bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing cochlear mechano-electric transduction in ears damaged with pure tones
Authors: Chertoff Mark E. , Steele Timothy C. , Bian Lin
Published: July 2002

Cochlear microphonics were recorded in response to Gaussian noise from the round window of Mongolian gerbils. A nonlinear systems identification procedure provided the frequency-domain parameters of a third-order polynomial equation describing cochlear mechano-electric transduction (MET). Exposure to an 8-kHz pure tone at 100 dB SPL for 20 min reduced the magnitude of the linear, quadratic, and cubic terms significantly. Animals exposed to a 1- or 4-kHz pure tone showed changes in the quadratic term. Differentiation of the polynomial equation and algebraic manipulations of the coefficients provided physiologic indices of MET. The sensitivity, saturation voltages, and sound pressures required to saturate MET were altered in animals exposed to an 8-kHz pure tone. Limited changes occurred in animals exposed to a 1- or 4-kHz pure tone.
Spatial aspects of reproduced sound in small rooms
Authors: Bech So/ren
Published: July 2002

This paper reports on the influence of individual reflections on the auditory spatial aspects of reproduced sound. The sound field produced by a single loudspeaker positioned in a normal listening room has been simulated using an electroacoustical synthesis of the direct sound, 17 individual reflections and the reverberant field. The threshold of detection was measured using the method of adjustment for five reflections using three subjects for noise and speech. The thresholds have been measured for two simulated situations (1) a loudspeaker with a frequency independent directivity characteristics and frequency independent absorption coefficients of the room surfaces and (2) a loudspeaker with directivity similar to a standard two-way system and absorption coefficients according to measurements of real materials. The results have shown that subjects can reliably distinguish between timbre and spatial aspect of the sound field, that the spectral energy above 2 kHz of the individual reflection determines the importance of the reflection for the spatial aspects, and that only the first order floor reflection will contribute to the spatial aspects.
Perceptual segregation of a harmonic from a vowel by interaural time difference in conjunction with mistuning and onset asynchrony
Authors: Darwin C. J. , Hukin R. W.
Published: July 2002

The two experiments reported here examine how an inter-aural time difference (ITD) interacts with two other cues, mistuning and onset asynchrony, in reducing the contribution of a single frequency component to the perception of a vowel’s identity. Previous experiments have shown that although ITD is generally rather ineffective at segregating a simultaneous harmonic frequency component from a vowel, it can produce some segregation when listeners have already been exposed to the isolated segregated component. A difference in ITD increases segregation overall in experiment 1 where the to-be-segregated component can also have a different onset time from the remainder of the vowel, and experiment 2 shows a similar result when the to-be-segregated component is mistuned. However, segregation by ITD is present just as strongly on trials when there is neither mistuning nor a difference in onset-time as on trials where these additional cues are present. Segregation on trials when there is neither mistuning nor a difference in onset-time is however larger in the present experiment which mixed all conditions together than in similar trials in an earlier experiment that had a blocked design [C. J. Darwin and R. W. Hukin, J. Acoust. Soc. Am. 102, 2316–2324 (1997)]. The results show that segregation by ITD increases when other more potent cues are present in the experiment.
Change in envelope beats as a possible cue in comodulation masking release (CMR)
Authors: Buss Emily , Hall Joseph W. , Grose John H.
Published: July 2002

The detection advantage associated with masker envelope coherence across frequency has typically been described in terms of comparisons of information across auditory channels. More recently it has been suggested that analysis of the output of a wider initial filter, similar to that suggested for the TMTF, can account for the data [B. G. Berg, J. Acoust. Soc. Am. 100, 1013–1023 (1996)]. This approach suggests that a change in envelope beats could serve as the cue to the addition of a pure-tone signal. Data are presented here for the detection of a tone added to multiple maskers with coherent envelopes. In one condition a change in envelope beats was an accurate potential cue, whereas in others the change was too unreliable to serve as an indicator of the presence of the signal. All conditions employing maskers with coherent envelopes produced very similar thresholds, and all showed improved sensitivity over the case of detecting a signal added to a single masker centered on the signal frequency. Results are interpreted as evidence that a change in envelope beats does not form the basis of detection in CMR.
Mechanical impedance of a piano soundboard
Authors: Giordano N.
Published: July 2002

An experimental study of the mechanical impedance Z of a piano soundboard in the frequency range ∼50–104 Hz is reported. The results differ significantly from the behavior reported by Wogram above a few kHz, but are consistent with the measurements of Conklin. The data presented here are also in good agreement with the predictions of our recent numerical calculations. Those calculations found that the soundboard ribs have an important effect on the frequency dependence of Z above a few kHz, and our measurements confirm that prediction.
Measurement and localization of interface wave reflections from a buried target
Authors: Smith Eric , Wilson Preston S. , Bacon Fred W. , Manning Jason F. , Behrens John A. , Muir Thomas G.
Published: July 2002

