bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Inlet Condition Effects on Outputs and Exhaust Emissions of High-Power Medium-Speed Diesel Engines
Authors: Chen Gong , Bedapudi Prakash , Flynn Paul L.
Published: February 2009

The understanding of the inlet condition effects on the output performance and exhaust emissions of high-power medium-speed diesel engines is an important issue in evaluating, testing and designing the type of engines. The inlet conditions under investigation included inlet air temperature, pressure and humidity, and intake manifold air temperature. Analytical and experimental investigation were conducted to achieve better understanding of the condition effects on the engine outputs and exhaust emissions. The operating and exhaust gas parameters for determining the engine brake specific outputs were studied. The major in-cylinder combustion process parameters affected by the inlet conditions were analyzed. Results from testing a high-power medium-speed locomotive diesel engine are presented and confirm the trends analytically predicted. The effects of the inlet conditions can not be neglected in obtaining comparable engine outputs and exhaust emissions. The main focus of the work in this paper is not on the determination of outputs correction factors for a particular engine, is on the understanding and methodology of the appropriate determination of engine outputs and exhaust emissions in general.
Selective Catalytic Reduction (SCR) System Installation and Commissioning at the Chow II Power Plant in Chowchilla, California
Authors: Newburry Don , Runnels Pat , Owings Mike
Published: February 2009

Lean burn, natural gas, reciprocating engines are becoming widely utilized for stationary industrial applications due to their high efficiency and low emissions. However, despite the low engine emissions, some locations still require exhaust after-treatment to meet the local emissions requirements. Due to the high oxygen content (greater than 4%) in the exhaust of lean burn engines, 3-Way (non-selective) catalysts are not suitable to reduce NOx. Selective catalytic reduction (SCR), which utilizes a consumable reductant to reduce NOx over a catalyst, is very effective at reducing NOx and is becoming an accepted technology for large, stationary engine applications. In the summer of 2001, Stewart & Stevenson installed 16 Deutz TGB632V16 natural gas fired engines for NEO Corporation at the Chow II power plant. MIRATECH SCR provided and commissioned 16 selective catalytic reduction systems for these engines using a 40% urea solution as the reductant. This paper describes the installed SCR systems and reports some of the emissions testing results and costs. With the SCR systems in place, the engines were successfully able to meet the permitted exhaust emissions requirements of 0.07 g/bhp-hr of NOx, 0.1 g/bhp-hr of CO, and 0.15 g/bhp-hr of VOC’s (volatile organic compounds) with less than 10 ppmvd of ammonia slip @ 15% O2. Additional measurements were made of formaldehyde and acrolein. Very low levels of these emissions were found after the SCR.
Experience With Gas Engines Optimized for H2-Rich Fuels
Authors: Herdin G. R. , Gruber F. , Plohberger D. , Wagner M.
Published: February 2009

The gas engine is a very efficient possibility of a technological approach for the conversion of chemically bound energy into mechanical or electrical power. Degrees of efficiency achieved thus far through the electrification of natural gas amount to up to 45% depending on the engine size and further potentials are already being opened up. Gas engines therefore do not need to fear a comparison with diesel engines in terms of efficiency. The modern gas engines have considerable advantages regarding emissions. The state of the art for the NOx emissions of natural gas engines can presently be given as 0.7 g/kWh (diesel 5 g NOx/kWh) with practically particle-free combustion. As a result of these features the gas engine is especially suitable for the very efficient process of cogeneration of heat and power, through which total degrees of fuel efficiency of about 90% can be attained. As such, the gas engine is even superior to all previously introduced types of fuel cells. The utilization of H2-rich gases as fuel can be seen as a new field of application of gas engines. Jenbacher AG already has many years of experience in the field of “H2-rich fuels” with optimization of combustion control and mixture formation. The H2 content extend from 100% to very low caloric values of gases in the range of 1.67 MJ/Nm3. The gases to be utilized by the gas engines come primarily from thermal pyrolysis processes of biomass or RDF fuels. A very good efficiency behavior with uncommonly low NOx emissions can be determined as the common result of all gas engine sizes. In the case of the high NH3 content of e.g. wood gas, despite the extreme lean-burn operation through the primary formation of NOx from the fuel, no NOx minimum can be attained. For the future, making the step into H2-rich fuel technology particularly regarding emissions means a big step towards the low NOx concepts and thus the further reduction of engine emissions.
A Generic Simulation Model for Cylinder Kit Vibro-Acoustics: Part II — Piston Slap and Engine Structure Interaction
Authors: Offner Gu¨nter , Herbst Hubert M. , Priebsch Hans H.
Published: February 2009

