bluuebunny/crossref_metadata_2025 huggingface dataset:
Backward Masking and the Perception of Temporal Order
Authors: Tomsic Richard T. , Elfner Lloyd F. , Homice Jerry L.
Published: September 2005

Four subjects were run in a backward-masking task in which the dependent variable was the duration of the silent interval between the signal and the noise. Three frequencies, 850, 1500, and 2600 Hz were employed as signals at sensation levels of 12, 24, and 36 dB. A narrow band of frequencies centered at 1500 Hz and presented at 70 dB SPL was employed as the noise. The method of limits was used to determine threshold values. Subsequently, seven subjects were run in a similar task but instructed to report the temporal order of the signal and the noise. The same frequencies and noise band reported above were employed. The method of constant stimuli was used to determine threshold values. Results of the study showed that the frequency centered in the band demonstrated the largest threshold values both in backward masking and in the perception of temporal order. The low-frequency signal demonstrated the smallest thresholds of backward masking and the perception of temporal order. The function relating intensity of the masked signal and threshold was similar for the backward masking and the perception of order. The threshold for perception of temporal order was, however, approximately 10 msec greater than that for backward masking. [This study was supported by grant frown NSF.]
Masking Level Differences Obtained with Pulsed, Tonal Maskers
Authors: Hafter Ervin R. , Carrier Sam C.
Published: September 2005

Bursts of tonal signals (125 msec) were masked by tones of the same duration and frequency. The masker was always diotic, while the signal was either diotic (a homophasic condition) or reversed in phase to one ear (an antiphasic condition). MLD's, the differences in detection between homophasic and antiphasic conditions were measured for signals of three frequencies, 250, 500, and 1000 Hz. The phase between signal and masker was set at 0°, 45°, 90°, or 135°; MLD's obtained for these conditions of signal-to-mask phase were 2, 2, 17, and 8 dB, respectively. In addition, MLD's were slightly higher for the higher frequencies. In the psychophysical procedure used, mask alone was followed by mask alone or signal plus mask, and subjects responded “SAME” or “DIFFERENT.” The interaural differences of time and intensity necessary for detection in the antiphasic conditions were considerably larger than those to be expected from other measures of lateralization.
Simultaneous and Time-Staggered Speech Signals in Monaural and Dichotic Listening
Authors: Berlin Charles I. , Lowe Sena , Thompson Carl
Published: September 2005

Rhyming monosyllabic pairs that differ only by the initial plosive consonant were recorded on separate channels to be “simultaneous in onset” within 5 msec. Onsets of the words were also staggered by 10, 20, 30, 40, 50, and 100 msec (±2.5 msec). Unvoiced consonants are perceived more readily in the simultaneous listening task. When control for frequency of occurrence of voiced versus voiceless consonants is made, central laterality effects are overshadowed by overriding intelligibility of voiceless consonants. The significance of these findings with respect to temporal coding of speech will be discussed. [Work supported by the National Institute for Neurological Diseases and Blindness.]
Spatial Averaging in Sound-Power Measurements
Authors: Lubman David
Published: September 2005

To measure sound power in a reverberation room, we need to estimate the space-time average of squared sound pressure. While the time average usually presents no special problem, the space average may, particularly for acoustic signals having pure-tone or extremely narrow-band spectra. The space average is subject to a random error due to finite sample size. Tables and formulas are presented from which an experimenter may determine the confidence level of his estimate in terms of signal-bandwidth reverberation time. and number of fixed microphones or the path length for a moving microphone. The space average is also subject to a bias error if the quantity averaged is sound level or rms pressure instead of squared pressure. The bias error is also estimated. Finally, the remarkable performance of rotating diffusers is described in terms of their improvement in the statistical accuracy of the measured mean. Two ways of computing their figure of merit are described. It is shown that the rotating diffuser is effectively a parametric modulator which introduces new frequencies in the room.
Automatic Data Reduction with Moving Microphone
Authors: Wells Richard J.
Published: September 2005

Equipment is described with which the microphone signal is accurately squared and integrated over any suitable traverse time. Comparisons are shown between data obtained with such a technique and by more conventional means. Use of “modified Schroeder method” for determining reverberation time is also described.
Computer Studies of the Properties of Sound Fields in a Reverberation Chamber
Authors: Maling G. C.
Published: September 2005

Development of standard procedures from accurate determination of the acoustic power radiated by pure-tone sources in a reverberation chamber requires a detailed knowledge of the properties of the reverberant environment. Computed sound-pressure distributions have been found to be in good agreement with the results of Waterhouse and Lubman. Variations in radiation impedance as a function of both source position and frequency are in good agreement with theoretical results obtained by Lyon. Contours that describe variations in mode-spacing statistics with changes in room dimensions have been computed for chambers having a volume of 200 m3, and are compared with contours computed by Sepmeyer for a different normalization. Some criteria applicable to the determination of the power output of a pure-tone source in a reverberation chamber are presented.
Coupling of Finite Sized Sources to a Modal Reverberant Sound Field
Authors: Eldred Kenneth McK. , Sharp Ben H. , Murray Fancher M.
Published: September 2005

