bluuebunny/crossref_metadata_2025 huggingface dataset:
Description and characterization of the novel hyperthermia‐ and thermoablation‐system for clinical magnetic fluid hyperthermia
Authors: Gneveckow Uwe , Jordan Andreas , Scholz Regina , Brüß Volker , Waldöfner Norbert , Ricke Jens , Feussner Annelie , Hildebrandt Bert , Rau Beate , Wust Peter
Published: July 2004

Magnetic fluid hyperthermia (MFH) is a new approach to deposit heat power in deep tissues by overcoming limitations of conventional heat treatments. After infiltration of the target tissue with nanosized magnetic particles, the power of an alternating magnetic field is transformed into heat. The combination of the 100 kHz magnetic field applicator and the magnetofluid (MF), which both are designed for medical use, is investigated with respect to its dosage recommendations and clinical applicability. We found a magnetic field strength of up to 18 kA/m in a cylindrical treatment area of 20 cm diameter and aperture height up to 300 mm. The specific absorption rate (SAR) can be controlled directly by the magnetic field strength during the treatment. The relationship between magnetic field strength and the iron normalized SAR is only slightly depending on the concentration of the MF and can be used for planning the target SAR. The achievable energy absorption rates of the MF distributed in the tissue is sufficient for either hyperthermia or thermoablation. The fluid has a visible contrast in therapeutic concentrations on a CT scanner and can be detected down to 0.01 g/l Fe in the MRI. The system has proved its capability and practicability for heat treatment in deep regions of the human body.
Feasibility of optimizing the dose distribution in lung tumors using fluorine‐18‐fluorodeoxyglucose positron emission tomography and single photon emission computed tomography guided dose prescriptions
Authors: Das S. K. , Miften M. M. , Zhou S. , Bell M. , Munley M. T. , Whiddon C. S. , Craciunescu O. , Baydush A. H. , Wong T. , Rosenman J. G. , Dewhirst M. W. , Marks L. B.
Published: July 2004

The information provided by functional images may be used to guide radiotherapy planning by identifying regions that require higher radiation dose. In this work we investigate the dosimetric feasibility of delivering dose to lung tumors in proportion to the fluorine‐18‐fluorodeoxyglucose activity distribution from positron emission tomography (FDG–PET). The rationale for delivering dose in proportion to the tumor FDG–PET activity distribution is based on studies showing that FDG uptake is correlated to tumor cell proliferation rate, which is shown to imply that this dose delivery strategy is theoretically capable of providing the same duration of local control at all voxels in tumor. Target dose delivery was constrained by single photon emission computed tomography (SPECT) maps of normal lung perfusion, which restricted irradiation of highly perfused lung and imposed dose‐function constraints. Dose‐volume constraints were imposed on all other critical structures. All dose‐volume/function constraints were considered to be soft, i.e., critical structure doses corresponding to volume/function constraint levels were minimized while satisfying the target prescription, thus permitting critical structure doses to minimally exceed dose constraint levels. An intensity modulation optimization methodology was developed to deliver this radiation, and applied to two lung cancer patients. Dosimetric feasibility was assessed by comparing spatially normalized dose‐volume histograms from the nonuniform dose prescription (FDG–PET proportional) to those from a uniform dose prescription with equivalent tumor integral dose. In both patients, the optimization was capable of delivering the nonuniform target prescription with the same ease as the uniform target prescription, despite SPECT restrictions that effectively diverted dose from high to low perfused normal lung. In one patient, both prescriptions incurred similar critical structure dosages, below dose‐volume/function limits. However, in the other patient, critical structure dosage from the nonuniform dose prescription exceeded dose‐volume/function limits, and greatly exceeded that from the uniform dose prescription. Strict compliance to dose‐volume/function limits would entail reducing dose proportionality to the FDG–PET activity distribution, thereby theoretically reducing the duration of local control. Thus, even though it appears feasible to tailor lung tumor dose to the FDG–PET activity distribution, despite SPECT restrictions, strict adherence to dose‐volume/function limits could compromise the effectiveness of functional image guided radiotherapy.
Solid‐state fluoroscopic imager for high‐resolution angiography: Physical characteristics of an 8 cm×8 cm experimental prototype
Authors: Vedantham Srinivasan , Karellas Andrew , Suryanarayanan Sankararaman , Onishi Steven K.
Published: July 2004