In specific speed and load ranges mechanical noise excitation contributes significantly to the overall noise of an internal combustion (IC) engine. Piston slap induced noise is a very important mechanical noise source. As the second part of two sequential papers, this contribution describes the numerical simulation of the structure noise of an entire IC engine. The findings for the cylinder kit models in part I are considered specifically. The mathematical model for an elasto-hydrodynamic contact of piston skirt and liner wall in a mixed lubrication regime is applied to a fully coupled simulation of the entire engine block vibration. The contribution of piston slap excitation is evaluated against other sources of excitation, like crankshaft dynamics and combustion gas pressure. Measurements of the engine block surface accelerations are performed in fired conditions and are compared to the results obtained by the simulation. It is shown how noise sources in the piston cylinder kit are transferred to the engine block surface structure. The paper demonstrates the reliability of a comprehensive model for engine noise simulation in the development process for future engine designs.
Optimal Control Strategy for a Pressure-Wave Supercharged SI Engine
Authors: Spring Peter , Guzzella Lino , Onder Christopher H.
Published: February 2009

On the basis of a control-oriented mean-value model of a spark-ignition engine supercharged with a pressure-wave supercharger, this paper introduces an operation strategy which minimizes the torque response time to driver commands. Since in pressure-wave superchargers fresh air and exhaust gas are in direct contact in the cell wheel, unwanted and excessive exhaust gas recirculation over the pressure-wave supercharger has to be limited by appropriate control actions. The most critical situation arises when large amounts of exhaust gas are recirculated during a hard acceleration, which causes the engine torque to drop sharply and thus to severely affect driveability. In order to prevent such situations, a set of actuators (throttles, valves, etc.) has to be controlled in a coordinated way. Conventional strategies cause the actuators to be closed at a fairly slow, steady rate. Our investigations show that driveability can be improved with a somewhat more complex strategy.
Predesign of an Internal Combustion Engine Intake Manifold by Numerical Solution of Induction Flow
Authors: Esfahanian Vahid , Sobhani Ehsan S. , Elyasi Mehrdad K. , Karbalaireza Hamid
Published: February 2009

A method is proposed to calculate the characteristics of compressible flow in intake manifold of an internal combustion engine, which can be used as an iterative process to determine the main dimensions of the manifold, such as pipes length and diameter, at the primary stages of internal combustion engine design. To calculate the flow field in the pipes, a computer code has been developed to solve the quasi 1-D Euler’s gas dynamics equations using flux-splitting method. Boundary conditions, such as valves, are modeled using experimental data along with some semi-empirical equations. To verify the accuracy of the method, a four cylinder SI engine manifold, with different intake manifold pipe lengths is simulated by the developed computer code and the overall performance characteristics of the engine such as power, torque and volumetric efficiency are obtained and compared with experiments.
Laser Based Ignition of Natural Gas-Air Mixtures
Authors: Gupta Sreenath B. , Sekar Raj R. , Xu Zhiyue , Leong Keng H. , Reed Claude B. , Pal Sibtosh , Cramer John , Santoro Robert J.
Published: February 2009

In current natural gas engines, lean operation to reduce NOx emissions along with the requirement to maintain high specific power results in in-cylinder conditions that demand spark voltages beyond the capabilities of present ignition systems. Unable to overcome such limitations, presently these engines are operated well below their full potential (about 15% less). Additionally, undue maintenance demands are placed for the upkeep of ignition systems. Laser based ignition (LBI) on the other hand, overcomes the above limitations and potentially reduces emissions and increases efficiency. Experimental studies were performed to identify such potential benefits while using lasers to ignite quiescent methane-air mixtures. Quiescent methane-air mixtures at various conditions (φ = 0.6–1.0, fill pressure = 2–20 Bar) were established in a pressure vessel and were ignited using lasers and by conventional ignition systems. Such tests showed lasers to ignite mixtures with initial pressures 30% higher than those limiting ignition by conventional ignition systems. However, extension of the lean ignition limit appeared to be marginal and was defined by φ = 0.675. Also, for single point ignition followed here, the rates of pressure rise and ignition delays were identical and did not depend upon the method of ignition. Other characteristics in terms of (a) effect of focal length, (b) effect of fuel composition, and (c) effect of laser beam polarization are presented. In practice, in-cylinder conditions such as turbulence, velocity and temperature are likely to have an additional bearing on the ignition characteristics. Such effects will be determined through future investigations.
In-Cylinder Pressure Measurement: Requirements for On-Board Engine Control
Authors: Ponti Fabrizio
Published: February 2009

