bluuebunny/crossref_metadata_2025 huggingface dataset:
Filtered backprojection formula for exact image reconstruction from cone‐beam data along a general scanning curve
Authors: Ye Yangbo , Wang Ge
Published: January 2005

Recently, Katsevich proved a filtered backprojection formula for exact image reconstruction from cone‐beam data along a helical scanning locus, which is an important breakthrough since 1991 when the spiral cone‐beam scanning mode was proposed. In this paper, we prove a generalized Katsevich's formula for exact image reconstruction from cone‐beam data collected along a rather flexible curve. We will also give a general condition on filtering directions. Based on this condition, we suggest a natural choice of filtering directions, which is more convenient than Katsevich's choice and can be applied to general scanning curves. In the derivation, we use analytical techniques instead of geometric arguments. As a result, we do not need the uniqueness of the PI lines. In fact, our formula can be used to reconstruct images on any chord as long as a scanning curve runs from one endpoint of the chord to the other endpoint. This can be considered as a generalization of Orlov's classical theorem. Specifically, our formula can be applied to (i) nonstandard spirals of variable radii and pitches (with PI‐ or ‐PI‐windows), and (ii) saddlelike curves.
Detection of IMRT delivery errors using a quantitative 2D dosimetric verification system
Authors: Childress Nathan L. , Bloch Charles , White R. Allen , Salehpour Mohammad , Rosen Isaac I.
Published: January 2005

We investigated the feasibility of detecting intensity modulated radiotherapy delivery errors automatically using a scalar evaluation of two‐dimensional (2D) transverse dose measurement of the complete treatment delivery. Techniques using the gamma index and the normalized agreement test (NAT) index were used to parametrize the agreement between measured and computed dose distributions to seven different scalar metrics. Simulated verifications with delivery errors calculated using a commercially available treatment planning system for 9 prostate and 7 paranasal sinus cases were compared to 433 clinical verifications. The NAT index with 5% and criteria that included cold areas outside the planning target volume detected the largest percent of delivery errors. Assuming a false positive rate of 5%, it was able to detect 88% of beam energy changes, 94% of a different patient's plan being delivered, 25% of plans with one beam's collimator rotated by 90°, 81% of rotating one beam's gantry angle by 10°, and 100% of omitting the delivery of one beam. However, no instances of changing one beam's monitor unit setting by 10% or shifting the isocenter by were detected. Although the phantom shift could not be detected by the small change it made in the dose distribution, our autopositioning algorithm clearly identified the spatial anomaly. Using tighter criteria or combining dose and distance disagreements in an either/or fashion resulted in poorer delivery error detection. The mean value of the 2D gamma index distribution was less sensitive to delivery errors than the other scalar metrics studied. Although we found that scalar metrics do not have sufficient delivery error detection rates to be used as the sole clinical analysis technique, manually examining 2D dose comparison images would result in a near 100% detection rate while performing an ion chamber measurement alone would only detect 54% of these errors.
Reference photon dosimetry data and reference phase space data for the photon beam from Varian Clinac 2100 series linear accelerators
Authors: Cho Sang Hyun , Vassiliev Oleg N. , Lee Seungsoo , Liu H. Helen , Ibbott Geoffrey S. , Mohan Radhe
Published: January 2005

The current study presents the reference photon dosimetry data (RPDD) and reference phase space data (RPSD) for the photon beam from Varian 2100 series linear accelerators. The RPDD provide the basic photon dosimetry data, typically collected during the initial commissioning of a new linear accelerator, including output factors, depth dose data, and beam profile data in air and in water. The RPSD provide the full phase space information, such as position, direction, and energy for each particle generated inside the head of any particular linear accelerator in question. The dosimetric characteristics of the photon beam from the majority of the aforementioned accelerators, which are unaltered from the manufacturer's original specifications, can be fully described with these two data sets within a clinically acceptable uncertainty . The current study also presents a detailed procedure to establish the RPDD and RPSD using measured data and Monte Carlo calculations. The RPDD were constructed by compiling our own measured data and the average data based on the analysis of more than 50 sets of measured data from the Radiological Physics Center (RPC) and 10 sets of clinical dosimetry data obtained from 10 different institutions participating in the RPC's quality assurance monitoring program. All the measured data from the RPC and the RPC‐monitored institutions were found to be within a statistically tight range (i.e., or less) for each dosimetric quantity. The manufacturer's standard data, except for in‐air off‐axis factors that are available only from the current study, were compared with the RPDD, showing that the manufacturer's standard data could also be used as the RPDD for the photon beam studied in this study. The RPSD were obtained from Monte Carlo calculations using the BEAMnrc/DOSXYZnrc code system with (a spread of 3% full width at half maximum) and full width at half maximum as the values of the energy and radial spread of a Gaussian electron pencil beam incident on the target, respectively. The RPSD were capable of generating Monte Carlo data that agreed with the RPDD within the acceptance criteria adopted in the current study (e.g., 1% or for depth dose). A complete set of the RPDD and RPSD from the current study is available from the RPC website (http://rpc.mdanderson.org) or via mass storage media such as DVD or CD‐ROM upon request.
Compact monochromatic flash x‐ray generator utilizing a disk‐cathode molybdenum tube
Authors: Sato Eiichi , Tanaka Etsuro , Mori Hidezo , Kawai Toshiaki , Ichimaru Toshio , Sato Shigehiro , Takayama Kazuyoshi , Ido Hideaki
Published: January 2005

