bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal-flow techniques for sub-35 nm contact-hole fabrication in electron-beam lithography
Authors: Chen H. L. , Chen C. H. , Ko F. H. , Chu T. C. , Pan C. T. , Lin H. C.
Published: December 2002

In this article, we demonstrate that 200 nm contact-hole resist patterns can easily be shrunk to less than 35 nm after a simple thermal-flow procedure. The optimal thermal-flow temperature was determined by differential-scanning calorimetry and wafer-curvature measurement. The effects of postapplied baked temperature, thermal-flow temperature, baking time period, and pattern density were evaluated. The resist after thermal flow is more intact than during dry-etching processes. The resist can overcome the resist-thickness loss during the thermal-flow procedure.
Fabrication of flexible polymer tubes for micro and nanofluidic applications
Authors: Ilic B. , Czaplewski D. , Zalalutdinov M. , Schmidt B. , Craighead H. G.
Published: December 2002

We describe a method for fabricating narrow, flexible, polymeric fluid conduction tubes with dimensions down to the 100 nm regime. Vapor deposited Parylene tubes of various dimensions were integrated into silicon substrates forming a microfluidic network. In one approach we replicated fluidic systems in polymer by detaching free-standing flexible Parylene tubes from the silicon mold. We demonstrated capillary flow and electrophoretic drive of ions through polymer tubes of up to 5 cm in length.
Fluoropolymer-based resists for a single-resist process of 157 nm lithography
Authors: Toriumi M. , Yamazaki T. , Furukawa T. , Irie S. , Ishikawa S. , Itani T.
Published: December 2002

We investigated two types of main-chain fluorinated polymers and found that incorporating fluorine into their backbones reduced their absorption coefficients to less than 1 μm−1 at 157 nm and showed good dry-etching resistance. Fluoropolymer dissolution during development was studied using a quartz-crystal microbalance and evaluated from the standpoint of molecular structures and polymer acidity. The fluorine and hydrophobic effects, rather than the polymer acidity effect, were found to play the dominant role in forming the swelling layer during development. The use of main-chain fluorinated polymers for the base resin of positive-tone resists results in fine imaging with a film thickness of 300 nm. The incorporation of fluorine into the backbones will thus enable these polymers to be used as single-layer resists for 157 nm lithography.
Molybdenum-based nanostructured mixed oxides for sensing applications: Effect of the Mo oxide composition on the structure of sol–gel thin films
Authors: Taurino A. , Catalano M. , Siciliano P. , Galatsis K. , Li Y. X. , Wlodarski W.
Published: December 2002

In this work, we report on the structural investigation by transmission electron microscopy of molybdenum-based mixed oxides for use as gas sensitive films. In particular, sol–gel thin films of molybdenum–titanium and molybdenum–tungsten oxides, deposited by spin coating on silicon substrates, have been analyzed by selected area electron diffraction, conventional, and high-resolution transmission electron microscopy. Our results show that the relative percentage of the molybdenum precursors used during the sol–gel deposition controls the morphology of the films, by modifying the size and the arrangements of the polycrystalline grains on the substrate.
Development of the point diffraction interferometer for extreme ultraviolet lithography: Design, fabrication, and evaluation
Authors: Otaki K. , Ota K. , Nishiyama I. , Yamamoto T. , Fukuda Y. , Okazaki S.
Published: December 2002

A point diffraction interferometer (PDI) for extreme ultraviolet lithography (EUVL) aspheric mirror measurement has been developed. In order to realize an accuracy of 0.1 nm rms, various optical error factors have been numerically analyzed and the maximum tolerable error has been determined. From the error estimation results, the optimal pinhole diameter has been determined as 0.5 μm. In a PDI, air turbulence reduces the precision and accuracy because of the long optical path. In order to avoid this problem, the apparatus is filled with helium gas, which has a smaller refractive index than that of air. By using this apparatus, precision of 0.03–0.04 nm rms and a system error of 0.10 (0.16) nm rms have been obtained for a spheric mirror with numerical aperture (NA) 0.08 (0.15). In aspheric mirror measurement, an accuracy of 0.74 (1.18) nm rms for NA 0.08 (0.15) has been obtained. The accuracy becomes 0.34 (0.97) nm rms for NA 0.08 (0.15) with 36-term Zernike polynomial fitting.
Comprehensive model of electron energy deposition
Authors: Han Geng , Khan Mumit , Fang Yanghua , Cerrina Franco
Published: December 2002

We present our effort in developing a complete model of electron energy transfer from fast electrons (0.1–100 keV) to the photoresist. Our model is based on the direct Monte Carlo method, instead of using continuous slowing down approximation, model and a stopping power curve. We separate the interaction events into four types: Elastic, ionization, excitation, and plasmon. Our results show that: First, secondary electrons are major mechanism of energy distribution; and second, plasmons are very efficient “friction” mechanism but do not create molecular changes; and finally, excitations lead to molecular changes.
Depth dependence of resist line-edge roughness: Relation to photoacid diffusion length
Authors: Shin J. , Ma Y. , Cerrina F.
Published: December 2002

