bluuebunny/crossref_metadata_2025 huggingface dataset:
A New, Iterative, Synchronous-Response Algorithm for Analyzing the Morton Effect
Authors: Childs Dara W. , Saha Rohit
Published: May 2012

Morton Effect problems involve the steady increase in rotor synchronous-response amplitudes due to differential heating across a fluid-film bearing that is induced by synchronous response. The present work presents a new computational algorithm for analyzing the Morton Effect. Previous approaches were based on Eigen or Nyquist analyses for stability studies and predicted an onset speed of instability. The present algorithm starts with a steady state elliptical orbit produced by the initial imbalance distribution, which is decomposed into a forward-precessing circular orbit and a backwards-precessing circular orbit. A separate (and numerically intensive) calculation based on the Reynolds equation plus the energy equation gives predictions for the temperature distributions induced by these separate orbits for a range of orbit radius-to-clearance ratios. Temperature distributions for the forward and backward orbits are calculated and added to produce the net temperature distribution due to the initial elliptic orbit. The temperature distribution is assumed to vary linearly across the bearing and produces a bent-shaft angle across the bearing following an analytical result due to Dimoragonas. This bent-shaft angle produces a synchronous rotor excitation in the form of equal and opposite moments acting at the bearing’s ends. For a rotor with an overhung section, the bend also produces a thermally induced imbalance. The response is due to: (1) the initial mechanical imbalance, (2) the bent-shaft excitation, and (3) the thermally-induced imbalance are added to produce a new elliptic orbit, and the process is repeated until a converged orbit is produced. For the work reported, no formal stability analysis is carried out on the converged orbit. The algorithm predicts synchronous response across the rotor’s speed range plus the speed where the response amplitudes becomes divergent by approaching the clearance. Predictions are presented for one example from the published literature, and elevated vibration levels are predicted well before the motion diverges. Synchronous-response amplitudes due to Morton Effect can be orders of magnitude greater than the response due only to mechanical imbalance, particularly near rotor critical speeds. For the example considered, bent-shaft-moment excitation produces significantly higher response levels than the mechanical imbalance induced by thermal bow. The impact of changes in: (1) bearing length-to-diameter ratio, (2) reduced lubricant viscosity, (3) bearing radius-to-clearance ratio and (4) overhung mass magnitude are investigated. Reducing lubricant viscosity and/or reducing the overhung mass are predicted to be the best remedies for Morton Effect problems.
A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Three Dimple Geometries
Authors: Valentino Michelle I. , Tran Lucky V. , Ricklick Mark , Kapat J. S.
Published: May 2012

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for waste heat recovery. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 28,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to isolate the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the nonfeatured portion of the channel wall resulting from the secondary flows created by the features. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with the highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested. Heat transfer within the dimple was shown to be less than that of the surrounding flat regions at low Reynolds numbers. Results for each dimple geometry show that dimples are capable of promoting heat transfer over the entire bottom wall surface as well as the side walls; thus the effects are not confined to within the dimple cavity.
Controlling Gasoline Low Temperature Combustion by Diesel Micro Pilot Injection
Authors: Eichmeier Johannes , Wagner Uwe , Spicher Ulrich
Published: May 2012

The simultaneous reduction of fuel consumption and pollutant emissions, namely NOx and soot, is the predominant goal in modern engine development. In this context, low temperature combustion concepts are believed to be the most promising approaches to resolve the above mentioned conflict of goals. Disadvantageously these combustion concepts show high peak pressures or high rates of pressure rise due to early ignition and high reaction rates especially at high loads. Furthermore, there are still challenges in controlling combustion phasing. In this context using a small amount of pilot diesel injected directly into the combustion chamber to ignite a highly diluted gasoline air mixture can overcome the aforementioned difficulties. As the gasoline does not ignite without the diesel, the pilot injection timing can be used to control combustion phasing. By increasing dilution even high loads with low rates of pressure rise and without knocking are possible. This paper shows the results of experimental investigations carried out on a heavy duty boosted single cylinder diesel engine. Based on the indicated cylinder pressure, the combustion process is characterized by performing knock analyses as well as thermodynamic analyses. Furthermore, an optically accessible engine has been set up to investigate both the diesel injection and the combustion process by means of digital high speed imaging. Together with the thermodynamic analyses the results of these optical investigations make up the base for the presented theoretical model of this combined diesel-gasoline combustion process. To show the load potential of this Dual-Fuel-CAI concept, the engine was operated at 2100 1/min with an IMEP of 19 bar. NOx emissions did not exceed 0.027 g/kWh.
Aero-Thermodynamic Consideration of Single-Crystal-Silicon Premixed-Fuel Microscale Can Combustor
Authors: Namura Moriaki , Toriyama Toshiyuki
Published: May 2012

