bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary Flow Control and Streamwise Vortices Formation
Authors: Doerffer Piotr P. , Amecke Jochen
Published: February 2015

The structure of a secondary flow in a linear turbine cascade has been investigated. In order to analyse streamwise vortices configuration and to control their formation two types of side wall boundary layer fences have been applied. Results obtained proved that the streamwise fence reduces significantly spanwise extent of secondary flows. Transverse fence has no such effect but causes very significant change of location and the losses level in a passage vortex. Presented results cast some new light on the contribution of passage vortex, horse shoe vortex and a shear plain in between, to the losses maximum where these flow elements are in direct neighbourhood.
The Flow Through an Annular Turbine Nozzle With Nonuniform Pitch
Authors: Kurz Rainer
Published: February 2015

This paper discusses flow measurement results both upstream and downstream of a transonic annular turbine nozzle with a nonuniform pitch. The downstream measurements are performed in the plane, where the leading edge of the rotor is located in the gas turbine.

The experiments were performed using total pressure probes and static wall pressure taps.

This type of nonuniformity creates a different behavior of the flow field both upstream and downstream of the blades. The effects on the wakes and on the inviscid flow are discussed separately.

The mean velocities show a strong sensitivity to the changes of the pitch, which is identified as a potential flow effect by using a simple vortex model.
Numerical Simulation for Aeroelasticity in Turbomachines With Vortex Method
Authors: Wu Wenquan , Sisto F.
Published: February 2015

A new method for quantitatively predicting the interaction between the unsteady aerodynamics and structural dynamics was developed. The unsteady flow with large scale separation is simulated numerically with the developed Discrete Vortex Method. In this calculation process, the instantaneous unsteady force and moment of force acting on the blades can be obtained at each time step. On other hand, the cascade is considered as an elasticity system with damping including the effects of the interblade phase angle. The blades are excited to vibrate by the unsteady force and moment. To deal with the above two respects, the resulting code consists of two basic subprograms which exchange their data between each other at every computational time step and the non-linear problem is then solved in a time-marching discrete continuation fashion.

A series of numerical tests are presented including the parameters studies, such as: effects of the damping, incidence etc. For each case, a large number of computational steps is intended to provide sufficient information about the non-linear behavior of the stall flutter. The applicability of the method is demonstrated numerically.
Enabling Technologies for Nuclear Gas Turbine (GT-MHR) Power Conversion System
Authors: McDonald Colin F.
Published: February 2015

Since the onset of gas-cooled reactor work, almost half a century ago, the potential for direct coupling of a nuclear heat source with a gas turbine power conversion system was recognized, however, the technologies for the realization of this were not available, and the plants operated to date have used Rankine steam turbine power conversion systems. In the early 1990s, technology transfer from the gas turbine and aerospace industries, now make possible the introduction of the gas turbine modular helium reactor (GT-MHR) for utility power generation within the next decade. In this paper the enabling technologies for the helium gas turbine power conversion system are discussed, and these include the turbomachinery, magnetic bearings, compact heat exchangers, and helium system operating experience. Utilizing proven technology, the first GT-MHR plant would operate with an efficiency of 47%, and by exploiting its full potential this could perhaps reach as high as 60% early in the next century.
Nuclear Gas Turbine Plant (GT-MHR) Performance Potential
Authors: McDonald Colin F. , Etzel Klaus T.
Published: February 2015

With the current hiatus in the U.S. nuclear industry it is projected that by the year 2010 combustion gas turbines will be generating more electrical power than light water reactors. These units, operating at high firing temperature, and with advanced thermodynamic cycles, will have efficiencies of over 60%. In this era these gas turbines will operate with fossil-fuels (i.e., natural gas and gasified coal), but as environmental concerns intensisy there will be a quest for “greener technologies,” and this is where the gas turbine modular helium reactor (GT-MHR) will play a major role.

Utilizing a high temperature gas-cooled reactor and a closed helium Brayton cycle, a plant efficiency of 47% is projected based on the use of proven technology, and the initial unit could be in utility service by the year 2005. Following penetration of the market place, efforts will be expended to exploit the performance potential of the GT-MHR. In this paper the potential for efficiency advancement to 60% or higher is discussed, together with the technologies necessary for this to be realized, perhaps two decades after the operation of the pioneer plant. Such a power plant, that is compatible with the environment, and operating with an indigenous fuel source (i.e., uranium) could be in service through the first century of the next millennium.
Arbitrary Surface Flank Milling of Fan, Compressor, and Impeller Blades
Authors: Wu C. Y.
Published: February 2015