We report the results of an experimental and simulation study of the correlation between line-edge roughness (LER) and height along the sidewall for resists patterned with electron-beam lithography. The characterization has been performed using atomic force microscopy with carbon nanotube tips and scanning electron microscopy. Experimental results generally support that LER depends on resist height and aerial image modulation. Finally, percolation simulation results based on stochastic modeling are compared with experimental results, and allow us to set an upper limit of 3–5 nm on acid diffusion length.
End point of silicon milling using an optical beam induced current signal for controlled access to integrated circuits for backside circuit editing
Authors: Antoniou N. , Bassom N. J. , Huynh C. , Monforte D. , Casey J. D. , Krechmer A. , Carleson P.
Published: December 2002

Integrated devices increasingly use flip chip packaging, which complicates modification of the circuitry using focused ion beam (FIB) systems, as the thickness of the silicon must be reduced to a few micrometers before work can begin. A technique for end pointing the milling of bulk silicon from the backside of flip chip devices, using laser illumination to produce an optical beam induced current (OBIC), is described. System design and operation are described and results shown. The OBIC signal varies strongly with the thickness of the silicon above the bulk to well junction—by monitoring the OBIC signal in real time and end pointing on a characteristic feature the technique can reliably end point the bulk-well interface. It is shown that this system represents a significant advance over previous techniques and provides a robust and reliable way of end pointing. Theory of operation and reasons for the improved performance are discussed.
Characterization of the Surface of BaCO3 Powder by XPS
Authors: Schmitz Peter J.
Published: December 2002

This work reports survey and core level x-ray photoemission spectra obtained from the surface of a barium carbonate powder. The high purity (99.997%) barium carbonate specimen was commercially obtained from Alfa/AESARS. The XPS spectra were acquired with a Kratos Axis 165 instrument using monochromatic Al Kα radiation. The survey spectrum was measured with an 80 eV pass energy and the core level spectra (Ba 3d, C 1s, and O 1s) were acquired using a 20 eV pass energy corresponding to analyzer resolutions of 1.12 and 0.28 eV, respectively. The data are consistent with the surface being exclusively barium carbonate. Adventitious carbon was the only contaminant observed.
Ni
2
P
(0001) by XPS
Authors: Kanama Daisuke , Oyama S. Ted , Otani Shigeki , Cox David F.
Published: December 2002

XPS spectra are reported for a well-ordered Ni2P (0001) surface. These are the first reported photoemission spectra for this transition metal phosphide in single crystal form. Ion bombardment and annealing produces an ordered surface.
Modification of prostate implants based on postimplant treatment margin assessment
Authors: Mueller Amy , Wallner Kent , Merrick Gregory , Couriveau Jacques , Sutlief Steven , Butler Wayne , Gong Lixin , Cho Paul
Published: December 2002

Purpose: To quantify the extent of additional source placement needed to perfect an implant after execution by standard techniques, assuming that uniform 5 mm treatment margins (TMs) is the criteria for perfection. Materials and Methods: Ten consecutive, unselected patients treated with I‐125 brachytherapy were studied. Source placement is planned just inside or outside of the prostatic margin, to achieve a minimum 5 mm TM and a central dose of 150%–200% of the prescription dose. The preimplant prostate volumes ranged from 24 to 85 cc (median: 35 cc). The number of sources implanted ranged from 48 to 102 (median: 63). Axial CT images were acquired within 2 h postoperatively for postimplant dosimetry. After completion of standard dosimetric calculations, the TMs were measured and tabulated at intervals around the prostate periphery at 0.0, 1.0, 2.0, and 3.0 cm planes. Sources were then added to the periphery to bring the TMs to a minimum of 5 mm at each measured TM, resulting in a modified implant. All margin modifications were done manually, without the aid of automated software. Results: Patients' original (unmodified) D90s ranged from 111% to 154%, with a median of 116%. The original V100s ranged from 94% to 99%, with a median of 96%. No patient required placement of additional sources to meet a minimum D90 of 90% or a minimum V100 of 80%. In contrast, patients required from 7 to 17 additional sources (median: 11) to achieve minimum 5 mm TMs around the entire prostatic periphery. Additional sources equaled from 12% to 24% of the initial number of sources placed (median: 17%). By adding sufficient peripheral sources to bring the TMs to a minimum 5 mm, patients' average V100 increased from 96% to 100%, and the average D90 increased from 124% to 160% of prescription dose. In the course of achieving a minimum 5 mm TM, the average treatment margin for all patients combined increased from 5.5 to 9.9 mm. The number of sources needed to bring the TMs to a minimum 5 mm was loosely correlated with the preimplant prostate volume and the change in prostate volume from implant‐related swelling. Adding sufficient sources to achieve minimum 5 mm TMs increased the prostate volume receiving greater than 200% of the prescription dose (V200) from 39% to 58%, and increased the average urethral point dose (2.00 cm inferior to the bladder) from 154% to 171% of the 144 Gy prescription isodose. Conclusions: Minimum 5 mm TMs are not uniformly achieved with current implant techniques. It seems that doing so, even in experienced hands, will require a reappraisal of our implant techniques, or the addition of intraoperative dosimetric analysis with the capacity to substantially modify the implant with extra sources.
Photoacoustic tomography of biological tissues with high cross‐section resolution: Reconstruction and experiment
Authors: Wang Xueding , Xu Yuan , Xu Minghua , Yokoo Seiichirou , Fry Edward S. , Wang Lihong V.
Published: December 2002