Much effort has been devoted to the development of statistical methods for the measurement of acoustic power levels and transmission loss in reverberant rooms. However, history is replete with unexplained interlaboratory variations in these measurements, particularly at low frequencies and when large specimens are involved. This paper examines some of the deterministic factors that govern the excitation of reverberant sound fields by finite sources. Such sound fields are investigated and compared with those produced by ideal point sources. Both analytical and experimental results show that the sound fields produced depend not only on the source position but on the source dimension. The relative amount of acoustic source power that is actually transferred to the modes is determined and the sound levels produced are compared with those that would exist under the assumption of diffuse conditions.
Use of Time-Averaged Optical Holographic Interferometry for Visualization of Standing Acoustic Waves
Authors: Salant R. F. , Alwang W. G. , Cavanaugh L. A. , Sammartino E.
Published: September 2005

The technique of time-averaged optical holographic interferometry is useful in investigating three-dimensional acoustic fields, since it provides a graphic three-dimensional record of the geometry of the nodal patterns of standing waves. This technique was used to obtain interferograms of longitudinal standing waves in a duct of square cross section. The three-dimensional fringe patterns clearly indicate the locations of the antinodal planes. Photographs of the hologram reconstructions of the virtual images illustrate the effects of acoustic wave frequency and amplitude on the fringe pattern.
Noise in Ultrasonic Image Converters
Authors: Jones H. W.
Published: September 2005

There does not appear to be a satisfactory analysis of the noise arising at the output electrode of Sokolov-type image-coverter tubes. If the secondary emission coefficient δ of the piezo-surface in such a tube is equal to unity then it follows [A. Van der Ziel, Noise (Prentice-Hall, Inc., Englewood Cliffs, N. J.)] that the space-charge noise-suppression factor F is also unity. At the other extreme, when δ ∞ the noise suppression factor F=0. Consequently, it follows that F is dependent on δ. An analysis is performed for a gridded tube to determine the nature of this dependence and consideration is given to the existence of optimum operating conditions from this point of view.
Sound Radiated by Spheres Falling in Dilute Aqueous Solutions of Polyethylene Oxide
Authors: Sanders J. V. , Sendek J. M.
Published: September 2005

It is experimentally well established that the addition of minute amounts of long-chain macromolecules to water can significantly reduce the drag experienced by a submerged body. Although the mechanism responsible is at present unknown, it is reasonable to expect that this drag reduction might be accompanied by some degree of noise reduction. To check this hypothesis, spheres were dropped in a reverberant tank containing first water and then a 100-weight ppm solution of Polyox WSR-301 and the radiated sound measured. In water, the Reynolds numbers (based on the terminal speed) covered the region of either side of the critical Reynolds number, but only those spheres with Reynolds numbers at or above the critical value radiated sufficient energy to be detected above the background. In the polymer solution, where all spheres displayed considerable increase in speed, the sound radiated by all spheres was reduced to below background. This reduction amounted to as much as 15 dB. [This research was partially supported by Naval Ship Systems Command.]
Nonisentropic Acoustic Wave Generation
Authors: Peter Abraham C.
Published: September 2005

The problem of aerodynamic noise generation is posed by theoretically isolating the nonisentropic effects of fluid flow. This is attained by expressing the dependent thermodynamic variables (e. g., pressure, density) in terms of space and time coordinates through the medium of two given thermodynamic functions. The resulting differential equation reduces to the form used in classical investigations when entropy variations tend to zero in the limit. Initial results indicate that nonisentropic effects are of first order magnitude when viewed in this framework. An application of the theory, by using an acoustic analogy, to shock emission has been initiated. An engineering application of the theory is reflected in the concept of an extended plug nozzle device. [This study was supported by the Unsteady Aerodynamics Branch of MSFC in Huntsville, Alab.]
Sound Transmission in a Fluid-Filled Duct with Transverse Resistivity
Authors: Shaw E. A. G.
Published: September 2005

A hard-walled duct of uniform cross section is filled with a fluid medium that has zero flow resistivity in the axial direction but substantial resistivity transverse to the axis. In such a system, the plane-wave mode is transmitted without attenuation but the higher-order modes are absorbed. The attenuation of the higher-order modes depends on the transverse resistivity of the fluid and on the equivalent angle of the mode. The discrete cutoff frequency associated with each higher-order mode in the loss free system is replaced by broad-band attenuation which, according to theory, may amount to many decibels per wavelength and extend over two or more octaves. Experimental values of attenuation constant for (1,0) waves in a rectangular duct are in good agreement with theory.
Thermoviscous Attenuation of Sound Traveling Parallel to a Rigid, Impermeable Wall
Authors: Blackstock David T.
Published: September 2005

The problem considered is that of a quasiplane wave passing at grazing incidence over a rigid, impermeable wall. The fluid through which the wave travels is viscous and thermally conducting. The attenuation of the wave is found to be α=αfree+12[1+(γ−1)Pr−12]νω2/c03, where αfree is the (thermoviscous) attenuation when no wall is present, γ is ratio of specific heats, Pr is Prandtl number, ν is kinematic viscosity, ω is angular frequency, and co is sound speed. This formula agrees with the one for attenuation in tubes [D. E. Weston, Proc. Phys. Soc. (London) B66, 695–701 (1953)] in the limit as the tube radius becomes infinite. Aside from being responsible for the presence of the second term in the attenuation formula, the wall has an appreciable influence on the sound field far beyond the boundary layer. Possibilities for checking the attenuation formula experimentally will be discussed. [Work supported by AFOSR.]
Limits of Validity of a Perturbation Solution for a Finite-Amplitude Standing Wave Confined to a Duct
Authors: Coppens Alan B. , Sanders J. V.
Published: September 2005

