High Frequency Testing Research Articles

Sensitive developmental periods for kanamycin ototoxic effects on distortion-product otoacoustic emissions

The developing rat is hypersensitive to aminoglycoside toxicity, which is expressed early on as a destruction of outer hair cells (OHC). In the current study, distortion-product otoacoustic emissions (DPOAE), which specifically measure the micromechanical activity of OHCs, were used to assess functional effects of administering a regimen of kanamycin to three groups of neonatal rats representing discrete postnatal developmental periods. In this manner, pigmented rats were treated at postnatal days 1–10, 11–20, and 21–30. A series of input-output (I/O) functions obtained for the 2f 1-f 2 DPOAE during the post-treatment period indicated that detection thresholds were significantly elevated for the animals treated on postnatal days 1–10 and 11–20, with the greatest elevations observed at the higher test frequencies.

Glycosylphosphatidylinositol-Alkaline Phosphatase from Calf Intestine as Substrate for Glycosylphosphatidylinositol-Specific Phospholipases - Microassay Using Hydrophobic Chromatography in Pipet Tips

An electrophoretically homogeneous glycosylphosphatidylinositol-alkaline phosphatase fraction from calf intestine, obtained by hydrophobic chromatography, was used as "enzyme-labeled" substrate for testing phospholipase activity. The reaction products were separated by (i) hydrophobic chromatography in pipet tips and (ii) Triton X-114 phase partitioning. The chromatographic method presented permits high test frequencies, does not need temperature controlled sample handling, and is only slightly disturbed by detergents, organic solvents, and proteins. The method was used to characterize phosphatidylinositol-specific phospholipase C from Bacillus cereus and phospholipase D from calf serum. Measurement of substrate hydrolysis by phospholipases is apparently linear to enzyme concentration and time. Relative activity of both enzymes is maximum at pH 6.5, corresponding to the optimal pH range found with other glycosylphosphatidylinositol substrates and phosphatidylinositol-specific phospholipases of other sources. Maximum activity of phospholipase C was found at 0.03% Triton X-100, 0.01% Brij 35, and 0.2% n-octylglucoside. The activity is not affected by Ca 2+, NaHCO 3, o-phenanthroline, or EDTA, increasingly inhibited by MgCl 2, MnCl 2, and ZnCl 2, and slightly activated by Na + and K +. Calf serum phospholipase D shows maximum activity at 0.05% Triton X-100, 0.02% Brij 35, and 0.4% n-octylglucoside. The apparent K m values for phospholipase C (12.25 μM) and phospholipase D (4.94 μM) found with glycosylphosphatidylinositol-alkaline phosphatase are compared with values published for other glycosylphosphatidylinositol substrates.

Zinc ions inhibit agonist binding by chelating histidine residues of A1 adenosine receptors

Cisplatin is a commonly used antineoplastic agent that causes ototoxicity through the formation of reactive oxygen species (ROS). Previous studies have shown that cisplatin causes an upregulation of A1 adenosine receptor (A1AR) in the cochlea, and that application of the adenosine agonist, R-phenylisopropyladenosine (R-PIA), to the round window (RW) results in significant increases in cochlear glutathione peroxidase and superoxide dismutase. These data suggest that adenosine receptors (ARs) are an important part of the cytoprotective system of the cochlea in response to oxidative stress. The purpose of the current study was to investigate the effect of various adenosine agonists on cisplatin ototoxicity using RW application. Auditory brainstem response (ABR) thresholds were recorded in anesthetized chinchillas at 1, 2, 4, 8 and 16 kHz. The auditory bullae were surgically opened, and 1 mM R-PIA, 10 μM 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)/R-PIA (1 mM) cocktail, 100 μM 2-chloro-N-cyclopentyladenosine (CCPA), 2-[4-(2-p-carboxy-ethyl)phenylamino]-5′-N-ethylcarboxamidoadenosine (CGS) or vehicle were applied to the RW. After 90 min, the remaining solution was removed and cisplatin was applied to the RW. The bullae were closed and the animals recovered for 72 h, after which, follow-up ABRs were performed. Cochleae were harvested for scanning electron microscopy (SEM) and for lipid peroxides. Pre-administration of the A1AR agonists R-PIA or CCPA significantly reduced cisplatin-induced threshold changes at all but the highest test frequency. In addition, A1AR agonists protected against cisplatin-induced hair cell damage and significantly reduced cisplatin-induced lipid peroxidation. Co-administration of the A1AR antagonist, DPCPX, completely reversed the protective effects of R-PIA. In contrast, pretreatment with CGS-21680, an A2A adenosine receptor (A2AAR) agonist, significantly increased cisplatin-induced threshold changes. Our findings are consistent with the notion that the A1AR contributes significantly to cytoprotection in the cochlea, and thereby protects against hearing loss.