This paper describes the aero-thermodynamic design, microfabrication and combustion test results for a single-crystal-silicon premixed-fuel microscale can combustor. The combustion chamber volume is 277 mm3, and the microscale can combustor was fabricated by silicon bulk micromachining technology. Hydrogen fuel-air premixing was performed in the combustion test. The operation space in which stable combustion occurred was experimentally determined from the combustion temperature and efficiency for various mass flow rates and equivalence ratios. The expression for the combustion efficiency under conditions where the overall rate of heat release is limited by the chemical kinetics was consistent with the burning velocity model. The flame stabilization, the range of equivalence ratios and the maximum air velocity that the combustor can tolerate before flame extinction occurs were in agreement with the well - stirred reactor (WSR) and combustion loading parameter (CLP) models. A proposed aero-thermodynamic design approach based on these three models provides a physical interpretation of the experimental results in the operation space of stable combustion. Furthermore, this approach provides a unified physical interpretation of the stable combustion operation spaces of microscale combustors with various dimensions and configurations. Therefore, it is demonstrated that the proposed aero-thermodynamic approach has an important role in predicting the preliminary aerodynamic design performances of new microscale combustors.
Establishment of Nonlinear Dynamic Model for Prediction of Rotordynamic Instability of Steam Turbine Rotor-Bearing System Caused by Partial Admission
Authors: Cui Ying , Liu Zhansheng , Yu Daren , Duan Yanfeng
Published: May 2012

A nonlinear dynamic model is developed for a rotor-bearing system with radial steam force due to partial admission, taking into account the prediction of subsynchronous instability of a steam turbine. The optimum schemes are obtained by comparing the rotor responses subjected to maximal radial steam forces in different partial admission schemes. It is found through comparison that the instability of a rotor-bearing system is directly related to the direction of the radial steam force in the partial admission scheme.
Large-Eddy Simulation of Flow and Convective Heat Transfer in a Gas Turbine Can Combustor With Synthetic Inlet Turbulence
Authors: Patil Sunil , Tafti Danesh
Published: May 2012

Large eddy simulations of swirling flow and the associated convective heat transfer in a gas turbine can combustor under cold flow conditions for Reynolds numbers of 50,000 and 80,000 with a characteristic Swirl number of 0.7 are carried out. A precursor Reynolds averaged Navier-Stokes (RANS) simulation is used to provide the inlet boundary conditions to the large-eddy simulation (LES) computational domain, which includes only the can combustor. A stochastic procedure based on the classical view of turbulence as a superposition of the coherent structures is used to simulate the turbulence at the inlet plane of the computational domain using the mean flow velocity and Reynolds stress data from the precursor RANS simulation. To further reduce the overall computational resource requirement and the total computational time, the near wall region is modeled using a zonal two layer model (WMLES). A novel formulation in the generalized co-ordinate system is used for the solution of effective tangential velocity and temperature in the inner layer virtual mesh. The WMLES predictions are compared with the experimental data of Patil et al. (2011, “Experimental and Numerical Investigation of Convective Heat Transfer in Gas Turbine Can Combustor,” ASME J. Turbomach., 133(1), p. 011028) for the local heat transfer distribution on the combustor liner wall obtained using robust infrared thermography technique. The heat transfer coefficient distribution on the liner wall predicted from the WMLES is in good agreement with experimental values. The location and the magnitude of the peak heat transfer are predicted in very close agreement with the experiments.
Use of Low/Mid-Temperature Solar Heat for Thermochemical Upgrading of Energy, Part I: Application to a Novel Chemically-Recuperated Gas-Turbine Power Generation (SOLRGT) System
Authors: Zhang Na , Lior Noam
Published: May 2012

This paper is the first part of a study presenting the concept of indirect thermochemical upgrading of low/mid temperature solar heat, and demonstration of its integration into a high efficiency novel hybrid power generation system. The proposed system consists of an intercooled chemically recuperated gas turbine (SOLRGT) cycle, in which the solar thermal energy collected at about 220 °C is first transformed into the latent heat of vapor supplied to a reformer and then via the reforming reactions to the produced syngas chemical exergy. The produced syngas is burned to provide high temperature working fluid to a gas turbine. The solar-driven steam production helps to improve both the chemical and thermal recuperation in the system. Using well established technologies including steam reforming and low/mid temperature solar heat collection, the hybrid system exhibits promising performance: the net solar-to-electricity efficiency, based on the gross solar thermal energy incident on the collector, was predicted to be 25–30%, and up to 38% when the solar share is reduced. In comparison to a conventional CRGT system, 20% of fossil fuel saving is feasible with the solar thermal share of 22%, and the system overall efficiency reaches 51.2% to 53.6% when the solar thermal share is increased from 11 to 28.8%. The overall efficiency is about 5.6%-points higher than that of a comparable intercooled CRGT system without solar assist. Production of NOx is near zero, and the reduction of fossil fuel use results in a commensurate ∼20% reduction of CO2 emissions. Comparison of the fuel-based efficiencies of the SOLRGT and a conventional commercial Combined Cycle (CC) shows that the efficiency of SOLRGT becomes higher than that of CC when the solar thermal fraction Xsol is above ∼14%, and since the SOLRGT system thus uses up to 12% less fossil fuel than the CC (within the parameter range of this study), it commensurately reduces CO2 emissions and saves depletable fossil fuel. An economic analysis of SOLRGT shows that the generated electricity cost by the system is about 0.06 $/kWh, and the payback period about 10.7 years (including 2 years of construction). The second part of the study is a separate paper (Part II) describing an advancement of this system guided by the exergy analysis of SOLRGT.
Intraoral Air Pressure during Vocal and Whispered Speech
Authors: Murry Thomas , Brown William S.
Published: May 2012