It is demonstrated that seismic interface waves on the surface of a natural beach can be used to identify the position of a buried object. For this experiment, the waves were created with a sediment-coupling transducer and received on a three-element horizontal line array of triaxial geophones. The source and its coupling to the medium provided a high degree of signal repeatability, which was useful in improving signal-to-noise ratio. Reception of all three directions of particle velocity made it possible to augment conventional beamforming techniques with polarization filters to enhance interface-wave components. Reverberation in the beach was found to be large, though, and coherent background subtraction was required to isolate the component of the sound field reflected by the target. Propagation loss measurements provided comparisons of reflected signal power with predictions made previously, and the two were found to agree closely.
The evolution of phase fronts and the method of strained coordinates
Authors: Snieder Roel
Published: July 2002

When waves propagate through a medium with smooth velocity perturbations the propagation of wavefronts is determined by the eikonal equation. Here the propagation of wavefronts through a medium with small-scale velocity perturbations is analyzed using the method of strained coordinates. A partial differential equation for the first-order perturbation of wavefronts is derived that includes frequency-dependent wave propagation effects. It is shown that for the special case of the scalar Helmholtz equation with a homogeneous reference medium this leads to the same perturbation of wavefronts as obtained from the Rytov approximation. However, the method presented here can possibly be generalized to more complex wave propagation problems where the Rytov approximation cannot be used, such as the propagation of vector waves.
Inverse imaging of the breast with a material classification technique
Authors: Manry Charles W. , Broschat Shira L.
Published: July 2002

In recent publications [Chew et al., IEEE Trans. Blomed. Eng. BME-9, 218–225 (1990); Borup et al., Ultrason. Imaging 14, 69–85 (1992)] the inverse imaging problem has been solved by means of a two-step iterative method. In this paper, a third step is introduced for ultrasound imaging of the breast. In this step, which is based on statistical pattern recognition, classification of tissue types and a priori knowledge of the anatomy of the breast are integrated into the iterative method. Use of this material classification technique results in more rapid convergence to the inverse solution—approximately 40% fewer iterations are required—as well as greater accuracy. In addition, tumors are detected early in the reconstruction process. Results for reconstructions of a simple two-dimensional model of the human breast are presented. These reconstructions are extremely accurate when system noise and variations in tissue parameters are not too great. However, for the algorithm used, degradation of the reconstructions and divergence from the correct solution occur when system noise and variations in parameters exceed threshold values. Even in this case, however, tumors are still identified within a few iterations.
Discrimination of frequency glides with superimposed random glides in level
Authors: Moore Brian C. J. , Sek Aleksander
Published: July 2002

These experiments were designed to test the hypothesis that glides in frequency are detected and discriminated by monitoring changes in excitation level on the low-frequency side of the excitation pattern. Thresholds were measured for detecting an increase in the extent of a frequency glide, for various standard extents (transition spans). The center frequency of each stimulus was roved, to prevent subjects from using the start or endpoint frequencies of the stimuli as cues. The level was either fixed at 70 dB SPL, or changed linearly in dB/s by an amount that varied randomly in extent and direction, keeping the level at the midpoint of the glide at 70 dB SPL. These random changes in level were intended to disrupt cues based on monitoring changes in excitation level on one side of the excitation pattern. For some conditions, performance was too good to be explained by subjects monitoring the start or endpoint frequencies of the stimuli. Performance was also too good to be explained in terms of the discrimination of changes in excitation level on one side of the excitation pattern. Thresholds, expressed as a proportion of the equivalent rectangular bandwidth (ERB) of the auditory filter, did not vary greatly with center frequency (0.5, 2, or 6 kHz), suggesting that discrimination did not depend strongly on information derived from phase locking. Glide duration (50 or 400 ms) and glide direction (upward or downward) also had little effect. Thresholds increased with increasing standard transition span, when that span was increased beyond 0.5 ERB. It is concluded that changes in glide extent per se can be discriminated, but this is not done by monitoring just one side of the excitation pattern.
Propagation in random stratified waveguides—A modal-spectral treatment
Authors: Frankenthal Shimshon , Beran Mark J.
Published: July 2002

The statistics of a forward-propagating wave is considered in a random, anisotropic, stratified three-dimensional waveguide, where modal analysis offers unique advantages. After extracting the vertical dependence in the usual way, the equations are formulated which govern the range evolution of the transverse horizontal spectra of the modal field coefficients (MTWS). A short-range perturbation solution is used to derive the difference equations governing the long-range behavior of the two lowest moments of the field spectra. The conditions under which these difference equations can be approximated as differential equations are given. These equations are not limited by the parabolic approximation, and are amenable to numerical treatment by marching techniques. They are used here to study the effect of scattering on the spectral redistribution of the modal power, and the related problem of the coherence of plane and cylindrical waves. It is shown that, as a result of scattering in the transverse horizontal direction, the total beam power is redistributed among the modes in proportion to the modal eigenvalues, rather than uniformly, as two-dimensional propagation models suggest.
The effect of reduced tonal space in Parkinsonian speech on the perception of Cantonese tones
Authors: Wong Patrick C. M. , Diehl Randy L.
Published: July 2002