During these last years, passenger vehicles have been equipped with an increasing number of sensors, in an effort to monitor and control their behavior in terms of global performance and emissions. This, together with constantly increasing Electronic Control Unit (ECU) computing power and data storage capabilities, allowed the development of more efficient engine–vehicle control strategies. In this perspective, new sensors will be employed as soon as their use will be shown to be necessary to design new engine control and diagnostic strategies, and their cost and expected life will be compatible with on-board application. A sensor that has been largely studied in recent years is the in-cylinder pressure one: advanced engine control strategies that make use of the signal coming from such a sensor have been investigated, while reliable and low-cost sensors are being developed to survive for the vehicle life the harsh on-board environment. The signal coming from the in-cylinder pressure is in fact very rich in information and could be used for example to improve engine torque management (by directly computing the instantaneous indicated torque), to improve Air/Fuel Ratio (AFR) control, misfire and knock detection capabilities, engine emission estimation (to be used for DeNOX catalysts purging management as an example), residual gas fraction estimation, … Many sensor concepts have been developed, although none seems to actually meet both the precision and low-cost requirements necessary for on-board application. This work deals with defining the sensor precision characteristics necessary to effectively implement the aforementioned engine control and diagnostic capabilities improvements. In particular it will be shown that only the low-frequency signal content has to be precisely measured and is critical for certain application. In addition the importance of a correct reference of the in-cylinder pressure signal is discussed, and a novel methodology to quickly obtain this information once the engine has been setup with a proper in-cylinder pressure sensor is discussed.
High Density Gas Engine With Micro Pilot Compression Ignition Method
Authors: Goto Satoru , Nishi Yoshifumi , Nakayama Sadao
Published: February 2009

Niigata Power Systems Co. has launched the strategic sales activity of the newly developed gas engine with high BMEP of 2.0MPa, high electric thermal efficiency of 40% or more. The 22AG engine, which denotes “Advanced Gas,” produced 30% higher power than a conventional spark ignition gas engine. The first three units of 8L22AG corresponding to 3780 kW / 900min−1 have been put into service operation since July of 2002 as the key-hardware in co-generation system of the chemical plant in Japan. The second delivered 6L22AG is operated using pyrolysis gas produced in the waste treatment process from December of 2002.
Analysis of the HCCI Combustion of a Turbocharged Truck Engine Using a Stochastic Reactor Model
Authors: Montorsi Luca , Mauss Fabian , Bianchi Gian Marco , Bhave Amit , Kraft Markus
Published: February 2009

Homogeneous Charge Compression Ignition (HCCI) engines arouse great interest due to their high thermal efficiency and very low emissions of nitrogen oxides (NOx) and particulates. Critical issue of the HCCI combustion is the control of the engine since the combustion process is mostly dominated by chemical kinetics. Therefore the accurate assessment of the chemical kinetic is fundamental in numerical simulation of this kind of engines. Experimentally it has been demonstrated that even in HCCI engine the charge within the cylinder is not fully homogeneous, but many quantities, such as temperature, density and equivalence ratio, vary along the combustion chamber. These inhomogeneities influence the combustion process and yield the homogeneous reactor model to be not completely adequate to simulate HCCI combustion. This paper focuses on the use of a stochastic rector model in order to account for temperature inhomogeneities in the numerical simulation of the HCCI combustion. Moreover, the chemical kinetic code has been coupled to GT - Power Code, a 1-D fluid–dynamics code, in order to accurately simulate the operation of a turbocharged truck engine.
The Emergency and Post-Lubrication System of TCA Turbochargers
Authors: Werdecker Ferdinand , Link Hermann
Published: February 2009

For the TCA turbocharger series a new emergency and post-lubrication system has been developed. This new system is supposed to maintain more than 10 seconds full load operation after an oil pump blackout. Moreover, the system has to efficiently supply oil for the run-out period and for cooling the bearings. In order to check this development target turbocharger TCA 77 was subjected to some tests. The tests were carried out under extreme conditions, i.e. maximum oil inlet temperature and minimum oil pressure. At maximum speed = 14900 rpm, toil = 60°C and poil = 1.3 bar the turbocharger continued its operation after stop of the oil pump without temperature increase in the bearings for 14 seconds before the pressure control device interrupted the fuel supply at 0.6 bar oil pressure. The pressurized part of the tank was sufficient for another 35 seconds during which the turbocharger speed dropped from 14900 rpm to a speed of about 7000 rpm. Both journal bearings and the axial bearings received oil for 2.5 minutes after pump stop. At this point the turbocharger still had a speed of 1500 rpm. After that the turbine bearing was cooled over a period of 1-1/2 hours by a geodetic driven oil flow. The maximum temperature at the turbine bearing of 180 °C (admissible approx. 220 °C) was achieved after 2 hours.
Fuel Consumption Measurement With Pulsating Flow
Authors: Flauger Thomas , Ifft Stephen A.
Published: February 2009

This paper describes the impact of pressure pulsation on a system for fuel consumption measurement. The generation of pressure pulses by the injection pump(s) on the low pressure side of Diesel engines for power generation, ship propulsion or rail traction is described. Pressure values at the location of the fuel consumption measurement system are shown. Along with measurement results of the dynamic pressure variation over a flowmeter. The relation between pressure variation and the pulse output of the flowmeter is presented. These measurements quantify the velocity variations of the fuel. With help of the measurement results, the reason for temporary reverse flow is explained. We present a system for engine related fuel consumption measurement that withstands the impact of mechanical force caused by pressure pulses, which follows the velocity variation of the fuel and which indicates and calculates short-time reverse flow to achieve an accurate measurement result.
Design of Modern Controls for the Controlled Advanced Research Turbine (CART)
Authors: Wright Alan D. , Balas Mark J.
Published: February 2009

