bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo and experimental derivation of TG43 dosimetric parameters for CSM‐type Cs‐137 sources
Authors: Pérez‐Calatayud J. , Granero D. , Casal E. , Ballester F. , Puchades V.
Published: January 2005

In this study, complete dosimetric datasets for the CSM2 and CSM3 Cs‐137 sources were obtained using the Monte Carlo GEANT4 code. The application of this calculation method was experimentally validated with thermoluminescent dosimetry (TLD). Functions and parameters following the TG43 formalism are presented: the dose rate constant, the radial dose functional, and the anisotropy function. In addition, to aid the quality control process on treatment planning systems, a two‐dimensional (2D) rectangular dose rate table (the traditional along‐away table), coherent with the TG43 dose calculation formalism, is given. The data given in this study complement existing information for both sources on the following aspects: (i) the source asymmetries were considered explicitly in the Monte Carlo calculations, (ii) TG43 data were derived directly from Monte Carlo calculations, (iii) the radial range of the different tables was increased as well as the angular resolution in the anisotropy function, including angles close to the longitudinal source axis. The CSM2 source TG‐43 data of Liu et al. [Med. Phys. 31, 477–483 (2004)] are not consistent with the Williamson 2D along‐away data [Int. J. Radiat. Oncol., Biol., Phys. 15, 227–237 (1988)] at distances closer than approximately from the source. The data presented here for this source are consistent with this 2D along‐away table, and are suitable for use in clinical practice.
Novel methods of measuring single scan dose profiles and cumulative dose in CT
Authors: Nakonechny K. D. , Fallone B. G. , Rathee S.
Published: January 2005

Computed tomography dose index (CTDI) is a conventional indicator of the patient dose in CT studies. It is measured as the integration of the longitudinal single scan dose profile (SSDP) by using a 100‐mm‐long pencil ionization chamber and a single axial scan. However, the assumption that most of the SSDP is contained within the chamber length may not be valid even for thin slices. We have measured the SSDPs for several slice widths on two CT scanners using a PTW diamond detector placed in a water‐equivalent plastic phantom. One SSDP was also measured using lithium fluoride (LiF) TLDs and an IC‐10 small volume ion chamber, verifying the general shape of the SSDP measured using the diamond detector. Standard cylindrical PMMA CT phantoms (140 mm length) were also used to qualitatively study the effects of phantom shape, length, and composition on the measured SSDP. The SSDPs measured with the diamond detector in the water‐equivalent phantom were numerically integrated to calculate the relative accumulated dose at the center of various scan lengths . reached an equilibrium value for , suggesting the need for phantoms longer than standard CT dose phantoms. We have also measured the absolute accumulated dose using an IC‐10 small volume ion chamber, , at three points in the phantom cross section for several beamwidths and scan lengths. For one CT system, these measurements were made in both axial and helical scanning modes. The absolute , measured with a 102 mm active length pencil chamber, were within 4% of measured with the small volume ion chamber for suggesting that nonpencil chambers can be successfully used for CT dosimetry. For nominal beam widths ranging from 3 to 20 mm and for , values at the center of the water‐equivalent phantom's elliptic cross section were approximately 25%–30% higher than the measured . For small beamwidths, the difference in for and reached up to 50%. Peripheral point doses at 70 mm depth along the major axis of the phantom for were up to 22% higher than for . The differences between and for were in good agreement with the predictions made from the numerical integration of the measured SSDPs. Due to the considerable dose measured beyond the length of standard CT phantoms, CT dosimetry for longer body scan series should be performed in longer phantoms. Measurements could be made as we have shown, using a small volume chamber translating through the beam using multiple scans.
Volume CT with a flat‐panel detector on a mobile, isocentric C‐arm: Pre‐clinical investigation in guidance of minimally invasive surgery
Authors: Siewerdsen J. H. , Moseley D. J. , Burch S. , Bisland S. K. , Bogaards A. , Wilson B. C. , Jaffray D. A.
Published: January 2005

A mobile isocentric C‐arm (Siemens PowerMobil) has been modified in our laboratory to include a large area flat‐panel detector (in place of the x‐ray image intensifier), providing multi‐mode fluoroscopy and cone‐beam computed tomography (CT) imaging capability. This platform represents a promising technology for minimally invasive, image‐guided surgical procedures where precision in the placement of interventional tools with respect to bony and soft‐tissue structures is critical. The image quality and performance in surgical guidance was investigated in pre‐clinical evaluation in image‐guided spinal surgery. The control, acquisition, and reconstruction system are described. The reproducibility of geometric calibration, essential to achieving high three‐dimensional (3D) image quality, is tested over extended time scales and across a broad range in C‐arm angulation (up to 45°), quantifying the effect of improper calibration on spatial resolution, soft‐tissue visibility, and image artifacts. Phantom studies were performed to investigate the precision of 3D localization (viz., fiber optic probes within a vertebral body) and effect of lateral projection truncation (limited field of view) on soft‐tissue detectability in image reconstructions. Pre‐clinical investigation was undertaken in a specific spinal procedure (photodynamic therapy of spinal metastases) in five animal subjects (pigs). In each procedure, placement of fiber optic catheters in two vertebrae (L1 and L2) was guided by fluoroscopy and cone‐beam CT. Experience across five procedures is reported, focusing on 3D image quality, the effects of respiratory motion, limited field of view, reconstruction filter, and imaging dose. Overall, the intraoperative cone‐beam CT images were sufficient for guidance of needles and catheters with respect to bony anatomy and improved surgical performance and confidence through 3D visualization and verification of transpedicular trajectories and tool placement. Future investigation includes improvement in image quality, particularly regarding x‐ray scatter, motion artifacts and field of view, and integration with optical tracking and navigation systems.
Respiration‐correlated treatment delivery using feedback‐guided breath hold: A technical study
Authors: Nelson Christopher , Starkschall George , Balter Peter , Fitzpatrick Mathew J. , Antolak John A. , Tolani Naresh , Prado Karl
Published: January 2005