The range of validity of a perturbation solution to the problem of nonlinear standing waves in rigid-walled ducts is discussed in the light of some recent published and unpublished data from a number of investigators. While most of the data were taken only at resonance frequencies, results can be inferred for frequencies slightly off resonance. The data suggest validity of two dimensionless parameters for both preshock and weakshock régimes. One parameter describes the strength of the wave and the other the frequency deviation from resonance, both with respect to a dimensionless dissipation constant.
On the Propagation of Sound Waves in an Axisymmetric Viscous Flow Bounded by an Elastic Cylindrical Duct
Authors: Rentzepis G. M. , Vogel J. W.
Published: September 2005

In this paper, the problem of propagation of sound waves in a viscous fluid moving through a cylindrical duct bounded by elastic walls is pursued. The field equations are the linearized variational equations of the conservation equations of gas dynamics in which the viscous shear terms and thermal losses are retained. Solutions of the field equations in this form yield the effects of the coupling of shear flow, heat transfer, fluid motion, and wall response on the propagation and attenuation of sound waves through the cylindrical duct. Specifically the problem of the axisymmetric velocity field is being investigated for rigid walls and for elastic walls. Solutions to these problems are obtained numerically and the first few modes of flow, viscosity, and impedance on the wave parameters and the propagation and attenuation of the sound waves through the duct. These results are compared with the stationary fluid, the nonviscous fluid and the case of rigid wall duct.
Response Analysis of a Rigid Piston in an Infinite Baffle Excited by a Random force
Authors: Runkle Charles J. , Hart Franklin D.
Published: September 2005

An analysis is made of the motion response of a rigid, circular piston imbedded in an infinite baffle. Classical development of the equation of motion of the piston and the acoustic impedance are used to determine the velocity-force admittance function of system and the acoustic pressure-force-transfer function. For the case of the piston subjected to a random exciting force with the characteristics of ideal white noise, the mean-square response velocity of the piston and the mean-square acoustic response pressure are calculated. The results in both cases are integrals that are numerically evaluated by the reduction of each to dimensionless form. Two approximate expressions for both large and small argument values are developed by the use of simplified expressions for the Bessel functions in the exact result. The results indicate the relative importance of mechanical damping in comparison to acoustic damping, the validity of the two approximate results compared to the exact one, and the useful ranges of parameters over which these approximate solutions are valid. [This work is sponsored by NASA, Langley Research Center.]
Transmission and Reflection of Sound by Plates Submerged in Water
Authors: Barss Walter M.
Published: September 2005

Techniques described at the 1967 Miami meeting have been refined and developed sufficiently to portray clearly the effects of both angle and frequency on the transmission and reflection of sound by submerged plates of various materials. The equipment permits quantitative results to be obtained from magnetic tape recording of analog signals but current emphasis is on the presentation and analysis of qualitative results. These are displayed graphically, as a continuous function of both angle and frequency, in the form of a shaded pattern in which the density increases with the amplitude of the acoustic signal. Some of the patterns are quite complex, having many maxima and minima, but the general features correlate well with the relative velocities of the various waves in the solid plate and the surrounding fluid. The reflection or scattering of sound by the plates, particularly in the direction toward the source, is being studied by these methods as an aid to understanding the reverberation of acoustic signals from sea ice.
Effects of Attenuation on the Rayleigh Critical Angle Reflection Factor
Authors: Becker F. L.
Published: September 2005

The minimum in the reflection factor for a liquid-to-solid interface at the Rayleigh critical angle has never been adequately explained using classical methods. It will be shown that when attenuation is included in the calculations, by the method of Fitch and Richardson, [Progr. Appl. Mater. Res. 8, 79 (1967)], it is possible to predict this minimum. Experimental results have been obtained that demonstrate very good agreement with this theory. It will also be shown that the principal factor influencing the depth of the minimum is the attenuation of shear waves. Each material possesses a critical frequency for which the reflection factor reaches an absolute minimum, approximately zero. Relationships between this frequency and attenuation parameters are presented. The phase of the reflected wave is also shown to be influenced by attenuation. [This work was supported by the U. S. Atomic Energy Commission under contract.]
Effect of Multimode Guided Wave Propagation on Ultrasonic Phase Velocity Measurements: Problem and Remedy
Authors: Papadakis Emmanuel P.
Published: September 2005

Multimode guided wave patterns in bounded ultrasonic specimens have been shown to interfere with phase delay measurements made by the pulse superposition method and the pulse-echo-overlap method. The phase shifts associated with the nodes in the multimode guided wave patterns invalidate the McSkimin ΔT criterion for the choice of the proper cyclic matching between echoes when the nodes are near the echoes used. The adverse effect of nodes upon the McSkimin criterion has been documented by extensive measurements employing shear waves in square bars and thick plates. A method employing video pulses to establish the proper cyclic match for rf measurements has been developed to supplement or replace the McSkimin ΔT criterion in all cases including those of adverse specimen geometry. Advantages and limitations of the video overlap criterion are discussed.
Variables Affecting Pulsed-Tone Békésy Thresholds
Authors: McCommons R. Bruce , Hodge David C.
Published: September 2005

