Authors: Tavakkoli Jahangir , Cathignol Dominique , Souchon Rémi , Sapozhnikov Oleg A.
Published: July 2002

A time-domain numerical model is presented for simulating the finite-amplitude focused acoustic pulse propagation in a dissipative and nonlinear medium with a symmetrical source geometry. In this method, the main effects responsible in finite-amplitude wave propagation, i.e., diffraction, nonlinearity, and absorption, are taken into account. These effects are treated independently using the method of fractional steps with a second-order operator-splitting algorithm. In this method, the acoustic beam propagates, plane-by-plane, from the surface of a highly focused radiator up to its focus. The results of calculations in an ideal (linear and nondissipative) medium show the validity of the model for simulating the effect of diffraction in highly focused pulse propagation. For real media, very good agreement was obtained in the shape of the theoretical and experimental pressure-time waveforms. A discrepancy in the amplitudes was observed with a maximum of around 20%, which can be explained by existing sources of error in our measurements and on the assumptions inherent in our theoretical model. The model has certain advantages over other time-domain methods previously reported in that it: (1) allows for arbitrary absorption and dispersion, and (2) makes use of full diffraction formulation. The latter point is particularly important for studying intense sources with high focusing gains.
Ultrasound induced cavitation and sonochemical yields
Authors: Gong Cuiling , Hart Douglas P.
Published: July 2002

The introduction of a strong acoustic field to an aqueous solution results in the generation of cavitation microbubbles. The growth and collapse of these microbubbles focuses and transfers energy from the macroscale (acoustic wave) to the microscale (vapor inside the bubbles) producing extremely high localized pressures and temperatures. This unique energy focusing process generates highly reactive free radicals that have been observed to significantly enhance chemical processing. This paper presents a model that combines the dynamics of bubble collapse with the chemical kinetics of a single cavitation event. The effects on sonochemical yields and bubble dynamics of gas composition and heat transfer are assessed and compared with previous theoretical and experimental studies. Results from this model are used to explain unusual experimentally observed sonochemical phenomena.
The effect of abdominal wall morphology on ultrasonic pulse distortion. Part I. Measurements
Authors: Hinkelman Laura M. , Mast T. Douglas , Metlay Leon A. , Waag Robert C.
Published: July 2002

The relative importance of the fat and muscle layers of the human abdominal wall in producing ultrasonic wavefront distortion was assessed by means of direct measurements. Specimens employed included six whole abdominal wall specimens and twelve partial specimens obtained by dividing each whole specimen into a fat and a muscle layer. In the measurement technique employed, a hemispheric transducer transmitted a 3.75-MHz ultrasonic pulse through a tissue section. The received wavefront was measured by a linear array translated in the elevation direction to synthesize a two-dimensional aperture. Insertion loss was also measured at various locations on each specimen. Differences in arrival time and energy level between the measured waveforms and computed references that account for geometric delay and spreading were calculated. After correction for the effects of geometry, the received waveforms were synthetically focused. The characteristics of the distortion produced by each specimen and the quality of the resulting focus were analyzed and compared. The measurements show that muscle produces greater arrival time distortion than fat while fat produces greater energy level distortion than muscle, but that the distortion produced by the entire abdominal wall is not equivalent to a simple combination of distortion effects produced by the layers. The results also indicate that both fat and muscle layers contribute significantly to the distortion of ultrasonic beams by the abdominal wall. However, the spatial characteristics of the distortion produced by fat and muscle layers differ substantially. Distortion produced by muscle layers, as well as focal images aberrated by muscle layers, show considerable anisotropy associated with muscle fiber orientation. Distortion produced by fat layers shows smaller-scale, granular structure associated with scattering from the septa surrounding individual fat lobules. Thick layers of fat may be expected to cause poor image quality due to both scattering and bulk absorption effects, while thick muscle layers may be expected to cause focus aberration due to large arrival time fluctuations. Correction of aberrated focuses using time-shift compensation shows more complete correction for muscle sections than for fat sections, so that correction methods based on phase screen models may be more appropriate for muscle layers than for fat layers.
A new transducer holder mechanism for efficient generation and reception of Lamb modes in large plates
Authors: Ghosh Triguna , Kundu Tribikram
Published: July 2002

A new transducer holder mechanism is described in this paper. This mechanism is very useful for inspecting large plates by Lamb waves. The new mechanism allows water coupling between the ultrasonic transducers and the specimen but requires neither a water jet nor a big water tank for immersing the specimen into it. This mechanism allows the transducers to rotate for changing the angle of strike of the incident beam and avoids undesirable multiply-reflected signals between the transducer and the specimen. An aluminum plate with fabricated internal defects has been inspected by the Lamb wave technique using the new transducer holder mechanism. The experimental results clearly show the superiority of the new design when compared with the conventional designs available today.
Propagation characteristics of leaky Lamb waves in a liquid-loaded double-layered substrate consisting of a thin piezoelectric ceramic plate and a thin glass plate
Authors: Toda Kohji , Motegi Kenji
Published: July 2002