It is generally conceived that a blade surface is flank millable if it can be closely approximated by a ruled surface; otherwise the slow machining process of point milling has to be employed. However, we have now demonstrated that the ruled surface criterion for flank milling is neither necessary nor sufficient Furthermore, many complex arbitrary surfaces typical of our blades in fans, axial compressors, and centrifugal impellers in aviation gas turbines are actually closely flank millable and can be rendered exactly flank millable with one or more passes per surface often without sacrificing, indeed sometimes with gain, in performance.
Performance Analysis of Combined Cycles: Steam Recompression vs Conventional Bottoming Cycles
Authors: Grimaldi Carlo N. , Desideri Umberto
Published: February 2015

A performance analysis was fulfilled to compare the steam recompression with the conventional single- and dual-pressure bottoming cycles. The optimal parameters for each cycle were found in order to maximize the exergetic efficiency. Heat transfer surface was also calculated to show the differences in the size of the heat recovery steam generator which have a direct influence on the plant’s costs.

The optimal configurations for each cycle were also studied when steam injection is employed. The relative performance when steam extraction is varied between 0 and 20% of the gas turbine’s compressor inlet mass flow rate, was also examined.
Development of a Dual Fuel LBTU Gas/Diesel Burning Combustion System for a 4.2 MW Gas Turbine
Authors: Al-Shaikhly A. F. , Mina T. I. , Neergaard M. O.
Published: February 2015

This paper describes the design and development of a gas turbine combustion system (combustion chamber and dual fuel injector) that is capable of burning a gasifier generated low heating value (LBTU) gas as well as a conventional gas turbine (diesel) fuel. The system will be installed in a 4.2 MW gas turbine and forms part of a 15 MW integrated gasification combined cycle heat and power generation technology demonstrator plant in Sweden. The combustion system design features a conventional combustor air distribution and aerodynamic pattern, discrete coaxial jets air blast liquid fuel atomisation and a combination of swirl and plain orifice LBTU gas fuel injection with a passive air purge arrangement. Rig tests were carried out at operating pressures of up to 7 bar simulating various engine operating points using LBTU gas and diesel fuel. The results showed that the emissions, exhaust temperature distribution and combustor metal temperature were in line with the program objectives. The lean flame stability margin using LBTU gas was more than adequate in relation to load change and fuel changeover requirements.
An Alternative Thermal Spray Process to Plasma Spray in the Aircraft and Stationary Gas Turbine Industry
Authors: Zwetsloot Menno P. , Sampson Elliott R.
Published: February 2015

Technological advances in arc spray have produced an arc spray system that competes very favorably with other thermal spray processes. In the past arc spray was thought of as a process for very large parts that need thick buildups. However, an attachment device has been developed which focuses the pattern and accelerates the particles and is known as the Arc Jet system. The advantages of this device were discussed by Zwetloot, Sampson and Thorpe (1993), Reference 4.

This attachment device coupled with the introduction of metal cored wires that provide the same chemistries as plasma sprayed powders, provides application engineers with a viable economic alternative to existing spray methods.

A comparative evaluation of a standard production plasma spray system was conducted with the arc spray process utilizing the device mentioned above. This evaluation was conducted by an airline company on four major parts coated with nickel aluminum and results show that, for those applications, the arc spray process demonstrated significant benefit. It is expected that other applications may benefit from the use of the arc spray process as well.
Unsteady Endwall/Tip-Clearance Flows and Losses due to Turbine Rotor-Stator Interaction
Authors: Yamamoto Atsumasa , Matsunuma Takayuki , Ikeuchi Kenichiro , Outa Eisuke
Published: February 2015

Unsteady static pressure on the tip endwall of a 1.5-stage low-speed axial-flow turbine was measured in detail using a micro high-response pressure transducer to investigate effects of rotor-stator interaction on the endwall and tip-clearance flows which play important roles in turbine loss generation process. In the present paper, distributions of the time-averaged and the time-dependent pressures over the rust-stage rotor and the second-stage stator are presented. Also time-averaged and time-dependent random fluctuations of the pressure were analyzed to understand unsteady behaviors of the flows and the associated losses over the endwall as well as inside the blade tip clearance. These unsteady characteristics were described for three rotor speeds with different incidences or loadings. Significantly large random fluctuations occur around the blade surfaces, particularly at the inlet and the outlet of the tip gap of the leakage flows, and in a flow separated region from the blade leading edge in a large negative incidence case A strong relation was found between the random fluctuation of the endwall static pressure and the total pressure loss inside the rotor, where large random fluctuation is attributed to high loss and vice versa. It can be seen clearly that the loss generation process is fairly unsteady due to the rotor-stator interaction.
Design Point Simulation of Multispool Industrial Compressor Trains
Authors: Blendulf Lars J. , Smith Graham D.
Published: February 2015

Software commonly used to predict Aeroengine performance has been adapted for the design point simulation of two large industrial compressor sets. A NOx gas compressor and an air compressor on a common shaft driven by a steam turbine and a tail gas turbine are modelled accurately after the inclusion of both exothermic and endothermic reactions in the NOx gas compressor. Experiment and theory agree to within 1.5%.

