bluuebunny/crossref_metadata_2025 huggingface dataset:
Fiber Optic Sensors for In Situ Real-Time Monitoring PEM Fuel Cell Operation
Authors: Tao Shiquan , Fanguy Joseph C. , Hu Xuemei , Yan Qiangu
Published: October 2008

Fiber optic sensors for monitoring moisture, temperature and trace hydrogen peroxide have been developed in DIAL/MSU. The moisture sensor responds to moisture changes from RH = 4% to RH < 95% in the tested range. The temperature sensor can sense temperature from room temperature 22 °C to 90 °C in the tested range. The hydrogen peroxide sensor can detect/monitor hydrogen peroxide in an aqueous solution down to 10 ppb. Techniques have been developed for deploying the fiber optic sensors to the gas channels and the Nafion membrane of a PEM fuel, cell. These sensors will be tested for in situ, real-time monitoring of the operation of a PEM fuel cell with a fuel cell test system developed by CAVS/MSU. The principle of the sensors and test results of the sensors will be presented.
Visualization Study of Cathode Flooding With Different Operating Conditions in a PEM Unit Fuel Cell
Authors: Kim Han-Sang , Ha Tae-Hun , Park Sung-Jin , Min Kyoungdoug , Kim Minsoo
Published: October 2008

Visualization technique was used to better understand the water build-up phenomena on the cathode side of a proton exchange membrane (PEM) unit fuel cell. In this study, a transparent PEM unit fuel cell with an active area of 25 cm2 was designed and fabricated to allow for the visualization of cathode channel with fuel cell performance characteristics. Two-phase flow due to the electrochemical reaction of fuel cell was experimentally investigated. The images photographed by CCD camera with various cell temperatures (30–50°C) and different inlet humidification levels were presented in this study. Results indicated that the flooding on the cathode side first occurs near the exit of cathode flow channel. As the fuel cell operating temperature increases, it was found that water droplets tend to evaporate easily because of increased saturation vapor pressure and it can have an influence on lowering the flooding level. The approaches of this study can effectively contribute to the detailed researches on water transport phenomena including modeling water transport of an operating PEM fuel cell.
Performance of Anode-Supported SOFC Cells Using Thin Electrolyte of Scandia-Doped Zirconia at Intermediate Temperatures
Authors: Yoo Young-Sung , Park Jae Keun , Yang Soo-Yong , Oh Je-Myung , Bae Joongmyeon
Published: October 2008

Our recent study on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused on higher performance of single cell at lower operating temperature. We have started the project to develop a 1 kW-class SOFC system for Residential Power Generation (RPG) application. For a 1 kW-class SOFC stack that can be operated at intermediate temperatures, we have developed anode-supported, planar type SOFC to have advantages for commercialization of SOFCs considering mass production and using cost-effective interconnects such as ferritic stainless steels. Single cells with thin electrolyte layer of YSZ and ScSZ, respectively, were fabricated by slurry coating and their performances were investigated. Mixtures of NiO and 8YSZ powders were pressed into rectangular plates of about 13 × 13 cm2, which were presintered at 1400°C for 1h. Then the 8YSZ (8mol% Y2O3 + ZrO2) or 10ScSZ (10mol% Sc2O3+1mol%CeO2+ZrO2) electrolytes dispersed in distilled water were coated on the upper side of anode substrate and co-fired at 1550 or 1500°C for 1h. Thereafter cathode pastes of La0.78Sr0.22MnO3 or (La0.6Sr0.4)(Co1-xFex)O3 were screen-printed on thin electrolytes and heat-treated at 1100°C for 2 h. The size of anode-supported single cells finally sintered was about 10 × 10 cm2, and the thickness of the electrolyte and the cathode layer was about 20μm and 30μm respectively. The I-V and AC impedance characteristics of these single cells were evaluated at intermediate temperature (650 ∼ 800°C) by using hydrogen gas as a fuel. The maximum power density of anode-supported cells was 0.5 ∼ 2.0 W/cm2 at 750°C and 0.18 ∼ 0.75 W/cm2 at 650°C depending on the composition and microstructure of electrolyte/electrodes.
Power Converter and Control Interface for a GEM Fuel Cell Vehicle
Authors: Anzicek Joshua , Thompson Mark
Published: October 2008

In this paper, we discuss the design and performance of a low cost, fully integrated power conversion and control system for a modified Global Electric Motors (GEM) fuel cell hybrid vehicle. The need for a custom converter and control system has become apparent as the commercial DC-DC market seems to have a void in the ranges of power and voltage required for fuel cell vehicle applications. The system incorporates a custom designed DC-DC boost converter which steps up the nominal 26 VDC fuel cell stack voltage to interface with the 72 VDC vehicle battery bus at an input power level of 1.2 kW. Additionally, several embedded control functions are implemented to integrate a Ballard Nexa™ fuel cell power module into the GEM vehicle. Design equations supported by preliminary performance data indicates that the DC-DC power converter achieves a conversion efficiency approaching 98% for a single fuel cell power module operating at full output power (1.2kW). The high efficiency allows for a simple and flexible air-cooled design with minimal heat sink requirements and cooling system weight. The control system incorporates algorithms to perform battery charging and power ramp rate, as well as fuel cell voltage, and current limiting algorithms. The control system exhibits stable performance characteristics throughout the entire vehicle load range and battery state of charge range, while tracking vehicle transient conditions.
Fuel Cell System Reliability for a Pressurised Integrated-Planar SOFC
Authors: Travis R. P. , Hart J. , Costamagna P. , Agnew G. D. , Attia O.
Published: October 2008