Operational performance of a leaky wave interdigital transducer on a double-layered substrate composed of two thin plates, a piezoelectric ceramic plate and a glass plate, is described for the purpose of two kinds of transducer functions—one for the effective radiation of underwater ultrasound and the other for liquid sensing. Two parameters, electromechanical coupling coefficient (k2) and mode conversion ratio (C), are evaluated on a two-dimensional p-fd plane as the fundamental factors for the leaky wave transducer, where p is the thickness ratio of the ceramic part and the double-layered substrate, and fd is the product of the frequency (f ) and the total thickness of the substrate (d). For an effective transducer for underwater ultrasound, both k2 and C should be large at a certain operation point of p and fd. The maximum transducer efficiency from the product of k2 and C in the second mode operation in the case of p=0.37 is three times as large as that in the case of a single-layered piezoelectric ceramic plate. For constructing a concise liquid sensing device, on the other hand, a combination of large k2 and small C is required. A condition satisfying the above requirement is recognized in the third mode operation in the case of p=0.55 and fd=3.4 MHz⋅mm. The combination of a piezoelectric ceramic plate and a glass plate is promising for realizing highly functional ultrasound transducers for underwater ultrasound and for liquid sensing.
Prediction of conductive hearing loss based on acoustic ear-canal response using a multivariate clinical decision theory
Authors: Piskorski Pawel , Keefe Douglas H. , Simmons Jeffrey L. , Gorga Michael P.
Published: July 2002

This study evaluated the accuracy of acoustic response tests in predicting conductive hearing loss in 161 ears of subjects from the age of 2 to 10 yr, using as a “gold standard” the air–bone gap to classify ears as normal or impaired. The acoustic tests included tympanometric peak-compensated static admittance magnitude (SA) and tympanometric gradient at 226 Hz, and admittancereflectance (YR) measurements from 0.5 to 8 kHz. The performance of individual, frequencyspecific, YR test variables as predictors was assessed. By applying logistic regression (LR) and discriminant analysis (DA) techniques to the multivariate YR response, two univariate functions were calculated as the linear combinations of YR variables across frequency that best separated normal and impaired ears. The tympanometric and YR tests were also combined in a multivariate manner to test whether predictive efficacy improved when 226-Hz tympanometry was added to the predictor set. Conductive hearing loss was predicted based on air–bone gap thresholds at 0.5 and 2 kHz, and on a maximum air–bone gap at any octave frequency from 0.5 to 4 kHz. Each air–bone gap threshold ranged from 5 to 30 dB in 5-dB steps. Areas under the relative operating characteristic curve for DA and LR were larger than for reflectance at 2 kHz, SA and Gr. For constant hit rates of 80% and 90%, both DA and LR scores had lower false-alarm rates than tympanometric tests–LR achieved a false-alarm rate of 6% for a sensitivity of 90%. In general, LR outperformed DA as the multivariate technique of choice. In predicting an impairment at 0.5 kHz, the reflectance scores at 0.5 kHz were less accurate predictors than reflectance at 2 and 4 kHz. This supports the hypothesis that the 2–4-kHz range is a particularly sensitive indicator of middle-ear status, in agreement with the spectral composition of the output predictor from the multivariate analyses. When tympanometric and YR tests were combined, the resulting predictor performed slightly better or the same as the predictor calculated from the use of the YR test alone. The main conclusion is that these multivariate acoustic tests of the middle ear, which are analyzed using a clinical decision theory, are effective predictors of conductive hearing loss.
Time-frequency analysis of the dispersion of Lamb modes
Authors: Prosser W. H. , Seale Michael D. , Smith Barry T.
Published: July 2002