The high‐voltage condensers in a polarity‐inversion two‐stage Marx surge generator are charged from −50 to −70 kV by a power supply, and the electric charges in the condensers are discharged to an x‐ray tube after closing gap switches in the surge generator with a trigger device. The x‐ray tube is a demountable diode, and the turbo molecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean molybdenum lines are produced using a 20 μm‐thick zirconium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of −70 kV, the instantaneous tube voltage and current were 120 kV and 1.0 kA, respectively. The x‐ray pulse widths were approximately 70 ns, and the generator produced instantaneous number of photons was approximately per pulse at 0.5 m from the source of 3.0 mm in diameter.
Motion‐encoded dose calculation through fluence/sinogram modification
Authors: Lu Weiguo , Olivera Gustavo H. , Mackie Thomas R.
Published: January 2005

Conventional radiotherapy treatment planning systems rely on a static computed tomography (CT) image for planning and evaluation. Intra/inter‐fraction patient motions may result in significant differences between the planned and the delivered dose. In this paper, we develop a method to incorporate the knowledge of intra/inter‐fraction patient motion directly into the dose calculation. By decomposing the motion into a parallel (to beam direction) component and perpendicular (to beam direction) component, we show that the motion effects can be accounted for by simply modifying the fluence distribution (sinogram). After such modification, dose calculation is the same as those based on a static planning image. This method is superior to the “dose‐convolution” method because it is not based on “shift invariant” assumption. Therefore, it deals with material heterogeneity and surface curvature very well. We test our method using extensive simulations, which include four phantoms, four motion patterns, and three plan beams. We compare our method with the “dose‐convolution” and the “stochastic simulation” methods (gold standard). As for the homogeneous flat surface phantom, our method has similar accuracy as the “dose‐convolution” method. As for all other phantoms, our method outperforms the “dose‐convolution.” The maximum motion encoded dose calculation error using our method is within 4% of the gold standard. It is shown that a treatment planning system that is based on “motion‐encoded dose calculation” can incorporate random and systematic motion errors in a very simple fashion. Under this approximation, in principle, a planning target volume definition is not required, since it already accounts for the intra/inter‐fraction motion variations and it automatically optimizes the cumulative dose rather than the single fraction dose.
Sliding slice: A novel approach for high accuracy and automatic 3D localization of seeds from CT scans
Authors: Tubic Dragan , Beaulieu Luc
Published: January 2005

We present a conceptually novel principle for 3D reconstruction of prostate seed implants. Unlike existing methods for implant reconstruction, the proposed algorithm uses raw CT data (sinograms) instead of reconstructed CT slices. Using raw CT data solves several inevitable problems related to the reconstruction from CT slices. First, the sinograms are not affected by reconstruction artifacts in the presence of metallic objects and seeds in the patient body. Second, the scanning axis is not undersampled as in the case of CT slices; as a matter of fact the scanning axis is the most densely sampled and each seed is typically represented by several hundred samples. Moreover, the shape of a single seed in a sinogram can be modeled exactly, thus facilitating the detection. All this allows very accurate 3D reconstruction of both position and the orientation of the seeds. Preliminary results indicate that the seed position can be estimated with accuracy (average), while the orientation estimate accuracy is within on average. Although the main contribution of the paper is to present a new principle of reconstruction, a preliminary implementation is also presented as a proof of concept. The implemented algorithm has been tested on a phantom and the obtained results are presented to validate the proposed approach.
Theoretical study of the influence of a heterogeneous activity distribution on intratumoral absorbed dose distribution
Authors: Bao Ande , Zhao Xia , Phillips William T. , Woolley F. Ross , Otto Randal A. , Goins Beth , Hevezi James M.
Published: January 2005

Radioimmunotherapy of hematopoeitic cancers and micrometastases has been shown to have significant therapeutic benefit. The treatment of solid tumors with radionuclide therapy has been less successful. Previous investigations of intratumoral activity distribution and studies on intratumoral drug delivery suggest that a probable reason for the disappointing results in solid tumor treatment is nonuniform intratumoral distribution coupled with restricted intratumoral drug penetrance, thus inhibiting antineoplastic agents from reaching the tumor's center. This paper describes a nonuniform intratumoral activity distribution identified by limited radiolabeled tracer diffusion from tumor surface to tumor center. This activity was simulated using techniques that allowed the absorbed dose distributions to be estimated using different intratumoral diffusion capabilities and calculated for tumors of varying diameters. The influences of these absorbed dose distributions on solid tumor radionuclide therapy are also discussed. The absorbed dose distribution was calculated using the dose point kernel method that provided for the application of a three‐dimensional (3D) convolution between a dose rate kernel function and an activity distribution function. These functions were incorporated into 3D matrices with voxels measuring . At this point fast Fourier transform (FFT) and multiplication in frequency domain followed by inverse FFT (iFFT) were used to effect this phase of the dose calculation process. The absorbed dose distribution for tumors of 1, 3, 5, 10, and in diameter were studied. Using the therapeutic radionuclides of , , , and , the total average dose, center dose, and surface dose for each of the different tumor diameters were reported. The absorbed dose in the nearby normal tissue was also evaluated. When the tumor diameters exceed , a much lower tumor center dose is delivered compared with tumors between 3 and in diameter. Based on these findings, the use of higher ‐energy radionuclides, such as and is more effective in delivering a higher absorbed dose to the tumor center at tumor diameters around .
DMLC leaf‐pair optimal control for mobile, deforming target
Authors: Papiez Lech , Rangaraj Dharanipathy
Published: January 2005

