Amplitude Rise Time Research Articles

Estimating Soil Water Content from Permittivity for Different Mineralogies and Bulk Densities

Time domain reflectometry (TDR) exploits the difference in dielectric permittivity between the soil solid, gas, and liquid phases and has become increasingly popular for the determination of soil water content. The electromagnetic determination of water content in soils with high clay contents requires a good understanding of the main factors that affect the relationship between the dielectric permittivity of clay minerals and soil water content. The objectives of this study were to: (i) investigate the relationships among soil bulk density, clay content, clay mineralogy, and the soil dielectric permittivity, and (ii) evaluate the performance of the approach to correct the dissipation effects due to high clay contents. Samples were taken from five areas with different textures and bulk densities, both topsoils and subsoils. Soil physical properties, i.e., organic matter, clay, silt, and sand contents, and clay mineralogy were determined. High clay contents caused an underestimation of soil water content in the low moisture range and its overestimation in the high moisture range. Results also demonstrated that soils with similar clay contents but different mineralogies showed different permittivity values. For soil samples with equal water contents, soils with higher bulk density, or lower porosity, had a larger permittivity than soils with low bulk density and high porosity. This behavior was the result of the increase in the ratio of solid particle volume to air because the solid particles have a larger dielectric permittivity than air. Soil bulk density and clay content impact the accuracy and calibration of TDR. Smectites also cause signal attenuation and dispersion, resulting in smaller signal amplitude and longer rise time. In addition, smectites cause dispersion of the reflected signal, resulting in a longer rise time.

Efficient high voltage pulser for piezoelectric air coupled transducer

The design of high voltage pulser for air coupled ultrasound imaging is presented. It is dedicated for air-coupled ultrasound applications when piezoelectric transducer design is used. Two identical N-channel MOSFETs are used together with 1200V high and low side driver IC. Simple driving pulses’ delay and skew circuit is used to reduce the cross-conduction. Analysis of switch peak current and channel resistance relation to maximum operation frequency and load capacitance is given. PSPICE simulation was used to analyze the gate driver resistance, gate pulse skew, pulse amplitude influence on energy consumption when loaded by capacitive load. Experimental investigation was verified against simulation and theoretical predictions. For 500pF capacitance, which is most common for piezoelectric air coupled transducers, pulser consumes 650μJ at 1kV pulse and 4μJ at 50V. Pulser is capable to produce up to 1MHz pulse trains with positive 50V–1kV pulses with up to 10A peak output current. When loaded by 200kHz transducer at 1kV pulse amplitude rise time is 40ns and fall time is 32ns which fully satisfies desired 1MHz bandwidth.

Low-level deficits in beat perception: Neither necessary nor sufficient for explaining developmental dyslexia in a consistent orthography

This article reports two different studies examining the theoretical account of low-level deficits in beat perception as an alternative explanation of developmental dyslexia in Greek, an orthographically consistent language. Study I examined the relationship of amplitude rise time and frequency discrimination with measures of phonological processing, working memory, and reading fluency in a large unselected sample of Grade 4 children. Study II examined the presence of beat perception deficits in groups of Grade 2, 4, and 6 children with dyslexia and their chronological age controls. The results provided no evidence to support meaningful associations between beat perception tasks and reading or the theoretical account of beat perception deficits as a sufficient explanation or contributing factor to dyslexia. Implications on the importance of auditory processing in reading in orthographically consistent languages are discussed.

Impaired non-speech auditory processing at a pre-reading age is a risk-factor for dyslexia but not a predictor: An ERP study

Impaired auditory sensitivity to amplitude rise time (ART) has been suggested to be a primary deficit in developmental dyslexia. The present study investigates whether impaired ART-sensitivity at a pre-reading age precedes and predicts later emerging reading problems in a sample of Dutch children. An oddball paradigm, with a deviant that differed from the standard stimulus in ART, was administered to 41-month-old children (30 genetically at-risk for developmental dyslexia and 14 controls) with concurrent EEG measurement. A second deviant that differed from the standard stimulus in frequency served as a control deviant. Grade two reading scores were used to divide the at-risks in a typical-reading and a dyslexic subgroup. We found that both ART- and frequency processing were related to later reading skill. We however also found that irrespective of reading level, the at-risks in general showed impaired basic auditory processing when compared to controls and that it was impossible to discriminate between the at-risk groups on basis of both auditory measures. A relatively higher quality of early expressive syntactic skills in the typical-reading at-risk group might indicate a protective factor against negative effects of impaired auditory processing on reading development. Based on these results we argue that ART- and frequency-processing measures, although they are related to reading skill, lack the power to be considered single-cause predictors of developmental dyslexia. More likely, they are genetically driven risk factors that may add to cumulative effects on processes that are critical for learning to read.