Results for the simulation of a three spool Ammonia Synthesis compressor with a deliver pressure of 207 bar agree to within 1% of experimental data. Since complex gas mixtures were used, Mollier diagrams or Compressibility factor techniques were not used and, instead, Departure Function theory was adopted to accommodate the real gas behaviour found at the high pressure.
Current and Future Materials in Advanced Gas Turbine Engines
Authors: Kool G. A.
Published: February 2015

Gas turbine engines are constructed of components with excellent strength and stiffness, a minimum density, a high temperature capability for long times, and at affordable cost. Metallic materials are the centrepiece in fulfilling these requirements. Future gas turbine engines will have to have higher thrust-to-weight ratios, better fuel efficiencies and still lower costs. This will require new and advanced lightweight materials with higher temperature capabilities.

This paper discusses some of the presently applied materials in the fan, compressor and turbine sections of gas turbines, and reviews the material developments that are occurring and will be necessary for the near and long term futures.
Current Status of 300 kW Class Industrial Ceramic Gas Turbine R&D in Japan
Authors: Murayama Takuki , Nagata Kunihiro , Taki Masanobu , Ogiyama Hisao
Published: February 2015

Advanced technologies in Ceramics Gas Turbine (CGT) are expected to make a great progress in energy conservation, anti-pollution, and fuel-diversification.

In Japan, R&D’s in industrial usage 300 kW class CGT have been advanced under a national project entitled “New Sunshine Program”, under the subsidy of Agency of Industrial Science and Technology (AIST), Ministry of International Trade and Industry (MITI) through the period of FY1988–1996.

In this project, three different type prototypes of the CGT are under development through New Energy and Industrial Technology Development Organization (NEDO).

Over the last six years, the basic designs have been completed and the ceramic elements such as turbine rotors, scrolls, and combustors were successfully fabricated. To check up the whole progress of the project, an interim evaluation is scheduled by the end of FY1993.

Toward this evaluation, each prototype has been programmed to demonstrate 1200°C of Turbine Inlet Temperature (TIT) and prove more than 30% of thermal efficiency. (The ultimate target in the project is 42% of thermal efficiency at 1350°C TIT.) They would also show enough environmental adaptability.

In this paper, overall status of the development in the 300kW CGT project is reviewed and the items in the interim evaluation are explained.
Ceramic Gas Turbine Technology Development
Authors: Easley M. L. , Smyth J. R.
Published: February 2015

AlliedSignal Engines is addressing critical concerns slowing the commercialization of structural ceramics in gas turbine engines. These issues include ceramic component reliability, commitment of ceramic suppliers to support production needs, and refinement of ceramic design technologies.

The stated goals of the current program are to develop and demonstrate structural ceramic technology that has the potential for extended operation in a gas turbine environment by incorporation in an auxiliary power unit (APU) to support automotive gas turbine development. AlliedSignal Engines changed the ATTAP ceramic engine test bed from the AGT101 automotive engine to the 331-200[CT] APU. The 331-200[CT] first-stage turbine nozzle segments and blades were redesigned using ceramic materials, employing design methods developed during the earlier DOE/NASA-funded Advanced Gas Turbine (AGT) and the ATTAP programs.

The ceramic design technologies under development in the present program include design methods for improved resistance to impact and contact damage, assessment of the effects of oxidation and corrosion on ceramic component life, and assessment of the effectiveness of nondestructive evaluation (NDE) and proof testing methods to reliably identify ceramic parts having critical flaws. AlliedSignal made progress in these activities during 1993 ATTAP efforts.

Ceramic parts for the 331-200[CT] engine have been fabricated and evaluated in component tests, to verify the design characteristics and assure structural integrity prior to full-up engine testing. Engine testing is currently underway.

The work summarized in this paper was funded by the U.S. Dept. of Energy (DOE) Office of Transportation Technologies and administered by NASA-Lewis Research Center, under Contract No. DEN3-335.
Non-Random Adaptive Grid Method for High Speed Optimization of Highly Dimensional Badly Behaving Real Time Functions
Authors: Shahroudi Kamran Eftekhari
Published: February 2015

The majority of optimization methods lose their applicability when solving Highly Dimensional Functions. The required calculation effort usually becomes enormous as dimensions increase, regardless of the elegance of the method. Most methods concern themselves with finding a single optimum which satisfies the required Accuracy, but which provide no quantitative measure (i.e. Probability of correctness) indicating whether the true optimum is found). Furthermore, there is usually no exact measure of the Calculation Effonprior to starting the procedure.