Existing algorithms of dynamic control of independent pairs of leaves allow optimal DMLC delivery of IMRT to rigid targets translating parallel to leaf trajectories. However, in numerous cases of radiotherapy treatments simplifying assumptions of rigid‐like motions of targets and surrounding tissues are clearly not satisfied. Therefore algorithms have to be developed that allow one to control MLC so that predetermined intensities are delivered to various points in targets that experience compression and expansion at the time of irradiation. Moreover, it is desirable for such algorithms to ensure that delivery of modulated intensity map will be done with minimal expense of monitor units. Derivation of the algorithm that optimizes the DMLC IMRT to mobile, deforming target is presented in this paper. [To illustrate the general algorithm two representative examples of DMLC IMRT delivery to deforming targets are presented in full detail.] Finally, similarities and differences between solutions for immobile targets, for moving, rigid targets and for moving, deforming targets are discussed.
SURLAS: A new clinical grade ultrasound system for sequential or concomitant thermoradiotherapy of superficial tumors: Applicator description
Authors: Novák Petr , Moros Eduardo G. , Straube William L. , Myerson Robert J.
Published: January 2005

A new ultrasound applicator with three‐dimensional power distribution control was developed for simultaneous thermoradiotherapy. The system was named SURLAS for Scanning Ultrasound Reflector Linear Arrays System. In this paper, the hardware of the first clinical grade SURLAS applicator is described with emphasis on clinically important static acoustic characteristics and on construction aspects not reported before. Functionally, the SURLAS applicator consists of two parallel opposed ultrasound linear arrays aiming their acoustic beams to a ‐shape scanning ultrasound reflector, which deflects the beams coming from opposite directions toward the treatment area. The reciprocating motion of the reflector in‐between the arrays spreads the ultrasonic energy over the target area scanned. Control of power deposition over the 16 cm by 16 cm treatment window area is achieved by adjusting the power input into the transducer elements of the arrays as a function of the position of the scanning reflector. Furthermore, the arrays operate at significantly different frequencies (1.9 and 4.9 MHz) so that intensity modulation of beams of different frequencies can be exploited to adjust the depth of energy penetration. With this design, external electron or photon beams can be concurrently delivered with hyperthermia by irradiating through the applicator's body. Safety features were implemented into the applicator's design to monitor its performance during operation. A detailed description of the applicator including impedance matching circuits/filters, radiation force balance power measurements, hydrophone pressure field distribution measurements, as well as safety test results are reported.
The American Board of Radiology Maintenance of Certification (MOC) Program in Radiologic Physics
Authors: Thomas Stephen R. , Hendee William R. , Paliwal Bhudatt R.
Published: January 2005

Maintenance of Certification (MOC) recognizes that in addition to medical knowledge, several essential elements involved in delivering quality care must be developed and maintained throughout one's career. The MOC process is designed to facilitate and document the professional development of each diplomate of The American Board of Radiology (ABR) through its focus on the essential elements of quality care in Diagnostic Radiology and its subspecialties, and in the specialties of Radiation Oncology and Radiologic Physics. The initial elements of the ABR‐MOC have been developed in accord with guidelines of The American Board of Medical Specialties. All diplomates with a ten‐year, time‐limited primary certificate in Diagnostic Radiologic Physics, Therapeutic Radiologic Physics, or Medical Nuclear Physics who wish to maintain certification must successfully complete the requirements of the appropriate ABR‐MOC program for their specialty. Holders of multiple certificates must meet ABR‐MOC requirements specific to the certificates held. Diplomates with lifelong certificates are not required to participate in the MOC, but are strongly encouraged to do so. MOC is based on documentation of individual participation in the four components of MOC: (1) professional standing, (2) lifelong learning and self‐assessment, (3) cognitive expertise, and (4) performance in practice. Within these components, MOC addresses six competencies: medical knowledge, patient care, interpersonal and communication skills, professionalism, practice‐based learning and improvement, and systems‐based practice.
Sound radiation from Caribbean steelpans
Authors: Copeland Brian , Morrison Andrew , Rossing Thomas D.
Published: January 2005