Wong and Diehl [J. Acoust. Soc. Am. 104 (1998)] showed that subjects’ perception of Cantonese level tones involves the assessment of the distance between the extreme fundamental frequency (F0) values in the carrier sentence and the F0 of the target syllable (‘‘the extreme-target distance’’). Listeners were best able to identify the tone when this distance was relatively large. This is true regardless of whether the carrier sentence is in English or Cantonese. However, only synthesized speech stimuli were used in that study. The present study used Parkinsonian speech stimuli. Because the speech of Parkinson’s Disease (PD) patients is monotonal, it naturally forms a reduced tonal space (the ratio between the speaker’s highest speaking F0 to the lowest), and thus the extreme-target distance should also be reduced. The results of the study confirmed the Wong and Diehl findings with natural PD speech, and showed that in addition to the extreme-target distance, the tonal space among the target tones themselves also affects tone perception; the smaller the tonal space, the worse the perception. Relation between misperception and tonal contours will also be discussed. [Work supported by NIDCD.]
Temporal integration and multiple looks, revisited: Weights as a function of time
Authors: Buus So/ren
Published: July 2002

This study tests the hypothesis that temporal integration for detection of tone bursts with various durations can be explained by optimally combining multiple looks of brief signal segments whose contribution to detection increases over time. Detectability was measured for signals consisting of six consecutive 25-ms, 1-kHz tone pulses presented in a 50-Hz-wide masker or in maskers consisting of seven 50-Hz-wide noises, one critical band apart, with either coherent or incoherent envelopes. The level of each signal pulse varied randomly around masked threshold according to a Gaussian distribution. The slopes of conditional psychometric functions—plotted in terms of d′2 as a function of the squared signal-pulse intensity for pulses in a particular temporal position—yielded estimates of the contribution to detection provided by each pulse. Results for three normal listeners showed a small, but significant, effect of the temporal location of the pulse. Multiple-looks predictions of temporal-integration functions based on the measured weights and on measured psychometric functions were compared to measured temporal-integration functions. For the single-band and incoherent maskers, the predicted temporal-integration slopes were reasonably consistent with those measured, but for the coherent masker it was not. Whereas no current theory can explain the very steep temporal-integration functions obtained in the coherent masker, the present results are not inconsistent with the multiple-looks hypothesis as an explanation for the decrease in threshold with increasing duration of signals presented in random maskers.
Center frequency modulation detection for harmonic complexes resembling vowel formants and its interference by off-frequency maskers
Authors: Lyzenga J. , Carlyon R. P.
Published: July 2002

Vowels are characterized by peaks in their spectral envelopes: the formants. To gain insight into the perception of speech as well as into the basic abilities of the ear, sensitivity to modulations in the positions of these formants is investigated. Frequency modulation detection thresholds (FMTs) were measured for the center frequency of formantlike harmonic complexes in the absence and in the presence of simultaneous off-frequency formants (maskers). Both the signals and the maskers were harmonic complexes which were band-pass filtered with a triangular spectral envelope, on a log-log scale, into either a LOW (near 500 Hz), a MID (near 1500 Hz), or a HIGH region (near 3000 Hz). They had a duration of 250 ms, and either an 80- or a 240-Hz fundamental. The modulation rate was 5 Hz for the signals and 10 Hz for the maskers. A pink noise background was presented continuously. In a first experiment no maskers were used. The measured FMTs were roughly two times larger than previously reported just-noticeable differences for formant frequency. In a second experiment, no significant differences were found between the FMTs in the absence of maskers and those in the presence of stationary (i.e., nonfrequency modulated) maskers. However, under many conditions the FMTs were increased by the presence of simultaneous modulated maskers. These results indicate that frequency modulation detection interference (FMDI) can exist for formantlike complex tones. The FMDI data could be divided into two groups. For stimuli characterized by a steep (200-dB/oct) slope, it was found that the size of the FMDI depended on which cues were used for detecting the signal and masker modulations. For stimuli with shallow (50-dB/oct) slopes, the FMDI was reduced when the signal and the masker had widely differing fundamentals, implying that the fundamental information is extracted before the interference occurs.
Bottom reverberation in shallow water: Coherent properties as a function of bandwidth, waveguide characteristics, and scatterer distributions
Authors: LePage Kevin
Published: July 2002