Accurate knowledge of the velocity dispersion of Lamb modes is important for ultrasonic nondestructive evaluation methods used in detecting and locating flaws in thin plates and in determining their elastic stiffness coefficients. Lamb mode dispersion is also important in the acoustic emission technique for accurately triangulating the location of emissions in thin plates. In this research, the ability to characterize Lamb mode dispersion through a time-frequency analysis (the pseudo-Wigner–Ville distribution) was demonstrated. A major advantage of time-frequency methods is the ability to analyze acoustic signals containing multiple propagation modes, which overlap and superimpose in the time domain signal. By combining time-frequency analysis with a broadband acoustic excitation source, the dispersion of multiple Lamb modes over a wide frequency range can be determined from as little as a single measurement. In addition, the technique provides a direct measurement of the group velocity dispersion. The technique was first demonstrated in the analysis of a simulated waveform in an aluminum plate in which the Lamb mode dispersion was well known. Portions of the dispersion curves of the A0, A1, S0, and S2 Lamb modes were obtained from this one waveform. The technique was also applied for the analysis of experimental waveforms from a unidirectional graphite/epoxy composite plate. Measurements were made both along and perpendicular to the fiber direction. In this case, the signals contained only the lowest order symmetric and antisymmetric modes. A least squares fit of the results from several source to detector distances was used. Theoretical dispersion curves were calculated and are shown to be in good agreement with experimental results.
A solution to diffraction biases in sonoelasticity: The acoustic impulse technique
Authors: Catheline Stefan , Wu François , Fink Mathias
Published: July 2002

Several methods have been proposed to estimate the viscoelastic properties of soft biological tissues using forced low-frequency vibrations (10–500 Hz). Those methods are based on the measurement of phase velocity of the shear waves (∼5 m/s). It is shown in this article that the measurements of velocity as well as attenuation are subjected to biases. These biases are related to reflected waves created at boundaries, to the nonnegligible size of the piston source which causes diffraction effects and to the influence of a low-frequency compressional wave. Indeed, a theoretical analysis of the field radiated by a point source explains how mechanical vibrations of a piston generate a shear wave with a longitudinal component and how this component can interfere with a low-frequency compressional wave. However, by using a low-frequency transient excitation, these biases can be avoided. Then the precise numerical values of elasticity and viscosity can be deduced. Experiments in phantoms and beef muscles are shown. Moreover, a relative hardness imaging of a phantom composed of two media with different elasticities is presented.
Quantitative assessment of second language learners’ fluency by means of automatic speech recognition technology
Authors: Cucchiarini Catia , Strik Helmer , Boves Lou
Published: July 2002

To determine whether expert fluency ratings of read speech can be predicted on the basis of automatically calculated temporal measures of speech quality, an experiment was conducted with read speech of 20 native and 60 non-native speakers of Dutch. The speech material was scored for fluency by nine experts and was then analyzed by means of an automatic speech recognizer in terms of quantitative measures such as speech rate, articulation rate, number and length of pauses, number of dysfluencies, mean length of runs, and phonation/time ratio. The results show that expert ratings of fluency in read speech are reliable (Cronbach’s α varies between 0.90 and 0.96) and that these ratings can be predicted on the basis of quantitative measures: for six automatic measures the magnitude of the correlations with the fluency scores varies between 0.81 and 0.93. Rate of speech appears to be the best predictor: correlations vary between 0.90 and 0.93. Two other important determinants of reading fluency are the rate at which speakers articulate the sounds and the number of pauses they make. Apparently, rate of speech is such a good predictor of perceived fluency because it incorporates these two aspects.
Acoustic scattering by baffled flexible surfaces: The discrete optical theorem
Authors: Kriegsmann G. A.
Published: July 2002

The optical theorem for acoustic scattering by baffled membranes and plates relates the total cross section of the scattered field, the directivity factor in the specular direction, and the energy dissipated by the structure. It is basically a statement of conservation of power. In this paper it is demonstrated that the discrete formulation of these problems, obtained by a Galerkin approximation, exactly satisfies the optical theorem. This discrete relationship holds regardless of the choice of basis functions and the size of the truncated system N. Thus, the adherence of the approximate numerical results to the power conservation law does not necessarily imply its accuracy.
Maximum-likelihood approach to strain imaging using ultrasound
Authors: Insana M. F. , Cook L. T. , Bilgen M. , Chaturvedi P. , Zhu Y.
Published: July 2002

A maximum-likelihood (ML) strategy for strain estimation is presented as a framework for designing and evaluating bioelasticity imaging systems. Concepts from continuum mechanics, signal analysis, and acoustic scattering are combined to develop a mathematical model of the ultrasonic waveforms used to form strain images. The model includes three-dimensional (3-D) object motion described by affine transformations, Rayleigh scattering from random media, and 3-D system response functions. The likelihood function for these waveforms is derived to express the Fisher information matrix and variance bounds for displacement and strain estimation. The ML estimator is a generalized cross correlator for pre- and post-compression echo waveforms that is realized by waveform warping and filtering prior to cross correlation and peak detection. Experiments involving soft tissuelike media show the ML estimator approaches the Cramér–Rao error bound for small scaling deformations: at 5 MHz and 1.2% compression, the predicted lower bound for displacement errors is 4.4 μm and the measured standard deviation is 5.7 μm.
Statistical Theory of Flow through Porous Media
Authors: Scheidegger Adrian E.
Published: July 2002