Békésy audiometry is commonly used for measuring the sensitivity of hearing both in a clinical setting and in studies of the effects of potentially harmful acoustic stimulation. Pulsing tones yield slightly more sensitive thresholds than continuous tones. Investigation has shown, however, that in most commercially available Békésy audiometers the parameters of pulsed tones (when used) have been based on intuitive judgments rather than upon empirical data. This paper reports the results of two (2) studies in which frequency, period, duty cycle, and attenuation rate were examined. The implications of the results are discussed primarily in terms of optimizing the parameters of pulsed tones. Scoring procedures and their effect on the data are also discussed.
Study of Per- and Poststimulatory Fatigue in Pitch Perception
Authors: Skinner Paul , Antinoro Frank
Published: September 2005

While changes and recovery in loudness sensitivity have been studied over time by many investigators, changes in the perception of pitch have been observed only at discrete time intervals and changes during these intervals can only be attributed to normal variation or error. No graphic display of an observer's pitch judgments over time has been available for inspection under the usual psychophysical procedures. The method used in this study permitted the continuous recording of the subjects' perception of pitch over time under perstimulatory and poststimulatory conditions. In Expt. 1, pitch perception was studied under per- and poststimulatory fatigue with 60 and 90 dB sensation-level signals at 250, 500, 1500, 2500, and 4500 Hz. In Expt. 2, pitch perception was examined after stimulation of 100 dB SL for 10 min at the above frequencies. In Expt. 3, a fatiguing stimulus at 750 Hz was presented for two minutes at 120 dB SPL. Pitch perception was then studied at adjacent frequencies: 550, 650, 850, 950 Hz. No systematic change in pitch perception was observed under any of the experimental conditions. Since these findings conflict with similar studies, special attention was given to procedural and theoretical reasons for the discrepancies.
TTS Following Exposure to Rock-and-Roll Music
Authors: Speaks Charles , Nelson David A.
Published: September 2005

TTS was measured on a series of band members following a 4-h exposure to music having an over-all SPL ranging from 110–125 dB. The greatest shift (10–30 dB, 25 min after exposure) was at 2 kHz. Difficulties in interpretation of PTS were confounded by recovery times that often exceeded the time interval between performances (20 h). Recovery generally had occurred by 18 h, although certain individuals required on the order of 50 h for complete recovery. In a second experiment, eight listeners were exposed for 10 min to recorded R-and-R music presented monaurally at 120 dB SPL. TTS approximated 15 dB at 2 kHz 2 min after exposure (TTS2). TTS2 for 1, 4, and 6 kHz ranged from 8–12 dB. Recovery was generally linear in log time, with complete recovery by approximately 2 h. Speech-discrimination tests also were administered to both participants and listeners before and after exposure. Slight shifts in speech threshold (2–6 dB) occurred; however, no change in speech-discrimination scores for higher intensities (70–110 dB SPL) were observed.
Temporary Threshold Shifts (TTS) Produced by Noise Exposures of Long Duration
Authors: Carder Henry M. , Miller James D.
Published: September 2005

Chinchillas were exposed to octave-band noise centered at 500 Hz for 2 to 21 days at intensities between 65 and 105 dB SPL. Growth of TTS for a test tone of 715 Hz was measured 4 min after removal from the noise, which was periodically interrupted for the threshold tests. TTS increased for the first 24 h of exposure and then reached an asymptote that was maintained for as long as the experiment continued. The TTS at asymptote increased about 1.5 dB for each dB of noise above 64. The time to recover to zero TTS after cessation of the noise ranged from 2 to 7 days and was directly related to the level of TTS at asymptote. The time to recover did not depend on the duration of exposure beyond 24 h. These results are interpreted as reflecting a physiological equilibrium state. [This research was supported in full by a U. S. Public Service, Department of Health, Education, and Welfare research grant from the National Institute of Neurological Diseases and Blindness.]
Generating and Calibrating a Uniform Aquatic Sonic Field for Behavioral Bioacoustics
Authors: Weiss Burton A.
Published: September 2005

The use of two matched projector faces as the ends of a small tank enabled the generation of a uniform aquatic sonic field. The projectors were operated 180° out of phase to maintain a push-pull system. Shock electrodes and a dividing barrier of rubber, acoustically transparent in water, made the tank an aquatic shuttle box for avoidance conditioning. In addition to applications for behavioral bioacoustics, the system can be employed for calibration of small hydrophones. [Research supported by NINDB and ONR.]
Ducting Approach to Atmospheric Sound Propagation
Authors: Polly Robert C.
Published: September 2005

The velocity profile V=V0/1+Az+Bz2)12 is investigated for nonfocus situations. When A is negative, sound rays are refracted back to the ground and are reflected. When A is positive, sound rays are refracted away from the ground and a shadow zone is formed. Using the principles of ray acoustics, a ducting concept is developed and applied to both of these cases. It is shown that the low-frequency sound field generated by a rocket engine can be predicted quite well with this method.
Atmosphere Effects on Sonic-Boom Overpressures
Authors: Pierce Allan D. , Thomas Charles L.
Published: September 2005