In this paper, the performance of an 8 cm×8 cm three‐side buttable charge‐coupled device (CCD)‐based imager specially designed for high‐resolution fluoroscopy and operating in fluoroscopic (30 frames/second) mode is presented in terms of the presampling modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). The 8 cm×8 cm CCD imager is coupled to a 450 μm thick CsI:Tl scintillator by nondemagnifying (straight, 1:1) fiberoptics. The CCD imager has a fundamental pixel pitch of 39 μm and incorporates an optically opaque interline (data) channel. The CCD imager was operated at 156 μm pixel pitch by binning 4×4 adjacent pixels prior to readout. The fluoroscopic image lag was measured and accounted for in the DQE estimate to provide lag‐corrected DQE. The measured limiting spatial resolution at 10% presampling MTF with the imager operated at 156 μm pixel pitch (Nyquist sampling limit: 3.21 cy/mm) was 3.6 cy/mm. In the pulsed fluoroscopic mode, the first‐frame image lag was less than 0.9%. The lag‐corrected DQE(0) of ∼0.62 was achieved even at a low fluoroscopic exposure rate of 1 μR/frame. Grid phantom measurements indicate no appreciable distortion. Results from DQE and image lag measurements at fluoroscopic exposure rates combined with the high spatial resolution observed from the MTF suggest that this type of imager or its variants may be a potential candidate for high‐resolution neuro‐interventional imaging, cardiovascular imaging, pediatric angiography, and small animal imaging. Since the CCD is three‐side buttable, four such CCD modules can be joined to form a 2×2 matrix providing a field of view of 16 cm×16 cm.
An extensive log‐file analysis of step‐and‐shoot intensity modulated radiation therapy segment delivery errors
Authors: Stell Anthony M. , Li Jonathan G. , Zeidan Omar A. , Dempsey James F.
Published: July 2004

We present a study to evaluate the monitor unit (MU), dosimetric, and leaf‐motion errors found in the delivery of 91 step‐and‐shoot IMRT treatment plans performed at three nominal dose rates using a dual modality high energy Linac (Varian 2100 C/D, Varian Medical Systems Inc., Palo Alto, CA) equipped with a 120‐leaf multileaf collimator (MLC). The analysis was performed by studying log files generated by the MLC controller system. Recent studies by our group have validated that the automatically generated MLC log files accurately record the actual system delivery. A total of 635 beams were delivered at three nominal dose rates: 100, 300, and 600 MU/min. The log files were manually retrieved and analysis software was developed to extract the recorded MU delivery and leaf positions for each segment. Our analysis revealed that the magnitude of segment MU errors were independent of the planned segment MUs. Segment MU errors were found to increase with dose rate having maximum errors per segment of ±1.8 MU at 600 MU/min, ±0.8 MU at 300 MU/min, and ±0.5 MU at 100 MU/min. The total absolute MU error in each plan was observed to increase with the number of plan segments, with the trend increasing more rapidly for higher dose rates. Three dimensional dose distributions were recomputed based on the observed segment MU errors for three plans with large cumulative absolute MU errors. Comparison with the original treatment plans indicated no clinically significant consequences due to these errors. In addition, approximately 80% of the total segment deliveries reported at least one collimator leaf moving at least 1 mm (projected at isocenter) during segment delivery. Such errors occur near the end of segment delivery and have been previously observed by our group using a fast video‐based electronic portal imaging device. At 600 MU/min, between 5% and 23% of the plan MUs were delivered during leaf motion that had exceeded a 1 mm position tolerance. These leaf motion errors were not included in the treatment plan recalculations performed in this study.
Geometrical accuracy and fusion of multimodal vascular images: A phantom study
Authors: Boussion Nicolas , Soulez Gilles , De Guise Jacques A. , Daronat Michel , Qin Zhao , Cloutier Guy
Published: July 2004

The aim of this work was to compare the geometrical accuracy of x‐ray angiography, magnetic resonance imaging (MRI), x‐ray computed tomography (XCT), and ultrasound imaging (B‐mode and IVUS, or intravascular ultrasound) for measuring the lumen diameters of blood vessels. An image fusion method was also developed to improve these measurements. The images were acquired from a phantom that mimic vessels of known diameters. After acquisition, the multimodal images were coregistered by manual alignment of fiducial markers, and then by maximization of mutual information. The fusion method was performed by means of a fuzzy logic modeling approach followed by a combination process based on a possibilistic theory. The results showed (i) the better geometrical accuracy of XCT and IVUS compared to the other modalities, and (ii) the better accuracy and smaller variability of fused images compared to single modalities, with respect to most diameters investigated. For XCT, the error varied from 0.4% to 5.4%, depending on the vessel diameter that ranged from 0.93 to 6.24 mm. For IVUS, the error ranged from −0.3% to 1.7% but the smallest vessel (0.93 mm) could not be investigated because of the probe size. Compared to others fusion schemes, the XCT‐MRI fused images provided the best results for both accuracy (from −1.6% to 0.2% for the three largest vessels) and robustness (mean relative error of 1.9%). To conclude, this work underlined both the usefulness of the multimodality vascular phantom as a validation tool and the utility of image fusion in the vascular context.
Development and validation of a CT‐3D rotational angiography registration method for AVM radiosurgery
Authors: Stancanello Joseph , Cavedon Carlo , Francescon Paolo , Cerveri Pietro , Ferrigno Giancarlo , Colombo Federico , Perini Stefano
Published: July 2004