Intraoral air pressure (P10) has been used to distinguish speech production parameters such as voicing and, to a lesser degree, place of articulation. At least four physiological mechanisms have been hypothesized to account for the variations in air pressure associated with consonant production. In this study, P10 was measured during whispered and vocal speech to examine the nature of the pressure variations found in voiced and voiceless consonants in the presence and absence of glottal closure and increased air volume. Subjects read a variety of sentences, CV syllables, and CV syllables in carrier phrases. From these protocols, intraoral air pressures were measured for consonants /p,b,m,t,d,n,s,z/ in initial, medial, and final phonetic positions. In one experimental condition, both P10 and expired air volume were measured. Results indicate that the vocal P10 is in agreement with previous data. For the whispered samples, there was little difference in peak pressure between the voiced and voiceless plosives; nasals showed lowest peak values. Whispered samples did not always produce the highest pressures for a given consonant; however, expelled air volume was always greater for the whispered samples.
Different Vocal Tract Shapes with Similar Formant Frequencies: Evidence from Twi
Authors: Lindau Mona
Published: May 2012

Tracings from cine x ray of the vowels of four speakers of Twi clearly demonstrated that vowels from harmony set 1 [/i,e,o,u/] systematically differed from vowels of harmony set 2 [ι,ε,(a),ɔ,ο/] by different vocal tract shapes: set 1 vowels had a wider pharynx and an advanced tongue root, while set 2 vowels had a narrower pharynx and a retracted tongue root. In spite of their different vocal tract shapes the two vowels /ι/ and /e/ have very similar formant frequencies. The difference in the vocal tract shapes is that /e/ has a wider pharynx and also a wider mouth cavity than /ι/. The fact that these vocal tract shapes produce similar formant frequencies can be explained with reference to perturbation theory: the area functions of these two vowels are approximately symmetric about the midpoint. Similar acoustic and articulatory data were found for one speaker of Ijo.
On the Relationship between Formant Bandwidths and Vocal-Tract Shape Features
Authors: Rice Lloyd , Ohman Sven
Published: May 2012

Theoretical and experimental studies by Borg, Pinson, Schroeder, Mermelstein, and Heinz have demonstrated that the formant frequencies of vocalic speech sounds do not uniquely determine the area function of the vocal tract. For instance, a constant area function corresponding to an idealized neutral vowel can be perturbed in infinitely many ways without changing the formant frequencies, provided that the perturbing function is sufficiently “small” and is symmetric about the midpoint of the glottis-to-lip midline. It will be shown that the acoustic import of the frequency invariant perturbations is systematically reflected in the bandwidths of the formants. This claim will be supported by data collected from model experiments in which the pressure response at the lips to a velocity impulse excitation at the glottis is computed for a variety of vocal tract shapes and analyzed by means of the fast Fourier transform. The frequencies and bandwidths of the formants observed in the amplitude spectra thus computed are determined through an analysis-by-synthesis technique and related to certain features of the perturbations. The results shed some light on the possible role of the band-widths in speech perception.
Effect of Speaking Rate on Labial Consonant-Vowel Articulation
Authors: Gay Thomas , Ushijima Tatsujiro , Hirose Hajime , Cooper Franklin S.
Published: May 2012

This paper describes the results of a study of the effect of speaking rate on the articulation of the consonants /p,w/, in combination with the vowels /i,a,u/. Two subjects read a list of nonsense syllables containing /p,w/, in all possible VCV combinations with /i,a,u,/ at both moderate and fast speaking rates. EMG recordings from muscles that control movements of the lips, tongue, and jaw were recorded simultaneously with high-speed lateral-view x-ray films of the tongue and jaw, and high-speed full-face motion pictures of the lips. For labial consonant production, an increase in speaking rate is accompanied by an increase in the activity level of the muscle (orbicularis oris) and slightly faster rates of lip movement (both closing and opening). Vowel production, however, shows opposite effects: an increase in speaking rate is accompanied by a decrease in the activity level of the genioglossus muscle and, as shown by the x-ray films, evidence of target undershoot. Jaw movement data show more variable, context-dependent effects of speaking rate. Observed differences are explained in terms of the muscle systems involved.
Measurement of Dipole Source Distributions on Components of an Axial Flow Fan
Authors: Leggat L. J.
Published: May 2012