The atmospheric correction factor for sonic-boom propagation is defined as the ratio of actual boom overpressure to that which would be expected at the same point were the atmosphere homogeneous with constant ambient properties equal to those at the location of the airplane. A linear theory is presented for correction factor estimation for the case of constant-velocity level flight in a temperature-and wind-stratified atmosphere. A modified wave equation for atmospheric acoustics is derived and subsequently solved using the eikonal approximation and Cauchy's method of characteristics. A simple expression for the atmospheric correction factor for points directly below the flight path is obtained with the neglect of crosswinds. Computations are presented for several representative temperature and wind profiles. An enhancement of boom overpressure on the ground is predicted for flight against the wind relative to that at the same flight Mach number in the absence of winds. The ratios of correction factors to the nominal correction factor [p(0)/p(zt)]12 are displayed for the U. S. Standard Atmosphere for different flight altitudes and Mach numbers.
Jet-Noise Tests to Determine Effects of Exhaust-Gas Heating
Authors: Haddle G. P. , Plumblee H. E.
Published: September 2005

An experimental program was conducted at the Lockheed-Georgia Aerospace Sciences Research Laboratory to determine the effects of jet-exhaust temperature on jet radiated noise levels. Four jet models were used. Tests were made in an anechoic room at jet-exhaust temperatures of 540°, 700°, 900°, and 1100° R. The velocity range used was 600 to 1400 fps. Over-all PWL and PWL spectra were determined for all test conditions. A short summary of the test procedures will be presented with test data.
Attenuation Characteristics of Lined Turns in Large Jet Engine Test Cells
Authors: Bell Lewis H.
Published: September 2005

With the arrival of the new generation of superaircraft such as C5A, Boeing 747, SST, etc., increased interest has been generated in the area of test-cell design. The new engines with two or three times the thrust of current engines, corresponding increased airflows and noise levels has required test cell designers to analyze, review, and to look for new concepts in design philosophy. In addition, the growing public concern over noise has required stricter attention to noise control. Among the more successful of the test-cell exhaust designs being used in the new supercells is the series of lined 180° turns (switchback). This design configuration has been incorporated in several new cells both here and abroad by engine manufacturers and for commercial airline overhaul facilities. Presented here are design data including acoustical spectral attenuation characteristics of the large lined bends based on full-scale measurements of recently completed cells, model test data, and the author's analysis. The elusive low-frequency cross-mode attenuation is theoretically analyzed and experimentally confirmed.
Air and Water Sirens—Their Analysis, Design, and Performance
Authors: Mitchell W. S. , Muster D.
Published: September 2005

The characteristics of air-operated sirens are described in the literature. There are also papers devoted to sirens using liquids. This paper is concerned with the characteristics of a siren which can function with either water or air. The siren was built and operated with air at a maximum pressure differential of four psig and at seven psig with water over a frequency range of from 50 Hz to 1 kHz. Comparison of the acoustic output of the device for both fluid media showed that, in general, there is little physical change in the siren response; the output pressure fluctuation has a sawtooth form. Fluid viscosity produces a damping effect on the response of the liquid-operated siren so that a more nearly sinusoidal pressure waveform occurs. In addition, it is found that the flow coefficient is dependent on frequency. The experimental results indicate that liquid-operated sirens should be further developed for use as underwater sound sources.
Measurement of the High-Pressure Propagation Constants in Various Materials
Authors: Higgs R. W. , Eriksson L. J.
Published: September 2005

An impedance-tube technique is used to measure the compressional wave propagation constants in rubbers, polyurethanes, and other materials as a function of pressure and frequency. The materials can function as windows, decouplers, and absorbers in a transducer assembly, and the high-pressure properties are required to design for a particular efficiency, bandwidth, and directivity at depth. The pressures used range from 100–2500 psi, frequency 8–40 kHz, and the temperature is 12°C. The characteristics of the materials as a function of pressure and frequency are presented.
Effect of Static and Dynamic Stress on the Mechanical Loss of Lead Zirconate Titanate Transducer Ceramic
Authors: Whymark R. R. , Triebes K.
Published: September 2005

The effect of dynamic and static stress on the mechanical loss of a transducer ceramic has been measured. Static stress was applied axially to a radially polarized tube of lead zirconate titanate measuring 2.54 cm long by 2.54 cm o.d. by 0.317 cm wall thickness. Dynamic stress was superimposed on the static stress by coupling the ceramic tube to an ultrasonic solid horn driver operating at 18.1 kHz. The mechanical loss of the ceramic: was determined by measuring the combined Q factor of the ceramic and its support. A correction for the support losses was obtained by substituting a LoW-loss brass tube for the ceramic. Initially, a static compressive stress of 3000 psi reduced the mechanical Q of the ceramic from 250 to 40. A dynamic stress of 2000 psi peak, applied for 15 sec, further reduced the Q factor from 40 to 16. Upon removing the dynamic stress, the Q factor gradually increased to 65. Surface temperature rise did not exceed 5°C. [Supported by Office of Naval Research, Code 468.]
Optical Means of Measurement of Rayleigh Wave Velocity and Attenuation
Authors: Kjosnes N. I. , Lester W. W. , Whymark R. R.
Published: September 2005