Besides radiating sound from the note area being struck, a steelpan radiates from neighboring note areas that vibrate sympathetically, from the areas between notes, and from the skirt [Rossing et al., Phys. Today 49(3), 24–29 (1996)]. Measurements were taken in an anechoic chamber using a four-microphone intensity probe to visualize the acoustic radiation from selected notes on a double second and a low tenor steelpan. Swept sinusoidal excitation was effected using an electromagnet. Sound intensity maps were drawn for the first three harmonics.
Identifying ultrasonic scattering sites from three-dimensional impedance maps
Authors: Mamou Jonathan , Oelze Michael L. , O’Brien William D. , Zachary James F.
Published: January 2005

Ultrasonic backscattered signals contain frequency-dependent information that is usually discarded to produce conventional B-mode images. It is hypothesized that parametrization of the quantitative ultrasound frequency-dependent information (i.e., estimating scatterer size and acoustic concentration) may be related to discrete scattering anatomic structures in tissues. Thus, an estimation technique is proposed to extract scatterer size and acoustic concentration from the power spectrum derived from a three-dimensional impedance map (3DZM) of a tissue volume. The 3DZM can be viewed as a computational phantom and is produced from a 3D histologic data set. The 3D histologic data set is constructed from tissue sections that have been appropriately stained to highlight specific tissue features. These tissue features are assigned acoustic impedance values to yield a 3DZM. From the power spectrum, scatterer size and acoustic concentration estimates were obtained by optimization. The 3DZM technique was validated by simulations that showed relative errors of less than 3% for all estimated parameters. Estimates using the 3DZM technique were obtained and compared against published ultrasonically derived estimates for two mammary tumors, a rat fibroadenoma and a 4T1 mouse mammary carcinoma. For both tumors, the relative difference between ultrasonic and 3DZM estimates was less than 10% for the average scatterer size.
On the reciprocity relationship between direct field radiation and diffuse reverberant loading
Authors: Shorter P. J. , Langley R. S.
Published: January 2005

This analysis is concerned with the derivation of a “diffuse field” reciprocity relationship between the diffuse field excitation of a connection to a structural or acoustic subsystem and the radiation impedance of the connection. Such a relationship has been derived previously for connections described by a single degree of freedom. In the present work it is shown that the diffuse–field reciprocity relationship also arises when describing the ensemble average response of connections to structural or acoustic subsystems with uncertain boundaries. Furthermore, it is shown that the existing diffuse–field reciprocity relationship can be extended to encompass connections that possess an arbitrary number of degrees of freedom. The present work has application to (i) the calculation of the diffuse field response of structural–acoustic systems modeled by Finite Elements, Boundary Elements, and Infinite Elements; (ii) the general calculation of the Coupling Loss Factors employed in Statistical Energy Analysis (SEA); and (iii) the derivation of an alternative analysis method for describing the dynamic interactions of coupled subsystems with uncertain boundaries (a generalized “boundary” approach to SEA).
The energetics and the stability of axially moving Kirchhoff strings (L)
Authors: Chen Li-Qun , Zhao Wei-Jia
Published: January 2005

The energetics and the stability of free transverse vibration of an axially moving string are investigated based on the Kirchhoff nonlinear model. The model is derived in a physically meaningful manner. The time-rate of the total mechanical energy associated with the vibration is calculated to show that the energy is not conserved. It is proved that there exists a conserved quantity that remains a constant during the nonlinear vibration. The conserved quantity is applied to verify the Lyapunov stability of the axially moving Kirchhoff string.
Stopped-pipe wind instruments: Acoustics of the panpipes
Authors: Fletcher N. H.
Published: January 2005

Stopped-pipe jet-excited musical instruments are known in many cultures, those best-known today being the panpipes or syrinx of Eastern Europe and of the Peruvian Andes. Although the playing style differs, in each case the instrument consists of a set of graduated bamboo pipes excited by blowing across the open tops. Details of the excitation aerodynamics warrant examination, particularly as the higher notes contain amplitudes of the even harmonics approaching those of the odd harmonics expected from a stopped pipe. Analysis shows that the jet offset is controlled by the fluid dynamics of the jet, and is such that appreciable even-harmonic excitation is generated. The theory is largely confirmed by measurements on a player.
Slow dynamics and anomalous nonlinear fast dynamics in diverse solids
Authors: Johnson Paul , Sutin Alexander
Published: January 2005

Results are reported of the first systematic study of anomalous nonlinear fast dynamics and slow dynamics in a number of solids. Observations are presented from seven diverse materials showing that anomalous nonlinear fast dynamics (ANFD) and slow dynamics (SD) occur together, significantly expanding the nonlinear mesoscopic elasticity class. The materials include samples of gray iron, alumina ceramic, quartzite, cracked Pyrex, marble, sintered metal, and perovskite ceramic. In addition, it is shown that materials which exhibit ANFD have very similar ratios of amplitude-dependent internal-friction to the resonance-frequency shift with strain amplitude. The ratios range between 0.28 and 0.63, except for cracked Pyrex glass, which exhibits a ratio of 1.1, and the ratio appears to be a material characteristic. The ratio of internal friction to resonance frequency shift as a function of time during SD is time independent, ranging from 0.23 to 0.43 for the materials studied.
The emergence of mature gestural patterns in the production of voiceless and voiced word-final stops
Authors: Nittrouer Susan , Estee Sandy , Lowenstein Joanna H. , Smith Jennifer
Published: January 2005