Simultaneous monitoring of static and dynamic intracranial pressure parameters from two separate sensors in patients with cerebral bleeds: comparison of findings

BackgroundWe recently reported that in an experimental setting the zero pressure level of solid intracranial pressure (ICP) sensors can be altered by electrostatics discharges. Changes in the zero pressure level would alter the ICP level (mean ICP); whether spontaneous changes in mean ICP happen in clinical settings is not known. This can be addressed by comparing the ICP parameters level and waveform of simultaneous ICP signals. To this end, we retrieved our recordings in patients with cerebral bleeds wherein the ICP had been recorded simultaneously from two different sensors. Materials and Methods: During a time period of 10 years, 17 patients with cerebral bleeds were monitored with two ICP sensors simultaneously; sensor 1 was always a solid sensor while Sensor 2 was a solid -, a fluid - or an air-pouch sensor. The simultaneous signals were analyzed with automatic identification of the cardiac induced ICP waves. The output was determined in consecutive 6-s time windows, both with regard to the static parameter mean ICP and the dynamic parameters (mean wave amplitude, MWA, and mean wave rise time, MWRT). Differences in mean ICP, MWA and MWRT between the two sensors were determined. Transfer functions between the sensors were determined to evaluate how sensors reproduce the ICP waveform.ResultsComparing findings in two solid sensors disclosed major differences in mean ICP in 2 of 5 patients (40%), despite marginal differences in MWA, MWRT, and linear phase magnitude and phase. Qualitative assessment of trend plots of mean ICP and MWA revealed shifts and drifts of mean ICP in the clinical setting. The transfer function analysis comparing the solid sensor with either the fluid or air-pouch sensors revealed more variable transfer function magnitude and greater differences in the ICP waveform derived indices.ConclusionsSimultaneous monitoring of ICP using two solid sensors may show marked differences in static ICP but close to identity in dynamic ICP waveforms. This indicates that shifts in ICP baseline pressure (sensor zero level) occur clinically; trend plots of the ICP parameters also confirm this. Solid sensors are superior to fluid – and air pouch sensors when evaluating the dynamic ICP parameters.

Estimation of Impulsive Noise in an Electricity Substation

Measurements of impulsive noise in a 400/275/132-kV electricity substation are presented. The measurements are made with three antennas having overlapping bands covering the range 100 MHz-6 GHz. This range includes those bands relevant to modern wireless local area network and wireless personal area network technologies (e.g., IEEE 802.11a/b/g and IEEE 802.15.1/4), which, if proved to be sufficiently robust in the presence of impulsive noise, could play a useful role in substation monitoring and control. Impulsive events are extracted from the measured data using the wavelet packet transform, and the statistical distributions of pulse rate, pulse amplitude, pulse duration, and pulse rise time are presented. An unexpected quasi-periodic component of the noise is observed.

Reduced sensitivity to slow-rate dynamic auditory information in children with dyslexia

The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade.

Common variance in amplitude envelope perception tasks and their impact on phoneme duration perception and reading and spelling in Finnish children with reading disabilities

ABSTRACTOur goal was to investigate auditory and speech perception abilities of children with and without reading disability (RD) and associations between auditory, speech perception, reading, and spelling skills. Participants were 9-year-old, Finnish-speaking children with RD (N = 30) and typically reading children (N = 30). Results showed significant group differences between the groups in phoneme duration discrimination but not in perception of amplitude modulation and rise time. Correlations among rise time discrimination, phoneme duration, and spelling accuracy were found for children with RD. Those children with poor rise time discrimination were also poor in phoneme duration discrimination and in spelling. Results suggest that auditory processing abilities could, at least in some children, affect speech perception skills, which in turn would lead to phonological processing deficits and dyslexia.