This paper discusses the various attempts along the lines of statistical mechanics that have been made to explain certain phenomena occurring in flow of fluids through porous media. The latter particularly concerns processes of mixing miscible phases during their passage through a porous medium. The statistical theories that can be proposed are based on the following theoretical models: random walk of individual fluid particles, quasi-turbulent flow analogy, analogy with thermodynamics, and finally, general statistical mechanics. In all cases, one ends up with equations that are very similar to a diffusivity equation.
The Effect of Pressure on the Shear Viscosity of Polymer Melts
Authors: Kamal M. R. , Nyun H.
Published: July 2002

In many polymer processing operations like injection molding, the polymer melt flows under the influence of high pressure, sometimes exceeding 20,000 psi. It has been suggested by a number of workers, on the basis of both experimental and theoretical considerations, that the effect of hydrostatic pressure on viscosity cannot be ignored in such instances. However, most of the proposed techniques to determine the effect of pressure on viscosity suffer from limitations especially at high shear rates. The present work proposes a more general and quantitative method for obtaining the effect of pressure on the viscosity of polymer melts from capillary viscometer data. In addition to its applicability over a wide range of practical shear rates, the proposed method employs less restrictive assumptions than previous techniques and contains corrections for the effect of viscous heating. The results obtained for the effect of pressure on the viscosity of polystyrene at 180°C are compared to rheological data obtained by conventional methods. Preliminary results on the pressure coefficient of viscosity appear to be in agreement with predictions based on the W-L-F equation.
Time-Dependent Response in the Flow Between Eccentric Rotating Disks
Authors: Willey S. Jack , Davis W. M. , Macosko C. W. , Goldstein Charles
Published: July 2002

The stress-growth phenomenon in the eccentric rotating disk (ERD) geometry is analyzed using a linearized Bird-Carreau integral model. Good agreement is found between experimental observations and predicted responses for a low-density polyethylene melt. Transient stress response is reported as time- and frequency-dependent moduli. In start-up, the approach of the viscous and elastic stresses to their steady-state values at angular velocity Ω is found to be directly related to the decay of the storage modulus in stress relaxation after steady rotation.
A Theoretical Model for the Cavity Filling Process in Injection Molding
Authors: Broyer E. , Gutfinger C. , Tadmor Z.
Published: July 2002

The flow analysis network (FAN) method previously developed for die design is adapted to the problem of the cavity filling process in injection molding. The method is applicable to relatively narrow gap cavities of any shape. It permits the computation of the advancing front of melt at any time, as well as prediction of weld-line location. The method was extended to nonisothermal flow in which solidification and “skin” formation during filling time was approximately accounted for. The nonisothermal analysis allows prediction of the possibility of a “short shot” situation. The analysis is applicable to any prescribed pressure or flow rate at the gate. Both can be arbitrary functions of time.
Bimodal model of concentrated suspension viscosity for distributed particle sizes
Authors: Probstein R. F. , Sengun M. Z. , Tseng T-C.
Published: July 2002

A polydisperse suspension with a particle size distribution from submicrometer to hundreds of micrometers is treated as bimodal, wherein it is made up of a colloidal fine fraction and a noncolloidal coarse fraction. According to the bimodal model, the fine fraction imparts to the suspension its non-Newtonian characteristics and behaves independently of the coarse fraction, whereas the coarse particles only raise the apparent viscosity through hydrodynamic interactions. It is shown that when the particle microstructure is random, the contribution to the viscosity of the coarse fraction, which is generally polymodal, is characterized by lubrication concepts with the maximum packing fraction φm as the scaling parameter. It is found that φm is equal to the dry random packing fraction divided by a filler dilatancy factor of 1.19. The bimodal model and lubrication concepts have also been successfully applied to bidisperse suspensions with a very large particle size ratio. An inverse procedure is described that makes use of the results from viscosity and dry random packing measurements to divide a continuous size distribution into a colloidal and a noncolloidal fraction.
Study of YBa2Cu3O7−x reaction kinetics by Rietveld method
Authors: Ferraz Maria Cristina Comunian , Basso Heitor Cury , Mascarenhas Yvonne P.
Published: July 2002

Using a recent proposed analysis procedure for quantitative phase determination by X-ray powder diffraction, YBa2Cu3O7−x solid state formation reaction kinetics at 900 °C was studied. Although there was the presence of partial amorphous components, it was possible to determine a reaction route for the synthesis of the title compound from X-ray powder diffraction data collected at various stages of the thermal treatment and using the Rietveld method for the quantitative determination of the phase composition