Effects of probe insertion depth on real ear measurements

The purpose of this article is to provide an overall summary of the role probe insertion depth has on real ear measurements, and to compare the real ear sound pressure level measured by a probe microphone system, using three methods for positioning the probe in an ear canal. The probe insertion techniques that were compared included: (1) an acoustic method that incorporates use of the quarter-wave antiresonance property of the ear to determine acoustically the location of the probe tube relative to the eardrum in an individual ear; (2) a constant insertion depth method (25 mm from the intratragal notch); and (3) the earmold +5 mm method, which places the probe 5 mm beyond the tip of the individual's earmold in the canal, thereby avoiding problems associated with the transition region, where sound exits from the bore of the earmold into the larger ear canal. Measurements were obtained for each method at 32 frequencies in the unoccluded ears of 17 subjects. Results indicated that the sound pressure levels measured by the acoustic method were significantly larger than those measured by the other two methods. This result was most evident in subjects with long ear canals (> 25 mm) and at high test frequencies (4.0 to 6.3 kHz). For subjects with short or average length ear canals, the three methods provided essentially equivalent results.

Temporary threshold and loudness shifts: frequency patterns and correlations.

Two experiments studied the frequency pattern of TLS (temporary loudness shift) as a function of the level and frequency of the fatiguing sound. In experiment 1, the fatiguing tones were intermittent 375-, 1500-, or 3000-Hz tones (10 s on/10 s off) at 75, 80, 85, 90, or 95 dB SPL. The TLS patterns were established for a continuous, 60-phon test tone at different frequencies presented simultaneously with the intermittent fatiguing tone. In experiment 2, a 1000-Hz exposure tone with an intermittency of 10 s on/20 s off was used with a continuous 60-dB test tone at different frequencies. In both experiments, the total exposure duration was 60 s; TLS was measured 5 s after the exposure ended. For the lowest two exposure levels, the TLS pattern had one peak centered on the exposure frequency. As the exposure level increased, a two-peak pattern became evident, with the second peak at higher test frequencies. This finding could be interpreted as psychoacoustical evidence for the double (passive and active) mode of displacement of the basilar membrane. In experiment 2, a TTS (temporary threshold shift) measurement after exposure to a 45-min, 1000-Hz tone at 90 dB was added to the TLS sessions. The correlations between maximum TTS after a 45-min exposure and the TLS obtained after a 60-s exposure were calculated for each of the exposure levels and test frequencies used in TLS measurements. The correlation reached as high as 0.9 for TLSs measured at 1120 Hz after a 90-dB exposure; it was smaller but significant for TLSs at the exposure frequency. Despite these correlations, differences in the overall patterns of TTS and TLS suggest that they stem from two different mechanisms.

Potentiation of noise induced threshold shifts and hair cell loss by carbon monoxide