In this paper a novel technique is proposed and validated for radiosurgery treatment planning of arteriovenous malformations (AVMs). The technique was developed for frameless radiosurgery by means of the CyberKnife, a nonisocentric, linac‐based system which allows highly conformed isodose surfaces to be obtained, while also being valid for other treatment strategies. The technique is based on registration between computed tomography (CT) and three‐dimensional rotational angiography (3DRA). Tests were initially performed on the effectiveness of the correction method for distortion offered by the angiographic system. These results determined the registration technique that was ultimately chosen. For CT‐3DRA registration, a twelve‐parameter affine transformation was selected, based on a mutual information maximization algorithm. The robustness of the algorithm was tested by attempting to register data sets increasingly distant from each other, both in translation and rotation. Registration accuracy was estimated by means of the “full circle consistency test.” A registration quality index (expressed in millimeters) based on these results was also defined. A hybrid subtraction between CT and 3DRA is proposed in order to improve 3D reconstruction. Preprocessing improved the ability of the algorithm to find an acceptable solution to the registration process. The robustness tests showed that data sets must be manually prealigned within approximately 15 mm and with respect to all three directions simultaneously. Results of the consistency test showed agreement between the quality index and registration accuracy stated by visual inspection in 20 good and 10 artificially worsened registration processes. The quality index showed values smaller than the maximum voxel size (mean 0.8 mm compared to 2 mm) for all successful registrations, while it resulted in much greater values (mean 20 mm) for unsuccessful registrations. Once registered, the two data sets can be used for CyberKnife treatment planning. Target delineation is performed on 3DRA while dose calculation and DRR generation are performed on CT. In conclusion, a method was developed for using 3DRA images for AVM frameless radiosurgery treatment planning. The method proved to be feasible, robust, and accurate for clinical use. 3DRA can be performed at different times or locations compared to standard, frame based stereotactic angiography. Unlike two‐dimensional angiography, 3DRA allows examination of the shape of the AVM and of the surrounding target from any arbitrary point of view during treatment planning. The method can be applied to any case of intermodality registration, is operator‐independent, and allows estimation of registration quality. Further research is desirable to improve time resolution in order to distinguish between feeding and draining vessels.
Monte Carlo calculation of the sensitivity of a commercial dose calibrator to gamma and beta radiation
Authors: Laedermann Jean‐Pascal , Valley Jean‐François , Bulling Shelley , Bochud François O.
Published: July 2004

The detection process used in a commercial dose calibrator was modeled using the GEANT 3 Monte Carlo code. Dose calibrator efficiency for gamma and beta emitters, and the response to monoenergetic photons and electrons was calculated. The model shows that beta emitters below 2.5 MeV deposit energy indirectly in the detector through bremsstrahlung produced in the chamber wall or in the source itself. Higher energy beta emitters deposit energy directly in the chamber sensitive volume, and dose calibrator sensitivity increases abruptly for these radionuclides. The Monte Carlo calculations were compared with gamma and beta emitter measurements. The calculations show that the variation in dose calibrator efficiency with measuring conditions (source volume, container diameter, container wall thickness and material, position of the source within the calibrator) is relatively small and can be considered insignificant for routine measurement applications. However, dose calibrator efficiency depends strongly on the inner‐wall thickness of the detector.
The design and the dosimetry of bi‐nuclide radioactive ophthalmic applicators
Authors: Flühs Dirk , Anastassiou Gerasimos , Wening Jan , Sauerwein Wolfgang , Bornfeld Norbert
Published: July 2004

A novel type of applicator for the treatment of intra‐ocular tumors has been developed, based on the two radionuclides and The dose distribution of this ophthalmic plaque combines advantageous features of both radionuclides and can be optimally adapted to a tumor thickness in the range 6.5–9 mm, a size which is beyond the dosimetric limitations of the plaque therapy. Compared with plaques a bi‐nuclide plaque allows to maintain the tumor dosage while the dose in the irradiated volume outside of the target volume is significantly reduced. Consequently, radiosensitive structures within the eye can be spared more effectively. Dedicated methods have been developed for the dosimetry of this plaque. These methods are based on our own extensive dosimetric investigations with plastic scintillators. The precondition was the availability, developed in recent years, of a more accurate determination of the absolute dose rate to water of beta‐ and low energy emitters.
A procedure to determine the radiation isocenter size in a linear accelerator
Authors: González A. , Castro I. , Martı́nez J. A.
Published: July 2004

Measurement of radiation isocenter is a fundamental part of commissioning and quality assurance (QA) for a linear accelerator (linac). In this work we present an automated procedure for the analysis of the stars‐shots employed in the radiation isocenter determination. Once the star‐shot film has been developed and digitized, the resulting image is analyzed by scanning concentric circles centered around the intersection of the lasers that had been previously marked on the film. The center and the radius of the minimum circle intersecting the central rays are determined with an accuracy and precision better than 1% of the pixel size. The procedure is applied to the position and size determination of the radiation isocenter by means of the analysis of star‐shots, placed in different planes with respect to the gantry, couch and collimator rotation axes.
Simultaneous optimization of beam orientations, wedge filters and field weights for inverse planning with anatomy‐based MLC fields
Authors: Beaulieu Frédéric , Beaulieu Luc , Tremblay Daniel , Roy René
Published: July 2004