A ceramic supported SOFC for operation at 950°C is being developed by Rolls Royce Fuel Cell Systems (RRFCS). In parallel with the evolving design of the fuel cell system, it is necessary to ensure reliability not only of the electrochemical cell, but also the main structure under both manufacture and operational constraints. With a ceramic based system for use at high temperature this presents particular challenges, and to address these, RRFCS is in partnership with leading academic institutions including Imperial College London and the University of Genoa supported by the European Union. This paper will identify potential areas of concern for reliability and integrity of the fuel cell system, and will indicate the work that is being undertaken to ensure reliability, including thermomechanical stresses arising from fluid flow, electrochemical reactions and operational temperature distributions; joining of components; assessment of the stresses within ceramic structures, manufacture tolerances of dimensions and material properties.
Investigation of Flooding Phenomena in PEMFC by Two-Phase Flow Numerical Simulation
Authors: Ito Kohei , Masuda Hiromitsu , Miyazaki Tomohiko , Kakimoto Yasushi , Masuoka Takashi
Published: October 2008

Water Problem, which is represented by the flooding and the drying in PEMFC, is one of the critical issues relating to the recent trend of high current density operation of it. For spreading the practical use of PEMFC, we must grasp this problem exactly and resolve it. Two-phase flow numerical simulation is useful for this purpose. In this study, we numerically analyzed a unit-PEMFC two-dimensionally considering the two-phase flow based on the multiphase mixture model developed by Cheng and Wang, adding the authors’ equivalent electric circuit. We simulated not only steady state but also unsteady state. A slightly abrupt change in current density distribution appeared on the point where the interface between the one- and the two-phase zone in GDL was appeared. The distribution of water saturation after cell operation start changed with time passed: the liquid water tend to focus on the GDL after once it spread in both GDL and flow channel.
Characterisation and Optimisation of Low Cost Activated Carbon Fabric as a Substrate Layer for PEMFC Electrodes
Authors: Rajalakshmi N. , Velayutham G. , Ramya K. , Subramaniyam C. K. , Dhathathreyan K. S.
Published: October 2008

In proton exchange membrane fuel cells (PEMFC), gas diffusion layers (GDL) play a critical role of supplying the oxidant and the fuel to the cathode and anode besides facilitating transfer of the electrons generated to the current collectors. In the present paper, a new low cost activated carbon fabric of high porous nature has been investigated for its suitability as substrate layer in PEMFC electrodes alternative to the carbon paper. The critical parameters like permeability, porosity, fuel cell performance are compared with standard substrate layer after optimizing the electrode structure. Economic analysis for a 1 kW power system reveals that there exists a considerable cost reduction by about 50%, with reference to the substrate layer.
Finding the onset of a room impulse response: Straightforward?
Authors: Defrance Guillaume , Daudet Laurent , Polack Jean-Dominique
Published: October 2008

This letter deals with precision issues in the determination of the timing of the room impulse responses (RIRs) onset. First, it is shown that while errors of onset timing estimation do not have that much effect on temporal indices, an erroneous onset estimation leads to significant differences in energetic and statistic acoustical indices. Twelve automatic onset detection methods are compared, in terms of precision, robustness, and complexity. Experimental validation made on a set of 100 RIRs provides good evidence in favor of spectral and/or energetic methods, according to the type of sound source.
Dolphin-inspired combined maneuvering and pinging for short-distance echolocation
Authors: Forsythe Stephen E. , Leinhos Henry A. , Bandyopadhyay Promode R.
Published: October 2008

The biorobotic emulation of swimming and flying animals carrying out short-distance echolocation while maneuvering is considered. A simple and lightweight sonar for use on a small, maneuverable underwater vehicle for short-distance echolocation is explored. This sonar has four sensors and uses broadband, high-frequency signals to echolocate. The frequency-time characteristics of these signals are compared to those of bats and dolphins. The biosonar is paired with a biologically inspired, maneuverable, underwater vehicle, the combined use of sensors and maneuverability being analogous to animal behavior. Homing experiments have been carried out in an acoustic test facility where identification and localization of multiple targets is based on fusion of acoustic returns from multiple pings.
Effect of instrument timbre on melodic contour identification by cochlear implant users
Authors: Galvin John J. , Fu Qian-Jie , Oba Sandra
Published: October 2008

Because of interactions between the signal processing and acoustic input, cochlear implant (CI) users’ melodic pitch perception may be influenced by instrument timbre. In the present study, CI listeners’ melodic contour identification was measured for six instruments (organ, glockenspiel, trumpet, clarinet, violin, and piano). While performance was generally best with the organ and poorest with the piano, individual CI subjects exhibited different patterns of results across instruments. CI subjects with the most music experience were less susceptible to timbre effects, suggesting that music training may help less experienced CI users extract melodic pitch from a variety of sound sources.
Born iterative reconstruction using perturbed-phase field estimates
Authors: Astheimer Jeffrey P. , Waag Robert C.
Published: October 2008