Control can improve the performance of wind turbines by enhancing energy capture and reducing dynamic loads. At the National Renewable Energy Laboratory, we are designing control algorithms for regulation of turbine speed and power using state-space control methods. In this paper, we describe the design of a control algorithm for regulation of rotor speed in full-load operation (region 3) for the Controlled Advanced Research Turbine (CART). This turbine is a two-bladed, teetering hub, upwind machine, adapted for testing a variety of control algorithms. We base our control design on simple linear models of a turbine, which contain rotor and generator rotation, drivetrain torsion, rotor flap, and tower fore-aft bending degrees of freedom. We account for wind-speed fluctuations using disturbance accommodating control (DAC). We show the capability of these control schemes to stabilize the modeled turbine modes via pole placement while using state estimation to reduce the required number of turbine measurements. We test these algorithms through simulation, incorporating them into two simulation codes and simulating the controlled system for various operating conditions. Finally, we report conclusions to this work and outline future studies.
Disturbance Tracking and Blade Load Control of Wind Turbines in Variable-Speed Operation
Authors: Stol Karl A.
Published: February 2009

A composite state-space controller was developed for a multi-objective problem in the variable-speed operation of wind turbines. Disturbance Tracking Control theory was applied to the design of a torque controller to optimize energy capture under the influence of persistent wind disturbances. A limitation in the theory for common multi-state models is described, which led to the design of a complementary pitch controller. The goal of the independent blade pitch design was to minimize blade root fatigue loads. Simulation results indicate an 11% reduction in fatigue damage using the proposed controllers, compared to a conventional torque-only design. Meanwhile, energy capture is almost identical, partly because of nonlinear effects.
Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment
Authors: Duque Earl P. N. , Burklund Michael D. , Johnson Wayne
Published: February 2009

A vortex lattice code, CAMRAD II, and a Reynolds-Averaged Navier-Stoke code, OVERFLOW-D2, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80-by 120-Foot Wind Tunnel. Computations were performed for both axial as well as yawed operating conditions. Various stall delay models and dynamics stall models were used by the CAMRAD II code. Comparisons between the experimental data and computed aerodynamic loads show that the OVERFLOW-D2 code can accurately predict the power and spanwise loading of a wind turbine rotor.
Continued Validation of the AeroDyn Subroutines Using NREL Unsteady Aerodynamics Experiment Data
Authors: Laino David J. , Hansen A. Craig
Published: February 2009

Full-scale wind tunnel tests of the NREL Unsteady Aerodynamics Experiment (UAE) Phase VI permitted unprecedented control and measurement of inflow to the UAE rotor. This in turn has allowed in-depth validation of the AeroDyn wind turbine aerodynamics software. This validation began with comparison of simple cases (i.e., fixed yaw, fixed pitch, no teeter), with results presented last year [2]. Among the findings of that study was the significant increase in section lift along the rotor blades due to the 3–dimensional flow over the UAE rotor. This delayed stall was not adequately accounted for in the AeroDyn model. This continued validation effort looks into delayed stall and the static and dynamic behavior of the Generalized Dynamic Wake (GDW) model in AeroDyn. Validation is accomplished through comparison of UAE data and simulation results for the following cases: • Uniform inflow (upwind, zero yaw error), • Step pitch changes on an operating rotor, • A teetering rotor at various yaw angles, and • Downwind rotor released into flee yaw from various initial yaw error positions. Results presented allow us to draw several conclusions. The Du and Selig delayed stall correction adequately models the increase in CL, but the suggested decrease in CD of that model does not agree with observations in the data. The time lag coefficient in the GDW model agrees well with observations in the rapid pitch change UAE data. The phase of teeter response for the GDW model agrees better with data than for the equilibrium wake model. Dynamic stall provides significant additional damping to the teeter motion. The choice of wake model also greatly affects the yaw rate in the yaw release simulations.
A Straight-Bladed Variable-Pitch VAWT Concept for Improved Power Generation
Authors: Staelens Yann , Saeed F. , Paraschivoiu I.
Published: February 2009

The paper presents three modifications for an improved performance in terms of increased power output of a straight-bladed VAWT by varying its pitch. Modification I examines the performance of a VAWT when the local angle of attack is kept just below the stall value throughout its rotation cycle. Although this modification results in a very significant increase in the power output for higher wind speeds, it requires abrupt changes in the local angle of attack making it physically and mechanically impossible to realize. Modification II improves upon the first by replacing the local angle of attack by the blade static-stall angle only when the former exceeds the latter. This step eliminates the two jumps in the local effective angle of attack curve but at the cost of a slight decrease in the power output. Moreover, it requires a discontinuous angle of attack correction function which may still be practically difficult to implement and also result in an early fatigue. Modification III overcomes the limitation of the second by ensuring a continuous variation in the local angle of attack correction during the rotation cycle through the use of a sinusoidal function. Although the power output obtained by using this modification is less than the two preceding ones, it has the inherent advantage of being practically feasible.
Prediction of Delamination in Wind Turbine Blade Structural Details
Authors: Mandell John F. , Cairns Douglas S. , Samborsky Daniel D. , Morehead Robert B. , Haugen Darrin H.
Published: February 2009