A modified back‐projection approach deduced from an exact reconstruction solution was applied to our photoacoustic tomography of the optical absorption in biological tissues. Pulses from a Ti:sapphire laser (4.7 ns FWHM at 789.2 nm) were employed to generate a distribution of photoacoustic sources in a sample. The sources were detected by a wide‐band nonfocused ultrasonic transducer at different positions around the imaging cross section perpendicular to the axis of the laser irradiation. Reconstructed images of phantoms made from chicken breast tissue agreed well with the structures of the samples. The resolution in the imaging cross section was experimentally demonstrated to be better than 60 μm when a 10 MHz transducer (140% bandwidth at −60 dB) was employed, which was nearly diffraction limited by the detectable photoacoustic waves of the highest frequency.
A technique of intensity‐modulated radiosurgery (IMRS) for spinal tumors
Authors: Yin Fang‐Fang , Ryu Samuel , Ajlouni Munther , Zhu Jingeng , Yan Hui , Guan Harrison , Faber Kathleen , Rock Jack , Abdalhak Muwaffak , Rogers Lisa , Rosenblum Mark , Kim Jae Ho
Published: December 2002

This study is to demonstrate the feasibility of spinal radiosurgery using an image‐guided intensity‐modulated radiosurgical (IMRS) procedure. A dedicated Novalis® shaped beam surgery unit equipped with a built‐in micro‐multileaf collimator (mMLC) with a single 6 MV photon beam was used. Each patient was simulated in the supine position using an AcQsim CT simulator with infrared sensitive markers for localization. A variety of different treatment plans were developed, but the most common plan was the use of seven coplanar intensity‐modulated beams to minimize radiation to critical organs such as the spinal cord and kidneys. An automatic localization device based on infrared and video cameras was used to guide the initial patient setup. Two keV x‐ray imaging systems were used to identify potential deviations from the planned isocenter. A total of 25 patients with spinal tumors have been treated using this procedure with a single prescription dose ranging from 6 to 12 Gy. The final verification images indicated that the average isocenter deviation from the planned isocenter was within 2 mm. The phantom verification of isocenter doses indicated that the average deviation of measured isocenter doses from the planned isocenter doses for all patients treated with intensity‐modulated beams was less than 2%. Film dose measurement in a phantom study demonstrated good agreement of above 50% isodose lines between the planned and measured results. Preliminary experience shows that precision delivery of high dose radiation could be administered to the planned target volume while the dose to the critical organs is kept within tolerable limits.
A personal‐computer‐based method to obtain “star‐shots” of mechanical and optical isocenters for gantry rotation of linear accelerators
Authors: Woo M. K.
Published: December 2002

This work describes a method to obtain “star‐shots” of the mechanical and optical isocenters of linear accelerators, similar to the star‐shots of radiation isocenters normally obtained using films. In this method a digital camera is connected to a personal computer so that multiply exposed images can be taken at a fixed camera position. A mechanical pointer or a wire aligned along the optical axis can then be imaged by the camera. Multiple exposures at varying gantry angles are then superimposed on a digital image which can be analyzed by the computer to give a high‐resolution star‐shot. The method provides a convenient way for a linear accelerator quality assurance procedure.
Experimental determination of beam quality conversion factors in clinical photon beams using ferrous sulphate (Fricke) dosimetry
Authors: Palm Åsa , Mattsson Olof
Published: December 2002

