bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of a Methane Fuelled Direct Carbon Fuel Cell System
Authors: Hemmes K. , Houwing M. , Woudstra N.
Published: October 2008

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO2 produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study in particular the integration of the production of clean and reactive carbon particles from methane as a fuel for the direct carbon fuel cell. In the thermal decomposition process heat is upgraded to chemical energy in the carbon and hydrogen produced. The hydrogen is seen as a product as well as the power and heat. Under the assumptions given the net system electric efficiency is 22.9 % (based on methane LHV) and 20.7 % (HHV). The hydrogen production efficiency is 65.5 % (based on methane LHV) and 59.1 % (HHV), which leads to a total system efficiency of 88.4 % (LHV) and 79.8 % (HHV). Although a pure CO2 stream is produced at the anode outlet, which is seen as a large advantage of DCFC systems, this advantage is unfortunately reduced due to the need for CO2 in the cathode air stream. Due to the applied assumed constraint that the cathode outlet stream should at least contain 4% CO2 for a proper functioning of the cathode, similar to MCFC cathodes a major part of the pure CO2 has to be mixed with incoming air. Further optimization of the DCFC and the system is needed to obtain a larger fraction of the output streams as pure CO2 for sequestration or reuse.
Extracting the local Green’s function on a horizontal array from ambient ocean noise
Authors: Fried S. E. , Kuperman W. A. , Sabra Karim G. , Roux Philippe
Published: October 2008

Using only ocean ambient noise recordings it is possible to approximate the local time domain Green’s function (TDGF) and extract the time delays associated with different ray path between the elements of a bottom hydrophone array. Comparing the strength of the noise correlation function taken over increasing time windows with residual fluctuations points to an optimum time window to use in the noise correlation function. Through comparison with computer simulations the resulting time series is shown to accurately approximate noise responses in the environment. Analysis of the TDGF gives accurate environmental detail, specifically the critical angle at the water-sediment interface.
Perceptual development of phoneme contrasts: How sensitivity changes along acoustic dimensions that contrast phoneme categories
Authors: Heeren W. F. L. , Schouten M. E. H.
Published: October 2008

Listeners discriminate acoustic differences between phoneme categories at a higher level than similarly sized differences within phoneme categories. The question this paper aims to answer is how this pattern in perceptual sensitivity develops along an acoustic dimension that contrasts two non-native speech sounds: through acquired distinctiveness, through acquired similarity, or through a combination of the two. A pretest–training–post-test experiment was designed to study perceptual development directly, i.e., by including (i) a discrimination task to measure perceptual sensitivity, (ii) a transfer test to ensure language learning instead of stimulus learning, and (iii) a control group to exclude task repetition as an explanation of improvement. It is shown that the typical peak in perceptual sensitivity near a phoneme boundary that native listeners show is not found in relatively inexperienced language learners, despite their ability to classify a continuum in a nativelike way after short laboratory training. Experiment II indicates that a discrimination peak may be achieved by language learners, but only after much more language experience than short-term laboratory training can offer. Furthermore, reasons are given why classification improvement in the laboratory should not be taken as evidence for (i) increased discrimination of the newly learned phonemes and (ii) learning of phoneme representations.
Observation of low-frequency acoustic surface waves in the nocturnal boundary layer
Authors: Talmadge Carrick L. , Waxler Roger , Di Xiao , Gilbert Kenneth E. , Kulichkov Sergey
Published: October 2008

A natural terrain surface, because of its porosity, can support an acoustic surface wave that is a mechanical analog of the familiar vertically polarized surface wave in AM radio transmission. At frequencies of several hundred hertz, the acoustic surface wave is attenuated over distances of a few hundred meters. At lower frequencies (e.g., below approximately 200Hz) the attenuation is much less, allowing surface waves to propagate thousands of meters. At night, a low-frequency surface wave is generally present at long ranges even when downward refraction is weak. Thus, surface waves represent a ubiquitous nighttime transmission mode that exists even when other transmission modes are weak or absent. Data from recent nighttime field experiments and theoretical calculations are presented, demonstrating the persistence of the surface wave under different meteorological conditions. The low-frequency surface wave described here is the “quasiharmonical” tail observed previously in nighttime measurements but not identified by S. Kulichkov and his colleagues (Chunchuzov, I. P. et al. 1990. “On acoustical impulse propagation in a moving inhomogeneous atmospheric layer,” J. Acoust. Soc. Am. 88, 455–461).
Numerical modeling of the sound propagation through a rarefied gas in a semi-infinite space on the basis of linearized kinetic equation
Authors: Sharipov Felix , Kalempa Denize
Published: October 2008