Delamination between plies is the root cause of many failures of composite materials structures such as wind turbine blades. Design methodologies to prevent such failures have not been widely available for the materials and processes used in blades. This paper presents simplified methodologies for the prediction of delamination under both static and fatigue loading at typical structural details in blades. The methodology is based on fracture mechanics. The critical strain energy release rate, GIC and GIIC, are determined for opening mode (I) and shearing mode (II) delamination cracks; fatigue crack growth in each mode is also characterized. These data can be used directly for matrix selection, and as properties for the prediction of delamination in structural details. The strain energy release rates are then determined for an assumed interlaminar flaw in the structural detail. The flaw is positioned based on finite element analysis (FEA), and the strain energy release rates are calculated using the virtual crack closure feature available in codes like ANSYS. The methodology has been validated for a skin-stiffener intersection. Two prediction methods differing in complexity and data requirements have been explored. Results for both methods show good agreement between predicted and experimental delamination loads under both static and fatigue loading.
Estimates of internal templates for the detection of sequential tonal patterns
Authors: Huang Rong , Richards Virginia M.
Published: February 2009

In this experiment, listeners detected sequential tonal patterns embedded in multitone multiburst random maskers. The maskers consisted of eight 30ms bursts of random-frequency tones. The signal, when present, occupied the central six bursts and was centered at 1000Hz. The six sequential signal tones formed several spectro-temporal patterns: an equal-frequency pattern, three ascending patterns with frequency ranges spanning 0.5-, 1-, and 2-equivalent rectangular bandwidths (ERBs), and a random pattern with frequencies drawn at random from the range of 925–1075Hz. The total number of tones in each burst, m, was varied to determine detection threshold. The detectability of the signal pattern declined as the frequency range of the signal pattern increased, and when the signal was random. Relative weights as a function of time and frequency, interpreted as listeners’ internal templates, depended systematically on the properties of the signal pattern tested. The templates indicated that when sensitivity was poor, listeners integrated increasingly broad spectro-temporal regions around the signal frequencies, and sometimes integrated energy from the final burst even though the signal tones never occupied the final burst.
Measuring the target strength spectra of fish using dolphin-like short broadband sonar signals
Authors: Imaizumi Tomohito , Furusawa Masahiko , Akamatsu Tomonari , Nishimori Yasushi
Published: February 2009

Dolphins identify their prey using broadband sonar signals. The broadband spectrum of the target strength (TS) of fish is believed to be a key factor in target discrimination. In this study, the TS spectrum was measured using sonar signals generated by two different dolphin species: finless porpoise and bottlenose dolphin. First, the broadband form functions of a tungsten carbide sphere and a copper sphere were measured in a water tank, and a close agreement between measurements and theoretical values was confirmed. Second, the TS spectra of anesthetized fish from three species were measured in a water tank. Although the results showed characteristics similar to previous measurements, they varied among species, individuals, and tilt angles. Third, the TS spectra of live fish suspended and tethered by nylon monofilament lines were measured at sea. The dolphin-like sonar signals were effective in obtaining the broadband TS spectra of the fish. Cross-correlation processing of the echo from a tungsten carbide sphere showed a further advantage of using the dolphin-like sonar signals: the signal-to-noise ratio increased by more than 10 dB. The variation of TS spectra with fish behavior provides useful information for target identification.
Noise reduction in binaural hearing aids: Analyzing the benefit over monaural systems
Authors: Srinivasan Sriram
Published: February 2009

Binaural beamforming using signals from both left and right hearing aids offers greater potential for noise reduction than using signals from a single aid. However, wireless transmission of data imposes power constraints. Since most modern hearing aids have multiple microphones and are capable of spatial filtering, it is of interest to study the conditions when a binaural system offers significant improvements over a multi-microphone monaural system, and the situations when the noise reduction benefits are only marginal. An intelligent transmission scheme could then be designed such that signals are exchanged between the hearing aids only when the benefits are significant.
Personal audio with multiple dark zones
Authors: Jones Matthew , Elliott Stephen J.
Published: February 2009

This work considers providing personal audio for a listener by use of a local array of acoustic sources driven in such a way as to maintain the reproduced levels in one seat, in the so-called “bright zone,” while minimizing the levels experienced by others sitting close by, in the so-called “dark zones.” Multiple dark zones are considered both adjacent to and in front of the listener, initially using monopole simulations to investigate three different control strategies, and it is shown that a particular orientation of two sources is able to provide good control over the dark zones in these directions. It is shown that minimizing the sound power radiated by the local array while constraining the reproduced level in the bright zone is an effective method of achieving isolation when the dark zones are numerous. The findings of the investigations are used to design an optimal source arrangement, for which the isolation performance is improved by about 20 dB up to 1 kHz, which is verified with Boundary Element Method (BEM) models and predictions based on measured responses.
High-resolution ultrasonic thermometer for radiation dosimetry
Authors: Malyarenko Eugene V. , Heyman Joseph S. , Chen-Mayer H. Heather , Tosh Ronald E.
Published: February 2009