A method of image reconstruction from scattering measurements for use in ultrasonic imaging is presented. The method employs distorted-wave Born iteration but does not require using a forward-problem solver or solving large systems of equations. These calculations are avoided by limiting intermediate estimates of medium variations to smooth functions in which the propagated fields can be approximated by phase perturbations derived from variations in a geometric path along rays. The reconstruction itself is formed by a modification of the filtered-backpropagation formula that includes correction terms to account for propagation through an estimated background. Numerical studies that validate the method for parameter ranges of interest in medical applications are presented. The efficiency of this method offers the possibility of real-time imaging from scattering measurements.
Horizontal structure of acoustic intensity fluctuations in the ocean
Authors: Uscinski B. J. , Nicholson J. R. S.
Published: October 2008

In April 1989 an acoustic experiment was carried out over the abyssal plain south of Madeira in which transmissions were made, for about an hour, at 482, 680, and 740Hz from a ship steaming at 5Kn to a receiving array towed by another ship 65km away traveling on a parallel course at the same speed. The signals arrived by two paths, an upper path trapped in the surface duct and a lower path via the main sound channel. This paper describes the experiment and analyses of the intensity fluctuations in the signal received by the lower path. This allows the authors to investigate the horizontal structure of acoustic intensity fluctuations in the ocean when these are due principally to internal waves. This aspect of such acoustic intensity fluctuations has received little attention until now. The experimental results are compared with theoretical predictions based on the parabolic moment equations for propagation and scattering in randomly irregular media, and on the standard Garrett–Munk model for ocean internal waves. The experimental results and theoretical predictions agree quite well but the comparison also raises some new questions, in particular, about the correlation of intensity fluctuations as the acoustic transmission frequency is varied.
Modeling sound propagation in acoustic waveguides using a hybrid numerical method
Authors: Kirby Ray
Published: October 2008

Sound propagation in an acoustic waveguide is examined using a hybrid numerical technique. Here, the waveguide is assumed to be infinite in length with an arbitrary but uniform cross section. Placed centrally within the guide is a short component section with an irregular nonuniform shape. The hybrid method utilizes a wave based modal solution for a uniform section of the guide and, using either a mode matching or point collocation approach, matches this to a standard finite element based solution for the component section. Thus, one needs only to generate a transverse finite element mesh in uniform sections of the waveguide and this significantly reduces the number of degrees of freedom required. Moreover, utilizing a wave based solution removes the need to numerically enforce a nonreflecting boundary condition at infinity using a necessarily finite mesh, which is often encountered in studies that use only the standard finite element method. Accordingly, the component transmission loss may readily be computed and predictions are presented here for three examples: an expansion chamber, a converging-diverging duct, and a circular cylinder. Good agreement with analytic models is observed, and transmission loss predictions are also presented for multimode incident and transmitted sound fields.
Hearing preservation surgery: Psychophysical estimates of cochlear damage in recipients of a short electrode array
Authors: Gifford René H. , Dorman Michael F. , Spahr Anthony J. , Bacon Sid P. , Skarzynski Henryk , Lorens Artur
Published: October 2008

In the newest implementation of cochlear implant surgery, electrode arrays of 10 or 20mm are inserted into the cochlea with the aim of preserving hearing in the region apical to the tip of the electrode array. In the current study two measures were used to assess hearing preservation: changes in audiometric threshold and changes in psychophysical estimates of nonlinear cochlear processing. Nonlinear cochlear processing was evaluated at signal frequencies of 250 and 500Hz using Schroeder phase maskers with various indices of masker phase curvature. A total of 15 normal-hearing listeners and 13 cochlear implant patients (7 with a 10mm insertion and 6 with a 20mm insertion) were tested. Following surgery the mean low-frequency threshold elevation was 12.7dB (125–750Hz). Nine patients had postimplant thresholds within 5–10dB of preimplant thresholds. Only one patient, however, demonstrated a completely normal nonlinear cochlear function following surgery—although most retained some degree of residual nonlinear processing. This result indicates (i) that Schroeder phase masking functions are a more sensitive index of surgical trauma than audiometric threshold and (ii) that preservation of a normal cochlear function in the apex of the cochlea is relatively uncommon but possible.
Verification of chaotic behavior in an experimental loudspeaker
Authors: Reiss Joshua D. , Djurek Ivan , Petosic Antonio , Djurek Danijel
Published: October 2008

The dynamics of an experimental electrodynamic loudspeaker is studied by using the tools of chaos theory and time series analysis. Delay time, embedding dimension, fractal dimension, and other empirical quantities are determined from experimental data. Particular attention is paid to issues of stationarity in a system in order to identify sources of uncertainty. Lyapunov exponents and fractal dimension are measured using several independent techniques. Results are compared in order to establish independent confirmation of low dimensional dynamics and a positive dominant Lyapunov exponent. We thus show that the loudspeaker may function as a chaotic system suitable for low dimensional modeling and the application of chaos control techniques.
Hybridizing conversational and clear speech to determine the degree of contribution of acoustic features to intelligibility
Authors: Kain Alexander , Amano-Kusumoto Akiko , Hosom John-Paul
Published: October 2008