The sound propagation through a rarefied gas is investigated on the basis of the linearized kinetic equation. A plate oscillating in the direction normal to its own plane is considered as a sound wave source. It is assumed a fully established oscillation so that the solution of the kinetic equation depends on time harmonically, while its dependence on the spatial coordinates is obtained numerically. The problem is solved over a wide range of the oscillation speed parameter defined as a ratio of the intermolecular collision frequency to the sound frequency. In order to evaluate the influence of the momentum and energy accommodation coefficients on the solution of the problem, the Cercignani–Lampis scattering kernel is applied as the boundary condition. An analysis of wave characteristics near the source surface shows that they are significantly different from those far from the surface even if the oscillation is slow, i.e., the solution is not harmonic in the space.
Acoustic characterization of high intensity focused ultrasound fields: A combined measurement and modeling approach
Authors: Canney Michael S. , Bailey Michael R. , Crum Lawrence A. , Khokhlova Vera A. , Sapozhnikov Oleg A.
Published: October 2008

Acoustic characterization of high intensity focused ultrasound (HIFU) fields is important both for the accurate prediction of ultrasound induced bioeffects in tissues and for the development of regulatory standards for clinical HIFU devices. In this paper, a method to determine HIFU field parameters at and around the focus is proposed. Nonlinear pressure waveforms were measured and modeled in water and in a tissue-mimicking gel phantom for a 2MHz transducer with an aperture and focal length of 4.4cm. Measurements were performed with a fiber optic probe hydrophone at intensity levels up to 24000W∕cm2. The inputs to a Khokhlov–Zabolotskaya–Kuznetsov-type numerical model were determined based on experimental low amplitude beam plots. Strongly asymmetric waveforms with peak positive pressures up to 80MPa and peak negative pressures up to 15MPa were obtained both numerically and experimentally. Numerical simulations and experimental measurements agreed well; however, when steep shocks were present in the waveform at focal intensity levels higher than 6000W∕cm2, lower values of the peak positive pressure were observed in the measured waveforms. This underrepresentation was attributed mainly to the limited hydrophone bandwidth of 100MHz. It is shown that a combination of measurements and modeling is necessary to enable accurate characterization of HIFU fields.
Numerical design of Alberich anechoic coatings with superellipsoidal cavities of mixed sizes
Authors: Ivansson Sven M.
Published: October 2008

Thin rubber coatings with cavities in a doubly periodic lattice are able to reduce reflections of underwater sound by redistributing normally incident energy such that absorption in the surrounding rubber is enhanced. For spherical scatterers, the anechoic effect can be studied numerically by the layer-multiple-scattering (LMS) method. In comparison to more flexible but also more computer intensive methods, such as finite-element method modeling, there are two important advantages. An improved physical understanding of the anechoic effect can be achieved by simplified semianalytical analysis, and the high computational speed allows modern global optimization techniques to be applied for coating design. In this paper, the flexibility of the LMS method is improved by combination with an efficient algorithm for numerical computation of transition matrices for superellipsoidal scatterers. (A superellipsoid is a generalization of an ellipsoid, allowing more box-filling shapes, for example.) Extensions to mixtures of nonspherical scatterers of different types are also considered, in order to enhance the broadband performance. Symmetry properties are used to reduce the size of the pertinent equation systems. Examples of numerical coating design for underwater acoustic applications are presented, using differential evolution algorithms for the optimization.
Performance analysis of theOrmia ochracea’scoupled ears
Authors: Akcakaya Murat , Nehorai Arye
Published: October 2008

The Ormia ochracea is able to locate a cricket’s mating call despite the small distance between its ears compared with the wavelength. This phenomenon has been explained by the mechanical coupling between the ears. In this paper, it is first shown that the coupling enhances the differences in times of arrival and frequency responses of the ears to the incoming source signals. Then, the accuracy of estimating directions of arrival (DOAs) by the O. ochracea is analyzed by computing the Cramér–Rao bound (CRB). The differential equations of the mechanical model are rewritten in state space and its frequency response is calculated. Using the spectral properties of the system, the CRB for multiple stochastic sources with unknown directions and spectra is asymptotically computed. Numerical examples compare the CRB for the coupled and the uncoupled cases, illustrating the effect of the coupling on reducing the errors in estimating the DOAs.
Speech perception of noise with binary gains
Authors: Wang DeLiang , Kjems Ulrik , Pedersen Michael S. , Boldt Jesper B. , Lunner Thomas
Published: October 2008