Complicated noise generators such as turbomachines can be represented by a geometrically fixed array of localized dipole sources whose distribution when integrated over the surfaces of the machine sum to the net surface dipole contribution to the farfield sound. Experiments were carried out on an off-the-shelf axial flow fan wherein blade surface pressures were detected with an embedded miniature pressure transducer, and motor support strut pressure fluctuations with an embedded quarter-inch microphone. These pressures were cross-correlated against the farfield sound, with time delay. Both the source and the farfield signals were bandpass filtered at the blade passage frequency of the fan, before being correlated. Results gave information revealing causes of the on-axis noise radiation from the fan at the blade passage frequency. The contribution of pure-tone radiation from the struts was compared to that from the fan blades. The effect on the overall sound pressure level of variations in phase of the sources, both on the gtruts and on the blades, was determined. Details of the experimental approach are presented, and the interpretation and usefulness of the data is discussed. [Work supported by Canadian DRB Grant No. 9611-03.]
Cross-Correlation Evaluation of the Contribution to Engine Exhaust Noise Made by Internal Sources
Authors: Plett E. G. , Summerfield M.
Published: May 2012

Internal sources of flow unsteadiness can contribute substantially to the airfield noise from jet engine exhausts. Since this noise contribution often takes an indirect path to the farfield observer, it is not always clear that the source is inside the duct and not in the jet, as a directional microphone might suggest. Direct cross correlations, between in-duct and farfield microphones can be used to demonstrate the relationship between the source region and the observed signal. In addition to knowing that the two are related, it is of interest to know how much of the farfield noise is due to sources inside the duct. Experiments in which a source in the duct is driven by sine waves, narrow-band noise, and broad-band noise are used to demonstrate the use of the normalized cross correlation to show a quantitative relationship between the source region and observer. Aerodynamic sources are added and the method of determining their relative importance is discussed. The technique is then applied to the evaluation of the contribution to overall exhaust noise made by unsteady combustion and/or flow over struts inside an engine. [Supported by NASA Grant NGR 31-001-241.]
Detection of Signals of Unpredictable Frequency with Simultaneous Contralateral Cue
Authors: Creelman C. Douglas
Published: May 2012

Thresholds were found and tracked for each of an ensemble of signal frequencies using the PEST adaptive testing procedure under three different conditions, for three observers. On each trial, the signal was in one of two time intervals, and was presented at the current best estimate of threshold for that frequency. The most interesting situation was where the signal frequency on each trials was selected at random from the ensemble, while during both intervals within the trial the chosen signal was presented to the contralateral ear without noise, in phase and equal in amplitude with the chosen signal. This is the MDCC paradigm (monaural detection with contralateral cue), which has been extensively investigated by M. M. Taylor and his co-workers. Other conditions involved presentation of the same frequency each of a long run of trials, with and without the contralateral cue. These results confirm those of Taylor and Forbes [J. Acoust. Soc. Am. 46, 1519–1526 (1969)] in showing lower frequencies aided by the contralateral cue more than higher frequencies, with considerable individual differences both in the magnitude of the threshold improvement and in the frequencies over which the MDCC paradigm is helpful. The contralateral cue was helpful to observers in overcoming the loss due to frequency uncertainty only in the case of those frequencies for which the observer was able to use the cue to lower his threshold with fixed-frequency detection. A contralateral cue is not necessarily successful in specifying the signal to be listened for when frequency is unpredictable. Some members of the ensemble continue to show the 3–5 dB effect of uncertainty, and these frequencies are those for which MDCC is not helpful to simple detection. [Supported by the Canadian National Research Council.]
Speed of Sound in Fluorocarbon Liquids
Authors: Madigosky W. M.
Published: May 2012

Fluorocarbon liquids are used as acoustic lens mediums in underwater sound focusing devices; therefore, the speed of sound in them as a function of pressure is essential information for the designer who wishes his equipment to operate in the ocean depths. Accordingly, sound speeds were measured as a function of temperature and pressure in a number of liquids likely to be used for this purpose. The temperature and pressure range of measurement covered was that which might be encountered in the ocean : 0° to 30°C and 0 to 700 kg/cm2. In addition, values were obtained for Rao's constant and Beyer's parameter of nonlinearity, B/A. The unusually high values of B/A found ofnonlinearity,in the fluorocarbon liquids is consistent with their low sound speeds and suggests that these liquids, or other low-velocity materials, may be of some use as a high-efficiency medium for parametric sound generation. The specific liquids investigated were Fluorolube (FS-5); FC-43, FC-75, and FC-88 (all fiuorinated hydrocarbons); FC-114B2 (1,2 dibromotetrafiuorethane) and Freon-C51-12 (perfluorodimethyocyclobutane) ; and Freon 113 (Freon TF, MS-182). The sound speed was determined using the method of Greenspan and Tsehiegg, which measures the pulse repetition rate necessary to overlap rf pulses of adjacent echo trains.
The Effect of Surface Tension on Rectified Diffusion Thresholds
Authors: Crum L. A.
Published: May 2012