As an alternative between manual planning and beamlet‐based IMRT, we have developed an optimization system for inverse planning with anatomy‐based MLC fields. In this system, named Ballista, the orientation (table and gantry), the wedge filter and the field weights are simultaneously optimized for every beam. An interesting feature is that the system is coupled to Pinnacle3 by means of the PinnComm interface, and uses its convolution dose calculation engine. A fully automatic MLC segmentation algorithm is also included. The plan evaluation is based on a quasi‐random sampling and on a quadratic objective function with penalty‐like constraints. For efficiency, optimal wedge angles and wedge orientations are determined using the concept of the super‐omni wedge. A bound‐constrained quasi‐Newton algorithm performs field weight optimization, while a fast simulated annealing algorithm selects the optimal beam orientations. Moreover, in order to generate directly deliverable plans, the following practical considerations have been incorporated in the system: collision between the gantry and the table as well as avoidance of the radio‐opaque elements of a table top. We illustrate the performance of the new system on two patients. In a rhabdomyosarcoma case, the system generated plans improving both the target coverage and the sparing of the parotide, as compared to a manually designed plan. In the second case presented, the system successfully produced an adequate plan for the treatment of the prostate while avoiding both hip prostheses. For the many cases where full IMRT may not be necessary, the system efficiently generates satisfactory plans meeting the clinical objectives, while keeping the treatment verification much simpler.
Design and tests of a portable mini gamma camera
Authors: Sánchez F. , Benlloch J. M. , Escat B. , Pavón N. , Porras E. , Kadi‐Hanifi D. , Ruiz J. A. , Mora F. J. , Sebastià A.
Published: July 2004

Design optimization, manufacturing, and tests, both laboratory and clinical, of a portable gamma camera for medical applications are presented. This camera, based on a continuous scintillation crystal and a position‐sensitive photomultiplier tube, has an intrinsic spatial resolution of , an energy resolution of 13% at 140 keV, and linearities of 0.28 mm (absolute) and 0.15 mm (differential), with a useful field of view of 4.6 cm diameter. Our camera can image small organs with high efficiency and so it can address the demand for devices of specific clinical applications like thyroid and sentinel node scintigraphy as well as scintimammography and radio‐guided surgery. The main advantages of the gamma camera with respect to those previously reported in the literature are high portability, low cost, and weight (2 kg), with no significant loss of sensitivity and spatial resolution. All the electronic components are packed inside the minigamma camera, and no external electronic devices are required. The camera is only connected through the universal serial bus port to a portable personal computer (PC), where a specific software allows to control both the camera parameters and the measuring process, by displaying on the PC the acquired image on “real time.” In this article, we present the camera and describe the procedures that have led us to choose its configuration. Laboratory and clinical tests are presented together with diagnostic capabilities of the gamma camera.
On the acoustic diffraction by the edges of benthic shells
Authors: Stanton Timothy K. , Chu Dezhang
Published: July 2004

Recent laboratory measurements of acoustic backscattering by individual benthic shells have isolated the edge-diffracted echo from echoes due to the surface of the main body of the shell. The data indicate that the echo near broadside incidence is generally the strongest for all orientations and is due principally to the surface of the main body. At angles well away from broadside, the echo levels are lower and are due primarily to the diffraction from the edge of the shell. The decrease in echo levels from broadside incidence to well off broadside is shown to be reasonably consistent with the decrease in acoustic backscattering from normal incidence to well off normal incidence by a shell-covered seafloor. The results suggest the importance of the edge of the shell in off-normal-incidence backscattering by a shell-covered seafloor. Furthermore, when considering bistatic diffraction by edges, there are implications that the edge of the shell (lying on the seafloor) can cause significant scattering in many directions, including at subcritical angles.
Accurate analysis of multitone signals using a DFT
Authors: Burgess John C.
Published: July 2004

Optimum data windows make it possible to determine accurately the amplitude, phase, and frequency of one or more tones (sinusoidal components) in a signal. Procedures presented in this paper can be applied to noisy signals, signals having moderate nonstationarity, and tones close in frequency. They are relevant to many areas of acoustics where sounds are quasistationary. Among these are acoustic probes transmitted through media and natural sounds, such as animal vocalization, speech, and music. The paper includes criteria for multitone FFT block design and an example of application to sound transmission in the atmosphere.
Separation of compressibility and shear deformation in the elastic energy density (L)
Authors: Hamilton Mark F. , Ilinskii Yurii A. , Zabolotskaya Evgenia A.
Published: July 2004