Rayleigh waves are useful in the study of the properties of metals. For example, flaws, grain structure, and residual machining stress may be examined. Simple apparatus using a laser optical probe of the order of 20 μ in diameter is described, which can yield accurate Rayleigh wave velocities on optically reflecting surfaces. Phase information in the Rayleigh wave is preserved as the probe diameter is more than an order of magnitude smaller than a Rayleigh wavelength up to 15 MHz. Velocities can be measured much higher in frequency. Another apparatus consisting of a Michelson interferometer with a Rayleigh wave traveling on one mirror is described. The mirror with the Rayleigh wave can be, for example, a steel sample with a particular grain structure. The interferometer is most useful for measuring Rayleigh wave attenuations. The use of the optical methods in detecting flaws is discussed. By using a thickness vibrating ceramic transducer as one mirror of the interferometer, a vibration amplitude of 28±3 Å was measured at 5 MHz with a 0.5-mm beam. [Supported by Air Force Materials Laboratory, U. S. Air Force.]
Development of a New, Large-Vehicle Acoustical Test Facility
Authors: Craft William H.
Published: September 2005

In recognition of the need for an adequate simulation of the dynamic environment experienced by a space vehicle during its launch operations, Lockheed Missiles and Space Company has built a new acoustical facility incorporating the latest state-of-the-art techniques in acoustical testing. The primary purpose of the facility is full-scale testing of large- and intermediate size space vehicles and their components. Design features include a 194 000 cu ft reverberant chamber, two smaller reverberant chambers, an anechoic room, and a centralized, digital data-acquisition and -control system. Topics discussed include test philosophy motivating the development of the facility, design goals, and an evaluation of the final results achieved.
Mobile Noise-Measurement Laboratory
Authors: Hemond Conrad J. , Stevensen Edward N.
Published: September 2005

Supported by a grant from the Connecticut Research Commission in December 1967, a feasibility study was undertaken to detail (a) the criteria for a mobile acoustics laboratory; (b) the selection of a field sound-spectral measurement system—with emphasis on the determination of highway noise; (c) the availability of a suitable vehicle; (d) the determination of a data-reduction system to be incorporated within the vehicle; and (e) the selection of auxiliary data systems to record weather conditions, traffic volume, and landscape features. The results of this study show that such a laboratory is feasible and can be equipped with standard laboratory-type instrumentation. Provision is made for complete data acquisition simultaneously from six measuring stations. Data are instantly displayed, stored, or converted to computer form. Provision for mobile telephone communication with the home office or central computer is also provided. Instant replay mobile television for scanning and identifying the noise source and its environment, vibration isolation of the equipment, and noise reduction procedures for the auxiliary power plant have been shown as feasible.
Radiation Impedance and Directivity of a Free-Flooding Ring (Squirter) Transducer
Authors: Yen T. , Duncan M. E. , Copley L. C.
Published: September 2005

The squirter presents formidable difficulties of analysis. D. H. Robey's theoretical model assumes infinite rigid flanges at each end and plane waves within the squirter, thus simplifying the analysis. Another approach (C. H. Sherman and N. G. Parke) applies separation-of-variables to a toroidal surface model, yielding accurate results for directivity but not for radiation reactance. The present study yielded numerical results from an integral equation formulation modeling the squirter as a vanishingly thin ring. Radiation impedance is computed accurately as a stationary integral functional whose integrand is previously computed as the solution of an integral equation. The directivity is computed by the stationary phase method. Results are presented in design graphs against frequency and transducer aspect ratio. These indicate the possibility of optimizing squirter design (see concurrent paper by M. C. Junger). Extensions of the present analysis to coaxial arrays of squirters or to include finite ring thickness appear straightforward, but require larger-scale computation. [Performed under contract with Office of Naval Research (Acoustics Programs).]
Auditory Neural Response Related to Microphonic Nonlinearity and Peripheral Activity of Olivocochlear Bundle
Authors: Nieder P. , Nieder I.
Published: September 2005

Neural and microphonic responses to bitonal stimuli of low-frequency components were recorded simultaneously from the basal turn of guinea pig cochleas using differential electrodes. Neural as well as microphonic responses to higher-frequency components are amplitude modulated by sufficiently intense lower-frequency components. These and published single-unit results imply the correlation of the microphonic derivative with the afferent neural generator. The demonstrated nonlinearity of the microphonic transfer characteristic is then of functional significance for the simultaneous transmission of multifrequency information by single units through pulse group coding, and is critical to masking and combination tone effects. Details of the asymmetrical modulation envelopes for both neural and microphonic responses implicate the olivocochlear bundle in the functioning of the group coding process—an inference supported by effects of OCB stimulation on bitonal response in the cat and fatigue studies. Cochlear efferents appear activated by a peripheral reflex loop firing during each cycle of a low-frequency stimulus but 180° out of phase with the afferent system. [Research supported in part by NIH grant.]
Acoustic and Electric Field Interaction for Neural Stimulation
Authors: Wolfe J. D. , Hixson E. L. , Harbourt C. O.
Published: September 2005