There is always an unavoidable coupling (i.e. relation) between the Accuracy, Probability and Calculation Effort of an optimization method but the exact form of this relation is dependant on the procedures followed to reach optimum. Ideally, an optimization method should facilitate the statement of required accuracy, required probability and the required calculation effort separately and the method should take care of the rest (i.e. total decoupling of the three requirements). Although this ideal case is generally not possible, it is possible to move towards it by finding procedures that reduce the strength of this unwanted coupling.

This report derives simple analytical relations between the required accuracy, probability and calculation effort of a general multidimensional adaptive grid Non-Gradient Guided (NGG) search method where the search points are generated either decisively or randomly. It is then shown that any adaptive method based on reducing the total solution space is heavily penalized. Further, it is analytically illustrated that if the adaptive grid is randomly generated, it is far less successful than the non random adaptive grid, because the amount of grid adaptation is less decisive at every step., due to the randomness.

As with many optimization techniques, the Dimensionality Problem limits the application of this method to cases where the function evaluation is real time (∼ milliseconds) and dimensions are lower than say 25, which occurs in Conceptual/Preliminary Design systems such as CAGEDR [Shahroudi, K.E. (Ref. 4)].
Verification and compensation of respiratory motion using an ultrasound imaging system
Authors: Chuang Ho‐Chiao , Hsu Hsiao‐Yu , Chiu Wei‐Hung , Tien Der‐Chi , Wu Ren‐Hong , Hsu Chung‐Hsien
Published: February 2015

Purpose:

The purpose of this study was to determine if it is feasible to use ultrasound imaging as an aid for moving the treatment couch during diagnosis and treatment procedures associated with radiation therapy, in order to offset organ displacement caused by respiratory motion. A noninvasive ultrasound system was used to replace the C‐arm device during diagnosis and treatment with the aims of reducing the x‐ray radiation dose on the human body while simultaneously being able to monitor organ displacements.

Methods:

This study used a proposed respiratory compensating system combined with an ultrasound imaging system to monitor the compensation effect of respiratory motion. The accuracy of the compensation effect was verified by fluoroscopy, which means that fluoroscopy could be replaced so as to reduce unnecessary radiation dose on patients. A respiratory simulation system was used to simulate the respiratory motion of the human abdomen and a strain gauge (respiratory signal acquisition device) was used to capture the simulated respiratory signals. The target displacements could be detected by an ultrasound probe and used as a reference for adjusting the gain value of the respiratory signal used by the respiratory compensating system. This ensured that the amplitude of the respiratory compensation signal was a faithful representation of the target displacement.

Results:

The results show that performing respiratory compensation with the assistance of the ultrasound images reduced the compensation error of the respiratory compensating system to 0.81–2.92 mm, both for sine‐wave input signals with amplitudes of 5, 10, and 15 mm, and human respiratory signals; this represented compensation of the respiratory motion by up to 92.48%. In addition, the respiratory signals of 10 patients were captured in clinical trials, while their diaphragm displacements were observed simultaneously using ultrasound. Using the respiratory compensating system to offset, the diaphragm displacement resulted in compensation rates of 60%–84.4%.

Conclusions:

This study has shown that a respiratory compensating system combined with noninvasive ultrasound can provide real‐time compensation of the respiratory motion of patients.
Development of solid‐state avalanche amorphous selenium for medical imaging
Authors: Scheuermann James R. , Goldan Amir H. , Tousignant Olivier , Léveillé Sébastien , Zhao Wei
Published: February 2015

Purpose:

Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a‐Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array.

Methods:

The HARP structure is fabricated on a glass substrate in the form of p‐i‐n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a‐Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area.

Results:

An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n‐i‐p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study.

Conclusions:

We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x‐ray photon per pixel.
Fast, automatic, and accurate catheter reconstruction in HDR brachytherapy using an electromagnetic 3D tracking system
Authors: Poulin Eric , Racine Emmanuel , Binnekamp Dirk , Beaulieu Luc
Published: February 2015

Purpose:

In high dose rate brachytherapy (HDR‐B), current catheter reconstruction protocols are relatively slow and error prone. The purpose of this technical note is to evaluate the accuracy and the robustness of an electromagnetic (EM) tracking system for automated and real‐time catheter reconstruction.

Methods:

For this preclinical study, a total of ten catheters were inserted in gelatin phantoms with different trajectories. Catheters were reconstructed using a 18G biopsy needle, used as an EM stylet and equipped with a miniaturized sensor, and the second generation Aurora® Planar Field Generator from Northern Digital Inc. The Aurora EM system provides position and orientation value with precisions of 0.7 mm and 0.2°, respectively. Phantoms were also scanned using a μCT (GE Healthcare) and Philips Big Bore clinical computed tomography (CT) system with a spatial resolution of 89 μm and 2 mm, respectively. Reconstructions using the EM stylet were compared to μCT and CT. To assess the robustness of the EM reconstruction, five catheters were reconstructed twice and compared.