The implementation of protocols based on absorbed dose to water standards requires beam quality conversion factors, Calculated values of are available for ionization chambers used for reference dosimetry. Ideally, should be experimentally determined at the same beam qualities as that of the user. In this work we measure factors in clinical photon beams and compare them with calculated and measured values. Beam quality conversion factors are determined for clinical photon beams of nominal energies 4 MV, 6 MV, 15 MV, and 25 MV, for commonly used cylindrical ionization chambers. Twelve chambers of eight different types are used. For three of them, no experimental data have previously been available. The experimental procedure is based on measurements with ionization chambers and Fricke dosimetry in the reference beam γ radiation) and in clinical linear accelerator beams. The values determined in this work generally agree within 0.5% with previously reported experimental values both when and are used for beam quality specification. The agreement with calculated data is generally within 0.5%, except for the 15 MV beam. For this beam the measured values are usually between 0.5% and 1% lower than the data taken from the TG‐51 protocol or the TRS‐398 code of practice. For three NE2571 chambers and three NE2581 chambers, the maximum observed deviation of individual values is 0.2% and 0.4%, respectively.
A Monte Carlo based phase space model for quality assurance of intensity modulated radiotherapy incorporating leaf specific characteristics
Authors: Aaronson Randi F. , DeMarco John J. , Chetty Indrin J. , Solberg Timothy D.
Published: December 2002

Dose calculations for intensity modulated radiation therapy (IMRT) require an accurate description of the radiation field defined by the multileaf collimator. A previously developed Monte Carlo phase space model has been modified to provide accurate dose verification for IMRT treatments on a Novalis linear accelerator. We have incorporated into the model the effects of the multileaf collimator geometry, including leaf transmission, interleaf leakage, the rounded leaf tips and the effects of leaf sequencing, as well as the beam divergence and energy variation across the field. The modified source model was benchmarked against standard depth dose and profile measurements, and the agreement between the calculation and measurement is within the AAPM Task Group No. 53 criteria for all benchmark fields used. Film dosimetry was used to evaluate the model for IMRT sequences and plans, and the ability of the model to account for leaf sequencing effects is also demonstrated.
Checking monitor unit calculations using coordinate transformations to calculate off‐axis distances in the collimator frame of reference
Authors: Petti Paula L.
Published: December 2002

An important part of treatment‐planning QA is to check Monitor Units (MUs) calculated by treatment‐planning programs. This is generally straightforward, unless the central axis is blocked. One way to check MUs in this case is to select a reference point in the open portion of the field and use the off‐axis distance (OAD), as well as other relevant data, to verify the dose. If wedges are employed in the treatment, the OAD must be specified in the collimator frame‐of‐reference because one must know where the calculation point is with respect to the wedge to calculate the dose correctly. The purpose of this paper is to describe a method of calculating the OAD in the collimator frame‐of‐reference using the system of coordinate transformations described by Siddon [Med. Phys. 8, 766–774 (1981)].
A CdZnTe slot‐scanned detector for digital mammography
Authors: Mainprize James G. , Ford Nancy L. , Yin Shi , Gordon Eli E. , Hamilton William J. , Tümer Tümay O. , Yaffe Martin J.
Published: December 2002

A new high‐resolution detector has been developed for use in a slot‐scanned digital mammography system. The detector is a hybrid device that consists of a CCD operating in time‐delay integration mode that is bonded to a 150‐μm‐thick CdZnTe photoconductor array. The CCD was designed with a detector element pitch of 50 μm. Two devices were evaluated with differing crystalline quality. Incomplete charge collection was a source of reduction in DQE. This occurs in both devices due to characteristically low mobility‐lifetime products for CdZnTe, with the greatest losses demonstrated by the multicrystalline sample. The mobility‐lifetime products for the multicrystalline device were found to be and for electrons and holes, respectively. The device constructed with higher quality single crystal CdZnTe demonstrated mobility‐lifetime products of and for electrons and holes. The MTF and DQE for the device were measured at several exposures and results were compared to predictions from a linear systems model of signal and noise propagation. The MTF at a spatial frequency of exceeded 0.18 and 0.56 along the scan and slot directions, respectively. Scanning motion and CCD design limited the resolution along the scan direction. For an x‐ray beam from a tungsten target tube with 40 μm molybdenum filtration operated at 26 kV, the single crystal device demonstrated a DQE(0) of at C/kg (27 mR) exposure to the detector, despite its relatively poor charge collection efficiency.
Optimization of a radiation source train stepping for intravascular brachytherapy
Authors: Miften Moyed M. , Das Shiva K. , Shafman Timothy D. , Marks Lawrence B.
Published: December 2002

A steepest‐descent gradient algorithm is developed to optimize the stepping of aradiation source train (RST) for intravascular brachytherapy (IVB). The objective function is to deliver a uniform dose in a coronary target vessel and minimize the dose in adjacent normal vessel tissue at the proximal and distal edges of the coronary target vessel. Based on the target length and number of dwell points (number of steps), the algorithm modulates the dwell times and corresponding dwell positions that optimize the weighted addition of staggeredEGS4Monte Carlo (MC) calculated dose distribution from a single RST. Stepping treatment plans are generated for target vessel lengths of 3.0, 3.3, and 3.8 cm. For both the unoptimized and optimized plans, the dose heterogeneity in the target vessel wall, and length of nontarget vessel receivingis assessed to compare plans. Optimization results show a 14% dose uniformity within the target is achievable for all vessel lengths. Further, the dose in the adjacent normal tissue is lower in the optimized plans than the unoptimized plans. The work presented in this paper provides a model to address the finite length of RST in IVB treatments. While the results presented are specific to theRST, the methods should apply to other finite length RSTs.
Accuracy of treatment planning calculations for conformal radiotherapy (in English)
Authors: van't Veld Aart
Published: December 2002