A formulation of the elastic energy density for an isotropic medium is presented that permits separation of effects due to compressibility and shear deformation. The motivation is to obtain an expansion of the energy density for soft elastic media in which the elastic constants accounting for shear effects are of comparable order. The expansion is carried out to fourth order to ensure that nonlinear effects in shear waves are taken into account. The result is E≃E0(ρ)+μI2+13AI3+DI22, where ρ is density, I2 and I3 are the second- and third-order Lagrangian strain invariants used by Landau and Lifshitz, μ is the shear modulus, A is one of the third-order elastic constants introduced by Landau and Lifshitz, and D is a new fourth-order elastic constant. For processes involving mainly compressibility E≃E0(ρ), and for processes involving mainly shear deformation E≃μI2+13AI3+DI22.
External and internal limitations in amplitude-modulation processing
Authors: Ewert Stephan D. , Dau Torsten
Published: July 2004

Three experiments are presented to explore the relative role of “external” signal variability and “internal” resolution limitations of the auditory system in the detection and discrimination of amplitude modulations (AM). In the first experiment, AM-depth discrimination performance was determined using sinusoidally modulated broadband-noise and pure-tone carriers. The AM index, m, of the standard ranged from −28 to −3 dB (expressed as 20 log m). AM-depth discrimination thresholds were found to be a fraction of the AM depth of the standard for standards down to −18 dB, in the case of the pure-tone carrier, and down to −8 dB, in the case of the broadband-noise carrier. For smaller standards, AM-depth discrimination required a fixed increase in AM depth, independent of the AM depth of the standard. In the second experiment, AM-detection thresholds were obtained for signal-modulation frequencies of 4, 16, 64, and 256 Hz, applied to either a band-limited random-noise carrier or a deterministic (“frozen”) noise carrier, as a function of carrier bandwidth (8 to 2048 Hz). In general, detection thresholds were higher for the random- than for the frozen-noise carriers. For both carrier types, thresholds followed the pattern expected from frequency-selective processing of the stimulus envelope. The third experiment investigated AM masking at 4, 16, and 64 Hz in the presence of a narrow-band masker modulation. The variability of the masker was changed from entirely frozen to entirely random, while the long-term average envelope power spectrum was held constant. The experiment examined the validity of a long-term average quantity as the decision variable, and the role of memory in experiments with frozen-noise maskers. The empirical results were compared to predictions obtained with two modulation-filterbank models. The predictions revealed that AM-depth discrimination and AM detection are limited by a combination of the external signal variability and an internal “Weber-fraction” noise process.
Mindlin plate theory for damage detection: Source solutions
Authors: Rose L. R. F. , Wang C. H.
Published: July 2004

A consideration of the relevant length scales and time scales suggests that Mindlin plate theory provides a judicious model for damage detection. A systematic investigation of this theory is presented that emphasizes its mixed vector-scalar character and analogies with 3D elasticity. These analogies lead to the use of Helmholtz potentials, and to compact statements of the reciprocal theorem and the representation theorem. The plate response for a point moment is derived using a direct source specification, rather than an indirect specification through boundary conditions. Solutions are presented for combinations of such point moments (doublets) that represent, respectively, a center of bending, a center of twist and a center of inplane twist. The flexural response due to finite sources, such as piezoelectric actuators, can be modeled by distributions of centers of bending. Detailed results are presented for a circular, and for a narrow rectangular actuator. The far-field radiation pattern for an array of equally spaced actuators parallel to a straight boundary is derived. The solutions presented for the point moment and the point force constitute the components of a dyadic Green’s function which is required, along with its spatial derivatives, for a representation of plate-wave scattering by flexural inhomogeneities.
Ultrasonic attenuation due to grain boundary scattering in copper and copper-aluminum
Authors: Zhang X.-G. , Simpson W. A. , Vitek J. M. , Barnard D. J. , Tweed L. J. , Foley J.
Published: July 2004

Ultrasonic attenuation in copper and copper-aluminum samples is measured as a function of frequency and average grain size. At low frequencies the attenuation scales quadratically with the frequency and linearly with average grain size. In addition, there is a large difference in attenuation between powder metallurgy samples and cast-and-wrought samples, although their qualitative behaviors are similar both in terms of frequency dependence and grain size dependence. Such difference and the discrepancy with the existing theory may point to mechanisms of scattering by grain boundaries that are not included in the current theoretical model.
Blind deconvolution in ocean waveguides using artificial time reversal
Authors: Sabra Karim G. , Dowling David R.
Published: July 2004

Sound that travels through the ocean from a source to a receiver is commonly distorted by multipath acoustic propagation. The severity and details of this distortion are determined by the sound channel’s characteristics, which may not be known. However, recovery or reconstruction of undistorted signals from recordings made in unknown complex multipath environments—a process commonly referred to as blind deconvolution—is advantageous in many applications of underwater acoustics. This paper presents a simple and robust means to achieve blind deconvolution in unknown sound channels with an array of receiving transducers. The technique, artificial time reversal (ATR), can be effective when there is a linear relationship between frequency and the phase of the low-order propagating modes of the sound channel. Broadband simulations of ATR in a generic shallow ocean sound channel show that the maximum correlation between the original signal and the reconstructed signal may approach 100% for signal pulses having a 258 Hz bandwidth and a 500 Hz center frequency. Application of ATR to ocean sound-propagation measurements produces original-to-reconstructed signal correlations from 80% to 95%. Possible extensions and improvements of ATR are discussed.
A theoretical study for the propagation of rolling noise over a porous road pavement
Authors: Keung Lui Wai , Ming Li Kai
Published: July 2004