Very Fast Rise-Time Short-Pulse High-Voltage Generator

This paper relates to the development of an ultrafast compact system readily applicable to the field of ultrawideband microwave applications such as transient radar or laser drivers. The design, production, and experimental results of a short-pulse generation system are presented in this paper. The coaxial generator technology based on the principle of a line discharge by means of a high-pressure gas switch in a simple transmission line arrangement is described. In the first stage of the process, the coaxial generator was charged by a high-voltage direct current source. Interesting results were obtained, but due to the jitter of the discharge formative time, the reproducibility of the output pulses was not sufficient. To improve the performance, a pulsed source was developed in order to apply an overvoltage to the gap switch and thus reduce the jitter of the discharge formative time. The characteristics of the pulsed source are defined. A thyristor Marx generator and a pulse transformer using magnetic properties of ferrite cores were combined in order to produce this pulsed source. The main performances of this source are a pulse amplitude of 60 kV, a rise time of 250 ns, and a maximum frequency of 900 Hz from a 1-kV dc supply. Finally, the complete generation system is able to generate pulses with 25-kV amplitude and 70-ps rise time through a 50-Omega impedance from the single shot mode up to 900 Hz. The output pulses reproducibility obtained is better than plusmn5%

Glial Glutamate Transporters Maintain One-to-One Relationship at the Climbing Fiber-Purkinje Cell Synapse by Preventing Glutamate Spillover

A glial glutamate transporter, GLAST, is expressed abundantly in Bergmann glia and plays a major role in glutamate uptake at the excitatory synapses in cerebellar Purkinje cells (PCs). It has been reported that a higher percentage of PCs in GLAST-deficient mice are multiply innervated by climbing fibers (CFs) than in the wild-type (WT) mice, and that CF-mediated EPSCs with small amplitude and slow rise time, designated as atypical slow CF-EPSCs, are observed in these mice. To clarify the mechanism(s) underlying the generation of these atypical CF-EPSCs, we used (2S,3S)-3-[3-(4-methoxybenzoylamino)benzyloxy]aspartate (PMB-TBOA), an inhibitor of glial glutamate transporters. After the application of PMB-TBOA, slow-rising CF-EPSCs were newly detected in WT mice, and their rise and decay kinetics were different from those of conventional fast-rising CF-EPSCs but similar to those of atypical CF-EPSCs in GLAST-deficient mice. Furthermore, both slow-rising CF-EPSCs in the presence of PMB-TBOA in WT mice and atypical CF-EPSCs in GLAST-deficient mice showed much greater paired-pulse depression compared with fast-rising CF-EPSCs. In addition, both of them were more markedly inhibited by gamma-d-glutamyl-glycine, a low-affinity competitive antagonist of AMPA receptors. These results indicated that both of these types of EPSCs were mediated by a low concentration of glutamate released from neighboring CFs. Based on all of these findings, we suggest that glial transporters prevent glutamate released from a single CF from spilling over to neighboring PCs other than the synaptically connected PC, and play an essential role in the maintenance of the functional one-to-one relationship between CFs and PCs.

The modeling of the shock response of powdered ceramic materials

A two-cap constitutive model that incorporates inelastic yielding, frictional sliding, and densification was modified for shock-loading applications, and used to model shock-wave propagation of a powdered ceramic that is constrained by aluminum layers in a system, which is impacted by a flyer plate. The numerical results included analyses of the effects of shock stress amplitudes on densification, unloading behaviors, stress attenuation and dispersion, and stress and pressure distributions. An understanding of how interfacial impedances affect shock-front attenuation, dispersion, and propagation were obtained through modeling different shock-load conditions. The constitutive and computational models were validated with detailed simulations of shock-front experiments pertaining to powdered ceramics. It is shown how shock amplitude duration and rise time are related to stress evolution, and how physically limiting values result in inelastic damage. This analysis underscores how modeling with the appropriate constitutive description can provide insights on how powdered ceramics behave under impact-loading conditions.