The electric potential Φ in a medium with varying conductivity is given by ∇2Φ+∇[ln(sgr;)]⋅∇ Φ=0. In a monovalent NaCl solution, the conductivity σ is linearly related to acoustic pressure. The above equation was solved by perturbation methods for a 1 MHz uniform electric field and spherically focused ultrasonic field. The maximum potential, in microvolts, in the focal region, in terms of peak applied potential V and acoustic radiated power W is given by Φmax=5.9 VW12. This expression and the potential distribution were verified experimentally in a normal saline solution. Potentials reportedly sufficient for neural stimulation were produced with safe electric and acoustic power levels. This method is recommended for nontraumatic in vivo stimulation in neural research. [Supported in part by Department of Defense Joint Services Electronics Program.]
Assembly of Cyclic Enterobacterial Common Antigen in
Escherichia coli
K-12
Authors: Kajimura Junko , Rahman Arifur , Rick Paul D.
Published: September 2005

We describe here the purification and quantification of a water-soluble cyclic form of enterobacterial common antigen (ECA
CYC
) from
Escherichia coli
K-12 as well as information regarding its subcellular location and the genetic loci involved in its assembly. Structural characterization of purified ECA
CYC
molecules obtained from
E. coli
K-12 revealed that they uniformly contained four trisaccharide repeat units, and they were substituted with from zero to four
O
-acetyl groups. Cells from overnight cultures contained approximately 2 μg ECA
CYC
per milligram (dry weight), and cell fractionation studies revealed that these molecules were localized exclusively in the periplasm. The synthesis and assembly of ECA
CYC
were found to require the
wzxE
and
wzyE
genes of the
wec
gene cluster. These genes encode proteins involved in the transmembrane translocation of undecaprenylpyrophosphate-linked ECA trisaccharide repeat units and the polymerization of trisaccharide repeat units, respectively. Surprisingly, synthesis of ECA
CYC
was dependent on the
wzzE
gene, which is required for the modulation of the polysaccharide chain lengths of phosphoglyceride-linked ECA (ECA
PG
). The presence of ECA
CYC
in extracts of several other gram-negative enteric organisms was also demonstrated; however, it was not detected in cell extracts of
Pseudomonas aeruginosa
. These data suggest that in addition to ECA
PG
, ECA
CYC
may be synthesized in many, if not all, members of the
Enterobacteriaceae
.
Effect of RyhB Small RNA on Global Iron Use in
Escherichia coli
Authors: Massé Eric , Vanderpool Carin K. , Gottesman Susan
Published: September 2005

RyhB is a noncoding RNA regulated by the Fur repressor. It has previously been shown to cause the rapid degradation of a number of mRNAs that encode proteins that utilize iron. Here we examine the effect of ectopic RyhB production on global gene expression by microarray analysis. Many of the previously identified targets were found, as well as other mRNAs encoding iron-binding proteins, bringing the total number of regulated operons to at least 18, encoding 56 genes. The two major operons involved in Fe-S cluster assembly showed different behavior; the
isc
operon appears to be a direct target of RyhB action, while the
suf
operon does not. This is consistent with previous findings suggesting that the
suf
genes but not the
isc
genes are important for Fe-S cluster synthesis under iron-limiting conditions, presumably for essential iron-binding proteins. In addition, we observed repression of Fur-regulated genes upon RyhB expression, interpreted as due to intracellular iron sparing resulting from reduced synthesis of iron-binding proteins. Our results demonstrate the broad effects of a single noncoding RNA on iron homeostasis.
Characterization of Sporulation Histidine Kinases ofBacillus anthracis
Authors: Brunsing Ryan L. , La Clair Chandra , Tang Sharon , Chiang Christina , Hancock Lynn E. , Perego Marta , Hoch James A.
Published: September 2005

The initiation of sporulation inBacillusspecies is regulated by the phosphorelay signal transduction pathway, which is activated by several histidine sensor kinases in response to cellular and metabolic signals. Comparison of the protein components of the phosphorelay betweenBacillus subtilisandBacillus anthracisrevealed high homology in the phosphorelay orthologs of Spo0F, Spo0B, and Spo0A. The sensor domains of sensor histidine kinases are poorly conserved between species, making ortholog recognition tenuous. Putative sporulation sensor histidine kinases ofB. anthraciswere identified by homology to the HisKA domain ofB. subtilissporulation sensor histidine kinases, which interacts with Spo0F. Nine possible kinases were uncovered, and their genes were assayed for complementation of kinase mutants ofB. subtilis, for ability to drivelacZexpression inB. subtilisandB. anthracis, and for the effect of deletion of each on the sporulation ofB. anthracis. Five of the nine sensor histidine kinases were inferred to be capable of inducing sporulation inB. anthracis. Four of the sensor kinases could not be shown to induce sporulation; however, the genes for two of these were frameshifted in allB. anthracisstrains and one of these was also frameshifted in the pathogenic pXO1-bearingBacillus cereusstrain G9241. It is proposed that acquisition of plasmid pXO1 and pathogenicity may require a dampening of sporulation regulation by mutational selection of sporulation sensor histidine kinase defects. The sporulation ofB. anthracisex vivo appears to result from any one or a combination of the sporulation sensor histidine kinases remaining.
The
lrp
Gene and Its Role in Type I Fimbriation in
Citrobacter rodentium
Authors: Cordone Angela , Mauriello Emilia M. F. , Pickard Derek J. , Dougan Gordon , De Felice Maurilio , Ricca Ezio
Published: September 2005