A simplified model based on the study of sound diffracted by a sphere is proposed for investigating the propagation of noise in a hornlike geometry between porous road surfaces and rolling tires. The simplified model is verified by comparing its predictions with the published numerical and experimental results of studies on the horn amplification of sound over a road pavement. In a parametric study, a point monopole source is assumed to be localized on the surface of a tire. In the frequency range of interest, a porous road pavement can effectively reduce the level of amplified sound due to the horn effect. It has been shown that an increase in the thickness and porosity of a porous layer, or the use of a double layer of porous road pavement, attenuates the horn amplification of sound. However, a decrease in the flow resistivity of a porous road pavement does little to reduce the horn amplification of sound. It has also been demonstrated that the horn effect over a porous road pavement is less dependent on the angular position of the source on the surface of tires.
Acoustic radiation force on a compressible cylinder in a standing wave
Authors: Wei Wei , Thiessen David B. , Marston Philip L.
Published: July 2004

The radiation force-per-length on an infinitely long circular cylinder in an acoustic plane standing wave is expressed in terms of partial-wave scattering coefficients for the corresponding traveling wave scattering problem. This information allows a dimensionless radiation force function to be expressed using coefficients available from two-dimensional scattering theory. Four examples are given for fluid circular cylinders: A hot gas column (used to approximate a small flame), a compressible liquid bridge in a Plateau tank, a liquid bridge in air, and a cylindrical bubble of air in water. A long-wavelength approximation for the force is also examined which is analogous to one for the radiation force on compressible spheres [K. Yosioka and Y. Kawasima, Acustica 5, 167–173 (1955)]. A long-wavelength approximation is also known for the monopole and dipole scattering coefficients of a compressible elliptical cylinder and the radiation force is also examined for that situation. Some of the results for the radiation force are relevant to the acoustic stabilization of liquid cylindrical bridges in reduced gravity.
Time–frequency analysis of auditory-nerve-fiber and basilar-membrane click responses reveal glide irregularities and non-characteristic-frequency skirts
Authors: Lin Tai , Guinan John J.
Published: July 2004

Although many properties of click responses can be accounted for by a single, frequency-dispersive traveling wave exciting a single, characteristic-frequency (CF) resonance, some properties, such as waxing and waning cannot. Joint time–frequency distributions (TFDs) were used to help understand click responses of cat single auditory-nerve (AN) fibers (CFs<4 kHz) and published measurements of chinchilla basilar-membrane (BM) motion. For CFs>800 Hz, the peak energy of the response decreased in latency and frequency as the level increased, as expected. However, at high levels the trend reversed for AN, but not BM, responses. Normalized TFDs, which show the frequency with the peak energy at each response time, revealed glides, as previously reported. Classical theory predicts smooth, upward glides. Instead, at low CFs there were downward glides, and at other CFs glides had substantial irregularities. Finally, click skirts, defined as the longest-latency part of click responses, sometimes showed deviations from CF for above-threshold sound levels. Most of these phenomena are not explained by a single, frequency-dispersive traveling wave exciting a single CF resonance, but they can be accounted for by the interaction of two (or more) excitation drives with different latencies and frequency contents.
The system-on-chip design of a silicon micromachined condenser microphone array
Authors: Bai Mingsian R. , Huang Shihwei
Published: July 2004

A miniature condenser microphone array that combines array signal processing and micro-electro-mechanical systems (MEMS) technologies is presented. A linear dynamic model and a quasistatic analysis are presented. The array configuration serves two purposes: enhancement of the signal-to-noise ratio (SNR) and the directivity of sensor. A least-squares beamforming design based on the template resulting from the Multiple Signals Classification algorithm is proposed to achieve a directive beam pattern. To minimize the parasitic effects on the MEMS device, a system-on-chip design composed of a microphone module, a dc bias circuit, an impedance matching circuit, and array beamforming filters is proposed in the paper. The performance of the proposed design is evaluated in terms of the frequency response, SNR improvement, and directional response through numerical simulations and experiments.
Blind normalization of speech from different channels
Authors: Levin David N.
Published: July 2004