Speakers naturally adopt a special “clear” (CLR) speaking style in order to be better understood by listeners who are moderately impaired in their ability to understand speech due to a hearing impairment, the presence of background noise, or both. In contrast, speech intended for nonimpaired listeners in quiet environments is referred to as “conversational” (CNV). Studies have shown that the intelligibility of CLR speech is usually higher than that of CNV speech in adverse circumstances. It is not known which individual acoustic features or combinations of features cause the higher intelligibility of CLR speech. The objective of this study is to determine the contribution of some acoustic features to intelligibility for a single speaker. The proposed method creates “hybrid” (HYB) speech stimuli that selectively combine acoustic features of one sentence spoken in the CNV and CLR styles. The intelligibility of these stimuli is then measured in perceptual tests, using 96 phonetically balanced sentences. Results for one speaker show significant sentence-level intelligibility improvements over CNV speech when replacing certain combinations of short-term spectra, phoneme identities, and phoneme durations of CNV speech with those from CLR speech, but no improvements for combinations involving fundamental frequency, energy, or nonspeech events (pauses).
Information theory analysis of Australian humpback whale song
Authors: Miksis-Olds Jennifer L. , Buck John R. , Noad Michael J. , Cato Douglas H. , Dale Stokes M.
Published: October 2008

Songs produced by migrating whales were recorded off the coast of Queensland, Australia, over six consecutive weeks in 2003. Forty-eight independent song sessions were analyzed using information theory techniques. The average length of the songs estimated by correlation analysis was approximately 100units, with song sessions lasting from 300 to over 3100units. Song entropy, a measure of structural constraints, was estimated using three different methodologies: (1) the independently identically distributed model, (2) a first-order Markov model, and (3) the nonparametric sliding window match length (SWML) method, as described by Suzuki et al. [(2006). “Information entropy of humpback whale song,” J. Acoust. Soc. Am. 119, 1849–1866]. The analysis finds that the song sequences of migrating Australian whales are consistent with the hierarchical structure proposed by Payne and McVay [(1971). “Songs of humpback whales,” Science 173, 587–597], and recently supported mathematically by Suzuki et al. (2006) for singers on the Hawaiian breeding grounds. Both the SWML entropy estimates and the song lengths for the Australian singers in 2003 were lower than that reported by Suzuki et al. (2006) for Hawaiian whales in 1976–1978; however, song redundancy did not differ between these two populations separated spatially and temporally. The average total information in the sequence of units in Australian song was approximately 35bits/song. Aberrant songs (8%) yielded entropies similar to the typical songs.
Effects of maturation on tympanometric wideband acoustic transfer functions in human infants
Authors: Sanford Chris A. , Feeney M. Patrick
Published: October 2008

Wideband acoustic transfer function (ATF) measurements of energy reflectance (ER) and admittance magnitude (∣Y∣) were obtained at varying static ear-canal pressures in 4-, 12-, and 27-week-old infants and young adults. Developmental changes in wideband ATF measurements varied as a function of frequency. For frequencies from 0.25to0.75kHz there was as much as a 30% change in mean ER and ∣Y∣ with changes in static ear-canal pressure between 4 and 24weeks of age. From 0.75to2kHz, the effects of pressure produced a small number of significant differences in ER and ∣Y∣ with age, suggestive of a developmentally stable frequency range. Between 2 and 6kHz, there were differential effects of pressure for the youngest infants; negative pressures caused increased ER and ∣Y∣ and positive pressures caused decreased ER and ∣Y∣; the magnitude of this effect decreased with age. Findings from this study demonstrate developmental differences in wideband tympanometric ATF measurements in 4-, 12- and 24-week-old infants and provide additional insight on the effects of static ear-canal pressure in the young infant’s ear. The maturational effects shown in the experimental data are discussed in light of known age-related anatomical changes in the developing outer and middle ear.
Multichannel array diagnosis using noise cross-correlation
Authors: Brooks Laura A. , Gerstoft Peter , Knobles David P.
Published: October 2008

A practical application of noise cross-correlation for the diagnosis of a multichannel ocean hydrophone array is derived. Acoustic data were recorded on a horizontal line array on the New Jersey Shelf while Tropical Storm Ernesto passed through. Results obtained from active source measurements reveal that signals from several hydrophones, which were recorded on certain channels before the storm, are recorded on different channels after the storm. Noise cross-correlation of data recorded during the storm show when, and in what manner, these changes took place.
Modeling of axisymmetric wave modes in a poroelastic cylinder using spectral method
Authors: Karpfinger Florian , Gurevich Boris , Bakulin Andrey
Published: October 2008