Previous studies have determined that severe systemic hypoxia disrupts cochlear function acutely, but have suggested that augmentation of cochlear perfusion may successfully protect cochlear function under all but the most profound hypoxic treatments. In the current study we report on the chronic effects of simultaneous exposures to noise and carbon monoxide on pure tone thresholds and hair cell survival in rats. Following initial threshold determination, rats received acute exposure to carbon monoxide, noise, or both agents concurrently. Thresholds were evaluated 2–4 and 6–8 weeks later. The data show that carbon monoxide alone does not affect either auditory thresholds or compromise hair cells at the light microscopic level. The noise exposure alone produced variable, but quite limited permanent threshold shifts which were related to the power spectrum of the broad band noise that was employed. Hair cell loss was restricted to the basal turn of the cochlea. Simultaneous exposure to carbon monoxide and noise induced large threshold shifts at all frequencies studied, but the effect was greatest at the highest test frequency; an effect not consistent with the noise power spectrum. Widespread hair cell loss persisted over fully half of the basilar membrane in the most severely affected rat. Outer hair cells appear to be particularly vulnerable. Carbon monoxide plus noise did not appear to preferentially disrupt a particular row of outer hair cells. These data complement existing evidence that hyperoxia can mitigate against noise induced injury and reinforce the view that some types of noise induced damage may result from metabolic insufficiencies.

A new AC technique for accurate determination of channel charge and mobility in very thin gate MOSFET's

A new method is described for determining the channel charge and mobility of a MOS transistor as a function of gate bias from the ac admittance measurements. The admittance of the conduction channel of the MOSFET is derived from a transmission line model. The peaks of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G/\omega</tex> versus ω curves are used to deduce gate-channel capacitance and mobility. The mobile carrier density and mobility in very thin-oxide MOSFET's can be measured more accurately using this ac method, since a zero lateral field and a uniform mobile charge distribution along the channel is maintained with zero drain-source voltage and interface trap effects are reduced by using high test frequencies. Measured data on the electron mobility versus gate voltage are presented for 90-A gate dielectric MOS transistors.

The effect of strain rate on the monotonic and cyclic properties of β-TiV alloys

The effects of strain rate and test environment on the low cycle fatigue and fatigue crack propagation behavior of three TiV alloys having different deformation mechanisms were studied. The strain rate affected both the cyclic stress strain response and the fracture mode. The details of the effect depended on deformation characteristics, with the sensitivity to changes in strain rate increasing with increasing planarity of slip. All alloys exhibited longer fatigue lives at the higher strain rate. This effect was related to changes in cyclic hardening behavior and in some cases changes in fracture mode. The fatigue crack propagation resistance was also greater at the higher test frequency, with the effect being most pronounced in the vacuum environment for the higher vanadium content alloy. The results can be explained by the influence of vanadium content on the strength and deformation characteristics.

New Perspectives on Noise-Induced Hearing Loss.

Hearing impairment is the third most prevalent chronic disability in the United States, and hearing loss in the speech frequency region (pure-tone average threshold at 0.5, 1, 2, and 4 kHz ≥ 25 dB) is currently estimated to affect 29 million Americans ages 20–69 years based on 2003–2004 data (16% of population; Agrawal et al. 2008). When the higher frequencies are considered (pure-tone average at 3, 4, and 6 kHz ≥ 25 HL), the number affected doubles (Agrawal et al. 2008). Consistent with this, the National Institutes of Health has estimated that some 15% of Americans between the ages of 20 and 69 have hearing loss at higher test frequencies, suggesting the hearing loss may have been caused by exposure to loud sound (National Institute on Deafness and Other Communication Disorders 2002).

Anelastic relaxation controlled cyclic creep and cyclic stress rupture behavior of an oxide dispersion strengthened alloy

Cyclic creep deceleration relative to static creep was observed in oxide dispersion strengthened alloy Inconel MA 754 at 760 °C and cyclic stresses of 221 MPa-41 MPa, 231 MPa-41 MPa, and 241 MPa-41 MPa. Tests were run over the range of frequency from 0.05 cycles per hour to six cycles per hour. The maximum cyclic deceleration, which was manifested as a reduced net creep rate and increased rupture life, was observed at the highest cyclic frequency. Considerable anelastic strain, having a magnitude of ea/ee∼ 1/3, is stored in MA 754 at 760 °C under these creep loads, and this strain may be recovered in the off-load half cycle of a cyclic creep test. During the higher frequency tests, the effect of an incomplete storage of anelastic strain on the accompanying nonrecoverable creep rate provides a mechanism for the frequency dependent cyclic creep deceleration. The proposed mechanism is in agreement with mixed-mode test results and with TEM examination of interrupted-test specimens.