This paper describes recent developments in the area of high-precision ultrasonic thermometry with the potential to provide on-site direct determination of radiation doses administered for cancer treatment. Conventional calorimeters used for this purpose measure radiation-induced heating in a water phantom at one point in space by means of immersed thermistors and are subject to various thermal disturbances due to Ohmic heating and interactions of the radiation with the sensor probes. By contrast, the method described here is based on a high-resolution ultrasonic system that determines the change of the speed of sound due to small temperature changes in an acoustic propagation path in the radiation-heated water, thereby avoiding such undesired thermal effects. The thermometer is able to measure tens of microkelvin changes in the water temperature averaged over the acoustic path of about 60 cm at room temperature, with root-mean-squared noise of about 5 μK. Both incandescent and ionizing radiation heating data are presented for analog and digital implementations of a laboratory prototype. This application of the ultrasonic technique opens up possibilities for a new approach to performing therapy-level radiation dosimetry for medical clinics and standards laboratories.
Acoustic characterization of single ultrasound contrast agent microbubbles
Authors: Sijl Jeroen , Gaud Emmanuel , Frinking Peter J. A. , Arditi Marcel , de Jong Nico , Lohse Detlef , Versluis Michel
Published: February 2009

Individual ultrasound contrast agent microbubbles (BR14) were characterized acoustically. The bubbles were excited at a frequency of 2MHz and at peak-negative pressure amplitudes of 60 and 100kPa. By measuring the transmit and receive transfer functions of both the transmit and receive transducers, echoes of individual bubbles were recorded quantitatively and compared to simulated data. At 100kPa driving pressure, a second harmonic response was observed for bubbles with a size close to their resonance size. Power spectra were derived from the echo waveforms of bubbles of different sizes. These spectra were in good agreement with those calculated from a Rayleigh–Plesset-type model, incorporating the viscoelastic properties of the phospholipid shell. Small bubbles excited below their resonance frequency have a response dominated by the characteristics of their phospholipid shell, whereas larger bubbles, excited above resonance, have a response identical to those of uncoated bubbles of similar size.
Speaker normalization using cortical strip maps: A neural model for steady-state vowel categorization
Authors: Ames Heather , Grossberg Stephen
Published: February 2009

Auditory signals of speech are speaker dependent, but representations of language meaning are speaker independent. The transformation from speaker-dependent to speaker-independent language representations enables speech to be learned and understood from different speakers. A neural model is presented that performs speaker normalization to generate a pitch-independent representation of speech sounds, while also preserving information about speaker identity. This speaker-invariant representation is categorized into unitized speech items, which input to sequential working memories whose distributed patterns can be categorized, or chunked, into syllable and word representations. The proposed model fits into an emerging model of auditory streaming and speech categorization. The auditory streaming and speaker normalization parts of the model both use multiple strip representations and asymmetric competitive circuits, thereby suggesting that these two circuits arose from similar neural designs. The normalized speech items are rapidly categorized and stably remembered by adaptive resonance theory circuits. Simulations use synthesized steady-state vowels from the Peterson and Barney [Peterson, G. E., and Barney, H.L., J. Acoust. Soc. Am. 24, 175–184 (1952).] vowel database and achieve accuracy rates similar to those achieved by human listeners. These results are compared to behavioral data and other speaker normalization models.
Finite element modeling of the temperature rise due to the propagation of ultrasonic waves in viscoelastic materials and experimental validation
Authors: Hosten B. , Bacon C. , Biateau C.
Published: February 2009

The ultrasound stimulated thermography method is usually used to detect the temperature rise at a defect position. The temperature rise can be due to the friction between the edges of the defect and/or the plastic deformation around the defect. This paper presents another aspect of the method when the ultrasounds are propagating in a viscoelastic anisotropic material, such as polymers or fiber-reinforced polymers. The attenuation of the waves produces a distributed temperature field. Therefore, even a defect that does not produce some heat can be detected, the ultrasonic field is modified. A finite element model is used for computing the temperature field and for predicting the possibility for an infrared camera of detecting the temperature rise and its modification due to a defect. The model computes the stress and displacement fields associated with the propagation and the loss of energy. Then the heat equation is solved with this loss as a source of heating. An experiment is done with a sonotrode that excites a PVC plate. The ultrasonic displacement at the top of the plate is measured with a laser velocimeter and introduced in the model. Finally, the model result is compared to the image produced by the camera.
Ultrasonic attenuation in parallel-nylon-wire cancellous-bone-mimicking phantoms
Authors: Wear Keith A.
Published: February 2009

Attenuation coefficients between 1.5 and 3.5MHz were measured on four parallel-nylon-wire arrays (simulating cancellous bone) with four different wire diameters (150, 200, 250, and 300μm). Interwire spacing was 800μm for all four parallel-nylon-wire arrays. The measured frequency dependencies of attenuation were consistent with theoretical predications based on Faran’s theory, which considers the component of attenuation due to scattering of longitudinal waves.
Estimates and bounds of dynamic permeability of granular media
Authors: Boutin Claude , Geindreau Christian
Published: February 2009