Results:

Reconstruction time for one catheter was 10 s, leading to a total reconstruction time inferior to 3 min for a typical 17‐catheter implant. When compared to the μCT, the mean EM tip identification error was 0.69 ± 0.29 mm while the CT error was 1.08 ± 0.67 mm. The mean 3D distance error was found to be 0.66 ± 0.33 mm and 1.08 ± 0.72 mm for the EM and CT, respectively. EM 3D catheter trajectories were found to be more accurate. A maximum difference of less than 0.6 mm was found between successive EM reconstructions.

Conclusions:

The EM reconstruction was found to be more accurate and precise than the conventional methods used for catheter reconstruction in HDR‐B. This approach can be applied to any type of catheters and applicators.
Patient position alters attenuation effects in multipinhole cardiac SPECT
Authors: Timmins Rachel , Ruddy Terrence D. , Wells R. Glenn
Published: February 2015

Purpose:

Dedicated cardiac cameras offer improved sensitivity over conventional SPECT cameras. Sensitivity gains are obtained by large numbers of detectors and novel collimator arrangements such as an array of multiple pinholes that focus on the heart. Pinholes lead to variable amounts of attenuation as a source is moved within the camera field of view. This study evaluated the effects of this variable attenuation on myocardial SPECT images.

Methods:

Computer simulations were performed for a set of nine point sources distributed in the left ventricular wall (LV). Sources were placed at the location of the heart in both an anthropomorphic and a water‐cylinder computer phantom. Sources were translated in x, y, and z by up to 5 cm from the center. Projections were simulated with and without attenuation and the changes in attenuation were compared. A LV with an inferior wall defect was also simulated in both phantoms over the same range of positions. Real camera data were acquired on a Discovery NM530c camera (GE Healthcare, Haifa, Israel) for five min in list‐mode using an anthropomorphic phantom (DataSpectrum, Durham, NC) with 100 MBq of Tc‐99m in the LV. Images were taken over the same range of positions as the simulations and were compared based on the summed perfusion score (SPS), defect width, and apparent defect uptake for each position.

Results:

Point sources in the water phantom showed absolute changes in attenuation of ≤8% over the range of positions and relative changes of ≤5% compared to the apex. In the anthropomorphic computer simulations, absolute change increased to 20%. The changes in relative attenuation caused a change in SPS of <1.5 for the water phantom but up to 4.2 in the anthropomorphic phantom. Changes were larger for axial than for transverse translations. These results were supported by SPS changes of up to six seen in the physical anthropomorphic phantom for axial translations. Defect width was also seen to significantly increase. The position‐dependent changes were removed with attenuation correction.

Conclusions:

Translation of a source relative to a multipinhole camera caused only small changes in homogeneous phantoms with SPS changing <1.5. Inhomogeneous attenuating media cause much larger changes to occur when the source is translated. Changes in SPS of up to six were seen in an anthropomorphic phantom for axial translations. Attenuation correction removes the position‐dependent changes in attenuation.
Making the Most of Your First Day of Class
Authors: Gaffney Jon D. H. , Whitaker Jacob T.
Published: February 2015

Instructors of physics courses face the demanding challenge of creating a safe, nurturing community in their classroom while maintaining sufficient rigor. First-day activities are especially important, because they need to both motivate their students and prepare them for the course. Experienced instructors happily share their successful first-day activities,1,2 but what works for one instructor or class might not be as successful for another. We postulate that to be successful, an activity will set expectations, attend to the face needs of the students, and build the instructor's credibility. By modeling the course activities and fostering a supportive learning community, well-suited activities can both orient and motivate students.
Hybrid silencers with micro-perforated panels and internal partitions
Authors: Yu Xiang , Cheng Li , You Xiangyu
Published: February 2015

A sub-structuring approach, along with a unit cell treatment, is proposed to model expansion chamber silencers with internal partitions and micro-perforated panels (MPPs) in the absence of internal flow. The side-branch of the silencer is treated as a combination of unit cells connected in series. It is shown that, by connecting multiple unit cells with varying parameters, the noise attenuation bandwidth can be enlarged. With MPPs, the hybrid noise attenuation mechanism of the silencer is revealed. Depending on the size of the perforation hole, noise attenuation can be dominated by dissipative, reactive, or combined effects together. For a broadband sound absorption, the hole size, together with the perforation ratio and other parameters, can be optimized to strike a balance between the dissipative and reactive effect, for ultimately achieving the desired noise attenuation performance within a prescribed frequency region. The modular nature of the proposed formulation allows doing this in a flexible, accurate, and cost effective manner. The accuracy of the proposed approach is validated through comparisons with finite element method and experiments.
Perception of glottalization and phrase-final creak
Authors: Garellek Marc
Published: February 2015