Response of semi-insulating GaAs detectors to near-infrared picosecond light pulses

Semi-insulating gallium arsenide (SI-GaAs) detectors, in the form of Schottky diodes, have been irradiated from the front or from the back contact or from the side, with light pulses from picosecond laser source, tunable in the range of 780–1020 nm and focused to a 50–100 μm spot on the surface of the detector. Energy per pulse was in the range of 4–25 pJ, with a 10 or 100 Hz repetition rate. Each pulse mimics the interaction of a single energetic particle with the substrate, but with a photon mean free path modulated in the range of 1 μm–1 cm, depending on the light wavelength. The SI-GaAs substrates have a thickness of 200 μm (VGF grown), or 600 μm (LEC) or 1000 μm (VGF). The time response of the detectors, analysed with the Transient Current Technique (using a fast digital sampling oscilloscope) in terms of peak signal amplitude and charge rise time, has been evaluated as a function of: reverse voltage bias (50–1200 V), light wavelength (780–1020 nm), side position between the electrodes, position on the front contact. The results are: (1) the shape of the transient current signal may show the presence of two peaks, about 1 ns apart; (2) the charge rise time, considered to be dominated by the charge collection time, is between 2 and 13 ns; (3) the charge rise time, as due to electron drift or hole drift in the region between the contacts, has been measured as 2–5 ns, also dependent on the applied bias; (4) the transient current (exponential) decay time, for front or back irradiation, increases with the bias voltage up to 2–20 ns and these data are considered to be consistent with the electron detrapping time; (5) under reverse bias, for 1 mm pad side and a large ohmic contact on the back, the electric field extends around the front contact up to about 200 μm.

Analysis of microdamage evolution histories in composites

Evolution of microdamage in advanced composites was experimentally studied in this paper. A new method of acoustic emission (AE) analysis of histories of different damage mechanisms was formulated based on a combination of transient AE classification and multiparameter filtering. The capabilities of the method were illustrated on examples of damage evolution in several graphite/epoxy composites. Three characteristic AE waveforms with different frequency spectra were identified based on the transient analysis. Regions occupied by these waveforms in the amplitude–rise time parametric space were identified for the [0] 8 and [90] 16 unidirectional composites. Multiparameter filtering was applied to extract evolution histories for the characteristic waveforms. The results were compared with actual damage in the specimens and the three characteristic AE waveforms were associated with matrix cracks, fiber breaks, and ‘macrodamage’, such as delaminations or longitudinal splitting in unidirectional plies. The multiparameter filters based on the analysis of the unidirectional composites were used to extract the damage evolution histories for the cross-ply [0/90] 3S and angle-ply [±45] 4S composites. The results compared favourably with the observed damage in these materials. An inverse analysis of the quality of the multiparameter filtering for the laminated composites indicated that the filters developed for unidirectional composites can be applied to the analysis of laminated composites with reasonable reliability. The new method of acoustic emission analysis of damage micromechanisms is expected to be especially advantageous for fatigue damage evolution studies in composites and structures.

Neuromuscular system of the flexible arm of the octopus: physiological characterization.

The octopus arm is an outstanding example of an efficient boneless and highly flexible appendage. We have begun characterizing the neuromuscular system of the octopus arm in both innervated muscle preparations and dissociated muscle cells. Functionally antagonistic longitudinal and transverse muscle fibers showed no differences in membrane properties and mode of innervation. The muscle cells are excitable but have a broad range of linear membrane properties. They are electrotonically very compact so that localized synaptic inputs can control the membrane potential of the entire muscle cell. Three distinct excitatory neuronal inputs to each arm muscle cell were identified; their reversal potentials were extrapolated to be about -10 mV. These appear to be cholinergic as they are blocked by hexamethonium, D-tubocurarine, and atropine. Two inputs have low quantal amplitude (1-7 mV) and slow rise times (4-15 ms), whereas the third has a large size (5-25 mV) and fast rise time (2-4 ms). This large synaptic input is most likely due to exceptionally large quantal events. The probability of release is rather low, suggesting a stochastic activation of muscle cells. All inputs demonstrated a modest activity-dependent plasticity typical of fast neuromuscular systems. The pre- and postsynaptic properties suggest a rather direct relation between neuronal activity and muscle action. The lack of significant electrical coupling between muscle fibers and the indications for the small size of the motor units suggest that the neuromuscular system of the octopus arm has evolved to ensure a high level of precise localization in the neural control of arm function.