For a given mixture of speech and noise, an ideal binary time-frequency mask is constructed by comparing speech energy and noise energy within local time-frequency units. It is observed that listeners achieve nearly perfect speech recognition from gated noise with binary gains prescribed by the ideal binary mask. Only 16 filter channels and a frame rate of 100Hz are sufficient for high intelligibility. The results show that, despite a dramatic reduction of speech information, a pattern of binary gains provides an adequate basis for speech perception.
Influences of modulation and spatial separation on detection of a masked broadband target
Authors: Kopčo Norbert , Shinn-Cunningham Barbara G.
Published: October 2008

Experiments explored the influence of amplitude modulation and spatial separation on detectability of a broadband noise target masked by an independent broadband noise. Thresholds were measured for all combinations of six spatial configurations of target and masker and five modulation conditions. Masker level was either fixed (Experiment 1) or roved between intervals within a trial to reduce the utility of overall intensity as a cue (Experiment 2). After accounting for acoustic changes, thresholds depended on whether a target and a masker were colocated or spatially separated, but not on the exact spatial configuration. Moreover, spatial unmasking exceeded that predicted by better-ear acoustics only when modulation cues for detection were weak. Roving increased the colocated but not the spatially separated thresholds, resulting in an increase in spatial release from masking. Differences in both how performance changed over time and the influence of spatial separation support the idea that the cues underlying performance depend on the modulation characteristics of the target and masker. Analysis suggests that detection is based on overall intensity when target and masker modulation and spatial cues are the same, on spatial attributes when sources are separated and modulation provides no target glimpses, and on modulation discrimination in the remaining conditions.
Informational masking increases the costs of monitoring multiple channels
Authors: Kidd Gerald , Richards Virginia M. , Mason Christine R. , Gallun Frederick J. , Huang Rong
Published: October 2008

This study examined the costs of simultaneously monitoring two frequency regions. Listeners detected low- and high-frequency tones in a 2I4AFC procedure. On every trial, each signal was presented in either the first or second interval independently. Comparison of thresholds in single- and dual-signal conditions provided an estimate of the costs. Thresholds were obtained in quiet, in notched-filtered noise, and in randomized multitone maskers. No cost was found in quiet, whereas large costs were found for the masked conditions, especially for the multitone masker. These results suggest that costs of dividing attention in frequency depend on both signal and nonsignal channels.
Angular influence on the scattering of fundamental shear horizontal guided waves by a through-thickness crack in an isotropic plate
Authors: Rajagopal P. , Lowe M. J. S.
Published: October 2008

The angular influence on the scattering of cylindrical-crested waves of the fundamental shear horizontal (SH0) guided mode by through-thickness cracks in an isotropic plate is studied in the context of array imaging using ultrasonic guided waves. Finite element simulations are used to obtain trends which are subject to analytical study and experimental confirmation. The influence of the incidence angle on reflection behavior is first studied in terms of two complementary cases, that of normal incidence and that of specular reflection at various oblique incidence angles. The normal incidence study suggests that for a given incidence angle, the peak reflection is concentrated around the specular direction, while the oblique incidence studies show that maximum specular reflection occurs in the case of normal incidence. The variation of diffraction with both the angle of incidence and that of monitoring is then taken up and this shows that when the first diffraction from the crack edges can be separated, its angular dependence can be obtained from literature on similar bulk elastic wave scattering problems.
Elastic medium equivalent to Fresnel’s double-refraction crystal
Authors: Carcione José M. , Helbig Klaus
Published: October 2008

In 1821, Fresnel obtained the wave surface of an optically biaxial crystal, assuming that light waves are vibrations of the ether in which longitudinal vibrations (P waves) do not propagate. An anisotropic elastic medium mathematically analogous to Fresnel’s crystal exists. The medium has four elastic constants: a P-wave modulus, associated with a spherical P wave surface, and three elastic constants, c44, c55, and c66, associated with the shear waves, which are mathematically equivalent to the three dielectric permittivity constants ϵ11, ϵ22, and ϵ33 as follows: μ0ϵ11⇔ρ∕c44, μ0ϵ22⇔ρ∕c55, μ0ϵ33⇔ρ∕c66, where μ0 is the magnetic permeability of vacuum and ρ is the mass density. These relations also represent the equivalence between the elastic and electromagnetic wave velocities along the principal axes of the medium. A complete mathematical equivalence can be obtained by setting the P-wave modulus equal to zero, but this yields an unstable elastic medium (the hypothetical ether). To obtain stability the P-wave velocity has to be assumed infinite (incompressibility). Another equivalent Fresnel’s wave surface corresponds to a medium with anomalous polarization. This medium is physically unstable even for a nonzero P-wave modulus.
Cell viability viscoelastic measurement in a rheometer used to stress and engineer tissues at low sonic frequencies
Authors: Klemuk Sarah A. , Jaiswal Sanyukta , Titze Ingo R.
Published: October 2008