Algorithm and code are presented which solve the dispersion equation for cylindrical poroelastic structures. The algorithm is based on the spectral method, which discretizes the underlying wave equations with the help of spectral differentiation matrices and solves the corresponding equations as a generalized eigenvalue problem. The results are illustrated for the case of a fluid-saturated free cylinder with open- and closed-pore boundary conditions on its surface. The computed dispersion curves are in good agreement with analytical results, which confirms the accuracy of the method.
On sound propagation from a slanted side branch into an infinitely long rectangular duct
Authors: Tang S. K. , Lam G. C. Y.
Published: October 2008

The transmission of sound from a slanted side branch into an infinitely long rectangular duct is studied numerically using the method of finite element with absorptive domain exit boundaries. The sound transmission coefficients associated with various acoustic modes are investigated in details. The results show that the plane wave assumption is only valid at very low frequency. It is also found that the intensities of the higher modes are stronger than that of the plane wave once they are excited. Besides, a critical side-branch slant angle is found over which a significant change of sound propagation mode takes place. This affects substantially the energy distribution between various acoustic modes inside the main duct. A simplified model is proposed to explain the phenomenon and the relationship of this critical angle with the width ratio between the side branch and the main duct is established.
Benefit of high-rate envelope cues in vocoder processing: Effect of number of channels and spectral region
Authors: Stone Michael A. , Füllgrabe Christian , Moore Brian C. J.
Published: October 2008

In cochlear implants, or vocoder simulations of cochlear implants, the transmission of envelope cues at high rates (related to voice fundamental frequency, f0) may be limited by the widths of the filters used to form the channels and/or by the cutoff frequency, flp, of the low-pass filters used for envelope extraction. The effect of varying flp in tone and noise vocoders was investigated for channel numbers, N, from 6 to 18. As N increased, the widths of the channels decreased. The value of flp was 45Hz (envelope or “E” filter), or 180Hz (pitch or “P” filter). The following combinations of cutoff frequencies were used for channels below and above 1500Hz, respectively: EE, PE, EP, and PP. Results from a competing-talker task showed that the tone vocoder led to better intelligibility than the noise vocoder. The PP condition led to the best intelligibility and the EE condition to the worst. For N=6, intelligibility was better for condition PE than for condition EP. For N=18, the reverse was true. The results indicate that the channel bandwidths can compromise the transmission of f0-related envelope information, and suggest that vocoder simulations of cochlear-implant processing have limitations.
Self-learning active noise control
Authors: Yuan J.
Published: October 2008

An important step for active noise control (ANC) systems to be practical is to develop model independent ANC (MIANC) systems that tolerate parameter variations in sound fields. Reliabilities and stabilities of many MIANC systems depend on results of online system identifications. Parameter errors due to system identifications may threaten closed-loop stabilities of MIANC systems. A self-learning active noise control (SLANC) system is proposed in this study to stabilize and optimize an ANC system in case identified parameters are unreliable. The proposed system uses an objective function to check closed-loop stability. If partial or full value of the objective function exceeds a conservatively preset threshold, a stability threat is detected and the SLANC system will stabilize and optimize the controller without using parameters of sound fields. If the reference signal is available, the SLANC system can be combined with a feedforward controller to generate both destructive interference and active damping in sound fields. The self-learning method is simple and stable for many feedback ANC systems to deal with a worst case discussed in this study.
Disentangling the effects of spatial cues on selection and formation of auditory objects
Authors: Ihlefeld Antje , Shinn-Cunningham Barbara
Published: October 2008

When competing sources come from different directions, a desired target is easier to hear than when the sources are co-located. How much of this improvement is the result of spatial attention rather than improved perceptual segregation of the competing sources is not well understood. Here, listeners’ attention was directed to spatial or nonspatial cues when they listened for a target masked by a competing message. A preceding cue signaled the target timbre, location, or both timbre and location. Spatial separation improved performance when the cue indicated the target location, or both the location and timbre, but not when the cue only indicated the target timbre. However, response errors were influenced by spatial configuration in all conditions. Both attention and streaming contributed to spatial effects when listeners actively attended to location. In contrast, when attention was directed to a nonspatial cue, spatial separation primarily appeared to improve the streaming of auditory objects across time. Thus, when attention is focused on location, spatial separation appears to improve both object selection and object formation; when attention is directed to nonspatial cues, separation affects object formation. These results highlight the need to distinguish between these separate mechanisms when considering how observers cope with complex auditory scenes.
Estimation of the acoustic impedance of lung versus level of inflation for different species and ages of animals
Authors: Oelze Michael L. , Miller Rita J. , Blue James P. , Zachary James F. , O’Brien William D.
Published: October 2008