This thesis presents methods to define and improve the accuracy of treatment planning dose and volume calculations for conformal radiotherapy, especially in regions with the highest expected benefits—the edges and shielded parts of the beams. The context of this thesis is a verification program of a treatment planning system. It is shown that an appropriately designed “combinatorial verification” makes such a program feasible. Results of this thesis apply to megavoltage photon beams in homogeneous and heterogeneous geometries, to proton beams, and to dose–volume representations. A “field accuracy” concept is shown to facilitate simultaneous checks of dose and distance criteria. This concept is applied to pencil beam calculations in partially blocked photon beams. In a lung tumor phantom large dose discrepancies were found between photon pencil beam calculations and film measurements. This is due to improper scatter handling, as is shown by comparison to results of a point spread kernel algorithm. Methods have been developed for high‐resolution measurements of photon beam edges with ionization chambers, thus in particular suited for a program of routine verification measurements. Improvements in accuracy of up to 2 mm in the penumbra have been achieved. Dose distributions and penumbras in small proton beams have been investigated with Monte Carlo calculations and a 2D scintillating screen detector. Accuracy of grid‐based volume sampling has been studied, yielding the required grid sizes for specific uncertainties in the volume representation of dose–volume histograms. Finally, bringing the concepts of combinatorial verification and field accuracy together, the feasibility of a comprehensive presentation of calculation accuracy in a conformal prostate treatment plan has been demonstrated.
Modal decomposition method for modeling the interaction of Lamb waves with cracks
Authors: Castaings Michel , Le Clezio Emmanuel , Hosten Bernard
Published: December 2002

The interaction of the low-order antisymmetric (a0) and symmetric (s0) Lamb waves with vertical cracks in aluminum plates is studied. Two types of slots are considered: (a) internal crack symmetrical with respect to the middle plane of the plate and (b) opening crack. The modal decomposition method is used to predict the reflection and transmission coefficients and also the through-thickness displacement fields on both sides of slots of various heights. The model assumes strip plates and cracks, thus considering two-dimensional plane strain conditions. However, mode conversion (a0 into s0 and vice versa) that occurs for single opening cracks is considered. The energy balance is always calculated from the reflection and transmission coefficients, in order to check the validity of the results. These coefficients together with the through-thickness displacement fields are also compared to those predicted using a finite element code widely used in the past for modeling Lamb mode diffraction problems. Experiments are also made for measuring the reflection and transmission coefficients for incident a0 or s0 lamb modes on opening cracks, and compared to the numerical predictions.
Supercritical parametric phase conjugation of ultrasound. Numerical simulation of nonlinear and nonstationary mode
Authors: Merlen Alain , Preobrazhensky Vladimir L. , Pernod Philippe
Published: December 2002

This paper investigates the saturation mechanism of the nonstationary supercritical mode of parametric wave phase conjugation in a magnetostrictive medium. The numerical simulation considers the two most probable nonlinear mechanisms of interaction between elastic deformation and electromagnetic excitation. For the qualitative study of the dynamics of the system, a one-dimensional numerical simulation is sufficient if applied to an infinite medium with a finite active zone. The temporal form of the conjugate wave is obtained for both hypotheses. Comparison with experiments shows that only one mechanism corresponds to the experimental behavior.
Traffic noise prediction with the parabolic equation method: Validation of a split-step Padé approach in complex environments
Authors: Gauvreau Benoit , Bérengier Michel , Blanc-Benon Philippe , Depollier Claude
Published: December 2002

This study deals with sound propagation in typical traffic noise conditions. The numerical results are obtained through the split-step Padé method and the discrete random Fourier modes technique. These are first evaluated qualitatively, by color contour maps showing noise propagation, diffraction by an impedance discontinuity or a screen edge, and scattering by atmospheric turbulence. Next, our numerical results are quantitatively validated by comparison with analytical models and other parabolic equation models. For all the atmospheric conditions and geometrical configurations available in literature, the agreement between the different methods is very good, except for some cases involving the atmospheric turbulence. However, in those particular cases, the split-step Padé results are shown to be more consistent with physical theory. Finally, our method seems to be very powerful and reliable for traffic noise prediction.
Sound power flux measurements in strongly exited ducts with flow
Authors: Holland Keith R. , Davies Peter O. A. L. , van der Walt Danie C.
Published: December 2002