The discrimination of Mandarin Chinese alveolo-palatal fricative and affricate contrasts by American English and Mandarin Chinese speakers

This study examined how language experience affects the perceptual sensitivity of adult speakers to nonnative phonetic contrasts. Three of Mandarin contrasts (two alveolo-palatal fricative versus affricate contrasts and one alveolo-palatal affricate aspirated versus unaspirated contrast) were computer synthesized. For each of these three contrasts, three different variations were contrasted by varying either amplitude rise time or fricative noise duration. Both English and Mandarin speakers participated in a speech discrimination task using these stimuli. When compared to the performance of Mandarin speakers, English speakers showed poorer performance for each stimulus pair in terms of accuracy and sensitivity measures (d′). However, both English and Mandarin speakers demonstrated similar difficulty when tested with three stimulus pairs that were not typical exemplars of Mandarin phonetic categories. The results show the effect of language experience on the discrimination of phonetic contrasts. [Research supported by NIH grant to P. K. Kuhl.]

Implementation of dynamic bias for neutron–photon pulse shape discrimination by using neural network classifiers

In order to accurately determine dose equivalent in radiation fields that include both neutrons and photons, it is necessary to measure the relative number of neutrons to photons and to characterize the energy dependence of the neutrons. The relationship between dose and dose equivalent begins to increase rapidly at about 100 keV; thus, it is necessary to separate neutrons from photons for neutron energies as low as about 100 keV in order to measure dose equivalent in a mixed radiation field that includes both neutrons and photons. Preceptron and back propagation neural networks that use pulse amplitude and pulse rise time information obtain separation of neutron and photons with about 5% error for neutrons with energies as low as 100 keV, and this is accomplished for neutrons with energies that range from 100 keV to several MeV. If the ratio of neutrons to photons is changed by a factor of 10, the classification error increases to about 15% for the neural networks tested. A technique that uses the output from the preceptron as a priori for a Bayesian classifier is more robust to changes in the relative number of neutrons to photons, and it obtains a 5% classification error when this ratio is changed by a factor of ten. Results from this research demonstrate that it is feasible to use commercially available instrumentation in combination with artificial intelligence techniques to develop a practical detector that will accurately measure dose equivalent in mixed neutron–photon radiation fields.

Biomechanical effects of ESWL shock waves

Impulsive stress in the repeated shock waves administered in ESWL is the mechanical stimulus of injury to the kidney. In order to better understand the mechanical origins of injury, the interaction of focused shock waves with simple, planar polymeric membranes immersed in tissue-mimicking fluids was studied. The ESWL shocks in uniform, noncavitating liquids do not cause damage, but after passing through tissue or simulated tissue they do. This result suggests that the acoustic inhomogeneity of tissue may contribute to injury from ESWL. Shocks with large amplitude and short rise time (e.g., in uniform media) cause no damage in noncavitating fluids, while long-rise-time, dispersed shock waves, though only moderately attenuated, do. A continuum model is described which incorporates the mechanical properties of the tissue and accounts for the effect on its strength of microscopic inhomogeneities. It is shown that when transient tensile stress is applied it takes a finite time for failure to occur, so if the pulse is not long enough the material survives, in qualitative agreement with the behavior described above. A definition of dose at failure is derived in terms of the stress applied to the membrane by each shock wave, the strain rate, and the material failure stress.

The pro-convulsant actions of corticotropin-releasing hormone in the hippocampus of infant rats