The organization of gestures was examined in children’s and adults’ samples of consonant–vowel–stop words differing in stop voicing. Children (5 and 7 years old) and adults produced words from five voiceless/voiced pairs, five times each in isolation and in sentences. Acoustic measurements were made of vocalic duration, and of the first and second formants at syllable center and voicing offset. The predicted acoustic correlates of syllable-final voicing were observed across speakers: vocalic segments were shorter and first formants were higher in words with voiceless, rather than voiced, final stops. In addition, the second formant was found to differ depending on the voicing of the final stop for all speakers. It was concluded that by 5 years of age children produce words ending in stops with the same overall gestural organization as adults. However, some age-related differences were observed for jaw gestures, and variability for all measures was greater for children than for adults. These results suggest that children are still refining their organization of articulatory gestures past the age of 7 years. Finally, context effects (isolation or sentence) showed that the acoustic correlates of syllable-final voicing are attenuated when words are produced in sentences, rather than in isolation.
Object-related brain potentials associated with the perceptual segregation of a dichotically embedded pitch
Authors: Hautus Michael J. , Johnson Blake W.
Published: January 2005

The cortical mechanisms of perceptual segregation of concurrent sound sources were examined, based on binaural detection of interaural timing differences. Auditory event-related potentials were measured from 11 healthy subjects. Binaural stimuli were created by introducing a dichotic delay of 500-ms duration to a narrow frequency region within a broadband noise, and resulted in a perception of a centrally located noise and a right-lateralized pitch (dichotic pitch). In separate listening conditions, subjects actively discriminated and responded to randomly interleaved binaural and control stimuli, or ignored random stimuli while watching silent cartoons. In a third listening condition subjects ignored stimuli presented in homogenous blocks. For all listening conditions, the dichotic pitch stimulus elicited an object-related negativity (ORN) at a latency of about 150–250 ms after stimulus onset. When subjects were required to actively respond to stimuli, the ORN was followed by a P400 wave with a latency of about 320–420 ms. These results support and extend a two-stage model of auditory scene analysis in which acoustic streams are automatically parsed into component sound sources based on source-relevant cues, followed by a controlled process involving identification and generation of a behavioral response.
A method for estimating the parameters of electrodynamic drivers in thermoacoustic coolers
Authors: Paek Insu , Mongeau Luc , Braun James E.
Published: January 2005

The electroacoustic efficiency of high-power actuators used in thermoacoustic coolers may be estimated using a linear model involving a combination of six parameters. A method to identify these equivalent driver parameters from measured total electrical impedance and velocity-voltage transfer function data was developed. A commercially available, moving-magnet driver coupled to a functional thermoacoustic cooler was used to demonstrate the procedure experimentally. The method, based on linear electrical circuit theory, allowed for the possible frequency and amplitude dependence of the driver parameters to be estimated. The results demonstrated that driver parameters measured in vacuo using this method can be used to predict the driver efficiency and performance for operating conditions which may be encountered under load.
Time delays in coupled multibubble systems (L)
Authors: Doinikov Alexander A. , Manasseh Richard , Ooi Andrew
Published: January 2005

Damping constants of free oscillations of coupled gas bubbles change considerably when time delays due to the finite speed of sound in the surrounding liquid are taken into account. This effect is illustrated analytically by the example of a two-bubble system and numerically by the example of a bubble chain. By comparing the numerical data with experimental measurements, it is shown that allowing for time delays considerably improves agreement between theory and experiment.
The processing and perception of size information in speech sounds
Authors: Smith David R. R. , Patterson Roy D. , Turner Richard , Kawahara Hideki , Irino Toshio
Published: January 2005

There is information in speech sounds about the length of the vocal tract; specifically, as a child grows, the resonators in the vocal tract grow and the formant frequencies of the vowels decrease. It has been hypothesized that the auditory system applies a scale transform to all sounds to segregate size information from resonator shape information, and thereby enhance both size perception and speech recognition [Irino and Patterson, Speech Commun. 36, 181–203 (2002)]. This paper describes size discrimination experiments and vowel recognition experiments designed to provide evidence for an auditory scaling mechanism. Vowels were scaled to represent people with vocal tracts much longer and shorter than normal, and with pitches much higher and lower than normal. The results of the discrimination experiments show that listeners can make fine judgments about the relative size of speakers, and they can do so for vowels scaled well beyond the normal range. Similarly, the recognition experiments show good performance for vowels in the normal range, and for vowels scaled well beyond the normal range of experience. Together, the experiments support the hypothesis that the auditory system automatically normalizes for the size information in communication sounds.
Sensitivity of a tucuxi (Sotalia fluviatilis guianensis) to airborne sound
Authors: Liebschner Alexander , Hanke Wolf , Miersch Lars , Dehnhardt Guido , Sauerland Matthias
Published: January 2005