Respiratory motion causes movement of internal structures in the thorax and abdomen, making accurate delivery of radiation therapy to tumors in those areas a challenge. To reduce the uncertainties caused by this motion, we have developed feedback‐guided breath hold (FGBH), a novel delivery technique in which radiation is delivered only during a voluntary breath hold that is sustained for as long as the patient feels comfortable. Here we present the technical aspects of FGBH, which involve (1) fabricating the hardware so the respiratory trace can be displayed to the patient, (2) assembling a delay box to be used as a breath‐hold detector, and (3) performing quality control tests to ensure that FGBH can be delivered accurately and safely. A commercial respiratory tracking system that uses an external fiducial to monitor abdominal wall motion generates and displays the breathing trace and specific positions in the breathing cycle where a breath hold needs to occur. Hardware was developed to present this display to the patient in the treatment position. Patients view the presentation either on a liquid crystal display or through a pair of virtual reality goggles. Using the respiratory trace as a visual aid, the patient performs a breath hold so that the position representing the location of a fiducial is held within a specified gating window. A delay box was fabricated to differentiate between gating signals received during free breathing and those received during breath hold, allowing radiation delivery only when the fiducial was within the breath‐hold gating window. A quality control analysis of the gating delay box and the integrated system was performed to ensure that all of the hardware and components were ready for clinical use.
The overtone structure of acoustic fluctuations due to harmonic variations in sound speed (L)
Authors: Field Robert L. , George Jacob
Published: January 2005

Explicit relations are derived between the acoustic pressure and a sound speed that is periodic. They are derived for the Pekeris waveguide, and extended to the range and depth-dependent adiabatic mode/WKB case. As expected, acoustic pressure is found to fluctuate at the sound speed fundamental and its overtones. A Pekeris model simulation qualitatively agrees with the intensity fluctuation spectrum from a range and depth-dependent parabolic equation (PE) simulation of a shelf edge experiment off the New Jersey coast. In this paper we show that the energy of the higher overtones can be significant and derive a modulation index that determines the factors that contribute to the overtone energy.
Delay dependence for the origin of the nonlinear derived transient evoked otoacoustic emission
Authors: Withnell Robert H. , McKinley Sarah
Published: January 2005

In the guinea pig it has been shown that the nonlinear derived transient evoked otoacoustic emission (TEOAEnl) is comprised of significant amounts of intermodulation distortion energy. It is expected that intermodulation distortion arising from a nonlinear distortion mechanism will contribute to the overall TEOAE in a stimulus-level-dependent manner, being greatest when basilar-membrane vibration in response to a click stimulus is greatest; with decay of vibration of the basilar membrane subsequent to stimulation by a click, nonlinear interaction along the cochlear partition should reduce and so provide for a linear mechanism to dominate TEOAEnl generation, i.e., the contributions of each of these mechanisms should be delay dependent. To examine this delay dependence, TEOAEnl evoked by acoustic clicks of varying bandwidth were time-domain windowed using a recursive exponential filter in an attempt to separate two components with amplitude and phase properties consistent with different mechanisms of OAE generation. It was found that the part of the TEOAEnl occurring first in time can have a relatively constant amplitude and shallow phase slope, consistent with a nonlinear distortion mechanism. The latter part of the TEOAEnl has an amplitude microstructure and a phase response more consistent with a place-fixed mechanism.
The energy method for analyzing the piezoelectric electroacoustic transducers
Authors: Aronov Boris
Published: January 2005

The energy method of calculating the properties of piezoelectric electroacoustic transducers is considered. The Lagrangian of an electroacoustic transducer as a system performing multiple energy conversions is introduced. The Euler equations describing operation of a transducer with many mechanical degrees of freedom are derived from the least action principle. The corresponding multicontour equivalent circuit of the transducer is introduced. For the particular case of a transducer having one mechanical degree of freedom the governing equations are obtained by applying the Energy Conservation Law, and equivalent circuit with one mechanical branch also introduced. Application of the energy method is illustrated with examples of the pulsating spherical transducer as the one degree of freedom system and the multimode cylindrical transducer comprised of circular rings as the system with multiple degrees of freedom. Advantages of the method for application with electroacoustic transducers are summarized.
Compressional and shear wave properties of marine sediments: Comparisons between theory and data
Authors: Buckingham Michael J.
Published: January 2005