Measurements have been made as a function of surface tension of the threshold for growth by rectified diffusion for air bubbles in a stationary sound field. The measurements were made in distilled water with varying amounts of surfactant added to reduce the surface tension. The air bubbles were trapped by the sound field and their radii monitored as the acoustic pressure amplitude was slowly increased. The radii of the bubbles were obtained by measuring terminal-velocity rise times and using a modified form of Stokes' law. Comparisons of theory and experiment show good agreement with the theoretical predictions of Eller [J. Acoust. Soc. Am. 52, 1447–1449 (1972)]. Comparisons will also be made with the variation with surface tension of the thresholds for vaporous and gaseous cavitation.
Low Dispersion Tube
Authors: Sachs Thomas D. , Grimes Ralph S.
Published: May 2012

Theory is presented to explain the observed low dispersion of a specially shaped tube described at the April 1969 meeting, compared with a cylindrical tube of comparable dimensions and operating frequency. A computer model which includes the nearfield phenomena of both transmitting and receiving transducers indicates the limitations and necessary mode of operation of the low-dispersion tube to permit perturbed propagation parameter measurements to be made in a confined space where the confining boundaries do not interfere with the measurement. Experimental results are given which are in good agreement with the predictions of the model.
The Real and Imaginary Parts of the Complex Viscoelastic Modulus for Boron Fiber Reinforced Plastics (BFRP)
Authors: Paxson E. B.
Published: May 2012

The general viscoelastic model was chosen to represent the mechanical properties of boron fiber reinforced plastics (BFRP). The experimental configuration selected was that of a thin beam subjected to transverse vibration. The mechanical properties of the beam (in the direction “x” parallel to the length of the beam) then manifest themselves in the form of a viscoelastic complex modulus, Exx* = Exx′+iExx″. In this investigation the purposes were to define parameters relative to the dynamic material properties of boron fiber reinforced plastic (BFRP), to establish quantitative values for these parameters by experimental measurement, and to compare these quantities for BFRP with the same parameters for a metallic material such as aluminum 2024-T4 alloy. Born laminates used in these studies were fabricated from NARMCO 5505 preim-pregnated boron fiber epoxy tape. Plots of storage modulus Exx′ and loss modulus Exx″ as a function of excitation frequency are presented for three fiber orientations, 0° (unidirectional), ±45° (crossply), and 90° (all transverse). Also presented is the damping (or loss) factor, nxx, as a function of excitation frequency for the three above-mentioned fiber orientations. The values obtained for damping factor are compared with those obtained by measuring the exponential decay of BFRP beams initially excited in the free-free mode of vibration. Damping factors obtained from free-free vibration experiments were lower than those obtained from the forced vibration experiments for all materials concerned.
Time Domain Pitch Extraction Algorithm
Authors: Schulman R. J.
Published: May 2012

An algorithm is described for determining the pitch period of voiced speech in real time. The input signal to the algorithm is the residual or error signal of a 10th-order adaptive linear predictor. The pitch period estimated is updated on each speech sample based on an analysis of the present and past input samples. Pitch period is determined by locating sharp pitch peaks in the short-term power of the prediction residual signal. The instantaneous pitch period is the time separation of two adjacent pitch peaks. The algorithm employs a time-moving search window and a time-varying threshold level to locate pitch peaks. Various tests and procedures are incorporated into the algorithm to handle the special cases of false and missed pitch peaks. Detected errors are corrected within the algorithm by employing past data. Unlike the correlation or averaging methods of pitch extraction, which require large amounts of storage and arithmetic operations, the time domain method requires a minimal of storage and only simple comparisons of amplitudes. Experimental results illustrating the algorithm performance will be presented.
A Theoretical Justification for the Asynchronous Application of Linear Prediction to Speech Analysis
Authors: Allen J. B.
Published: May 2012

It is well known that if one has an unknown, causal, linear system h(t) excited by an input signal x(t) and having an output y(t), then minimization of J1 =  ∫ −∞∞ [y(t) − ĥ(t)* x(t)]2dt, by variation of ĥ(t), is attained when ĥ(t) equals h(t). Thus, one may determine the unknown system h(t) by this procedure given the system input and output. Not so well known is that h(t) may also be determined, assuming that it is minimum phase and causal, by a minimization with respect to q(t) of the quantity J2 =  ∫ −∞∞ [q(t)*y(t))2dt] when the input x(t) is known to be either uncorrelated noise or an impulse, but is otherwise unknown. It will be argued that the above result justified the asynchronous application of linear prediction to speech analysis.
A Comparison of the Intonation Patterns of Nonstandard Black English and Standard English
Authors: Winkler Henry J.
Published: May 2012