American English has several linguistic sources of creaky voice. Two common sources are /t/-glottalization (where /t/ is produced as a glottal stop and/or with creaky voice, as in “button”) and phrase-final creak. Both /t/-glottalization and phrase-final creak have similar acoustic properties, but they can co-occur in English. The goal of this study is to determine whether /t/-glottalization and phrase-final creak are perceived distinctly. Sixteen English listeners were asked to identify words in a two-alternative forced choice task. The auditory targets were (near-) minimal pairs, in which one word could have /t/-glottalization (e.g., “button”) but the other could not (e.g., “bun”). Stimuli were presented with and without phrase-final creak. Listeners made few identification errors overall, even when /t/-glottalization co-occurred with phrase-final creak, suggesting that /t/-glottalization and phrase-final creak remain perceptually distinct to English listeners. This supports the view that creaky voice is not a single category, but one comprised of distinct voice qualities.
Tuning of vocal tract model parameters for nasals using sensitivity functions
Authors: Kreuzer W. , Kasess C. H.
Published: February 2015

Determining the cross-sectional areas of the vocal tract models from the linear predictive coding or autoregressive-moving-average analysis of speech signals from vowels has been of research interest for several decades now. To tune the shape of the vocal tract to given sets of formant frequencies, iterative methods using sensitivity functions have been developed. In this paper, the idea of sensitivity functions is expanded to a three-tube model used in connection with nasals, and the energy-based sensitivity function is compared with a Jacobian-based sensitivity function for the branched-tube model. It is shown that the difference between both functions is negligible if the sensitivity is taken with respect to the formant frequency only. Results for an iterative tuning a three-tube vocal tract model based on the sensitivity functions for a nasal (/m/) are given. It is shown that besides the polar angle, the absolute value of the poles and zeros of the rational transfer function also needs to be considered in the tuning process. To test the effectiveness of the iterative solver, the steepest descent method is compared with the Gauss–Newton method. It is shown, that the Gauss–Newton method converges faster if a good starting value for the iteration is given.
Spectro-temporal modulation masking patterns reveal frequency selectivity
Authors: Oetjen Arne , Verhey Jesko L.
Published: February 2015

The present study investigated the possibility that the human auditory system demonstrates frequency selectivity to spectro-temporal amplitude modulations. Threshold modulation depth for detecting sinusoidal spectro-temporal modulations was measured using a generalized masked threshold pattern paradigm with narrowband masker modulations. Four target spectro-temporal modulations were examined, differing in their temporal and spectral modulation frequencies: a temporal modulation of −8, 8, or 16 Hz combined with a spectral modulation of 1 cycle/octave and a temporal modulation of 4 Hz combined with a spectral modulation of 0.5 cycles/octave. The temporal center frequencies of the masker modulation ranged from 0.25 to 4 times the target temporal modulation. The spectral masker-modulation center-frequencies were 0, 0.5, 1, 1.5, and 2 times the target spectral modulation. For all target modulations, the pattern of average thresholds for the eight normal-hearing listeners was consistent with the hypothesis of a spectro-temporal modulation filter. Such a pattern of modulation-frequency sensitivity was predicted on the basis of psychoacoustical data for purely temporal amplitude modulations and purely spectral amplitude modulations. An analysis of separability indicates that, for the present data set, selectivity in the spectro-temporal modulation domain can be described by a combination of a purely spectral and a purely temporal modulation filter function.
Acoustic contrast control in an arc-shaped area using a linear loudspeaker array
Authors: Zhao Sipei , Qiu Xiaojun , Burnett Ian
Published: February 2015

This paper proposes a method of creating acoustic contrast control in an arc-shaped area using a linear loudspeaker array. The boundary of the arc-shaped area is treated as the envelope of the tangent lines that can be formed by manipulating the phase profile of the loudspeakers in the array. When compared with the existing acoustic contrast control method, the proposed method is able to generate sound field inside an arc-shaped area and achieve a trade-off between acoustic uniformity and acoustic contrast. The acoustic contrast created by the proposed method increases while the acoustic uniformity decreases with frequency.
Duration of voicing and silence periods of continuous speech in different acoustic environments
Authors: Astolfi Arianna , Carullo Alessio , Pavese Lorenzo , Puglisi Giuseppina Emma
Published: February 2015

This work deals with the duration of voicing and silence periods of continuous speech in rooms with very different reverberation times (RTs). Measurements were conducted using the Ambulatory Phonation Monitoring (APM) 3200 (Kaypentax, Montvale, NJ) and Voice-Care devices (developed at the Politecnico di Torino, Italy), both of which have a contact microphone placed on the base of the neck to detect skin vibrations during phonation. Six university professors and 22 university students made short laboratory monologs in which they explained something that they knew well to a listener 6 m away. Seven students also described a map with the intention of correctly explaining directions to a listener who drew the path on a blank chart. Longer speech samples were made by 25 primary school teachers in classrooms. A tendency to increase the voicing periods as the RT increased was on average observed for the university professors, the school teachers, and the university students who described a map. These students also showed longer silence periods than the students who made short monologs. The recognized trends concerned voice professionals or subjects who were highly motivated to make themselves understood in a perturbed speaking situation. Nonparametric statistical tests, which were applied to detect the differences in distributions of voicing and silence periods, have basically supported the findings.
Subjective ranking of concert halls substantiated through orthogonal objective parameters
Authors: Cerdá Salvador , Giménez Alicia , Cibrián Rosa , Girón Sara , Zamarreño Teófilo
Published: February 2015