Auditory systems of cetaceans are considered highly specialized for underwater sound processing, whereas the extent of their hearing capacity in air is still a point of issue. In this study, the sensitivity to airborne sound in a male tucuxi (Sotalia fluviatilis guianensis) was tested by means of a go/no go response paradigm. Auditory thresholds were obtained from 2 to 31.5 kHz. Compared to the hearing thresholds of other dolphins as well as of amphibian mammals, the sensitivity to airborne sound of the test subject is low from 2 to 8 kHz, with the highest threshold at 4 kHz. Thresholds at 16 and 31.5 kHz reveal a sharp increase in hearing sensitivity. Thus, although not obtained in this study, the upper aerial hearing limit is in the ultrasonic range. A comparison of the present data with the underwater audiogram of the same test subject referred to sound intensity indicates that the sensitivity of Sotalia to underwater sound is generally better than to airborne sound.
Evaluation of stage acoustics in Seoul Arts Center Concert Hall by measuring stage support
Authors: Jeon Jin Yong , Barron Michael
Published: January 2005

Stage acoustics is an important characteristic for concert halls, both for the acoustic quality on stage and for the audience. However, relatively little research has been conducted into the question. This study was based on the investigation of an actual concert hall stage, that of the Seoul Arts Center Concert Hall in Korea. The stage acoustics was evaluated in the actual hall, and with two models: a 1:25 scale model and a computer model. The study was based on the stage support parameter ST1 proposed by Gade as a measure of support for individual performers [Acustica 65, 193–203 (1989)]. The variation of support was measured on the empty stage of the actual hall and in the two models. The effect of musicians on stage, the effect of moving the orchestra, the effect of ceiling height and of stage-wall profile were also investigated. Conclusions are drawn both relating to the Seoul Concert Hall stage and stages in general.
Response of bare 1–3 piezocomposite array to localized electrical excitation
Authors: Guyonvarch Jérôme , Certon Dominique , Ratsimandresy Leong , Patat Frédéric , Lethiecq Marc
Published: January 2005

The theoretical response of a 1–3 piezocomposite plate submitted to localized electrical excitation was studied with the theory of guided waves. The theoretical modeling was based on the global matrix method, and the piezocomposite material was considered as a homogeneous medium. To validate the theoretical results, experimental displacement measurements were performed with an interferometric probe on two piezocomposite plates, one with a single element and one with an array of electrodes. The measured response on the single-element plate was mainly supported by the S0 and S3 modes of the plate. Homogenization limits of the composite in terms of frequency and wave number are defined on the basis of data from this sample. Within these limits, the piezocomposite material operates as a homogeneous medium, and comparison between theoretical and experimental results allows the equivalent electroacoustic parameters to be evaluated. A second sample was measured to study the effects of the electrode array on the electroacoustic response of the plate. Two kinds of electrical excitation were studied.
Arrival-time structure of the time-averaged ambient noise cross-correlation function in an oceanic waveguide
Authors: Sabra Karim G. , Roux Philippe , Kuperman W. A.
Published: January 2005

Coherent deterministic arrival times can be extracted from the derivative of the time-averaged ambient noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green’s function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the noise cross-correlation function, for a uniform distribution of noise sources in a Pekeris waveguide. This image formulation determines the influence of the noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the ambient noise cross-correlation function. Practical implications of these results for sea experiments are also discussed.
A hybrid active/passive exhaust noise control system for locomotives
Authors: Remington Paul J. , Knight J. Scott , Hanna Doug , Rowley Craig
Published: January 2005

A prototype hybrid system consisting of active and passive components for controlling far-field locomotive exhaust noise has been designed, assembled, and tested on a locomotive. The system consisted of a resistive passive silencer for controlling high-frequency broadband noise and a feedforward multiple-input, multiple-output active control system for suppressing low-frequency tonal noise. The active system used ten roof-mounted bandpass speaker enclosures with 2–12-in. speakers per enclosure as actuators, eight roof-mounted electret microphones as residual sensors, and an optical tachometer that sensed locomotive engine speed as a reference sensor. The system was installed on a passenger locomotive and tested in an operating rail yard. Details of the system are described and the near-field and far-field noise reductions are compared against the design goal.
Predicting the eigenmodes of a cavity containing an array of circular pipes
Authors: Fenech Benjamin , Jacobsen Finn
Published: January 2005

An array of pipes inside a cavity, as found, for example, in a shell-and-tube heat exchanger, changes the eigenfrequencies of the cavity. It can be tedious to determine the shifted eigenfrequencies with a finite-element model. Based on previous work by Meyer and Neumann, Parker proposed a simple relationship for predicting the shifted eigenfrequencies. In this paper, results obtained from this relationship are compared with eigenfrequencies obtained from very accurate finite element simulations. From the results it can be concluded that Parker’s relationship gives fairly good predictions of the eigenfrequencies for the first few modes in a cavity with pipes arranged in a rectangular configuration. The predictions are not so accurate for pipes arranged in a diamond configuration, and a modified version of the relationship is suggested for this configuration. If the number of pipes in the cavity is small, the simple relationship is no longer valid.
Surface Proteins ofStreptococcus agalactiaeand Related Proteins in Other Bacterial Pathogens
Authors: Lindahl Gunnar , Stålhammar-Carlemalm Margaretha , Areschoug Thomas
Published: January 2005