According to a recently developed theory of wave propagation in marine sediments, the dispersion relationships for the phase speed and attenuation of the compressional and the shear wave depend on only three macroscopic physical variables: porosity, grain size, and depth in the sediment. The dispersion relations also involve three (real) parameters, assigned fixed values, representing microscopic processes occurring at grain contacts. The dispersion relationships are compared with extensive data sets, taken from the literature, covering the four wave properties as functions of all three physical variables. With no adjustable parameters available, the theory matches accurately the trends of all the data sets. This agreement extends to the compressional and shear attenuations, in that the theory accurately traces out the lower bound to the widely distributed measured attenuations: the theory predicts the intrinsic attenuation, arising from the irreversible conversion of wave energy into heat, whereas the measurements return the effective attenuation, which includes the intrinsic attenuation plus additional sources of loss such as scattering from shell fragments and other inhomogeneities in the medium. Provided one wave or physical property is known, say the compressional speed or the porosity, all the remaining sediment properties may be reliably estimated from the theory.
Acoustic measurements of the sound-speed profile in the bubbly wake formed by a small motor boat
Authors: Vagle Svein , Burch Holly
Published: January 2005

In situ measurements of the bubble field within wakes generated by a small motorboat show that the bubble field, shortly after the initial turbulent generation period, consists mainly of bubbles with radii between 20 and 200 μm. The subsequent dispersion of the wake field can be described using a model that includes bubble buoyancy and dissolution only, and the air volume fraction within the wakes decay exponentially with an e-folding time of between 40 and 60 s. Simultaneous measurements of sound propagating through the bubbly wake exhibit spectral banding due to waveguide propagation. Inversions using the inverse-square theory developed by Buckingham [Philos. Trans. R. Soc. London, Ser. A 335, 513–555 (1991)] show that this acoustic inversion technique provide a viable means of estimating the low-frequency sound-speed profile in an upward refractive bubble layer when dispersion can be neglected.
Primarily nonlinear effects observed in a driven asymmetrical vibrating wire
Authors: Hanson Roger J. , Macomber H. Kent , Morrison Andrew C. , Boucher Matthew A.
Published: January 2005

The purpose of the work reported here is to further experimentally explore the wide variety of behaviors exhibited by driven vibrating wires, primarily in the nonlinear regime. When the wire is driven near a resonant frequency, it is found that most such behaviors are significantly affected by the splitting of the resonant frequency and by the existence of a “characteristic” axis associated with each split frequency. It is shown that frequency splitting decreases with increasing wire tension and can be altered by twisting. Two methods are described for determining the orientation of characteristic axes. Evidence is provided, with a possible explanation, that each axis has the same orientation everywhere along the wire. Frequency response data exhibiting nonlinear generation of transverse motion perpendicular to the driving direction, hysteresis, linear generation of perpendicular motion (sometimes tubular), and generation of motion at harmonics of the driving frequency are exhibited and discussed. Also reported under seemingly unchanging conditions are abrupt large changes in the harmonic content of the motion that sometimes involve large subharmonics and harmonics thereof. Slow transitions from one stable state of vibration to another and quasiperiodic motions are also exhibited. Possible musical significance is discussed.
Controlled ultrasound tissue erosion: The role of dynamic interaction between insonation and microbubble activity
Authors: Xu Zhen , Fowlkes J. Brian , Rothman Edward D. , Levin Albert M. , Cain Charles A.
Published: January 2005

Previous studies showed that ultrasound can mechanically remove tissue in a localized, controlled manner. Moreover, enhanced acoustic backscatter is highly correlated with the erosion process. “Initiation” and “extinction” of this highly backscattering environment were studied in this paper. The relationship between initiation and erosion, variability of initiation and extinction, and effects of pulse intensity and gas saturation on time to initiation (initiation delay time) were investigated. A 788-kHz single-element transducer was used. Multiple pulses at a 3-cycle pulse duration and a 20-kHz pulse repetition frequency were applied. ISPPA values between 1000 and 9000 W/cm2 and gas saturation ranges of 24%–28%, 39%–49%, and 77%–81% were tested. Results show the following: (1) without initiation, erosion was never observed; (2) initiation and extinction of the highly backscattering environment were stochastic in nature and dependent on acoustic parameters; (3) initiation delay times were shorter with higher intensity and higher gas saturation (e.g., the mean initiation delay time was 66.9 s at ISPPA of 4000 W/cm2 and 3.6 ms at ISPPA of 9000 W/cm2); and (4) once initiated by high-intensity pulses, the highly backscattering environment and erosion can be sustained using a significantly lower intensity than that required to initiate the process.
Designing musical structures using a constrained optimization approach
Authors: Petrolito J. , Legge K. A.
Published: January 2005

The paper discusses the application of numerical optimizing techniques to musical structures. It is shown that the natural tendency to emulate the instrument maker by optimizing the characteristic frequencies of the structure is not always the most appropriate strategy, and that in cases where one or more possible solutions exist it is more appropriate to specify the frequency requirements as a constraint. The strategy is illustrated using a xylophone bar.
Effect of resonator dimensions on nonlinear standing waves
Authors: Luo C. , Huang X. Y. , Nguyen N. T.
Published: January 2005