We show how to construct a channel-independent representation of speech that has propagated through a noisy reverberant channel. This is done by blindly rescaling the cepstral time series by a nonlinear function, with the form of this scale function being determined by previously encountered cepstra from that channel. The rescaled form of the time series is an invariant property of it in the following sense: It is unaffected if the time series is transformed by any time-independent invertible distortion. Because a linear channel with stationary noise and impulse response transforms cepstra in this way, the new technique can be used to remove the channel dependence of a cepstral time series. In experiments, the method achieved greater channel-independence than cepstral mean normalization, and it was comparable to the combination of cepstral mean normalization and spectral subtraction, despite the fact that no measurements of channel noise or reverberations were required (unlike spectral subtraction).
On the acoustic vaporization of micrometer-sized droplets
Authors: Kripfgans Oliver D. , Fabiilli Mario L. , Carson Paul L. , Fowlkes J. Brian
Published: July 2004

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 μs tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 μm, independent of droplet diameter which ranged from 5 to 27 μm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet’s imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.
Calculated effects of pressure-driven temperature oscillations on heat exchangers in thermoacoustic devices with and without a stack
Authors: Wakeland Ray Scott , Keolian Robert M.
Published: July 2004

A Lagrangian computational method is used to explore the performance of heat exchangers in conditions of oscillating flow and oscillating pressure relevant to thermoacoustic devices. Pressure oscillations cause temperature oscillations within the working gas. Depending on phase, these “pressure-driven temperature oscillations” can enhance or degrade heat transfer within the exchangers of a thermoacoustic device.
Ultrasonic wave propagation in human cancellous bone: Application of Biot theory
Authors: Fellah Z. E. A. , Chapelon J. Y. , Berger S. , Lauriks W. , Depollier C.
Published: July 2004

Ultrasonic wave propagation in human cancellous bone is considered. Reflection and transmission coefficients are derived for a slab of cancellous bone having an elastic frame using Biot’s theory modified by the model of Johnson et al. [J. Fluid Mech. 176, 379–402 (1987)] for viscous exchange between fluid and structure. Numerical simulations of transmitted waves in the time domain are worked out by varying the modified Biot parameters. The variation is applied to the governing parameters and is about 20%. From this study, we can gain an insight into the sensitivity of each physical parameter used in this theory. Some parameters play an important role in slow-wave wave form, such as the viscous characteristic length Λ and pore fluid bulk modulus Kf. However, other parameters play an important role in the fast-wave wave form, such as solid density ρs and shear modulus N. We also note from these simulations that some parameters such as porosity φ, tortuosity α∞, thickness, solid bulk modulus Ks, and skeletal compressibility frame Kb, play an important role simultaneously in both fast and slow wave forms compared to other parameters which act on the wave form of just one of the two waves. The sensitivity of the modified Biot parameters with respect to the transmitted wave depends strongly on the coupling between the solid and fluid phases of the cancellous bone. Experimental results for slow and fast waves transmitted through human cancellous bone samples are given and compared with theoretical predictions.
Annoyance with aircraft noise in local recreational areas, contingent on changes in exposure and other context variables
Authors: Krog Norun Hjertager , Engdahl Bo
Published: July 2004

Few socioacoustic studies have examined the effect of noise on outdoor recreationists. The areas studied have been mountain and wilderness areas that people typically travel for a distance to visit. In this article we examine the reactions to aircraft noise in local recreational areas experiencing either decreased (1930 survey respondents), or increased noise exposure (1001 survey respondents). Field studies were conducted before and after the relocation the main airport of Norway in 1998 in one area near each airport. The relationship between individual noise exposure (LAeq for the aircraft events, percentage of time aircraft were audible, and LAsel) for the aircraft events. The analyses included the “situation” in which data were collected (before or after the relocation), and variables describing the recreational context. A strong effect of the “situation” was found in both cases, but the size of the effect was influenced by the choice of exposure variable in one of the study areas. Other context variables were also influencing annoyance. The effect of the situation (before/after a change in exposure) on the dose–response relationship may be influenced by the initial noise levels, the amount of change, and the time elapsed since the change at the time of the second survey. Further research should investigate the significance of these variables.
Behavioral criterion quantifying the effects of circumferential air gaps on porous materials in the standing wave tube
Authors: Pilon Dominic , Panneton Raymond , Sgard Franck
Published: July 2004

The influence of mounting conditions on the measurement of the absorption coefficient in the standing wave tube (swt) is investigated. In a previous paper [D. Pilon, R. Panneton, and F. Sgard, J. Acoust. Soc. Am. 114, 1980–1987 (2003)], a behavioral criterion was developed to access the effect of a circumferential edge constraint on elastic foams. Similarly, the effect of circumferential air gaps on porous materials is studied here. The objective is to identify the materials, in terms of a ratio based on their physical properties, for which it is possible to measure the theoretical absorption coefficient when mounted inside the swt with a circumferential air gap. The difference between the measured and theoretical absorption coefficient is evaluated for a wide range of materials with various sample sizes. These errors are then sorted in terms of the chosen ratio. It is shown that for certain values of the ratio, the theoretical absorption coefficient can be efficiently measured using the swt. Through the use of this acousto-visco-inertial criterion, an experimenter can determine which absorption is going to be measured: the theoretical absorption or one that will be influenced by the circumferential air gaps.
Effectiveness of acoustic power dissipation in lossy layers
Authors: Razansky Daniel , Einziger Pinchas D. , Adam Dan R.
Published: July 2004