Streptococcus agalactiae(group B Streptococcus) is the major cause of invasive bacterial disease, including meningitis, in the neonatal period. Although prophylactic measures have contributed to a substantial reduction in the number of infections, development of a vaccine remains an important goal. While much work in this field has focused on theS. agalactiaepolysaccharide capsule, which is an important virulence factor that elicits protective immunity, surface proteins have received increasing attention as potential virulence factors and vaccine components. Here, we summarize current knowledge aboutS. agalactiaesurface proteins, with emphasis on proteins that have been characterized immunochemically and/or elicit protective immunity in animal models. These surface proteins have been implicated in interactions with human epithelial cells, binding to extracellular matrix components, and/or evasion of host immunity. Of note, severalS. agalactiaesurface proteins are related to surface proteins identified in other bacterial pathogens, emphasizing the general interest of theS. agalactiaeproteins. Because someS. agalactiaesurface proteins elicit protective immunity, they hold promise as components in a vaccine based only on proteins or as carriers in polysaccharide conjugate vaccines.
Proposed Function of the Accumulation of Plasma Membrane-Type Ca
2+
-ATPase mRNA in Resting Cysts of the Ciliate
Sterkiella histriomuscorum
Authors: Lescasse Rachel , Grisvard Jeanine , Fryd Ghislaine , Fleury-Aubusson Anne , Baroin-Tourancheau Anne
Published: January 2005

From an mRNA differential-display analysis of the encystment-excystment cycle of the ciliate
Sterkiella histriomuscorum
, we have isolated an expressed sequence tag encoding a plasma membrane-type Ca
2+
-ATPase (PMCA). PMCAs are located either in the plasma membranes or in the membranes of intracellular organelles, and their function is to pump calcium either out of the cell or into the intracellular calcium stores, respectively. The
S. histriomuscorum
macronuclear
PMCA
gene (
ShPMCA
) and its corresponding cDNA were cloned; it is the first member of the Ca
2+
-ATPase family identified in
Sterkiella
. The predicted protein of 1,065 amino acids exhibits 37% identity with PMCAs of diverse organisms. A phylogenetic analysis showed its relatedness to homologs of two alveolates: the ciliate
Paramecium tetraurelia
and the apicomplexan
Toxoplasma gondii
. Overexpression of the protein ShPMCA failed to rescue the wild-type phenotype of three Ca
2+
-ATPase-defective mutant strains of
Saccharomyces cerevisiae
; this failure contrasts with the reported ability of the PMCAs of parasites to complement defects in yeast.
ShPMCA
mRNA is markedly accumulated during encystment and in resting cysts, suggesting a function during excystment. To address the possibility of a signaling role for calcium at excystment, the capacity of calcium to induce excystment was examined.
A Homolog of Ste6, the
a
-Factor Transporter in
Saccharomyces cerevisiae
, Is Required for Mating but Not for Monokaryotic Fruiting in
Cryptococcus neoformans
Authors: Hsueh Yen-Ping , Shen Wei-Chiang
Published: January 2005

Fungal pheromones function during the initial recognition stage of the mating process. One type of peptide pheromone identified in ascomycetes and basidiomycetes terminates in a conserved CAAX motif and requires extensive posttranslational modifications to become mature and active. A well-studied representative is the
a
-factor of
Saccharomyces cerevisiae
. Unlike the typical secretory pathway utilized by most peptides, an alternative mechanism involving the ATP-binding cassette transporter Ste6 is used for the export of mature
a
-factor.
Cryptococcus neoformans
, a bipolar human pathogenic basidiomycete, produces CAAX motif-containing lipopeptide pheromones in both
MAT
a
and
MAT
α cells. Virulence studies with a congenic pair of
C. neoformans
serotype D strains have shown that
MAT
α cells are more virulent than
MAT
a
cells. Characterization of the
MAT
α pheromones indicated that an autocrine signaling loop may contribute to the differentiation and virulence of
MAT
α cells. To further address the role of pheromones in the signaling loop, we identified a
STE6
homolog in the
C. neoformans
genome and determined its function by gene disruption. The
ste6
mutants in either mating-type background showed partially impaired mating functions, and mating was completely abolished in a bilateral mutant cross. Surprisingly, the
MAT
α
ste6
mutant does not exhibit a defect in monokaryotic fruiting, suggesting that the activation of the autocrine signaling loop by the pheromone is via a Ste6-independent mechanism. MFα pheromone itself is essential for this process and could induce the signaling response intracellularly in
MAT
α cells. Our data demonstrate that Ste6 is evolutionarily conserved for mating and is not required for monokaryotic fruiting in
C. neoformans
.
Distinct Stress Responses of Two Functional Laccases in
Cryptococcus neoformans
Are Revealed in the Absence of the Thiol-Specific Antioxidant Tsa1
Authors: Missall Tricia A. , Moran Jason M. , Corbett John A. , Lodge Jennifer K.
Published: January 2005