This paper studies the global subjective assessment, obtained from mean values of the results of surveys addressed to members of the audience of live concerts in Spanish auditoriums, through the mean values of the three orthogonal objective parameters (Tmid, IACCE3, and LEV), expressed in just noticeable differences (JNDs), regarding the best-valued hall. Results show that a linear combination of the relative variations of orthogonal parameters can largely explain the overall perceived quality of the sample. However, the mean values of certain orthogonal parameters are not representative, which shows that an alternative approach to the problem is necessary. Various possibilities are proposed.
Diffraction by a right-angled impedance wedge: An edge source formulation
Authors: Hewett David P. , Morris Aaron
Published: February 2015

This paper concerns the frequency domain problem of diffraction of a plane wave incident on an infinite right-angled wedge on which impedance (absorbing) boundary conditions are imposed. It is demonstrated that the exact Sommerfeld-Malyuzhinets contour integral solution for the diffracted field can be transformed to a line integral over a physical variable along the diffracting edge. This integral can be interpreted as a superposition of secondary point sources (with directivity) positioned along the edge, in the spirit of the edge source formulations for rigid (sound-hard) wedges derived by Svensson et al. [Acta Acust. Acust. 95, 568–572 (2009)]. However, when surface waves are present the physical interpretation of the edge source integral must be altered: it no longer represents solely the diffracted field, but rather it includes surface wave contributions.
The effects of delayed auditory and visual feedback on speech production
Authors: Chesters Jennifer , Baghai-Ravary Ladan , Möttönen Riikka
Published: February 2015

Monitoring the sensory consequences of articulatory movements supports speaking. For example, delaying auditory feedback of a speaker's voice disrupts speech production. Also, there is evidence that this disruption may be decreased by immediate visual feedback, i.e., seeing one's own articulatory movements. It is, however, unknown whether delayed visual feedback affects speech production in fluent speakers. Here, the effects of delayed auditory and visual feedback on speech fluency (i.e., speech rate and errors), vocal control (i.e., intensity and pitch), and speech rhythm were investigated. Participants received delayed (by 200 ms) or immediate auditory feedback, while repeating sentences. Moreover, they received either no visual feedback, immediate visual feedback, or delayed visual feedback (by 200, 400, and 600 ms). Delayed auditory feedback affected fluency, vocal control, and rhythm. Immediate visual feedback had no effect on any of the speech measures when it was combined with delayed auditory feedback. Delayed visual feedback did, however, affect speech fluency when it was combined with delayed auditory feedback. In sum, the findings show that delayed auditory feedback disrupts fluency, vocal control, and rhythm and that delayed visual feedback can strengthen the disruptive effect of delayed auditory feedback on fluency.
On time delay estimation from a sparse linear prediction perspective
Authors: He Hongsen , Yang Tao , Chen Jingdong
Published: February 2015

This paper proposes a sparse linear prediction based algorithm to estimate time difference of arrival. This algorithm unifies the cross correlation method without prewhitening and that with prewhitening via an ℓ2/ℓ1 optimization process, which is solved by an augmented Lagrangian alternating direction method. It also forms a set of time delay estimators that make a tradeoff between prewhitening and non-prewhitening through adjusting a regularization parameter. The effectiveness of the proposed algorithm is demonstrated in noisy and reverberant environments.
Effects of age and hearing loss on the intelligibility of interrupted speech
Authors: Shafiro Valeriy , Sheft Stanley , Risley Robert , Gygi Brian
Published: February 2015

How age and hearing loss affect the perception of interrupted speech may vary based on both the physical properties of preserved or obliterated speech fragments and individual listener characteristics. To investigate perceptual processes and interruption parameters influencing intelligibility across interruption rates, participants of different age and hearing status heard sentences interrupted by silence at either a single primary rate (0.5–8 Hz; 25%, 50%, 75% duty cycle) or at an additional concurrent secondary rate (24 Hz; 50% duty cycle). Although age and hearing loss significantly affected intelligibility, the ability to integrate sub-phonemic speech fragments produced by the fast secondary rate was similar in all listener groups. Age and hearing loss interacted with rate with smallest group differences observed at the lowest and highest interruption rates of 0.5 and 24 Hz. Furthermore, intelligibility of dual-rate gated sentences was higher than single-rate gated sentences with the same proportion of retained speech. Correlations of intelligibility of interrupted speech to pure-tone thresholds, age, or measures of working memory and auditory spectro-temporal pattern discrimination were generally low-to-moderate and mostly nonsignificant. These findings demonstrate rate-dependent effects of age and hearing loss on the perception of interrupted speech, suggesting complex interactions of perceptual processes across different time scales.
On the spatial distribution of the reflection sources of different latency components of otoacoustic emissions
Authors: Sisto Renata , Moleti Arturo , Shera Christopher A.
Published: February 2015