Effect of duct configuration on oil activity at liquid/solid dielectric interfaces

A test cell has been designed to allow simultaneous determination of the currents flowing at the surfaces of two spacers in a 5mm oil gap. The spacers were asymmetrically disposed so their surfaces were at different distances from the bulk oil. Electrical measurements and Schlieren observations showed that the currents and activity in the oil at the spacer surface are influenced to a considerable degree by the length of duct: the current increasing by an order of magnitude in the longer duct. The technique tends to reduce the difficulties often experienced when attempting to compare results from direct voltage tests carried out in different cells. During the application of 50Hz alternating voltages to the system, different phenomena were observed at the spacers. These are considered to be due to the effect of dielectric losses in the spacer material. At higher stresses (of the order of 4 × 10 6V/m) EHD effects appeared to be present in certain regions resulting in movement of the oil: an increase in partial discharge activity was recorded for this condition. Higher frequency tests, up to 1000Hz, and similar stresses indicated that no EHD effects were present: it is postulated that the changes observed were due to losses in the oil itself. The work is continuing in an attempt to explain in more detail the various phenomena and to determine their possible significance in technology.

Real-time correction of counting losses in nuclear pulse spectroscopy

Reviewing the current status of real-time correction of counting losses in nuclear pulse spectroscopy, the pileup problem is identified as the last question not resolved satisfactorily up to now. Correction of pileup losses in provided, at least in principle, by the classical pulse generator method, however, severe limitations in test frequency prohibit its application to real-time correction of counting losses. A solution is offered by the novel principle of the virtual pulse generator which obviates the shortcomings of the classical method simply by not introducing pulses into the spectroscopy system. Instead, the probability for pileup-free pulse processing is determined by suitable tests of the system status at arbitrarily high test frequencies. After a discussion of the principles of the new method and its application to a real-time correction system experimental evidence is provided for the complete correction of counting losses of more than 98% under conditions of stationary as well as variable counting rates up to the limit of stable operation of the underlying spectroscopy system which is 800 000 c/s for an experimental high-rate gamma spectrometer.

Fatigue crack growth at 20 kHz-a new technique

A method is described for investigating fatigue crack propagation at very low crack propagation rates using resonant transverse 20 kHz oscillations of a three-point bend specimen. With this method the same fatigue crack propagation behaviour could be found as in conventional tests. At this high testing frequency fatigue crack propagation rates down to some 10-14 m/cycle could be measured in reasonable times.

Influence of an impurity profile on the determination of interface states

In order to determine the density of interface states from C(V) curves for high test frequencies, a comparison is made with a computed curve for uniform impurity concentration but identical minimum capacitance. The curves calculated for a doping profile (due, say, to acceptor depletion near the surface of a p-type semiconductor) are assumed to represent the measured C( V) curves of MOS diodes. A number of “charges in interface states” (8 × 10 10 cm −2 in the given example) are simulated by the impurity profile. This shows that it is not sufficient to introduce a mean effective substrate impurity concentration by adapting the minimum capacitance in the inversion region. The same accordingly applies for the C( V) curves for low test frequencies. The error due to “simulated interface states” is reduced somewhat, but it remains the altered relation between the applied voltage and the surface potential.

High-frequency hearing losses caused by low-frequency noises.

Human subjects were exposed to an octave-band noise for 24 hours. Temporary threshold shifts increased for the first eight hours of exposure and then were asymptotic. While threshold shifts were largest at about one-half octave above the center frequency of the noise, a second maximum was observed at higher test frequencies. The exact frequency of this second maximum decreased from 7.0 kHz, for a noise centered at 2.0 kHz, to 5.5 kHz for a noise centered at 0.5 kHz. This result could be caused by the travelling wave pattern along the cochlear partition or to the production of distortion products.

Absolute thresholds for frequency-modulated signals: effects of rate, pattern, and percentage of modulation.

Absolute monaural thresholds for continuous unmodulated and frequency-modulated signals were determined for five normal-hearing subjects using the method of adjustment. Three carrier signals (250, 1000, and 4000 HZ) were modulated at rates of 2 and 20 times per sec using frequency deviations of +/- 5, 10, and 20%, and both ramp and sinusoidal modulation. Thresholds measured at the slower modulation rate were 5 to 10 dB lower than those measured for unmodulated signals at the two higher test frequencies. Suggestions are presented as to how the clinician may minimize the possible discrepancy between modulated and unmodulated signals using currently available warble-tone equipment.