The purpose of this study was to determine if intonation pattern differences exist between Black and Standard English as spoken in a formal (school) situation. Taped speech samples of Black English and Standard English were gathered from seventh and eighth grade males. The interview was divided into script reading and free discourse sections. A total of 60 subjects were interviewed, 30 Black English speakers and 30 Standard English speakers. Samples of declarative and interrogative sentences in both the reading and free discourse situations were rerecorded for analysis. A computer pitch extraction routine and a spectrograph were utilized to develop graphic and tabular data displays. All data are presently undergoing analysis.
Interaction between Test Word Duration and Length of Utterance
Authors: Lehiste Ilse
Published: May 2012

It has been found that in Dutch and Swedish, the duration of the syllable nucleus decreases as the number of syllables which remain to be produced in the word at the beginning of the syllable concerned increases. The present study was designed to test, for English, whether this principle holds for whole utterances. Four lists of words, totaling 122 items, were recorded by two speakers in three different frames. The duration of words placed in the basic frame “Say … instead” was compared with the durations of the same words placed in the frames “Sometimes it's useful to say the word … instead” and “The word … is sometimes a useful example.” The results indicate that at the utterance level, the length of the whole utterance has a greater effect on the duration of the test words than the number of syllables preceding or following the test word in the frame.
Convection and Refraction in Jet Noise
Authors: Ribner H. S.
Published: May 2012

Lighthill's theory of jet noise employs a nonconvected wave equation forced by a certain source term. In its exact form this term accounts fully for the co-moving fluid, including convection and refraction effects. In practice, holding the density factor constant suppresses the latter and throws some doubt on values of the former. Alternate formulations via convected wave equations are gaining interest. An attempt is made to bring some coherence into the subject.
Use of Normalized Filtered Cross Correlation to Determine the Sources of Aerodynamic Noise Radiation
Authors: Scharton T. D. , White P. H.
Published: May 2012

The normalized cross correlation between the aerodynamic pressure measured at a point in the source region and the sound pressure measured at a farfield receiver point is interpreted as the percentage of the mean-square sound radiated to the receiver point by the pressure fluctuation at the source point. By filtering and varying the angle to the receiver point, the normalized source-receiver cross correlation yields the spectral and directional characteristics of the radiation. When these source-receiver cross-correlation data are combined with pressure cross correlations measured at two points in the source region, a complete description of the sources of radiated aerodynamic noise is obtained. Examples of the application of normalized cross-correlation measurements to jet noise and surface noise problems are presented.
A New Anechoic Facility for Supersonic Hot Jet Noise Research at Lockheed-Georgia
Authors: Burrin R. H. , Dean P. D. , Tanna H. K.
Published: May 2012

Much confusion about jet noise has come about as a direct result of inadequate facilities and insufficient knowledge and control of test conditions, in many cases giving rise to completely erroneous conclusions. The facility described here has been carefully designed, accounting for the shortcomings of other facilities and being guided by the stringent demands of ongoing jet noise research at Lockheed. The design goal was the capability of testing model jets up to 2000°F at pressure ratios as high as 8, in a free-field environment anechoic at all frequencies above 200 Hz. A comprehensive series of flow visualization and temperature mapping experiments in a one-sixth scale-model anechoic room was conducted. The results dictated the design of the exhaust collector/muffler to provide entrainment and room cooling air in the quantities demanded by the jet operating conditions. In order to optimize the choice of material and anechoic wedge design to achieve the 200-Hz requirement, a special impedance tube was used extensively in performance evaluations. Some features of the facility are (1) an exhaust collector providing air in quantities dictated by the particular jet operating condition with no special forced-air injection or fan installation and (2) a “cherry-picker” crane used to gain access to instrumentation, etc., for maintenance, calibration, and setup, thus eliminating the need for access platforms, etc. The crane is stowed by remote control under an anechoic cover during all test operations. The superior performance of the room is described by intensity/distance plots obtained from a fixed loudspeaker source and moving microphone installation.
Role of the Difference Tone f
2-f
1 in Masking
Authors: Krammer F. G. , Greenwood D. D.
Published: May 2012

When signals are presented on the immediate high-frequency side of a pure-tone masker, it is not the signals, but rather combination tones, that are detected at masked threshold [Greenwood, J. Acoust. Soc. Am. 50, 502–543 (1971)]. At low to moderate masker intensities, the detected combination tone is 2f1 -f2, where f1 is the masker frequency and f2 is the signal frequency. At higher masker levels, the combination tone f2 - f1 becomes large enough to play a role. To investigate this role, the combination tones f2 - f1 and 2f1 - f2 were selectively masked in different low-frequency regions, to identify their effects. As has been known, the notch region on the high side of the pure-tone masking pattern creates a secondary peak, which shifts upward in frequency and height as masker intensity is raised. At masker levels sufficient to shift this secondary peak upward, beyond 1.5 times f1 (masker), both 2f1 - f2(C1) and 2f2 - f1(D1) are detected with about equal likelihood in the higher-frequency part of the notch region. Either C1, D1 or both may be detected since their intensities become quite similar at higher masker levels, as supported by more direct estimates [Greenwood, J. Acoust. Soc. Am. 52, 1137–1167 (1972); Hall, J. Acoust. Soc. Am. 51, 1863–1881 (1972)].
The Effect of Masker Duration on Forward and Backward Masking
Authors: Penner M. J. , Cudahy E. , Jenkins G. W.
Published: May 2012