This contribution describes new robust procedures for the measurement of sound power flux at appropriate axial positions along a duct with flow, using pairs of flush wall mounted microphones, or pressure transducers. The technology includes the application of selective averaging, order tracking, and optimized sampling rate methods to identify the small fraction of the total fluctuating wave energy that is being propagated along the flow path in a reverberent, or highly reactive duct system. Such measurements can also be used to quantify the local acoustic characteristics that govern the generation, transfer, and propagation of wave energy in the system. Illustrative examples include the determination of the acoustic characteristics of individual silencing elements installed in IC engine intakes and exhausts both on the flow bench and during controlled acceleration or run down on a test bed, where the wave component spectral levels approached 170 dB.
On the steady-state and the transient decay methods for the estimation of reverberation time
Authors: Sum K. S. , Pan J.
Published: December 2002

The discrepancy between reverberation times of an enclosed sound field measured by the steady-state method and by the transient decay method is well-known. So far, no clear explanation has been obtained. In this paper, the steady-state bandlimited energy in an enclosure and bandlimited power flow into modally reactive boundaries are derived to describe the energy balance relationship and thus the reverberation time in a frequency band. This reverberation time is then compared to that obtained from the transient decay of the sound field based on the modal analysis. The comparison provides an understanding of the discrepancy mentioned above as well as the physical interpretations of the reverberation times estimated by both methods.
Effect of modulator asynchrony of sinusoidal and noise modulators on frequency and amplitude modulation detection interference
Authors: Gockel Hedwig , Carlyon Robert P. , Deeks John M.
Published: December 2002

The effect on modulation detection interference (MDI) of timing of gating of the modulation of target and interferer, with synchronously gated carriers, was investigated in three experiments. In a two-interval, two-alternative forced choice adaptive procedure, listeners had to detect 15 Hz sinusoidal amplitude modulation (AM) or frequency modulation (FM) imposed for 200 ms in the temporal center of a 600 ms target sinusoidal carrier. In the first experiment, 15 Hz sinusoidal FM was imposed in phase on both target and interferer carriers. Thresholds were lower for nonoverlapping than for synchronous modulation of target and interferer, but MDI still occurred for the former. Thresholds were significantly higher when the modulators were gated synchronously than when the interferer modulator was gated on before and off after that of the target. This contrasts with the findings of Oxenham and Dau [J. Acoust. Soc. Am. 110, 402–408 (2001)], who reported no effect of modulation asynchrony on AM detection thresholds, using a narrowband noise modulator. Using FM, experiment 2 showed that for temporally overlapping modulation of target and interferer, modulator asynchrony had no significant effect when the interferer was modulated by a narrowband noise. Experiment 3 showed that, for AM, synchronous gating of modulation of the target and interferer produced lower thresholds than asynchronous gating, especially for sinusoidal modulation of the interferer. Results are discussed in terms of specific cues available for periodic modulation, and differences between perceptual grouping on the basis of common AM and FM.
Sound transmission across a smooth nonuniform section in an infinitely long duct
Authors: Tang S. K. , Lau C. K.
Published: December 2002

Sound transmission across a nonuniform section in an infinite duct is studied numerically using the finite element method. An impedance matched absorptive portion is added to each end of the computational domain so as to avoid the undesirable higher mode reflection that will otherwise take place there. Results suggest that the sound fields downstream of the nonuniform section inlet are complicated and cannot be easily described by the conventional solution of the wave equation. The distribution of acoustic energy among the various propagating modes well downstream from the outlet of the nonuniform section is also discussed. Results show that the first symmetrical higher mode is important for all cases. The plane wave becomes important at high frequency with high rate of change of the cross-sectional area when the section is a convergent one.
Complete mode identification for resonance ultrasound spectroscopy
Authors: Ogi Hirotsugu , Sato Keiji , Asada Takeyasu , Hirao Masahiko
Published: December 2002

This study is devoted to deducing exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by incorporating a displacement-distribution measurement into resonant ultrasound spectroscopy (RUS). The usual RUS method measures free-vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal.
Within-ear and across-ear interference in a cocktail-party listening task
Authors: Brungart Douglas S. , Simpson Brian D.
Published: December 2002

Although many researchers have shown that listeners are able to selectively attend to a target speech signal when a masking talker is present in the same ear as the target speech or when a masking talker is present in a different ear than the target speech, little is known about selective auditory attention in tasks with a target talker in one ear and independent masking talkers in both ears at the same time. In this series of experiments, listeners were asked to respond to a target speech signal spoken by one of two competing talkers in their right (target) ear while ignoring a simultaneous masking sound in their left (unattended) ear. When the masking sound in the unattended ear was noise, listeners were able to segregate the competing talkers in the target ear nearly as well as they could with no sound in the unattended ear. When the masking sound in the unattended ear was speech, however, speech segregation in the target ear was substantially worse than with no sound in the unattended ear. When the masking sound in the unattended ear was time-reversed speech, speech segregation was degraded only when the target speech was presented at a lower level than the masking speech in the target ear. These results show that within-ear and across-ear speech segregation are closely related processes that cannot be performed simultaneously when the interfering sound in the unattended ear is qualitatively similar to speech.
Time domain investigation of transceiver functions using a known reference target
Authors: Feuillade C. , Meredith R. W. , Chotiros N. P. , Clay C. S.
Published: December 2002