In a previous study, it was hypothesized that ultrasound-induced lung damage was related to the transfer of ultrasonic energy into the lungs (W. D. O’Brien et al. 2002, “Ultrasound-induced lung hemorrhage: Role of acoustic boundary conditions at the pleural surface,” J. Acoust. Soc. Am. 111, 1102–1109). From this study a technique was developed to: 1) estimate the impedance (Mrayl) of fresh, excised, ex vivo rat lung versus its level of inflation (cm H2O) and 2) predict the fraction of ultrasonic energy transmitted into the lung (M. Oelze et al. 2003, “Impedance measurements of ex vivo rat lung at different volumes of inflation.” J. Acoust. Soc. Am. 114, 3384–3393). In the current study, the same technique was used to estimate the frequency-dependent impedance of lungs from rats, rabbits, and pigs of various ages. Impedance values were estimated from lungs under deflation (atmospheric pressure, 0cm H2O) and three volumes of inflation pressure [7cm H2O (5cm H2O for pigs), 10cm H2O, and 15cm H2O]. Lungs were scanned in a tank of degassed 37°C water. The frequency-dependent acoustic pressure reflection coefficient was determined over a frequency range of 3.5–10MHz. From the reflection coefficient, the frequency-dependent lung impedance was calculated with values ranging from an average of 1.4Mrayl in deflated lungs (atmospheric pressure) to 0.1Mrayl for fully inflated lungs (15cm H2O). Across all species, deflated lung (i.e., approximately 7% of the total lung capacity) had impedance values closer to tissue values, suggesting that more acoustic energy was transmitted into the lung under deflated conditions. Finally, the impedance values of deflated lungs from different species at different ages were compared with the thresholds for ultrasound-induced lung damage. The comparison revealed that increases in ultrasonic energy transmission corresponded to lower injury threshold values.
Vibration of fluid loaded conical shells
Authors: Caresta Mauro , Kessissoglou Nicole J.
Published: October 2008

An analytical model is presented to describe the vibration of a truncated conical shell with fluid loading in the low frequency range. The solution for the dynamic response of the shell is presented in the form of a power series. Fluid loading is taken into account by dividing the shell into narrow strips which are considered to be locally cylindrical. Analytical results are presented for different boundary conditions and have been compared with the computational results from a boundary element model. Limitations of the model to the low frequency range are discussed.
The cultural eutrophication of Lac la Biche, Alberta, Canada: a paleoecological study
Authors: Schindler D. W. , Wolfe Alexander P. , Vinebrooke Rolf , Crowe Angela , Blais Jules M. , Miskimmin Brenda , Freed Rina , Perren Bianca
Published: October 2008

A multiproxy paleoecological investigation of Lac la Biche, a large boreal lake in northeastern Alberta, Canada, revealed that the lake was eutrophic before European settlement but has undergone additional cultural eutrophication in the past 30 to 50 years. Annual fluxes to sediments of phosphorus, nitrogen, carbon, and inorganic sediments have increased with time. A declining N–P ratio has increasingly favored nitrogen-fixing cyanobacteria. Increased deposition of microbial pigments and diatom frustules and a recent shift in diatom species also indicate increasing eutrophication. Biogenic silica increased with time, but there is no evidence of a near-surface decline that would indicate silica limitation. Stable isotopes suggest that an increasing proportion of carbon deposited in sediments is of in-lake origin, indicating increased productivity. In the basin nearest the town of Lac La Biche, an increase in δ15N followed the construction of the sewage treatment plant, but more recently, decreased δ15N in both basins suggests that nitrogen fixation has become a more important source of nitrogen. Despite documented damage to the fishery of the lake, zooplankton fossils do not show evidence of a strong trophic cascade. The study illustrates the power of a multiproxy approach in obtaining reliable paleolimnological conclusions.
Oxygen concentration in the water boundary layer next to rainbow trout (Oncorhynchus mykiss) embryos is influenced by hypoxia exposure time, metabolic rate, and water flow
Authors: Miller Silvana C. , Reeb Shannon E. , Wright Patricia A. , Gillis Todd E.
Published: October 2008

The objective of this study was to examine the influence of hypoxia exposure time, metabolic rate, and water flow rate on the O2concentration in the boundary layer outside and inside the chorion of rainbow trout ( Oncorhynchus mykiss ) embryos. Oxygen consumption, growth, and dissolved O2in the boundary layer were measured at 15, 22, and 29 days post fertilization (dpf) from embryos reared in normoxia (O2concentration at 100% saturation) and chronic hypoxia (>24 h, 50% saturation) and exposed to acute hypoxia (30 min, 50% saturation). Chronic and acute hypoxia exposure decreased the dissolved O2in the boundary layer to the same extent at 15 and 22 dpf; however, at 29 dpf, O2levels were significantly lower in acute relative to chronic hypoxia. At 29 dpf, O2uptake per individual was significantly lower in embryos exposed to chronic relative to acute hypoxia. In addition, mass-specific O2uptake in chronic hypoxia-exposed embryos was ~40% less than that of controls but the same as that of acutely exposed embryos. This correlates with reduced growth in embryos exposed to chronic hypoxia. We conclude that boundary layer O2is lower after 30 min of hypoxia compared with 2 weeks of hypoxia simply because embryos exposed to chronic hypoxia grow slower and consume less O2.
Spatial and temporal variation of maturation schedules of lake whitefish (Coregonus clupeaformis) in the Great Lakes
Authors: Wang Hui-Yu , Höök Tomas O. , Ebener Mark P. , Mohr Lloyd C. , Schneeberger Philip J.
Published: October 2008