An investigation of the effect of resonator dimensions on nonlinear standing waves in shaped resonators is conducted. Simple forms of the shear viscosity term in the momentum equations are developed for an axisymmetric (2D) resonator and a low aspect ratio rectangular (3D) resonator. The cross sections of the resonators are exponentially expanded and the one-dimensional wave equations are solved by using the Galerkin’s method. The quality factors, pressure waveforms, compression ratios, and resonance frequencies are calculated for different dimensionless cross sections and lengths of the resonators. The results show that, apart from the resonator length, the ratio of the cross-section dimension to the length of the resonator is an important parameter. If the ratio is greater than 0.04, the characteristics of the shaped resonator are not affected significantly. However, when the ratio is less than 0.01, the resonance becomes weak, the compression ratio drops substantially, and the frequency response changes as well.
Time domain simulation of nonlinear acoustic beams generated by rectangular pistons with application to harmonic imaging
Authors: Yang Xinmai , Cleveland Robin O.
Published: January 2005

A time-domain numerical code (the so-called Texas code) that solves the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation has been extended from an axis-symmetric coordinate system to a three-dimensional (3D) Cartesian coordinate system. The code accounts for diffraction (in the parabolic approximation), nonlinearity and absorption and dispersion associated with thermoviscous and relaxation processes. The 3D time domain code was shown to be in agreement with benchmark solutions for circular and rectangular sources, focused and unfocused beams, and linear and nonlinear propagation. The 3D code was used to model the nonlinear propagation of diagnostic ultrasound pulses through tissue. The prediction of the second-harmonic field was sensitive to the choice of frequency-dependent absorption: a frequency squared f2 dependence produced a second-harmonic field which peaked closer to the transducer and had a lower amplitude than that computed for an f1.1 dependence. In comparing spatial maps of the harmonics we found that the second harmonic had dramatically reduced amplitude in the near field and also lower amplitude side lobes in the focal region than the fundamental. These findings were consistent for both uniform and apodized sources and could be contributing factors in the improved imaging reported with clinical scanners using tissue harmonic imaging.
Numerical description of the edge mode at the beveled extremity of a plate
Authors: Wilkie-Chancellier Nicolas , Duflo Hugues , Tinel Alain , Duclos Jean
Published: January 2005

This paper deals with the reflection of a two-dimensional harmonic Lamb wave at the beveled end of a plate. The existence of a resonant edge mode is described by a numerical model. It is proved that the edge mode is the resonance of different complex modes. The behavior of this mode as a function of the bevel angle is studied. Its amplitude decreases and its resonance frequency shifts as the bevel angle decreases from 90 to 85 deg. An unexpected strong variation of the repartition of the reflected energy is linked to this phenomenon.
Are high perches in the blackcapSylvia atricapillasong or listening posts? A sound transmission study
Authors: Mathevon Nicolas , Dabelsteen Torben , Blumenrath Sandra H.
Published: January 2005

Birds often sing from high perches referred to as song posts. However, birds also listen and keep a lookout from these perches. We used a sound transmission experiment to investigate the changes for receiving and sending conditions that a territorial songbird may experience by moving upwards in the vegetation. Representative song elements of the blackcap Sylvia atricapilla were transmitted in a forest habitat in spring using a complete factorial design with natural transmission distances and speaker and microphone heights. Four aspects of sound degradation were quantified: signal-to-noise ratio, excess attenuation, distortion within the sounds determined as a blur ratio, and prolongation of the sounds with “tails” of echoes determined as a tail-to-signal ratio. All four measures indicated that degradation decreased with speaker and microphone height. However, the decrease was considerably higher for the microphone than for the speaker. This suggests that choosing high perches in a forest at spring results in more benefits to blackcaps in terms of improved communication conditions when they act as receivers than as senders.
Inferring basilar-membrane motion from tone-burst otoacoustic emissions and psychoacoustic measurements
Authors: Epstein Michael , Florentine Mary
Published: January 2005

The amplitude of otoacoustic emissions, which arise on the basilar membrane, is assumed to be proportional to basilar-membrane motion. It should then be possible to assess basilar-membrane motion on the basis of otoacoustic emissions. The present study provides support for this possibility by comparing basilar-membrane motion inferred from emissions to that inferred from psychoacoustic measures. Three psychoacoustic measurements believed to be associated with basilar-membrane motion were investigated: (1) pulsation threshold; (2) loudness functions derived from temporal integration; and (3) loudness functions derived from loudness matches between pure tones and multitone complexes. Results of the psychoacoustic measurements and of the tone-burst otoacoustic emissions led to very similar estimations of basilar-membrane motion. Accordingly, emissions could serve as an excellent tool—one that is objective, noninvasive, and rapid—for estimating relative basilar-membrane motion.
Discrimination of first- and second-order regular intervals from random intervals as a function of high-pass filter cutoff frequency
Authors: Yost William A. , Mapes-Riordan Dan , Dye Raymond , Sheft Stanley , Shofner William
Published: January 2005