This paper presents a study of dynamic permeability of porous media combining homogenization of periodic media (HPM) and the self-consistent method (SCM). By taking advantage of the physical principles identified with HPM, the application of SCM leads to the determination of two physically admissible dynamic permeability assessments, both different from that given by the cell model. A comparison with numerical modeling demonstrates the fairly good reliability of the three estimates for granular media consisting of a periodic array of spherical grains. Furthermore, the self-consistent values enable exact bounds for the dynamic permeability of a wide class of porous media to be derived with a clear identification of their microstructure (grain and fluid size distribution).
Sound transmission through a microperforated-panel structure with subdivided air cavities
Authors: Toyoda Masahiro , Takahashi Daiji
Published: February 2009

The absorption characteristics of a microperforated-panel (MPP) absorber have been widely investigated, and MPPs are recognized as a next-generation absorbing material due to their fiber-free nature and attractive appearance. Herein, further possibilities of MPPs are investigated theoretically from a sound transmission viewpoint. Employing an analytical model composed of a typical MPP and a back wall with an infinite extent, transmission loss through the structure is obtained. Although MPP structures generally have great potential for sound absorption, an improvement in the transmission loss at midfrequencies, which is important for architectural sound insulation, is not sufficient when using a backing cavity alone. Hence, to improve transmission loss at midfrequencies, an air-cavity-subdivision technique is applied to MPP structures. By subdividing the air cavity with partitions, each cell can create a local one-dimensional sound field as well as lead to a normal incidence into the apertures, which is the most effective condition for Helmholtz-type resonance absorption. Moreover, by providing the same motion as the back wall to the MPP, the sound-insulation performance can be further improved at midfrequencies.
Wideband absorbance tympanometry using pressure sweeps: System development and results on adults with normal hearing
Authors: Liu Yi-Wen , Sanford Chris A. , Ellison John C. , Fitzpatrick Denis F. , Gorga Michael P. , Keefe Douglas H.
Published: February 2009

A system with potential for middle-ear screening and diagnostic testing was developed for the measurement of wideband energy absorbance (EA) in the ear canal as a function of air pressure, and tested on adults with normal hearing. Using a click stimulus, the EA was measured at 60 frequencies between 0.226 and 8kHz. Ambient-pressure results were similar to past studies. To perform tympanometry, air pressure in the ear canal was controlled automatically to sweep between −300 and 200daPa (ascending/descending directions) using sweep speeds of approximately 75, 100, 200, and 400daPa∕s. Thus, the measurement time for wideband tympanometry ranged from 1.5to7s and was suitable for clinical applications. A bandpass tympanogram, calculated for each ear by frequency averaging EA from 0.38to2kHz, had a single-peak shape; however, its tympanometric peak pressure (TPP) shifted as a function of sweep speed and direction. EA estimated at the TPP was similar across different sweep speeds, but was higher below 2kHz than EA measured at ambient pressure. Future studies of EA on normal ears of a different age group or on impaired ears may be compared with the adult normal baseline obtained in this study.
Velocity dispersion in trabecular bone: Influence of multiple scattering and of absorption
Authors: Haïat G. , Lhémery A. , Renaud F. , Padilla F. , Laugier P. , Naili S.
Published: February 2009

Speed of sound measurements are widely used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured, this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite cylinders immersed in a saturating matrix, and to derive the physical determinants of velocity dispersion. A homogenization model accounting for the coupling of multiple scattering and absorption phenomena allows the computation of phase velocity and of dispersion while varying bone properties. The present model is adapted from the generalized self-consistent method developed in the work of Yang and Mal [(1994). “Multiple-scattering of elastic waves in a fiber-reinforced composite,” J. Mech. Phys. Solids 42, 1945–1968]. It predicts negative values of velocity dispersion, in agreement with experimental results obtained in phantoms mimicking trabecular bone. In trabecular bone, mostly negative and also positive values of velocity dispersion are predicted by the model, which span within the range of values measured experimentally. Scattering effects are responsible for the negative values of dispersion, whereas the frequency dependence of the absorption coefficient in bone marrow and/or in the trabeculae results in an increase in dispersion, which may then become positive.
Source of level dependent minima in rabbit distortion product otoacoustic emissions
Authors: Fahey P. F. , Stagner B. B. , Martin G. K.
Published: February 2009

Sharp level dependent minima (commonly called nulls or notches) in the distortion product otoacoustic emissions (DPOAEs) have been postulated to be due to two different mechanisms. It is shown here that the level dependent nulls in rabbit 2f1−f2 DPOAEs carry the signature of the mixing of a third order nonlinear term with a fifth order nonlinear term. This suggests that the minima are not due to the mixing of signals from two different physical sites of origin, but rather are due to the nature of the nonlinearity itself. Model simulations show that null production is indifferent to several properties of nonlinear input/output functions.
Speech enhancement in discontinuous transmission systems using the constrained-stability least-mean-squares algorithm
Authors: Górriz J. M. , Ramírez J. , Cruces-Álvarez S. , Erdogmus D. , Puntonet C. G. , Lang E. W.
Published: February 2009