Citrobacter rodentium
is a murine pathogen that is now widely used as an in vivo model for gastrointestinal infections due to its similarities with human enteropathogens, such as the possession of a locus for enterocyte effacement (the LEE island). We studied the
lrp
gene of
C. rodentium
and found that it encodes a product highly similar to members of the Lrp (leucine-responsive regulatory protein) family of transcriptional regulators, able to recognize leucine as an effector and to repress the expression of its own structural gene. In enterobacteria, Lrp is a global regulator of gene expression, as it controls a large variety of genes, including those coding for cell appendages and other potential virulence factors. Based on the well-established role of Lrp on the expression of pilus genes in
Escherichia coli
, we also studied the role of Lrp in controlling the formation of the type I pilus in
C. rodentium
. Type I pili, produced by the
fim
system, are virulence factors of uropathogens, involved in mediating bacterial adhesion to bladder epithelial cells. Yeast agglutination assays showed that Lrp is needed for type I pilus formation and real-time PCR experiments indicated that Lrp has a strong leucine-mediated effect on the expression of the
fimAICDFGH
operon. Mutant studies indicated that this positive action is exerted mainly through a positive control of Lrp on the phase variation mechanism that regulates
fimAICDFGH
expression. A quantitative analysis of its expression suggested that this operon may also be negatively regulated at the level of transcription.
Analysis of Global Gene Expression and Double-Strand-Break Formation in DNA Adenine Methyltransferase- and Mismatch Repair-DeficientEscherichia coli
Authors: Robbins-Manke Jennifer L. , Zdraveski Zoran Z. , Marinus Martin , Essigmann John M.
Published: September 2005

DNA adenine methylation by DNA adenine methyltransferase (Dam) inEscherichia coliplays an important role in processes such as DNA replication initiation, gene expression regulation, and mismatch repair. In addition,E. colistrains deficient in Dam are hypersensitive to DNA-damaging agents. We used genome microarrays to compare the transcriptional profiles ofE. colistrains deficient in Dam and mismatch repair (dam, dam mutS, andmutSmutants). Our results show that >200 genes are expressed at a higher level in thedamstrain, while an additional mutation inmutSsuppresses the induction of many of the same genes. We also show by microarray and semiquantitative real-time reverse transcription-PCR that bothdamanddam mutSstrains show derepression of LexA-regulated SOS genes as well as the up-regulation of other non-SOS genes involved in DNA repair. To correlate the level of SOS induction and the up-regulation of genes involved in recombinational repair with the level of DNA damage, we used neutral single-cell electrophoresis to determine the number of double-strand breaks per cell in each of the strains. We find thatdammutantE. colistrains have a significantly higher level of double-strand breaks than the other strains. We also observe a broad range in the number of double-strand breaks indammutant cells, with a minority of cells showing as many as 10 or more double-strand breaks. We propose that the up-regulation of recombinational repair indammutants allows for the efficient repair of double-strand breaks whose formation is dependent on functional mismatch repair.
Biochemical Properties of a Putative Signal Peptide Peptidase from the Hyperthermophilic Archaeon
Thermococcus kodakaraensis
KOD1
Authors: Matsumi Rie , Atomi Haruyuki , Imanaka Tadayuki
Published: September 2005

We have performed the first biochemical characterization of a putative archaeal signal peptide peptidase (SppA
Tk
) from the hyperthermophilic archaeon
Thermococcus kodakaraensis
KOD1. SppA
Tk
, comprised of 334 residues, was much smaller than its counterpart from
Escherichia coli
(618 residues) and harbored a single predicted transmembrane domain near its N terminus. A truncated mutant protein without the N-terminal 54 amino acid residues (ΔN54SppA
Tk
) was found to be stable against autoproteolysis and was examined further. ΔN54SppA
Tk
exhibited peptidase activity towards fluorogenic peptide substrates and was found to be highly thermostable. Moreover, the enzyme displayed a remarkable stability and preference for alkaline pH, with optimal activity detected at pH 10. ΔN54SppA
Tk
displayed a

K
m

of 240 ± 18 μM and a
V
max
of 27.8 ± 0.7 μmol min
−1
mg
−1
towards Ala-Ala-Phe-4-methyl-coumaryl-7-amide at 80°C and pH 10. The substrate specificity of the enzyme was examined in detail with a FRETS peptide library. By analyzing the cleavage products with liquid chromatography-mass spectrometry, ΔN54SppA
Tk
was found to efficiently cleave peptides with a relatively small side chain at the P-1 position and a hydrophobic or aromatic residue at the P-3 position. The positively charged Arg residue was preferred at the P-4 position, while substrates with negatively charged residues at the P-2, P-3, or P-4 position were not cleaved. When predicted signal sequences from the
T. kodakaraensis
genome sequence were examined, we found that the substrate specificity of ΔN54SppA
Tk
was in good agreement with its presumed role as a signal peptide peptidase in this archaeon.