The effect of losses in the dissipative object becomes crucial when maximal power absorption of the incident wave is of top priority. In order to assess the phenomenon of acoustic power absorption in finite size dissipative medium, a prototype model of linear pressure waves absorption in dissipative layer is considered. The conditions, parameters and bounds for the optimal (maximal) incident power absorption within the layer have been found analytically and explicitly versus its normalized thickness. These conditions are presented in terms of the basic wave propagation parameters, namely sound velocity and attenuation constant. It is shown that, for thin layers (in terms of acoustic wavelength), the upper bound on the absorptivity tends to the value of 50%, when prescribed resonant dispersion/absorption conditions, characterized by the so-called Kramers–Kronig relations, are met within the layer. For sufficiently thick layers absorption of close to 100% of the incident wave power can be achieved, when specific optimal values are selected for the corresponding real and imaginary parts of dissipative layer wave number. The model may serve as a canonical prototype problem for engineered dissipative materials design and optimization of the sound/ultrasound absorption in lossy targets, e.g., biological tissues.
The Laplace transform to describe bounded inhomogeneous waves
Authors: Declercq Nico F. , Degrieck Joris , Leroy Oswald
Published: July 2004

The inhomogeneous waves theory deals with plane waves having complex valued wave vectors and with their superposition to form bounded beams. Since infinite inhomogeneous plane waves cannot be formed experimentally, verifications of the theory have to be performed using bounded inhomogeneous waves. In this paper we clarify how a bounded inhomogeneous wave is described as a superposition of inhomogeneous waves. This is done by applying the Laplace transform. The paper also shows from a theoretical point of view why bounded inhomogeneous waves behave like infinite inhomogeneous waves in numerous experiments.
Determining the pulse-echo electromechanical characteristic of a transducer using flat plates and point targets
Authors: Szabo Thomas L. , Karbeyaz Başak Ülker , Cleveland Robin O. , Miller Eric L.
Published: July 2004

A common technique to determine the electromechanical response of a spherically focusing transducer is to use a reference pulse echo from a flat plate in the focal plane of the transducer. We show that when the pressure focusing gain of the transducer is much greater than unity, the focal plane reflection is a valid approximation of the desired electromechanical response. An alternative calibration target is a point scatterer and we show theoretically and experimentally that this waveform is the double time differential of the flat-plate response. The use of calibration to describe general scatterers through a Born approximation (Jensen, J. A. (1991), J. Acoust. Soc. Am. 89, 182–190) is discussed.
Experimental verification of an interpolation algorithm for improved estimates of animal position
Authors: Schell Chad , Jaffe Jules S.
Published: July 2004

This article presents experimental verification of an interpolation algorithm that was previously proposed in Jaffe [J. Acoust. Soc. Am. 105, 3168–3175 (1999)]. The goal of the algorithm is to improve estimates of both target position and target strength by minimizing a least-squares residual between noise-corrupted target measurement data and the output of a model of the sonar’s amplitude response to a target at a set of known locations. Although this positional estimator was shown to be a maximum likelihood estimator, in principle, experimental verification was desired because of interest in understanding its true performance. Here, the accuracy of the algorithm is investigated by analyzing the correspondence between a target’s true position and the algorithm’s estimate. True target position was measured by precise translation of a small test target (bead) or from the analysis of images of fish from a coregistered optical imaging system. Results with the stationary spherical test bead in a high signal-to-noise environment indicate that a large increase in resolution is possible, while results with commercial aquarium fish indicate a smaller increase is obtainable. However, in both experiments the algorithm provides improved estimates of target position over those obtained by simply accepting the angular positions of the sonar beam with maximum output as target position. In addition, increased accuracy in target strength estimation is possible by considering the effects of the sonar beam patterns relative to the interpolated position. A benefit of the algorithm is that it can be applied “ex post facto” to existing data sets from commercial multibeam sonar systems when only the beam intensities have been stored after suitable calibration.
Simple discrimination method between False Acoustic Emission and Acoustic Emission revealed by piezoelectric sensors, in Gran Sasso mountain measurements (L)
Authors: Diodati Paolo , Piazza Stefano
Published: July 2004

Recently it was shown, studying data acquired with in-situ measurements on the Gran Sasso mountain (Italy), for about ten years, by means of a high sensitivity transducer coupled to the free-end section of a stainless steel rod fixed by cement in a rock-drill hole 10 m high, about 2500 m above sea level, that Acoustic Emission (AE) can be affected by more than 90% False Acoustic Emission (FAE) of an electromagnetic origin. A very simple method to solve the problem of the discrimination between AE events due to elastic waves, from FAE signals, due to electromagnetic noise, both coming from the same “reception-point,” is presented. The reliability of the obtained separation is confirmed also by the reported amplitude and time distribution of AE events, typical of fracture dynamics and those of FAE events, similar to those of noise.