Temporal masking of clicks by noise was investigated using forward and backward masking paradigms. Both the noise duration and the temporal separation, Δt, between the click and the noise were varied. For very brief Δt's (100 μsec) and for very long Δt's (100 μsec) the duration of the masker did not greatly affect the click threshold. However, for intermediate Δt's, the threshold of the click increased by as much as 44 dB as the noise duration increased from 0.1 to 100 msec. Temporal weighting functions, which describe the relative effectiveness of the noise as a function of Δt, were computed from these data.
Additivity of Forward and Backward Tonal Masking
Authors: Bergert B. , Yost W. A.
Published: May 2012

The temporal masking of a 1000-Hz probe tone by a 70-dB-SPL 1000-Hz masker was investigated using a forward masking paradigm, a backward masking paradigm and a combined forward-backward masking piradigm. The duration of the probe tone was 10 msec with a 4-msec rise-fall time, while the masker duration was 60 msec with a 4-msec rise-fall time. In the forward and backward masking conditions, the masking of the probe tone was measured as a function of the time (ΔT) between the masker and the probe tone. Selected ΔT's from 0 to 20 msec were used. In the combined forward-backward masking conditions, masking was measured as a function of both the inter-masker-interval and the position of the probe in time with respect to the forward and backward maskers. Inter-masker-intervals ranged from 10 to SO msec. Observers' thresholds were measured using a 2ATFC procedure. Combined forward-backward masking conditions produced masking levels which were higher than expected on the basis of a residual power prediction. The difference between observed and predicted masking levels decreased as ΔT-forward or ΔT-backward was increased.
Tone-on-Tone Masking
Authors: Cudahy E. , Leshowitz B.
Published: May 2012

Detection of a brief (5-msec) sinusoid in the presence of a simultaneous tonal masker was inviatigated. The masker was either a gated sinusoid or a continuous tone. Both signal and gated masker were bandpass filtered. In the continuous-masker condition, when masker frequency was lower than signal frequency, a notch or shelf, similar to that reported by Greenwood [J. Acoust. Soc. Am. 51, 502–543 (1971)] was exhibited. The failure to find a comparable notch for the gated-masker condition suggests that combination tones may not be involved in detection in this condition. When masker frequency was higher than signal frequency, signal threshold in the continuous-masker condition was lower than in the gated-masker condition by as much as 20 dB. This difference in masking between continuous and gated conditions cannot be attributed to the presence of combination tonee; or to energy splatter produced by the gated masker. [This research was supported by an NIH grant.]
Masking with Narrow-Band FM Noise
Authors: Margolis R. H. , Small A. M.
Published: May 2012

Masked thresholds were measured for signal frequencies below, within, and above two 190-Hz noise bands centered arithmetically at 1125 Hz. One noise band was computer synthesized and had amplitude fluctuations characteristic of analog noise bands typically used in masking experiments. The other noise band, matched in spectrum and level to the synthesized noise band, was generated by modulating the frequency of a sinusoid with a low-pass filtered, clipped, Gaussian noise. The resulting waveform was free of envelope fluctuations. Masked thresholds in the FM noise were 5–10 dB lower than in the synthetic noise in the flat portions of the spectra. Synthesized noise resulted in trapezoidal appearing audiograms. The FM noise audiogram tended to be unimodal. These results are interpreted as evidence in support of envelope detection hypotheses which predict substantially improved performance in the detection of signals in noise when the noise has a constant envelope.
Sound Radiation from a Moving Rigid Sphere
Authors: Wu Peter T. K. , Eisler Thomas J.
Published: May 2012

Most treatments of moving spatially extended sources in some way model the source as a point. Thus, in effect they approximate the solution by the first term in a multipole expansion. The latter is similar to a Taylor expansion in the sense that it is valid when evaluated at a retarded time at which the velocity has time derivatives of all orders [T. J. Eisler, J. Acoust. Soc. Am. 52, 210 (1972)]. In contrast, the present treatment is similar to an eigenfunction expansion which can be used for less regular functions, for example, a velo-city-versus-time curve which has a corner. We find that such singularities cause a burst of sound radiation. Our method, which is applicable to source distributions which move as a rigid sphere, is based on an expansion theorem for spherical wave functions [R. A. Sack, J. Math. Phys. 5, 252 (1964)]. This is used to expand the integrand of the retarded solution of the wave equation, and the resulting expansion can be summed in certain special cases. The solution is found to depend on the history of the source over an interval of finite duration which includes the retarded time of the center. The method has been applied to a moving rigid sphere using the theory of Ffowcs-Williams and Hawkings [Phil. Trans. Roy. Soc. London A264, 321 (1969)].
Broad-Band Scattering Characteristics as a Basis for Object Identification
Authors: Essex D. D. , Fransdal L. A. , Simmons R. L. , Lockwood J. C.
Published: May 2012