This study extends the work of Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2998–2306 (1998)] in which regular interval stimuli (RIS) click trains with first-order intervals could be discriminated from random-interval click trains, but RIS with second-order intervals could not. Kaernbach and Demany concluded that their results cast doubt on autocorrelation as a method of analysis for such stimuli. The present study investigated the same stimuli, but for a variety of filter conditions. The results suggest that while RIS click trains with first-order intervals are more easily discriminated from random-interval stimuli than second-order interval RIS click trains, discrimination based on second-order intervals is possible except when the stimuli are high-pass filtered above 8 kHz, i.e., above the spectral region of phase locking.
Perceptually motivated time-frequency analysis
Authors: O’Donovan Jonathan J. , Furlong Dermot J.
Published: January 2005

This paper describes the design of a bilinear time-frequency distribution which is a joint model of temporal and spectral masking. The distribution is used to generate temporally evolving excitation patterns of nonstationary signals and systems and is conceived as a tool for acousticians and engineers for perceptual time-frequency analysis. Distribution time and frequency resolutions are controlled by a separable kernel consisting of a set of low-pass time and frequency smoothing windows. These windows are designed by adapting existing psychoacoustic models of auditory resolution, rather than using mathematical window functions. Cross-term interference and windowing clutter are highly suppressed for the distribution, ensuring resolution accuracy over a dynamic range sufficient to encompass that of the auditory system (in excess of 100 dB). Application to the analysis of a synthetic and two real signals are included to demonstrate the approach.
Time reversal of ocean noise
Authors: Roux Philippe , Kuperman W. A.
Published: January 2005

It has recently been shown [Roux et al., “Extracting coherent wave fronts from acoustic ambient noise in the ocean,” J. Acoust. Soc. Am. 116, 1995–2003 (2004)] that the time-averaged correlation of ocean noise between two points yields a deterministic waveguide arrival structure embedded in the time-domain Green’s function. By performing a set of these correlations between a vertical receive array and a single receiver, transfer functions necessary for time reversal can be extracted from ocean noise. Theory and simulation demonstrate this process and data of opportunity from the North Pacific Acoustic Laboratory experiment confirm the expected performance of a noise-based time reversal mirror.
Cavitation bubble-driven cell and particle behavior in an ultrasound standing wave
Authors: Kuznetsova Larisa A. , Khanna Sanjay , Amso Nazar N. , Coakley W. Terence , Doinikov Alexander A.
Published: January 2005

The behavior of human erythrocytes and 1-μm-diameter fluorescent latex beads in the presence of Optison® contrast agent in a single half-wavelength (λ/2) ultrasound standing wave (USSW) resonator has been studied. The particle movements were observed with an epi-fluorescent microscope and the velocity of the particles and cells was measured by particle image velocimetry (PIV). Acoustic emissions were monitored with a microphone and a spectrum analyzer. Optison® contrast agent disintegrated immediately on exposure to ultrasound of 0.98-MPa acoustic pressure amplitude or higher in a chamber driven at its resonance frequency of 1.56 MHz. A discrete cloud of active microbubbles, detected at the pressure node plane, disappeared gradually and was completely lost within 15 s. The microscopy showed three-dimensional regions of circulation of both 1-μm tracer particles and erythrocytes in planes perpendicular to the pressure node plane. A numerical simulation showed that, for parameters that conform to the experimental conditions, a bubble of a subresonance size moves towards and translates about a pressure node plane. This result is in agreement with the experimental observation that the particle and cell circulation is induced by the presence and/or translational motion of microbubbles at the pressure node plane.
Predicting the similarity between expressive performances of music from measurements of tempo and dynamics
Authors: Timmers Renee
Published: January 2005

Measurements of tempo and dynamics from audio files or MIDI data are frequently used to get insight into a performer’s contribution to music. The measured variations in tempo and dynamics are often represented in different formats by different authors. Few systematic comparisons have been made between these representations. Moreover, it is unknown what data representation comes closest to subjective perception. The reported study tests the perceptual validity of existing data representations by comparing their ability to explain the subjective similarity between pairs of performances. In two experiments, 40 participants rated the similarity between performances of a Chopin prelude and a Mozart sonata. Models based on different representations of the tempo and dynamics of the performances were fitted to these similarity ratings. The results favor other data representations of performances than generally used, and imply that comparisons between performances are made perceptually in a different way than often assumed. For example, the best fit was obtained with models based on absolute tempo and absolute tempo times loudness, while conventional models based on normalized variations, or on correlations between tempo profiles and loudness profiles, did not explain the similarity ratings well.
Across-ear interference from parametrically degraded synthetic speech signals in a dichotic cocktail-party listening task
Authors: Brungart Douglas S. , Simpson Brian D. , Darwin Christopher J. , Arbogast Tanya L. , Kidd Gerald
Published: January 2005