Shallow water presents a difficult, reverberation-limited environment for active SONAR operations. It is important to understand the predictable structure of shallow-water reverberation in order to aid the design of processors and detectors which work properly in these environments. In this paper, the temporal characteristics of monostatic reverberation are predicted as a function of source bandwidth, source–receiver depth, and the propagation characteristics of range-independent shallow water. Results show that at early time, reverberation can be highly coherent across a vertical line array, violating the homogeneous noise assumption, while at late time the reverberation becomes increasingly uncorrelated. This is shown to be due to the insonification of independent bottom patches at late time. It is also shown that this decorrelation of the reverberation is dependent both on the propagation characteristics of the particular shallow-water environment, the correlation length scale of the scatterers, and the bandwidth of the source, with high-bandwidth sources causing decorrelated reverberation sooner than low-bandwidth sources. The results also show that there are several identifying characteristics in reverberation time series which may be useful for identifying the types of scatterers which cause reverberation during particular experiments.
Reverberation time and maximum background-noise level for classrooms from a comparative study of speech intelligibility metrics
Authors: Bistafa Sylvio R. , Bradley John S.
Published: July 2002

Speech intelligibility metrics that take into account sound reflections in the room and the background noise have been compared, assuming diffuse sound field. Under this assumption, sound decays exponentially with a decay constant inversely proportional to reverberation time. Analytical formulas were obtained for each speech intelligibility metric providing a common basis for comparison. These formulas were applied to three sizes of rectangular classrooms. The sound source was the human voice without amplification, and background noise was taken into account by a noise-to-signal ratio. Correlations between the metrics and speech intelligibility are presented and applied to the classrooms under study. Relationships between some speech intelligibility metrics were also established. For each noise-to-signal ratio, the value of each speech intelligibility metric is maximized for a specific reverberation time. For quiet classrooms, the reverberation time that maximizes these speech intelligibility metrics is between 0.1 and 0.3 s. Speech intelligibility of 100% is possible with reverberation times up to 0.4–0.5 s and this is the recommended range. The study suggests “ideal” and “acceptable” maximum background-noise level for classrooms of 25 and 20 dB, respectively, below the voice level at 1 m in front of the talker.
Effects of pitch-shift velocity on voice F0 responses
Authors: Larson Charles R. , Burnett Theresa A. , Kiran Swathi , Hain Timothy C.
Published: July 2002

Previous studies have shown that voice fundamental frequency (F0) is modified by changes in the pitch of vocal feedback and have demonstrated that the audio–vocal control system has both open- and closed-loop control properties. However, the extent to which this system operates in closed-loop fashion may have been underestimated in previous work. Because the step-type stimuli used were very rapid, and people are physically unable to change their voice F0 as rapidly as the stimuli, feedback responses might have been reduced or suppressed. In the present study, pitch-shift stimuli, consisting of a disparity between voice F0 and feedback pitch of varying ramp onset velocities, were presented to subjects vocalizing a steady /ah/ sound to examine the effect of stimulus onset on voice F0 responses. Results showed that response velocity covaried with stimulus velocity. Response latency and time of the peak response decreased with increases in stimulus velocity, while response magnitude decreased. A simple feedback model reproduced most features of these responses. These results strongly support previous suggestions that the audio-vocal system monitors auditory feedback and, through closed-loop negative feedback, adjusts voice F0 so as to cancel low-level fluctuations in F0.
Indications of different distortion product otoacoustic emission mechanisms from a detailed f1,f2 area study
Authors: Knight Richard D. , Kemp David T.
Published: July 2002

The primary site of generation on the basilar membrane for the 2 f1–f2 distortion product (DP) is generally considered to be near where the higher-frequency stimulus tone peaks. This site has also been shown to be a source of DP otoacoustic emission (DPOAE) in the ear canal, but a second source of emission is known to exist in the region of the DP frequency place. The DPOAE phase versus frequency gradient provides a means of investigating the emission mechanisms. “Wave-fixed” and “place-fixed” mechanisms have been proposed to account for the very different phase gradients found depending on whether the 2 f1–f2 DPOAE is evoked by a small or large stimulus-frequency ratio. DPOAE phase versus frequency gradients can be investigated either by sweeping f1,f2 or by sweeping both frequencies maintaining a constant frequency ratio. Each manipulation gives only a partial description of DP behavior. In this study, the place-fixed/wave-fixed dichotomy is analyzed using extensive 2 f1–f2 and 2 f2–f1 DP stimulus-frequency sweep data presented on matrices of f1 vs f2 and f2/f1 ratio versus DP frequency. These show how the DPs are related and provide a more complete picture of 2 f1–f2 and 2 f2–f1 DPOAE phase and amplitude versus frequency behavior. The phase data contain evidence for a systematic variation in the proportions of wave- and place-fixed emission. The results suggest that 2 f1–f2 DPOAEs with a wide stimulus frequency ratio are wave fixed, while all other DPOAEs are place fixed. A transition occurs within the 2 f1–f2 DP data region at a frequency ratio of about f2/f1=1.1. The 2 f1–f2 DP and 2 f2–f1 DP phase behavior is continuous across the f2/f1=1 boundary. As the 2 f2–f1 DP generation region must be strongly influenced by the DP frequency place, the results imply that the place-fixed component of the 2 f1–f2 DP is also linked to its frequency place. A similar pattern was obtained with the 3f1–2 f2 and 3f2–2 f1 DPs. The results support the following model: For the limited set of stimulus conditions that gives rise to 2 f1–f2 wave-fixed emissions, DP energy is largely generated in the f2 region and is emitted directly. All other DPOAEs are place-fixed emissions, and while nonlinearity within the f2 stimulus envelope remains the generator, the DP is not directly emitted but travels apically until it is re-emitted basally via a separate reflection mechanism in the region of the DP place.
Three-dimensional numerical modeling for global cochlear dynamics
Authors: Parthasarathi Anand A. , Grosh Karl , Nuttall Alfred L.
Published: July 2002