A preliminary experimental investigation of the identification of simple geometric objects by means of their broad-band scattering characteristics has been conducted. The objective of the investigation was to determine the feasibility of identifying the backscattered signature of an object insonified by pseudo-random noise by comparing the unknown measured signature with each of a group of known recorded signatures that includes the signature of the unknown object. Spheres, cylinders, and cubes of various materials, flooded and airfilled, were suspended in water in a free field and insonified with pulses of pseudorandom noise. Echoes in the 0–50-kHz band were received and analyzed by means of a fast-Fourier processor. Correlations were performed that supported the contention that the signatures at a given aspect of an object are unique and re-peatable and, hence, may be used as a basis for identification. Continuing work includes an effort to determine the number of different-aspect signatures required to completely characterize an object. [This work was supported by the Naval Research Laboratory.]
Doppler Structure in Echoes from Schools of Pelagic Fish
Authors: Holliday D. V.
Published: May 2012

The frequency distribution of energy in direct path echoes from three schools of pelagic fish is presented. One-half-second 30-kHz CW pulses were used to study motions internal to the fish schools from distances up to 1200 m. The measured Doppler spread at side aspect is related to swimming motions by a simple algebraic model based on Bainbridge's equation relating fish swimming speed, length, tail-beat amplitude, and tail-beat frequency. The mathematical model was used to estimate the length of the fish in two of the schools. These length estimates agree with average fish lengths derived from school cruising speeds. Near head or tail aspect, the observed Doppler structure appears to be related to behaviorial swimming characteristics.
Acoustic Modeling of Finite Ground Plane Effect on Radiation Patterns of Electromagnetic Sources
Authors: Hayre H. S.
Published: May 2012

A unique approach to laboratory modeling of electromagnetic sources by employing acoustic radiation elements and wavelength scaled models of special streamlined ground plane airframes is discussed with some practical results. This technique is based on the analogy between the longitudinal acoustic and the vertically polarized electromagnetic waves, and the identical propagation and scattering characteristics of uniform plane or spherical waves in both cases assuming the medium is lossless and uniform by layers at least. The case of a linear lossy medium may also be successfully treated by normalizing it and appropriately reducing the available transmitted power for an equivalent lossless case. Another unique contribution of this work is in modeling the radiation elements of the electromagnetic type by acoustic antennas and slots, and vice versa. For instance, a special case of a monopole and a slot in electromagnetic case is shown to be equivalent to the spherical radiator in the acoustic case. Furthermore, this theoretical work is supported by laboratory data.
Analog Computer Demonstration of Traveling and Standing Waves
Authors: Russell G. A.
Published: May 2012

An analog computer program was used to demonstrate traveling and standing waves., the effect of various reflection coefficients, standing-wave ra tios, and other wave phenomena. Voltage signals generated on the analog were viewed on a dual-trace storage scope to provide a vivid, easily understood, and controllable classroom demonstration. The computer mechanization did not solve the wave equation directly, but generated a signal which, when viewed on the oscilloscope, gave an optical illusion of a traveling or a standing wave. By adding appropriate logic operations to the basic analog program, it was possible to demonstrate a sinusoidal traveling wave moving down a line, hitting a terminating impedance, folding back on itself, and finally becoming a standing wave all along the line.
Acoustic Pulse Techniques for the Nondestructive Determination of Material Parameters
Authors: Mattei M. D. , Shapton W. R.
Published: May 2012

The natural frequencies and damping properties of physical systems have provided investigators with valuable information for solving various problems associated with vibrating structures. This paper uses the information associated with natural frequencies and damping in order to determine two physical parameters of a material. Using pulse excitation and noncontacting instrumentation, unique methods are presented for nondestructively determining Young's modulus and martensite start transformation temperature. The material used for this investigation was a nickel-titanium alloy referred to as Nitinol. There is no reason, however, that the procedures and techniques described cannot be used for a variety of other materials.
Acoustic Processing in a Syntactically Guided Speech-Understanding System
Authors: Becker Richard , Poza Fausto
Published: May 2012

The acoustic processing in the SRI speech-understanding system is described. This system relies heavily upon semantic and syntactic information for understanding the spoken utterance. This information predicts the presence of various words at particular places in the utterance and thereby guides the acoustic processor. The acoustic processor is implemented as a set of word-verification functions which establish the likelihood that a predicted word actually is present at a specified point in the utterance. This approach allows a straight-forward solution of problems of segmentation and within-word coarticulation, which have caused great difficulty in traditional attempts at continuous speech recognition. Typical word verification functions are presented, with illustrations of different methods of analyzing coarticulation effects. The possibility of incorporating these techniques in traditional systems is discussed. Finally, methods of extending these techniques to deal with coarticulation effects which occur across word boundaries are discussed.