During August 1998, a bottom scattering tank experiment was performed at the Applied Research Laboratory, University of Texas to measure wideband acoustic reverberation from multiple objects (e.g., cobbles and pebbles) placed on a sediment simulation of the sea floor. In preparation for processing and analyzing the experimental data, time domain scattering measurements made with stainless steel and glass balls suspended in the water column were used to calibrate the sonar transceiver system by deconvolving the theoretical impulse response for steel and glass spheres, obtained via the Faran elastic sphere scattering model, from the scattered time signals. It is the analysis of these calibration measurements which forms the subject of this paper. Results show the critical importance of accurate input–output system calibrations for time domain sound scattering research, and successfully demonstrate a time domain method for accurately calibrating the complete sonar transceiver function, i.e., both the amplitude and time dependence, using a known reference target. The work has implications for boundary and volume scattering applications.
Analysis of flexural wave velocity and vibration mode in thin cylindrical shell
Authors: Saijyou Kenji , Yoshikawa Shigeru
Published: December 2002

The relationship between the flexural wave velocity and the excited vibration mode of a thin cylindrical shell is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, all of these vibration modes are not excited actually. To estimate the excited vibration mode, the concept of “modified bending stiffness” is introduced, and the influence of each stress component upon the modified bending stiffness is analyzed. The excited mode is theoretically discriminated from the nonexcited mode based on the smallness of this modified bending stiffness. The validity of our theory is confirmed by an excellent agreement between theoretical and experimental results on flexural wave velocity.
Adaptive beamforming for nonstationary arrays
Authors: Greening Michael V. , Perkins Jane E.
Published: December 2002

Adaptive beamformers automatically adjust to the input data on the sensors in an attempt to maximize the bearing resolution of a signal and minimize the effects of noise or interfering signals. To the author’s knowledge, all adaptive beamformers currently available in the literature assume that the sensors are stationary over the time required to collect the data. This assumption is invalid on arrays of sensors mounted on nonstationary platforms, and results in poor beamforming performance. In this paper we present an adaptive beamformer that has been designed to operate on nonstationary arrays. The beamformer directly incorporates any changes in array shape or heading that may occur during the time required to collect the data. The output of the adaptive beamformer is shown for both synthetic data and for real data collected on a towed array. Results show that signal detection, bearing accuracy, bearing resolution, and interference suppression all increase when the array shape and track are incorporated into the beamformer if the sensor platform is not stationary.
Reduction of sound transmission into a circular cylindrical shell using distributed vibration absorbers and Helmholtz resonators
Authors: Estève Simon J. , Johnson Marty E.
Published: December 2002

A modal expansion method is used to model a cylindrical enclosure excited by an external plane wave. A set of distributed vibration absorbers (DVAs) and Helmholtz resonators (HRs) are applied to the structure to control the interior acoustic levels. Using an impedance matching method, the structure, the acoustic cavity, and the noise reduction devices are fully coupled to yield an analytical formulation of the structural kinetic energy and acoustic potential energy of a treated cylindrical cavity. Lightweight DVAs and small HRs tuned to the natural frequencies of the targeted structural and acoustic modes, respectively, result in significant acoustic and structural attenuation when the devices are optimally damped. Simulations show that significant interior noise reduction can only be achieved by adding damping to both structural and acoustic modes, which are resonant in the frequency bandwidth of interest. In order to be independent of the azimuth angle of the excitation and to avoid unwanted modal interactions, the devices are distributed evenly around the cylinder in rings. This treatment can only achieve good performance if the structure and the acoustic cavity are lightly damped.
Virtual pitch integration for asynchronous harmonics
Authors: Grose John H. , Hall Joseph W. , Buss Emily
Published: December 2002

This experiment examined the generation of virtual pitch for harmonically related tones that do not overlap in time. The interval between successive tones was systematically varied in order to gauge the integration period for virtual pitch. A pitch discrimination task was employed, and both harmonic and nonharmonic tone series were tested. The results confirmed that a virtual pitch can be generated by a series of brief, harmonically related tones that are separated in time. Robust virtual pitch information can be derived for intervals between successive 40-ms tones of up to about 45 ms, consistent with a minimum estimate of integration period of about 210 ms. Beyond intertone intervals of 45 ms, performance becomes more variable and approaches an upper limit where discrimination of tone sequences can be undertaken on the basis of the individual frequency components. The individual differences observed in this experiment suggest that the ability to derive a salient virtual pitch varies across listeners.
Crack detection by measurement of mechanical impedance of a rotor-bearing system
Authors: Prabhakar S. , Mohanty A. R. , Sekhar A. S.
Published: December 2002