A hybrid analytical-numerical model using Galerkin approximation to variational equations has been developed for predicting global cochlear responses. The formulation provides a flexible framework capable of incorporating morphologically based mechanical models of the cochlear partition and realistic geometry. The framework is applied for a simplified model with an emphasis on application of hybrid methods for three-dimensional modeling. The resulting formulation is modular, where matrices representing fluid and cochlear partition are constructed independently. Computational cost is reduced using two methods, a modal–finite-element method and a boundary element–finite-element method. The first uses a cross-mode expansion of fluid pressure (2.5D model) and the second uses a waveguide Green’s-function-based boundary element method (BEM). A novel wave number approach to the boundary element formulation for interior problem results in efficient computation of the finite-element matrix. For the two methods a convergence study is undertaken using a simplified passive structural model of cochlear partition. It is shown that basilar membrane velocity close to best place is influenced by fluid and structural discretization. Cochlear duct pressure fields are also shown demonstrating the 3D nature of pressure near best place.
Broadband control of plate radiation using a piezoelectric, double-amplifier active-skin and structural acoustic sensing
Authors: Johnson Brody D. , Fuller Chris R.
Published: July 2002

The potential of a piezoelectric, double-amplifier active-skin with structural acoustic sensing (SAS) is demonstrated for the reduction of broadband acoustic radiation from a clamped, aluminum plate. The active-skin is a continuous covering of the vibrating portions of the plate with active, independently controllable piezoelectric, double-amplifier elements and is designed to affect control by altering the continuous structural radiation impedance rather than structural vibration. In simulation, acoustic models are sought for the primary and secondary sources that incorporate finite element methods. Simulation indicates that a total radiated power attenuation in excess of 10 dB may be achieved between 250 and 750 Hz with microphone error sensing, while under SAS the radiated power is reduced by nearly 8 dB in the same frequency range. In experiment, the adaptive feed forward filtered-x LMS (least mean square) algorithm, implemented on a Texas Instruments C40 DSP, was used in conjunction with the 6I6O control system. With microphone error sensing, 11.8-dB attenuation was achieved in the overall radiated power between 175 and 600 Hz, while inclusion of SAS resulted in a 7.3-dB overall power reduction in this frequency band.
A mapping approach for handling sloping interfaces
Authors: Collins Michael D. , Dacol Dalcio K.
Published: July 2002

A mapping approach for handling sloping interfaces in parabolic equation solutions is developed and tested. At each range, the medium is rigidly translated vertically so that a sloping interface becomes horizontal. To simplify the approach, the slope is assumed to be small and the extra terms that arise in the wave equation under the mapping are neglected. The effects of these terms can be approximately accounted for by applying a leading-order correction to the phase. The mapping introduces variations in topography, which are relatively easy to handle for the case of a pressure-release boundary condition. The accuracy of the approach is demonstrated for problems involving fluid sediments. The approach should also be accurate for problems involving elastic sediments and should be useful for solving three-dimensional problems involving variable topography.
Estimation of fuzzy structure parameters for continuous junctions
Authors: Soize Christian , Bjaoui Karina
Published: July 2002

The fuzzy structure theory introduced 15 years ago is designed to predict the frequency response functions of structures and structural acoustic systems with structural complexity, in the low- and medium-frequency ranges. This paper constitutes a first validation of the fuzzy structure theory for continuous junctions between the master structure and the fuzzy substructures. In addition, a method to estimate the fuzzy structure parameters introduced in the fuzzy structure theory is presented and it is validated for the case of continuous junctions. This validation obtained by numerical simulations opens the field of experimental identifications.
Circular asymmetric Helmholtz resonators
Authors: Selamet A. , Ji Z. L.
Published: July 2002

A three-dimensional (3D) analytical approach is developed to account for the nonplanar wave propagation in the cavity and neck of “piston-driven” circular asymmetric Helmholtz resonators. The present 3D analytical results are compared with (1) the numerical predictions from the boundary element method (BEM) to evaluate the analytical approach; and (2) the one-dimensional (1D) solution to examine the effect of nonplanar waves at area discontinuity between the neck and the cavity. In order to improve the 1D solution, the end correction is also determined by using the 3D analytical approach. The effect of neck offset on the resonance frequency of circular asymmetric Helmholtz resonators is investigated. Predictions of resonance frequency and transmission loss from the present 3D and corrected 1D analytical approaches are, respectively, identical and close to the BEM results, while the corrected 1D approach provides a better accuracy compared to the 1D solutions with Ingard’s correction. Finally, the boundary element method is employed to determine the wave attenuation performance of the “pipe-mounted” Helmholtz resonators to examine the effect of multidimensional waves in the vicinity of the main duct and neck junction.
Evolution of the vibrational behavior of a guitar soundboard along successive construction phases by means of the modal analysis technique
Authors: Elejabarrieta M. J. , Ezcurra A. , Santamarı́a C.
Published: July 2002