Experimental study of the effects of water repellent treatment on the acoustic properties of Kevlar

The effects of water repellant treatment of the acoustic properties of a bulk absorber have been investigated. The bulk absorber consisted of a synthetic fibrous material (Kevlar 29, style 1270) manufactured by DuPont. The propagation constant, γ, and the characteristic impedance Zc were measured over the frequency range 0.5 to 3.5 kHz. The measurements were conducted before and after a controlled application of water repellent treatment (“Zepel” DA-24M), also manufactured by DuPont. A comparison of test results indicated changes in both γ and Zc. These changes in γ and Zc generally increased with frequency. At the highest test frequency, the attenuation constant (real part of γ) and phase constant (imaginary part of γ) decreased by about 8% and 10%, respectively, when the treatment was applied. Corresponding changes in the real and imaginary parts of Zc at the test frequency of 3.5 kHz were about 6% and 25%, respectively.

On the generality of discontinuous fatigue crack growth in glassy polymers

Fatigue fracture surface characteristics of five commercially available amorphous polymers [poly(methylmethacrylate) (PMMA), polycarbonate (PC), poly(vinyl chloride) (PVC), polystyrene (PS), and polysulphone (PSF)] as well as bulk-polymerized PMMA prepared over a wide range of molecular weights were studied to determine if common mechanisms of fatigue crack propagation prevail among these glassy polymers. In those polymers with viscosity-average molecular weight ¯Mv≲2×105, the macroscopic appearance of the fracture surface showed the presence of a highly reflective mirror-like region which formed at low values of stress intensity and high cyclic test frequencies (∼100 Hz). The microscopic appearance of this region revealed that many parallel bands exist oriented perpendicular to the direction of crack growth and that the bands increase in size with ΔK. In all instances, the crack front advanced discontinuously in increments equal to the band width after remaining stationary for hundreds of fatigue cycles. Electron fractographic studies verified the discontinuous nature of crack extension through a craze which developed continuously with the load fluctuations. By equating the band size to the Dugdale plastic zone dimension ahead of the crack, a relatively constant yield strength was inferred which agreed well with reported craze stress values for each material. At higher stress intensity levels in all polymers and all values of ¯Mv, another series of parallel bands were observed. These were also oriented perpendicular to the direction of crack growth and likewise increased in size with the range in stress intensity factor, ΔK. Each band corresponded to the incremental advance of the crack during one load cycle, indicating these markings to be classical fatigue striations.

Hearing in ethnically different longshoremen.

A total of 836 longshoremen, members of the International Longshoreman's Association, who have worked in the same environment for periods up to and exceeding 41 years, were tested for pure-tone threshold sensitivity. When their audiograms were separated according to the subject's subcultural origins it was found that the thresholds of the black Americans were better at the higher test frequencies than those of the other groups, all of which were white.

Masking by Single and Double Sinusoids

Two-sinusoid masking results reported earlier [J. C. Booth and J. F. Brandt, J. Acoust. Soc. Amer. 48, 77(A) (1970)] demonstrated a peak (increase) in the masking audiogram that was dependent on spacing and SPL of the maskers. As spacing was increased, this peak occurred at a higher test frequency. In the present study, the effect of the individual components in the two-sinusoid masker on a test frequency located between the maskers in the region of the peak was of interest. Masking data for one and two sinusoids are reported. Masked thresholds were obtained in three conditions: masker(s) above, below, and combined (40 dB SPL) for spacings of 100, 300, and 500 Hz at test frequencies from 400 to 3000 Hz. More masking was observed for the higher component than for the lower. The relation between the three masking patterns was found to be dependent on spacing. For the 500-Hz spacing, the combined maskers' pattern was not distinguishable from the masker-above pattern. For the 100-Hz spacing, the combined maskers showed summation of masking over all frequencies. The results of this study could be explained by the overlap in the displacement patterns of the signal and masker(s) on the basilar membrane.