The experimental observation of long- and short-latency components in both stimulus-frequency and transient-evoked otoacoustic emissions admits a comprehensive explanation within the coherent reflection mechanism, in a linear active transmission-line cochlear model. A local complex reflectivity function associated with roughness was defined and analyzed by varying the tuning factor of the model, systematically showing, for each frequency, a multiple-peak spatial structure, compatible with the observed multiple-latency structure of otoacoustic emissions. Although this spatial pattern and the peak relative intensity changes with the chosen random roughness function, the multiple-peak structure is a reproducible feature of different “digital ears,” in good agreement with experimental data. If one computes the predicted transmission delays as a function of frequency and position for each source, one gets a good match to the latency-frequency patterns that are directly computed from synthesized otoacoustic spectra using time-frequency analysis. This result clarifies the role of the spatial distribution of the otoacoustic emission sources, further supporting the interpretation of different-latency otoacoustic components as due to reflection sources localized at different places along the basilar membrane.
Auditory, visual, and auditory-visual processing performance in typically developing children: Modality independence versus dependence
Authors: Pillai Roshni , Yathiraj Asha
Published: February 2015

The study was carried out to determine whether cross-modal interactions occur during processing of auditory and/or visual signals that require separation/closure, integration, and duration pattern perception in typically developing children. Thirty typically developing children were evaluated on three auditory processing tests (speech-in-noise test in Indian-English, dichotic-consonant vowel test, and duration pattern test) that tapped separation/closure, integration and duration pattern perception. The children were also evaluated on the visual and auditory-visual analogues of the auditory tests. Differences in modality were found in each of the processes that were tested. The performance when the auditory and visual modalities were tested simultaneously was significantly higher than the auditory or visual modality for tests that involved separation/closure and integration. In contrast, scores on the analogous auditory-visual duration pattern test were significantly higher than the auditory test but not the visual analogous test. Further, the scores of the auditory modality were significantly poorer than the visual modality for separation/closure and duration patterning but not for integration. Findings of the study indicate that performance on higher level processing varies depending on the modality that is assessed and supports the presence of cross-modality interactions.
A hybrid finite element–transfer matrix model for vibroacoustic systems with flat and homogeneous acoustic treatments
Authors: Alimonti Luca , Atalla Noureddine , Berry Alain , Sgard Franck
Published: February 2015

Practical vibroacoustic systems involve passive acoustic treatments consisting of highly dissipative media such as poroelastic materials. The numerical modeling of such systems at low to mid frequencies typically relies on substructuring methodologies based on finite element models. Namely, the master subsystems (i.e., structural and acoustic domains) are described by a finite set of uncoupled modes, whereas condensation procedures are typically preferred for the acoustic treatments. However, although accurate, such methodology is computationally expensive when real life applications are considered. A potential reduction of the computational burden could be obtained by approximating the effect of the acoustic treatment on the master subsystems without introducing physical degrees of freedom. To do that, the treatment has to be assumed homogeneous, flat, and of infinite lateral extent. Under these hypotheses, simple analytical tools like the transfer matrix method can be employed. In this paper, a hybrid finite element–transfer matrix methodology is proposed. The impact of the limiting assumptions inherent within the analytical framework are assessed for the case of plate-cavity systems involving flat and homogeneous acoustic treatments. The results prove that the hybrid model can capture the qualitative behavior of the vibroacoustic system while reducing the computational effort.
Placental Transfer of Rilpivirine in an
Ex Vivo
Human Cotyledon Perfusion Model
Authors: Mandelbrot Laurent , Duro Dominique , Belissa Emilie , Peytavin Gilles
Published: February 2015

Placental transfers of the HIV nonnucleoside reverse transcriptase inhibitor rilpivirine were investigated in 8 term human cotyledons perfused with rilpivirine (400 ng/ml) in the maternal-to-fetal direction. The mean fetal transfer rate (FTR) (fetal/maternal concentration at steady state from 15 to 90 min) was 26% ± 8% (mean ± standard deviation), and the clearance index (rilpivirine FTR/antipyrine FTR) was 61% ± 20%. This shows that rilpivirine crosses the placenta at a relatively high rate, suggesting that the fetus is exposed to the compound during treatment of the mother.