Recent results have shown that listeners attending to the quieter of two speech signals in one ear (the target ear) are highly susceptible to interference from normal or time-reversed speech signals presented in the unattended ear. However, speech-shaped noise signals have little impact on the segregation of speech in the opposite ear. This suggests that there is a fundamental difference between the across-ear interference effects of speech and nonspeech signals. In this experiment, the intelligibility and contralateral-ear masking characteristics of three synthetic speech signals with parametrically adjustable speech-like properties were examined: (1) a modulated noise-band (MNB) speech signal composed of fixed-frequency bands of envelope-modulated noise; (2) a modulated sine-band (MSB) speech signal composed of fixed-frequency amplitude-modulated sinewaves; and (3) a “sinewave speech” signal composed of sine waves tracking the first four formants of speech. In all three cases, a systematic decrease in performance in the two-talker target-ear listening task was found as the number of bands in the contralateral speech-like masker increased. These results suggest that speech-like fluctuations in the spectral envelope of a signal play an important role in determining the amount of across-ear interference that a signal will produce in a dichotic cocktail-party listening task.
Estimation of vocal dysperiodicities in disordered connected speech by means of distant-sample bidirectional linear predictive analysis
Authors: Bettens Frédéric , Grenez Francis , Schoentgen Jean
Published: January 2005

The article presents an analysis of vocal dysperiodicities in connected speech produced by dysphonic speakers. The processing is based on a comparison of the present speech fragment with future and past fragments. The size of the dysperiodicity estimate is zero for periodic speech signals. A feeble increase of the vocal dysperiodicity is guaranteed to produce a feeble increase of the estimate. No spurious noise boosting occurs owing to cycle insertion and omission errors, or phonetic segment boundary artifacts. Additional objectives of the study have been investigating whether deviations from periodicity are larger or more commonplace in connected speech than in sustained vowels, and whether sentences that comprise frequent voice onsets and offsets are noisier than sentences that comprise few. The corpora contain sustained vowels as well as grammatically- and phonetically matched sentences. An acoustic marker that correlates with the perceived degree of hoarseness summarizes the size of the dysperiodicities. The marker values for sustained vowels have been highly correlated with those for connected speech, and the marker values for sentences that comprise few voiced/unvoiced transients have been highly correlated with the marker values for sentences that comprise many.
Enhancing intelligibility of narrowband speech with out-of-band noise: Evidence for lateral suppression at high-normal intensity
Authors: Bashford James A. , Warren Richard M. , Lenz Peter W.
Published: January 2005

Previous studies have shown that the intelligibility of filtered speech can be enhanced by filling stopbands with noise. The present study found that this enhancement occurred only when speech intensity was sufficiently high to degrade performance. Intelligibility decreased by about 15% when narrowband speech was increased from 45 to 65 dBA (corresponding to broadband speech levels of about 60 and 80 dBA), and decreased by 20% at a level of 75 dBA. However, when flanking bands of low-pass and high-pass filtered white noise were added at spectrum levels of −40 to −20 dB relative to the speech, intelligibility of the 75-dBA speech band increased by about 13%. Additional findings confirm that this enhancement of intelligibility depends upon out-of-band stimulation, in agreement with theories proposing that lateral suppressive interactions extend the dynamic range of intensity coding by counteracting effects of auditory-nerve firing-rate saturation at high signal levels.
Development of vocal tract length during early childhood: A magnetic resonance imaging study
Authors: Vorperian Houri K. , Kent Ray D. , Lindstrom Mary J. , Kalina Cliff M. , Gentry Lindell R. , Yandell Brian S.
Published: January 2005

Speech development in children is predicated partly on the growth and anatomic restructuring of the vocal tract. This study examines the growth pattern of the various hard and soft tissue vocal tract structures as visualized by magnetic resonance imaging (MRI), and assesses their relational growth with vocal tract length (VTL). Measurements on lip thickness, hard- and soft-palate length, tongue length, naso-oro-pharyngeal length, mandibular length and depth, and distance of the hyoid bone and larynx from the posterior nasal spine were used from 63 pediatric cases (ages birth to 6 years and 9 months) and 12 adults. Results indicate (a) ongoing growth of all oral and pharyngeal vocal tract structures with no sexual dimorphism, and a period of accelerated growth between birth and 18 months; (b) vocal tract structure’s region (oral/anterior versus pharyngeal/posterior) and orientation (horizontal versus vertical) determine its growth pattern; and (c) the relational growth of the different structures with VTL changes with development—while the increase in VTL throughout development is predominantly due to growth of pharyngeal/posterior structures, VTL is also substantially affected by the growth of oral/anterior structures during the first 18 months of life. Findings provide normative data that can be used for modeling the development of the vocal tract.
Coccidioides posadasii
Contains a Single 1,3-β-Glucan Synthase Gene That Appears To Be Essential for Growth
Authors: Kellner Ellen M. , Orsborn Kris I. , Siegel Erin M. , Mandel M. Alejandra , Orbach Marc J. , Galgiani John N.
Published: January 2005

1,3-β-Glucan synthase is responsible for the synthesis of β-glucan, an essential cell wall structural component in most fungi. We sought to determine whether
Coccidioides posadasii
possesses genes homologous to known fungal FKS genes that encode the catalytic subunit of 1,3-β-glucan synthase. A single gene, designated
FKS1
, was identified, and examination of its predicted protein product showed a high degree of conservation with Fks proteins from other filamentous fungi.
FKS1
is expressed at similar levels in mycelia and early spherulating cultures, and expression decreases as the spherules mature. We used
Agrobacterium
-mediated transformation to create strains that harbor Δ
FKS1
::
hygB
, a null allele of
FKS1
, and hypothesize that Fks1p function is essential, due to our inability to purify this allele away from a complementing wild-type
FKS1
allele in a heterokaryotic strain. The heterokaryon appears normal with respect to growth rate and arthroconidium production; however, microscopic examination of strains with Δ
FKS1
::
hygB
alleles revealed abnormal swelling of hyphal elements.
Role for RNA-Binding Proteins Implicated in Pathogenic Development of
Ustilago maydis
Authors: Becht Philip , Vollmeister Evelyn , Feldbrügge Michael
Published: January 2005