Laccases are thought to be important to the virulence of many fungal pathogens by producing melanin, a presumed oxygen radical scavenger. A laccase in
Cryptococcus neoformans
has been shown to synthesize melanin and contributes to the virulence and the survival in macrophages of this fungal pathogen. One
C. neoformans
laccase gene,
LAC1
, previously called
CNLAC1
, has been extensively studied, and we describe a homologous gene,
LAC2
, that is found 8 kb away from
LAC1
in the genome. In this study we report a role for both laccases, in addition to the thiol peroxidase, Tsa1, in oxidative and nitrosative stress resistance mechanisms of
C. neoformans
. With use of real-time PCR, similar changes in expression of the two laccase genes occur in response to oxidative and nitrosative stresses, but only the regulation of the
LAC2
gene during stress is influenced by Tsa1. Both laccases contribute to melanin production using L-dopa as a substrate and are differentially localized in the cell based on green fluorescent protein fusions. A single deletion of either
LAC1
or
LAC2
alone had no effect on sensitivity to H
2
O
2
or nitric oxide. However, deletion of either
LAC1
or
LAC2
in combination with a
TSA1
deletion resulted in a slight peroxide sensitivity, and a
lac2
Δ
tsa1
Δ deletion strain was sensitive to nitric oxide stress. In addition, the deletion of both laccases reduces survival of
C. neoformans
in primary macrophages. Based on our expression and functional analysis, we propose a novel model for the interaction of these two systems, which are both important for virulence.
Separation of the
Saccharomyces cerevisiae
Paf1 Complex from RNA Polymerase II Results in Changes in Its Subnuclear Localization
Authors: Porter Stephanie E. , Penheiter Kristi L. , Jaehning Judith A.
Published: January 2005

The yeast Paf1 complex (Paf1C), composed of Paf1, Ctr9, Cdc73, Rtf1, and Leo1, associates with RNA polymerase II (Pol II) at promoters and in the actively transcribed portions of mRNA genes. Loss of Paf1 results in severe phenotypes and significantly reduced levels of the other Paf1C components. In contrast, loss of Rtf1 causes relatively subtle phenotypic changes and no reduction in the other Paf1C factors but disrupts the association of these factors with Pol II and chromatin. To elucidate the fate of the Paf1C when dissociated from Pol II, we examined the localization of the Paf1C components in
paf1
and
rtf1
mutant yeast strains. We found that although the Paf1C factors remain nuclear in
paf1
and
rtf1
strains, loss of Paf1 or Rtf1 results in a change in the subnuclear distribution of the remaining factors. In wild-type cells, Paf1C components are present in the nucleoplasm but not the nucleolus. In contrast, in both
paf1
and
rtf1
strains, the remaining factors are found in the nucleolus as well as the nucleoplasm. Loss of Paf1 affects nucleolar function; we observed that expression of
MAK21
and
RRP12
, important for rRNA processing, is reduced concomitant with an increase in rRNA precursors in a
paf1
strain. However, these changes are not the result of relocalization of the Paf1C because loss of Rtf1 does not cause similar changes in rRNA processing. Instead, we speculate that the change in localization may reflect a link between the Paf1C and newly synthesized mRNAs as they exit the nucleus.
Molecular Analysis Reveals Localization ofSaccharomyces cerevisiaeProtein Kinase C to Sites of Polarized Growth and Pkc1p Targeting to the Nucleus and Mitotic Spindle
Authors: Denis Valérie , Cyert Martha S.
Published: January 2005

The catalytic activity and intracellular localization of protein kinase C (PKC) are both highly regulated in vivo. This family of kinases contains conserved regulatory motifs, i.e., the C1, C2, and HR1 domains, which target PKC isoforms to specific subcellular compartments and restrict their activity spatially.Saccharomyces cerevisiaecontains a single PKC isozyme, Pkc1p, which contains all of the regulatory motifs found in mammalian PKCs. Pkc1p localizes to sites of polarized growth, consistent with its main function in maintaining cell integrity. We dissected the molecular basis of Pkc1p localization by expressing each of its domains individually and in combinations as green fluorescent protein fusions. We find that the Rho1p-binding domains, HR1 and C1, are responsible for targeting Pkc1p to the bud tip and cell periphery, respectively. We demonstrate that Pkc1p activity is required for its normal localization to the bud neck, which also depends on the integrity of the septin ring. In addition, we show for the first time that yeast protein kinase C can accumulate in the nucleus, and we identify a nuclear exit signal as well as nuclear localization signals within the Pkc1p sequence. Thus, we propose that Pkc1p shuttles in and out of the nucleus and consequently has access to nuclear substrates. Surprisingly, we find that deletion of the HR1 domain results in Pkc1p localization to the mitotic spindle and that the C2 domain is responsible for this targeting. This novel nuclear and spindle localization of Pkc1p may provide a molecular explanation for previous observations that suggest a role for Pkc1p in regulating microtubule function.