Measurements were done to determine the influence of a transverse crack on the mobility of a rotor-bearing system. The results show that the mobility changes substantially due to the presence of crack and follows definite trends with the crack depth and direction of force application. The significant changes in mobility were observed at the natural frequency and at the running frequency of the rotor system. Good agreement between the experimental results and numerical simulations has been observed. The measurement of mobility has been suggested for crack detection and condition monitoring of rotor-bearing systems.
The effects of familiarization on intelligibility and lexical segmentation in hypokinetic and ataxic dysarthria
Authors: Liss Julie M. , Spitzer Stephanie M. , Caviness John N. , Adler Charles
Published: December 2002

This study is the third in a series that has explored the source of intelligibility decrement in dysarthria by jointly considering signal characteristics and the cognitive–perceptual processes employed by listeners. A paradigm of lexical boundary error analysis was used to examine this interface by manipulating listener constraints with a brief familiarization procedure. If familiarization allows listeners to extract relevant segmental and suprasegmental information from dysarthric speech, they should obtain higher intelligibility scores than nonfamiliarized listeners, and their lexical boundary error patterns should approximate those obtained in misperceptions of normal speech. Listeners transcribed phrases produced by speakers with either hypokinetic or ataxic dysarthria after being familiarized with other phrases produced by these speakers. Data were compared to those of nonfamiliarized listeners [Liss et al., J. Acoust. Soc. Am. 107, 3415–3424 (2000)]. The familiarized groups obtained higher intelligibility scores than nonfamiliarized groups, and the effects were greater when the dysarthria type of the familiarization procedure matched the dysarthria type of the transcription task. Remarkably, no differences in lexical boundary error patterns were discovered between the familiarized and nonfamiliarized groups. Transcribers of the ataxic speech appeared to have difficulty distinguishing strong and weak syllables in spite of the familiarization. Results suggest that intelligibility decrements arise from the perceptual challenges posed by the degraded segmental and suprasegmental aspects of the signal, but that this type of familiarization process may differentially facilitate mapping segmental information onto existing phonological categories.
Temperature dependence of acoustic impedance for specific fluorocarbon liquids
Authors: Marsh Jon N. , Hall Christopher S. , Wickline Samuel A. , Lanza Gregory M.
Published: December 2002

Recent studies by our group have demonstrated the efficacy of perfluorocarbon liquid nanoparticles for enhancing the reflectivity of tissuelike surfaces to which they are bound. The magnitude of this enhancement depends in large part on the difference in impedances of the perfluorocarbon, the bound substrate, and the propagating medium. The impedance varies directly with temperature because both the speed of sound and the mass density of perfluorocarbon liquids are highly temperature dependent. However, there are relatively little data in the literature pertaining to the temperature dependence of the acoustic impedance of these compounds. In this study, the speed of sound and density of seven different fluorocarbon liquids were measured at specific temperatures between 20 °C and 45 °C. All of the samples demonstrated negative, linear dependencies on temperature for both speed of sound and density and, consequently, for the acoustic impedance. The slope of sound speed was greatest for perfluorohexane (−278±1.5 cm/s-°C) and lowest for perfluorodichlorooctane (−222±0.9 cm/s-°C). Of the compounds measured, perfluorohexane exhibited the lowest acoustic impedance at all temperatures, and perfluorodecalin the highest at all temperatures. Computations from a simple transmission-line model used to predict reflectivity enhancement from surface-bound nanoparticles are discussed in light of these results.
Prediction of sound level at high-frequency bands by means of a simplified boundary element method
Authors: Kim Jae-Kwon , Ih Jeong-Guon
Published: December 2002

A simplified boundary element method (BEM) for dealing with high-frequency sound is proposed. The boundary integral equation is modified into a quadratic form to enable the prediction of sound levels in the one-third octave band analysis. Monopole and dipole source terms in the conventional BEM are transformed into the auto- and cross-spectra of two vibrating sources, in which the cross-spectra are eventually neglected by assuming that the correlation coefficients involved are negligible. The present method is compared with the Rayleigh integral for calculating the sound pressure radiated from a baffled panel, in terms of the application limit. The characteristic length of the boundary element and the applicable frequency range can be determined by the lower limit value of the correlation coefficient. As a test example, the field pressure radiated from a partially vibrating sphere is predicted and the resultant trend is in good agreement with the analytic solution as far as the related correlation coefficient satisfies the assumption. The overdetermination process for overcoming nonuniqueness in exterior radiation problems is unnecessary in the present method because phase information can be ignored. The results of the calculation show that the proposed method is acceptable for solving the exterior radiation problem at a high-frequency range in a timely manner.