In this paper a novel constrained-stability least-mean-squares (LMS) algorithm for filtering speech sounds is proposed in the adaptive noise cancellation (ANC) problem. It is based on the minimization of the squared Euclidean norm of the weight vector change under a stability constraint over the a posteriori estimation errors. To this purpose, the Lagrangian methodology has been used in order to propose a nonlinear adaptation in terms of the product of differential input and error. Convergence analysis is also studied in terms of the evolution of the natural modes to the optimal Wiener–Hopf solution so that the stability performance depends exclusively on the adaptation parameter μ and the eigenvalues of the difference matrix ΔR(1). The algorithm shows superior performance over the referenced algorithms in the ANC problem of speech discontinuous transmission systems, which are characterized by rapid transitions of the desired signal. The experimental analysis carried out on the AURORA 3 speech databases provides an extensive performance evaluation together with an exhaustive comparison to the standard LMS algorithms, i.e., the normalized LMS (NLMS), and other recently reported LMS algorithms such as the modified NLMS, the error nonlinearity LMS, or the normalized data nonlinearity LMS adaptation.
Reply to “Comment on ‘Linear and nonlinear frequency shifts in acoustical resonators with varying cross sections’ [J. Acoust. Soc. Am. 110, 109–119 (2001)]”
Authors: Hamilton Mark F. , Ilinskii Yurii A. , Zabolotskaya Evgenia A.
Published: February 2009

M. P. Mortell and B. R. Seymour [M. P. Mortell and B. R. Seymour [J. Acoust. Soc. Am. 124, 3381–3385 (2008)] offer commentary on the analysis and the conclusions reached in a paper by Hamilton et al. [M. F. Hamilton, Yu. A. Ilinskii, and E. A. Zabolotskaya, J. Acoust. Soc. Am. 110, 109–119 (2001)] on linear and nonlinear frequency shifts in acoustical resonators that are close to cylindrical in shape. The present reply demonstrates that the criticisms made in the Comment are unwarranted when placed in context of the stated restrictions on the theory and the applications for which the theory is intended. It is also shown that the strongest criticisms made in the Comment stem from a mathematical error they introduced when attempting to reproduce the results of Hamilton et al.
Frequency distributions of uniphones, diphones, and triphones in spontaneous speech
Authors: Kuperman Victor , Ernestus Mirjam , Baayen Harald
Published: February 2009

This paper explores the relationship between the acoustic duration of phonemic sequences and their frequencies of occurrence. The data were obtained from large (sub)corpora of spontaneous speech in Dutch, English, German, and Italian. Acoustic duration of an n-phone is shown to codetermine the n-phone’s frequency of use, such that languages preferentially use diphones and triphones that are neither very long nor very short. The observed distributions are well approximated by a theoretical function that quantifies the concurrent action of the self-regulatory processes of minimization of articulatory effort and minimization of perception effort.
On the use of a loudspeaker for measuring the viscoelastic properties of sound absorbing materials
Authors: Doutres Olivier , Dauchez Nicolas , Génevaux Jean-Michel , Lemarquand Guy
Published: February 2009

This paper investigates the feasibility to use an electrodynamic loudspeaker to determine viscoelastic properties of sound-absorbing materials in the audible frequency range. The loudspeaker compresses the porous sample in a cavity, and a measurement of its electrical impedance allows one to determine the mechanical impedance of the sample: no additional sensors are required. Viscoelastic properties of the material are then estimated by inverting a 1D Biot model. The method is applied to two sound-absorbing materials (glass wool and polymer foam). Results are in good agreement with the classical compression quasistatic method.
From children to adults: How binaural cues and ear canal impedances grow
Authors: Fels Janina
Published: February 2009

In this thesis the growth dependency of head-related transfer functions and their resulting parameters (interaural time and level differences) are analyzed as well as ear canal impedances. Differences in the anatomy of children and adults thus result in different binaural cues. The individual anthropometric parameters, however, affect the binaural cues to a varying extent. In this thesis the most important anthropometric parameter with regard to their influence on binaural cues, is determined. Ear canal impedances are undergoing certain changes as well while children are growing up and finally reach adulthood. This thesis presents, for the first time, the age-related development of data that is most decisive for the impedances. These new findings open up new possibilities to develop artificial child heads and couplers for hearing aids that are suitable for children. Thus, improvements in certain fields of applications, such as the development and fitting of hearing aids for children, are now possible, and measurement techniques that are used for classroom acoustics can now be optimized significantly as well. Moreover, these new findings are vital when it comes to re-evaluating standardized artificial heads. Publisher: Logos Verlag Berlin, 2008; ISBN: 978-3-8325-1855-4.