The crucial piece of a craft guitar is the soundboard since it determines the quality of the sound given by the instrument. From the initial phase (the gross plate with no hole) until the last construction phase (the plate with the full structure) several stages are followed to modify the dynamic behavior of the structure and hence the acoustic response of the final guitar. The aim of this work is to analyze the effect of each modification on the vibrational response of the plate. With this in mind, an experimental modal analysis of all the construction phases has been performed in the low frequency range under free conditions. The response of the plate in each stage is defined by vibration patterns, resonance frequencies, quality factors, and admittance curves.
Molecular Fractionation in the Flow of Polymeric Fluids
Authors: Schreiber H. P. , Storey S. H. , Bagley E. B.
Published: July 2002

The kinetic theory of liquids has been used to derive two crude models which rationalize the establishment of a molecular weight gradient during the capillary extrusion of polydisperse thermoplastic melts. A molecular weight decrease near the polymer/die wall interface is predicted along with a decay in the degree of extrudate swelling with increasing die length, each model giving equations relating decay rate with die dimensions and shear rate. Polyethylene data indicate some shortcomings in the theory, but both models fit experimental extrudate swelling data well, and appreciably better than an empirical equation of exponential decay. Further in keeping with theory, surface sections of broad molecular weight distribution polyethylene extrudates have lower molecular weights than whole extrudates, the magnitude of the effect increasing with increasing die length. No significant molecular effect was found for a fractionated linear polyethylene. The decay in extrudate swelling was also found to be much greater for broad molecular weight polyethylene samples than for the fractionated polymer. It is suggested that molecular fractionation in capillary flow is a significant contributing cause to the difference in die length variation of melt viscosity and melt elasticity.
Time-Temperature Strain and Molecular Weight Effects in the Environmental Stress Cracking of 0.95 Density Polyethylene
Authors: Fulmer Glenn E.
Published: July 2002

Reduced variables of time-temperature and molecular weight are used to describe the stress relaxation failure of 0.95 density polyethylene in a stress cracking agent, Igepal CO-630. This method was previously shown to work for 0.96 density linear polyethylene. The 0.95 density polyethylene has an apparent activation energy of 38 kcal for stress cracking. This is appreciably higher than the 22 kcal found for 0.96 density linear polyethylene. A much higher dependence on molecular weight was also found. The 0.95 density polyethylene has a lifetime that is proportional to Mv5.8 while the 0.96 density polyethylene has a lifetime proportional to Mv3.4. Some data are also shown which indicate a difference in the sensitivity to strain for the two materials. This can lead to appreciably longer lifetimes for the 0.95 density polyethylene at low strain.
Large Multi-Axial Deformation Behavior of a Filled Rubber
Authors: Valanis K. C. , Landel R. F.
Published: July 2002

Biaxial and uniaxial stress relaxation data are used to show that dimethyl siloxane rubber containing 28 wt.-% SiO2 as filler, exhibits, in the presence of large deformation, material behavior which is “viscoelastic” in the sense that it can be described, accurately, by the rheological equations of finite linear viscoelasticity. In particular, a constitutive equation for this material is found which contains three relaxation functions all of which are (a) proportional to the same function of time and are (b) independent of the deformation.
Relaxation in Polyurethanes in the Glass Transition Region
Authors: Kajiyama T. , MacKnight W. J.
Published: July 2002

A study has been made of the relaxation phenomena in three series of polyurethanes in the neighborhood of their glass transition temperatures and above. The technique of dynamic mechanical relaxation was used in the investigation at various frequencies up to 110 Hz. Differential Scanning Calorimetry (DSC) was also used as a supplement to the mechanical measurements. The series are: (1) H series based on polymerization of hexamethylene diisocyanate and various diols, (2) DP series based on polymerization of 4,4′ diphenylmethane diisocyanate and various diols, and (3) 4M series based on polymerization of 4-methyl meta phenylene diisocyanate and various diols. Four relaxation regions are discernible in the temperature range investigated and these are labelled β, α, αt and αc in order of increasing temperature. The following molecular mechanisms are associated with these relaxations: (1) The β relaxation (DP and 4M series only) arises from phenyl group motion in the chain backbone, (2) the α relaxation (all series) arises from microbrownian segmental motion associated with the glass transition, (3) the αt relaxation (H series only) is associated with a solid-solid phase transition involving the change from one crystalline modification to another, (4) the αc relaxation (H and DP series only) involves rotational or translational motion of the chains in the crystalline phase.
Stability of Viscoelastic Fluids: Plane Couette Flow with Superposed Temperature Gradient
Authors: McIntire L. V. , Schowalter W. R.
Published: July 2002