Whole-cell patch-clamp and extracellular field recordings were obtained from 450- μm-thick brain slices of infant rats (10–13 days postnatal) to determine the actions of corticotropin-releasing hormone on glutamate- and GABA-mediated synaptic transmission in the hippocampus. Synthetic corticotropin-releasing hormone (0.15 μM) reversibly increased the excitability of hippocampal pyramidal cells, as determined by the increase in the amplitude of the CA1 population spikes evoked by stimulation of the Schaffer collateral pathway. This increase in population spike amplitude could be prevented by the corticotropin-releasing hormone receptor antagonist α-helical (9–41)-corticotropin-releasing hormone (10 μM). Whole-cell patch-clamp recordings revealed that, in the presence of blockers of fast excitatory and inhibitory synaptic transmission, corticotropin-releasing hormone caused only a small (1–2 mV) depolarization of the resting membrane potential in CA3 pyramidal cells, and it did not significantly alter the input resistance. However, corticotropin-releasing hormone, in addition to decreasing the slow afterhyperpolarization, caused an increase in the number of action potentials per burst evoked by depolarizing current pulses. Corticotropin-releasing hormone did not significantly change the frequency, amplitude or kinetics of miniature excitatory postsynaptic currents. However, it increased the frequency of the spontaneous excitatory postsynaptic currents in CA3 pyramidal cells, without altering their amplitude and single exponential rise and decay time constants. Corticotropin-releasing hormone did not change the amplitude of the pharmacologically isolated (i.e. recorded in the presence of GABA A receptor antagonist bicuculline) excitatory postsynaptic currents in CA3 and CA1 pyramidal cells evoked by stimulation of the mossy fibers and the Schaffer collaterals, respectively. Current-clamp recordings in bicuculline-containing medium showed that, in the presence of corticotropin-releasing hormone, mossy fiber stimulation leads to large, synchronized, polysynaptically-evoked bursts of action potentials in CA3 pyramidal cells. In addition, the peptide caused a small, reversible decrease in the amplitude of the pharmacologically isolated (i.e. recorded in the presence of glutamate receptor antagonists) evoked inhibitory postsynaptic currents in CA3 pyramidal cells, but it did not significantly alter the frequency, amplitude, rise and decay time constants of spontaneous or miniature inhibitory postsynaptic currents. These data demonstrate that corticotropin-releasing hormone, an endogenous neuropeptide whose intracerebroventricular infusion results in seizure activity in immature rats, has diverse effects in the hippocampus which may contribute to epileptogenesis. It is proposed that the net effect of corticotropin-releasing hormone is a preferential amplification of those incoming excitatory signals which are strong enough to reach firing threshold in at least a subpopulation of CA3 cells. These findings suggest that the actions of corticotropin-releasing hormone on neuronal excitability in the immature hippocampus may play a role in human developmental epilepsies.

In vitro study of the mechanical effects of shock-wave lithotripsy

Impulsive stress in repeated shock waves administered during extracorporeal shock-wave lithotripsy (ESWL) causes injury to kidney tissue. In a study of the mechanical input of ESWL, the effects of focused shock waves on thin planar polymeric membranes immersed in a variety of tissue-mimicking fluids have been examined. A direct mechanism of failure by shock compression and an indirect mechanism by bubble collapse have been observed. Thin membranes are easily damaged by bubble collapse. After propagating through cavitation-free acoustically heterogeneous media (liquids mixed with hollow glass spheres, and tissue) shock waves cause membranes to fail in fatigue by a shearing mechanism. As is characteristic of dynamic fatigue, the failure stress increases with strain rate, determined by the amplitude and rise time of the attenuated shock wave. Shocks with large amplitude and short rise time ( i.e., in uniform media) cause no damage. Thus the inhomogeneity of tissue is likely to contribute to injury in ESWL. A definition of dose is proposed which yields a criterion for damage based on measurable shock wave properties.

Acoustic correlates of fricatives and affricates.

Six adult speakers of American English produced voiceless fricatives and affricates in word initial position in a carrier phrase, varying vowel context, and stress patterns. From each of the productions, the following acoustic measurements were made: silence duration, frication duration, amplitude rise time, amplitude rise slope, frication onset centroid frequency, and following vowel duration. A discriminant function analysis revealed that silence duration was the best at discriminating between the fricatives and affricates, followed by frication duration, onset frequency, and rise slope. No additional discrimination was found due to either rise time or vowel duration. The traditional acoustic measure of rise time, which includes the duration and the slope of the rise, may be due entirely to the contribution of the slope rather than the duration itself. Although rise time has long been considered an important perceptual cue in the distinction between fricatives and affricates, recent research has brought this into question [K. R. Kluender and M. A. Walsh, Percept. Psychophys. 51, 328–333 (1992)]. The results of this study suggest that duration measurements (preceding silence interval and frication duration) are more salient acoustic correlates than amplitude rise-time measures. [Work supported by NIDCD.]