Fish maturation schedules vary greatly among systems and over time, reflecting both plastic and adaptive responses to ecosystem structure, physical habitats, and mortality (natural and fishing). We examined maturation schedules of commercially exploited lake whitefish ( Coregonus clupeaformis ) in the Laurentian Great Lakes (Lakes Michigan, Huron, and Superior) by estimating ages and lengths at 50% maturity, age-specific maturity ogives (age-specific probability of being mature), and probabilistic maturation reaction norms (PMRNs; a metric that accounts for effects of growth and mortality). Collectively, these estimates indicated variation in maturation schedules between sexes (i.e., males tend to mature at younger ages and shorter lengths than females) and among systems (midpoint estimates of PMRNs were smallest for Lake Michigan fish, intermediate for fish in the main basin of Lake Huron, and largest for fish in Lake Huron’s Georgian Bay and Lake Superior). Temporally, recent increases in age at 50% maturity in Lakes Huron and Michigan may primarily reflect plastic responses to decreased growth rates associated with ecosystem changes (e.g., declines of the native amphipod, Diporeia spp.). As plastic and adaptive changes in maturation schedules of fish stocks may occur simultaneously and require different management considerations, we recommend the concomitant analysis of multiple maturation indices.
Marine survival of steelhead (Oncorhynchus mykiss) enhanced by a seasonally closed estuary
Authors: Bond Morgan H. , Hayes Sean A. , Hanson Chad V. , MacFarlane R. Bruce
Published: October 2008

To investigate the role that estuaries play in the survival of steelhead, Oncorhynchus mykiss , we compared juvenile size at ocean entry with back-calculated measures of size at ocean entry for returning adults in Scott Creek, a representative California coastal stream. During the annual spring emigration, the largest smolts (>150 mm fork length (FL)) move directly to sea, while some smaller smolts remain in the estuary until sandbar formation creates a closed freshwater lagoon. High growth rates in the estuary throughout the summer result in a near doubling of fork length from the time of estuary entry (mean FL of spring migrants = 102.2 mm; mean FL of fall lagoon resident = 195.9 mm). Analysis of the scale morphology of returning adult steelhead indicates that there is strong size-dependent mortality at sea, with estuary-reared steelhead showing a large survival advantage, comprising between 87% and 95.5% (based on tag returns and scale analysis, respectively) of the returning adult population despite being between 8% and 48% of the annual downstream migrating population. Although the estuary forms less than 5% of the watershed area, it is critical nursery habitat, and steelhead population persistence in southern margin ecosystems may well depend upon healthy estuaries.
The influence of food quality and availability on trophic position, carbon signature, and growth rate of an omnivorous crayfish
Authors: Olsson Karin , Nyström Per , Stenroth Patrik , Nilsson Erika , Svensson Marie , Granéli Wilhelm
Published: October 2008

Fourteen sites in 13 streams were surveyed to address the importance of food quality and quantity on trophic position, carbon signature, and growth rate of noble crayfish ( Astacus astacus ) by combining the analyses of gut content, stable isotopes, and RNA–DNA ratio. The gut content analysis showed an omnivorous feeding habit, but total animal food sources contributed more to the nitrogen and carbon isotope signals of this species. The biomass of invertebrates (i.e., high quality food) influenced the trophic position, carbon signature, and growth rate. Our results show that crayfish in streams with a high biomass of invertebrates were at a higher trophic position and had a higher growth rate than crayfish in streams with a low biomass of invertebrates. A high biomass of relatively sedentary invertebrates indicates a habitat with high algae biomass, which is reflected in the more autochthonous carbon signature of crayfish. Further, noble crayfish in temperate streams seem to have dual functional roles by acting as predator and as shredder by processing large amounts of detritus.
New approach to determine number of lanes on freeway upgrades
Authors: Chen Chen , Liu Chiu , Wang Zhongren
Published: October 2008

A slow-moving heavy vehicle can substantially reduce traffic flow because the vehicle acts as a moving bottleneck. In particular, the bottleneck can be initiated on a long uphill freeway section where heavy trucks gain little acceleration and propagate upstream when the percentage of loaded trucks in the traffic is high. This paper finds an interesting relation between the bottlenecks and some physical factors including heavy vehicle characteristics, road geometry, traffic flow theory, and percentage of trucks in traffic. According to this relation, the paper provides two dimensionless physical parameters to characterize the formation and propagation of the queues initiated by loaded trucks on uniform upgrades, respectively. Based on the critical values of these parameters aforementioned, the paper can help transportation engineers to determine that the number of design lanes under the conditions that the growing bottlenecks initiate along upgrade section cannot be resolved by simply using equations and rules suggested in the 2000 edition of the Highway capacity manual.
Rebirthing particle swarm optimization algorithm: application to storm water network design
Authors: Afshar M. H.
Published: October 2008