Ustilago maydis
causes smut disease on corn. Successful infection depends on a number of morphological transitions, such as pheromone-dependent formation of conjugation tubes and the switch to filamentous dikaryotic growth, as well as different types of mycelial structures during growth within the host plant. In order to address the involvement of RNA-binding proteins during this developmental program, we identified 27 open reading frames from the genome sequence encoding potential RNA-binding proteins. They exhibit similarities to RNA-binding proteins with Pumilio homology domains (PUM), the K homology domain (KHD), the double-stranded RNA binding motif (DSRM), and the RNA recognition motif (RRM). For 18 of these genes, we generated replacement mutants in compatible haploid strains. Through analysis of growth behavior, morphology, cyclic AMP response, mating, and pathogenicity, we identified three candidates with aberrant phenotypes. Loss of Khd1, a K homology protein containing three KHDs, resulted in a cold-sensitive growth phenotype. Deletion of
khd4
encoding a protein with five KHDs led to abnormal cell morphology, reduced mating, and virulence.
rrm4
Δ strains were affected in filamentous growth and pathogenicity. Rrm4 is an RRM protein with a so far unique domain organization consisting of three N-terminal RRMs as well as a domain found in the C terminus of poly(A)-binding proteins. These results indicate a role for RNA-binding proteins in regulation of morphology as well as in pathogenic development in
U. maydis
.
Novel Interaction between Apc5p and Rsp5p in an Intracellular Signaling Pathway in
Saccharomyces cerevisiae
Authors: Arnason Terra G. , Pisclevich Marnie G. , Dash Megan D. , Davies Gerald F. , Harkness Troy A. A.
Published: January 2005

The ubiquitin-targeting pathway is evolutionarily conserved and critical for many cellular functions. Recently, we discovered a role for two ubiquitin-protein ligases (E3s), Rsp5p and the Apc5p subunit of the anaphase-promoting complex (APC), in mitotic chromatin assembly in
Saccharomyces cerevisiae
. In the present study, we investigated whether Rsp5p and Apc5p interact in an intracellular pathway regulating chromatin remodeling. Our genetic studies strongly suggest that Rsp5p and Apc5p do interact and that Rsp5p acts upstream of Apc5p. Since E3 enzymes typically require the action of a ubiquitin-conjugating enzyme (E2), we screened E2 mutants for chromatin assembly defects, which resulted in the identification of Cdc34p and Ubc7p. Cdc34p is the E2 component of the SCF (Skp1p/Cdc53p/F-box protein). Therefore, we analyzed additional SCF mutants for chromatin assembly defects. Defective chromatin assembly extracts generated from strains harboring a mutation in the Cdc53p SCF subunit or a nondegradable SCF target, Sic1
Δphos
, confirmed that the SCF was involved in mitotic chromatin assembly. Furthermore, we demonstrated that Ubc7p physically and genetically interacts with Rsp5p, suggesting that Ubc7p acts as an E2 for Rsp5p. However,
rsp5

CA

and
Δubc7
mutations had opposite genetic effects on
apc5

CA

and
cdc34
-
2
phenotypes. Therefore, the antagonistic interplay between
Δubc7
and
rsp5

CA

, with respect to
cdc34
-
2
and
apc5

CA

, indicates that the outcome of Rsp5p's interaction with Cdc34p and Apc5p may depend on the E2 interacting with Rsp5p.
Demonstration of Loss of Heterozygosity by Single-Nucleotide Polymorphism Microarray Analysis and Alterations in Strain Morphology in
Candida albicans
Strains during Infection
Authors: Forche Anja , May Georgiana , Magee P. T.
Published: January 2005

Candida albicans
is a diploid yeast with a predominantly clonal mode of reproduction, and no complete sexual cycle is known. As a commensal organism, it inhabits a variety of niches in humans. It becomes an opportunistic pathogen in immunocompromised patients and can cause both superficial and disseminated infections. It has been demonstrated that genome rearrangement and genetic variation in isolates of
C. albicans
are quite common. One possible mechanism for generating genome-level variation among individuals of this primarily clonal fungus is mutation and mitotic recombination leading to loss of heterozygosity (LOH). Taking advantage of a recently published genome-wide single-nucleotide polymorphism (SNP) map (A. Forche, P. T. Magee, B. B. Magee, and G. May, Eukaryot. Cell 3:705-714, 2004), an SNP microarray was developed for 23 SNP loci residing on chromosomes 5, 6, and 7. It was used to examine 21 strains previously shown to have undergone mitotic recombination at the
GAL1
locus on chromosome 1 during infection in mice. In addition, karyotypes and morphological properties of these strains were evaluated. Our results show that during in vivo passaging, LOH events occur at observable frequencies, that such mitotic recombination events occur independently in different loci across the genome, and that changes in karyotypes and alterations of phenotypic characteristics can be observed alone, in combination, or together with LOH.
Mcl1p Is a Polymerase α Replication Accessory Factor Important for S-Phase DNA Damage Survival
Authors: Williams Dewight R. , McIntosh J. R.
Published: January 2005