A linearized stability analysis has been applied to a fluid flowing in a gravity field between horizontal planes in Couette flow under conditions such that the temperature of the bottom plane exceeds that of the top. The analysis was carried out for two different forms of constitutive equations: (1) a “generalized second-order equation,” which is a differential model usually associated with continuum theories, and (2) an integral equation which has its basis in a molecular model and accounts for network junctions which rupture at a certain critical strain. Both models lead, after application of a number of simplifying assumptions, to the same set of differential equations which must be satisfied at a condition of nonoscillatory marginal stability. In contrast to the case for Newtonian fluids, there is coupling between the equations describing momentum and energy disturbances. This fact leads, for viscoelastic fluids, to a critical Rayleigh number which is dependent upon flow properties. In particular, the critical Rayleigh number is highly sensitive to the sign and magnitude of the second normal stress difference, a result shared with earlier studies of some other stability problems. Significance of the results is discussed.
Modifications of an R-16 Weissenberg Rheogoniometer
Authors: Lee K. H. , Jones L. G. , Pandalai K. , Brodkey Robert S.
Published: July 2002

In the course of our work on the characterization of materials by our kinetic interpretation of non-Newtonian flow, it had become desirable to make measurements other than at steady state constant shear rate and the sudden application of a steady shear. The present paper describes four modifications we have made and used: (1) a torque detection system to eliminate upper cone motion during transient and oscillatory measurements; (2) measurements under both unsteady and steady state condition in a constant stress field; (3) a versatile and inexpensive oscillatory capability to allow both amplitude and frequency variation of nearly any wave form desired; and, finally, (4) the measurement of the primary normal force difference under any conditions, with essentially no change in gap setting. Examples of typical results on a concentrated polymer solution are presented.
Kinematics of Deformable Suspensions
Authors: Allen S. J. , Kline K. A. , Ling C. C.
Published: July 2002

In this paper we investigate the ability of recent microstructure theories of fluid mechanics to explain the behavior of polyisobutylene. In particular it is shown that a director microstructure theory yields a natural explanation of the observed “tank-tread” motion of the macromolecules as well as shear rate dependence of apparent viscosity and normal stress differences. This is accomplished by means of linear constitutive equations involving only four new material coefficients.
Nonlinear Viscoelastic Properties of Semisolid Emulsions
Authors: Komatsu Hideo , Mitsui Takeo , Onogi Shigeharu
Published: July 2002

The dynamic viscoelastic properties of semisolid emulsions (commercial cosmetic creams) at 25°C were measured by means of a Weissenberg rheogoniometer at frequencies ranging from 1.582×10−3 to 1.582 Hz. In general, these emulsions manifested remarkable nonlinear viscoelasticity even at very small strains; when sinusoidal strains were applied to the emulsions, the resultant stresses were not sinusoidal, in marked contrast to the case in ordinary linear viscoelastic materials. Such nonsinusoidal stresses were analyzed by the method proposed by Onogi et al. to give nonlinear viscoelastic functions. The frequency dependences of these nonlinear functions for the emulsions were quite different from those of the viscoelastic functions for polymer solutions or melts, especially in the low frequency range; the viscoelastic functions for the semisolid emulsions showed second plateaus lower than the so-called rubbery plateau. Some considerations concerning the origin of the nonsinusoidal stresses were given, and it was concluded that the origin was the dynamic yield stress which was originated from the structure in the semisolid emulsions.
Nonlinear Viscoelasticity of Polymer Melts
Authors: Tee T.-T. , Dealy J. M.
Published: July 2002

Large amplitude oscillatory shear has been employed to study the nonlinear viscoelastic properties of three polymer melts. The resins studied included a DuPont high-density polyethylene, a Union Carbide low-density polyethylene, and a Dow polystyrene. The equipment used consisted of a small-gap, concentric cylinder rheometer with a controlled-speed motor unit and a rack-pinion, oscillating drive mechanism. The torque was monitored by means of a torquemeter based on magnetic stress anisotropy in a steel tube and the strain was monitored by means of a displacement transducer. A signal proportional to the rate of strain was generated by integrating the strain with respect to time. Strain amplitudes up to 10 and frequencies between 0.5 and 30 sec−1 were employed. For purposes of material characterization, plots of stress versus rate-of-strain are employed. This is a closed stationary curve. Its “openness” is an indication of elasticity and its deviation from an elliptical shape is an indication of nonlinearity. Three material functions, obtainable from these curves, are defined and used for characterization. The first function is the amplitude ratio; the second function is related to the extent of the elastic component of the response, and the third one is a measure of nonlinearity. It was found that the extent of nonlinearity in the response is primarily a function of the strain amplitude rather than the frequency. The amplitude below which the response is practically linear depends strongly on the molecular structure. The response of the high-density polyethylene was practically linear up to a strain amplitude of 10.
Effect of Hard Segment Chemical Structure on the Processibility of Organo-Siloxane Block Copolymers
Authors: Matzner M. , Noshay A. , McGrath J. E.
Published: July 2002