Stochastic search methods, such as the particle swarm optimization (PSO) algorithm, are primarily directed by two main features — exploration and exploitation. Exploration is the ability of the algorithm to broadly search through the solution space for new quality solutions, whereas exploitation is responsible for refining the search in the neighborhood of the good solutions found previously. Proper balance between these features is sought, to obtain good performance of these algorithms. An explorative mechanism is introduced in this paper to improve the performance of the PSO algorithm. The method is based on introducing artificial exploration into the algorithm by randomly repositioning the particles approaching stationary status. A velocity measure is used to distinguish between flying and stationary particles. This can be sought as a sudden death followed by a rebirth of these particles. Two options are tested for the rebirthing mechanism, which are (i) clearing and (ii) keeping the memory of rebirthing particles. The global best particle is exempted from rebirthing process so that the most useful of the swarm’s past experiences is not lost. The method is applied to a benchmark storm water network design problem and the results are presented and compared with those of the original algorithm and other methods. The proposed method, though simple, is shown to be very effective in avoiding local optima, leading to an improved version of the algorithm at no extra computational effort.
Experimental evaluation of an orthotropic, monolithic, modular wooden-dome structural system
Authors: Kharrazi Mehdi H.K. , Eldeib Salah , Prion Helmut G.L.
Published: October 2008

Canadian Wooden Dome (CWD) is an innovative orthotropic, monolithic modular sectional building system. The main frame of these structures is built using mill trim ends that are normally chipped or used for finger-jointing. The structure, in comparison to conventional wood-frame single-family housing, has a rapid manufacturing process, and quick, on-site assembly attempts to reduce overall construction time. Presented with these advantages and the uniqueness of the wooden-dome system, a technical study was initiated to investigate the structural performance of the modular wooden dome in earthquake-prone areas and to examine its load resistance to heavy snow. This paper describes the results from a series of static and dynamic load tests conducted on the CWD as part of this study. The test results generally indicated that based on the structural performance of the CWD under static and dynamic loads, the CWD could be an alternative to the conventional wood-frame construction system. The test results are then compared with those obtained from the tests conducted on conventional single-family wood-frame houses as part of the Earthquake 99 (EQ-99) Woodframe House Project at The University of British Columbia. The seismic performance of the CWD was superior to that of the nonengineered housing system and comparable to that of the engineered wood-frame housing system.
Analysis of plunging phenomenon in dam reservoirs using three-dimensional density flow simulations
Authors: Üneş Fatih
Published: October 2008

Density flow is investigated in a three-dimensional model through a dam reservoir with diverging and sloping bottom channels. When an inflow of higher density enters ambient dam reservoir water, it plunges below the ambient water and becomes density underflow. In the present model, nonlinear and unsteady continuity, momentum, energy, and turbulence model equations are formulated in the Cartesian coordinates. The k–ε turbulence model is used with an extension to include production or destruction of turbulent kinetic energy. To investigate the Coriolis force effect on the density flow in a dam reservoir, a Coriolis force parameter is included in the governing equations. The equations of the model are solved based on the initial and boundary conditions of the dam reservoir flow for a range of bottom slopes and divergence angles. In this paper, variation in density flow parameters, such as velocity, temperature, and turbulence viscosity through the dam reservoir, is investigated. Moreover, mixing rate, plunging points, and plunging depths are determined from the simulation results. The results of the present model are compared with the previous experimental work and model. The present model results follow the expected basic trend. The three-dimensional model simulation and analysis improve the understanding of density flow, underflow, divergence flow, mass transport, and dam–reservoir flow interaction.
Available plastic rotation in continuous high-strength concrete beams
Authors: do Carmo Ricardo N.F. , Lopes Sérgio M.R.
Published: October 2008

An experimental program was formulated to study moment redistribution in continuous high-strength concrete beams. The evaluation of ductility is important for this type of beam as, for high-strength concrete, the ductility decreases as the concrete strength increases. It is therefore necessary to determine whether the critical sections are able to develop appreciable plastic rotations to justify the application of a linear elastic analysis with moment redistribution. This work specifically examined the influence of the tensile reinforcement ratio and the transverse reinforcement ratio on the rotation capacity of plastic hinges. The moment redistribution obtained experimentally is compared with the guidelines recommended in Eurocode 2, CEB-FIP Model Code 1990, and ACI 318. The results show that ACI 318 recommendations for linear analysis with moment redistribution are too conservative and that the predictions, according to Eurocode 2 and CEB-FIP Model Code 1990, agree with experimental evidence.
Cyclotrons and Fixed-Field Alternating-Gradient Accelerators
Authors: Craddock M. K. , Symon K. R.
Published: October 2008

This article describes particle accelerators using magnets whose field strengths are fixed in time to steer and focus ion beams in a spiral orbit so that they pass between (and can be accelerated by) the same electrodes many times. The first example of such a device, Lawrence's cyclotron, revolutionized nuclear physics in the 1930s, but was limited in energy by relativistic effects. To overcome these limits two approaches were taken, enabling energies of many hundreds of MeV/u to be reached: either frequency-modulating the rf accelerating field (the synchrocyclotron) or introducing an azimuthal variation in the magnetic field (the isochronous or sector-focused cyclotron). Both techniques are applied in fixed-field alternating-gradient accelerators (FFAGs), which were intensively studied in the 1950s and '60s with electron models. Technological advances have made possible the recent construction of several proton FFAGs, and a wide variety of designs is being studied for diverse applications with electrons, muons, protons and heavier ions. All fixed-field accelerators offer high beam intensity: classical and isochronous cyclotrons operate in cw mode and in some cases deliver beams of 2 mA; synchrocyclotrons and most FFAGs operate in pulsed mode, but are capable of much higher pulse repetition rates (≤ kHz) than synchrotrons.