Mcl1p is an essential fission yeast chromatin-binding protein that belongs to a family of highly conserved eukaryotic proteins important for sister chromatid cohesion. The essential function is believed to result from its role as a Pol1p (polymerase α) accessory protein, a conclusion based primarily on analogy to Ctf4p's interaction with Pol1p. In this study, we show that Mcl1p also binds to Pol1p with high affinity for the N terminus of Pol1p during S phase and DNA damage. Characterization of an inducible allele of
mcl1
+
,

nmt41

mcl1-MH
, shows that altered expression levels of Mcl1p lead to sensitivity to DNA-damaging agents and synthetic lethality with the replication checkpoint mutations
rad3
Δ,
rqh1
Δ, and
hsk1
-
1312
. Further, we find that the overexpression of the S-phase checkpoint kinase, Cds1, or the loss of Hsk1 kinase activity can disrupt Mcl1p's interaction with chromatin and Pol1p during replication arrest with hydroxyurea. We take these data to mean that Mcl1p is a dynamic component of the polymerase α complex during replication and is important for the replication stress response in fission yeast.
Sphingosine Kinase Regulates the Sensitivity of
Dictyostelium discoideum
Cells to the Anticancer Drug Cisplatin
Authors: Min Junxia , Traynor David , Stegner Andrew L. , Zhang Lei , Hanigan Marie H. , Alexander Hannah , Alexander Stephen
Published: January 2005

The drug cisplatin is widely used to treat a number of tumor types. However, resistance to the drug, which remains poorly understood, limits its usefulness. Previous work using
Dictyostelium discoideum
as a model for studying drug resistance showed that mutants lacking sphingosine-1-phosphate (S-1-P) lyase, the enzyme that degrades S-1-P, had increased resistance to cisplatin, whereas mutants overexpressing the enzyme were more sensitive to the drug. S-1-P is synthesized from sphingosine and ATP by the enzyme sphingosine kinase. We have identified two sphingosine kinase genes in
D. discoideum
—
sgkA
and
sgkB
—that are homologous to those of other species. The biochemical properties of the SgkA and SgkB enzymes suggest that they are the equivalent of the human Sphk1 and Sphk2 enzymes, respectively. Disruption of the kinases by homologous recombination (both single and double mutants) or overexpression of the
sgkA
gene resulted in altered growth rates and altered response to cisplatin. The null mutants showed increased sensitivity to cisplatin, whereas mutants overexpressing the sphingosine kinase resulted in increased resistance compared to the parental cells. The results indicate that both the SgkA and the SgkB enzymes function in regulating cisplatin sensitivity. The increase in sensitivity of the sphingosine kinase-null mutants was reversed by the addition of S-1-P, and the increased resistance of the sphingosine kinase overexpressor mutant was reversed by the inhibitor
N
,
N
-dimethylsphingosine. Parallel changes in sensitivity of the null mutants are seen with the platinum-based drug carboplatin but not with doxorubicin, 5-fluorouracil, and etoposide. This pattern of specificity is similar to that observed with the S-1-P lyase mutants and should be useful in designing therapeutic schemes involving more than one drug. This study identifies the sphingosine kinases as new drug targets for modulating the sensitivity to platinum-based drugs.
Transcriptional Network of Multiple Capsule and Melanin Genes Governed by theCryptococcus neoformansCyclic AMP Cascade
Authors: Pukkila-Worley Read , Gerrald Quincy D. , Kraus Peter R. , Boily Marie-Josée , Davis Matthew J. , Giles Steven S. , Cox Gary M. , Heitman Joseph , Alspaugh J. Andrew
Published: January 2005

Cryptococcus neoformansis an opportunistic human fungal pathogen that elaborates several virulence attributes, including a polysaccharide capsule and melanin pigments. A conserved Gα protein/cyclic AMP (cAMP) pathway controls melanin and capsule production. To identify targets of this pathway, we used an expression profiling approach to define genes that are transcriptionally regulated by the Gα protein Gpa1. This approach revealed that Gpa1 transcriptionally regulates multiple genes involved in capsule assembly and identified two additional genes with a marked dependence on Gpa1 for transcription. The first is theLAC1gene, encoding the laccase enzyme that catalyzes a rate-limiting step in diphenol oxidation and melanin production. The second gene identified (LAC2) is adjacent to theLAC1gene and encodes a second laccase that shares 75% nucleotide identity withLAC1. Similar to theLAC1gene,LAC2is induced in response to glucose deprivation. However,LAC2basal transcript levels are much lower than those forLAC1. Accordingly, alac2mutation results in only a modest delay in melanin formation.LAC2overexpression suppresses the melanin defects ofgpa1andlac1mutants and partially restores virulence of these strains. These studies provide mechanistic insights into the regulation of capsule and melanin production by theC. neoformanscAMP pathway and demonstrate that multiple laccases contribute toC. neoformansmelanin production and pathogenesis.