A series of polydimethylsiloxane based multiblock [AB]n copolymers was prepared and characterized. The hard blocks included poly(aryl ethers), poly(aryl esters), poly(aryl carbonates), a poly(cycloaliphatic carbonate), polystyrene, and poly(α-methylsytrene). All of these materials could be solution cast into films which had attractive physical properties and which displayed two-phase behavior. However, their rheological characteristics (in particular their melt processibility) were found to differ dramatically when the chemical structure of the hard block was varied. Thus, the polysulfone-polydimethylsiloxane block copolymer could not even be satisfactorily compression molded owing to its inordinately high melt viscosity and melt elasticity. On the other hand, the copolymer prepared from the polycarbonate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol could be readily molded and extruded. The behavior is believed to be related to the retention of a physical network at temperatures well above the upper glass transition. Available data are in agreement with this interpretation. It is proposed that processibility characteristics of block copolymers are related to the intersegment solubility parameter differential, Δ. Our preliminary results suggest that an optimum balance of engineering properties and processibility in two-phase block or graft copolymers should be observed when the value of Δ is approximately unity. For crystallizable systems, the Δ value in the polymer melt should be essentially zero, if one or both of the segments can subsequently crystallize and hence induce microphase separation.
Powder X-ray diffraction of oriented and intercalated lead iodide
Authors: Schaeffer Richard W. , Ardelean Monica
Published: July 2002

Polycrystalline lead iodide, PbI2, was recrystallized from hot water to reproducibly obtain flat plate-like crystals, which manifested extreme preferred orientation greatly favoring the 001, 002, 003, and 004 planes. Polycrystalline samples of PbI2 were intercalated with tripropylamine, simultaneously producing a “new” intercalate 001 peak at 7.791°2θ (d=1.1347 nm) and diminishing the host PbI2 001 peak at 12.67°2θ (d=0.6980 nm). This is consistent with large increases in the c direction of the unit cell associated with inserting a guest between adjacent iodide layers of the host PbI2. Experimental powder diffraction results are compared to theoretical values calculated using CRYSTALMAKER and CRYSTALDIFFRACT software
Development of ferrocene‐appended benzimidazopyridine and pyrroloquinoxaline probes for structure regulated distinct signalling of Fe3+ in aqueous media and HeLa cells
Authors: Srivastava Suman , Thakur Neha , Nayak Namyashree , Garg Neha , Pandey Rampal
Published: April 2022

Two ferrocenyl (Fc) derivatives Fc‐benzimidazopyridine (5) and Fc‐pyrroloquinoxaline (6) have been synthesized through an inexpensive and metal‐free approach and via tailoring the reaction conditions. X‐ray single crystal analysis revealed that same reactants in the presence of different reagents and reaction condition afforded structurally distinct products 5 and 6. Markedly, 5 and 6 act as fluorescent probes for Fe3+ through discrete signalling with high selectivity and ppb level sensitivity. Based on the fluorescence changes, Job's plot, 1H NMR titration and mass spectral studies, it has been proposed that the probe‐metal binding stoichiometry and nitrogen atoms present at different positions in 5 and 6 lead to the distinct fluorescent signalling (turn‐on for 5 and turn‐off for 6). Further, it has been observed that position of donor atom plays major role in fluorescence signalling and probe‐cation stoichiometry. This work reports deeper insights and straightforward comparison between 5 and 6 in terms of exactly opposite fluorescence detection behaviour towards Fe3+ in aqueous media as well as cell lines to the best of our knowledge.
Obtaining biologically active substances from Amaranthus caudatus L. seeds in one technological cycle
Authors: Korabel Ivan M. , Panchak Lidiia V. , Zyn Alina R. , Antonyuk Volodymyr O.
Published: April 2022

Nowadays, amaranth is a valuable multipurpose crop and a source of a number of very important biologically active substances. The aim of this study was to develop a comprehensive scheme for obtaining fatty oil, triterpenoids and lectin from the seeds of Amaranthus caudatus L. in one technological cycle. Two variants of the lectin and triterpene compound purification method from amaranth seeds were tested. It was determined that the extraction of triterpene compounds should be carried out after purification of the lectin from degreased seeds. The rationality of this sequence of technological operations is explained by the lability of the lectin and the insolubility in water of triterpene compounds from amaranth seeds. The study also presents a scheme for obtaining squalene from amaranth oil by chromatography on silica gel and proposes a more effective affinity sorbent for purification of the lectin. The use of such a sorbent also opens up the possibility of preserving other water‐soluble substances from amaranth seeds. The physicochemical characteristics and carbohydrate specificity of the lectin are described and new data on the results of the interaction of lectin with human and animal erythrocytes are given. The obtained results are discussed in the light of the complex use of raw materials.