Effects of vibration on human vocal fold extracellular matrix composition and the resultant tissue viscoelastic properties are difficult to study in vivo. Therefore, an in vitro bioreactor, simulating the in vivo physiological environment, was explored. A stress-controlled commercial rheometer was used to administer shear vibrations to living tissues at stresses and frequencies corresponding to male phonation, while simultaneously measuring tissue viscoelastic properties. Tissue environment was evaluated and adjustments made in order to sustain cell life for short term experimentation up to 6h. Cell nutrient medium evaporation, osmolality, pH, and cell viability of cells cultured in three-dimensional synthetic scaffolds were quantified under comparably challenging environments to the rheometer bioreactor for 4 or 6h. The functionality of the rheometer bioreactor was demonstrated by applying three vibration regimes to cell-seeded three-dimensional substrates for 2h. Resulting strain was quantified throughout the test period. Rheologic data and cell viability are reported for each condition, and future improvements are discussed.
Perception of rhythmic grouping depends on auditory experience
Authors: Iversen John R. , Patel Aniruddh D. , Ohgushi Kengo
Published: October 2008

Many aspects of perception are known to be shaped by experience, but others are thought to be innate universal properties of the brain. A specific example comes from rhythm perception, where one of the fundamental perceptual operations is the grouping of successive events into higher-level patterns, an operation critical to the perception of language and music. Grouping has long been thought to be governed by innate perceptual principles established a century ago. The current work demonstrates instead that grouping can be strongly dependent on culture. Native English and Japanese speakers were tested for their perception of grouping of simple rhythmic sequences of tones. Members of the two cultures showed different patterns of perceptual grouping, demonstrating that these basic auditory processes are not universal but are shaped by experience. It is suggested that the observed perceptual differences reflect the rhythms of the two languages, and that native language can exert an influence on general auditory perception at a basic level.
Distortion product otoacoustic emission contralateral suppression functions obtained with ramped stimuli
Authors: Purcell David W. , Butler Blake E. , Saunders Tracy J. , Allen Prudence
Published: October 2008

The purpose of this research was to investigate the changes that occur in human distortion product otoacoustic emission (DPOAE) level functions over continuous frequency bands in response to activation of the medial olivocochlear (MOC) efferent system by contralateral broadband noise. DPOAEs were obtained using continuous upward ramps of the lower frequency tone (f1) while the higher frequency tone (f2) was fixed. These ramps were designed to change the stimulus frequency ratio f2∕f1 over a fixed range for each fixed f2 value of 2, 3, and 4kHz. Contralateral noise was presented on alternating ramps and the DPOAEs with and without contralateral noise were averaged separately. Stimulus frequency ratios of 1.10 and 1.22, and noise levels of 60 and 50dB sound pressure level (SPL) were employed. Changes in DPOAE level were generally suppression (a reduction in DPOAE magnitude), but enhancement was also observed. For most participants, changes were evident for much of the frequency ranges tested. Average absolute changes for 60dB SPL noise were 0.95, 0.81, and 0.42dB for the wider stimulus frequency ratios and f2 of 2, 3, and 4kHz, respectively. For the narrower ratio and 60dB SPL noise, the changes were larger with average absolute changes of 1.33, 1.09, and 0.87dB. For the narrower ratio and 50dB SPL noise, the changes were 1.08, 0.78, and 0.55dB with f2 of 2, 3, and 4kHz, respectively. DPOAE nulls were observed and a common response pattern was a shift of emission morphology to higher frequencies with contralateral acoustic stimulation. The method appears promising for relatively rapid evaluation of the MOC efferent system in humans and offers information complementary to measurement strategies that explore the effects of stimulus level.
On the transient solutions of three acoustic wave equations: van Wijngaarden’s equation, Stokes’ equation and the time-dependent diffusion equation
Authors: Buckingham Michael J.
Published: October 2008

Acoustic wave propagation in a dispersive medium may be described by a wave equation containing one or more dissipation terms. Three such equations are examined in this article: van Wijngaarden’s equation (VWE) for sound propagating through a bubbly liquid; Stokes’ equation for acoustic waves in a viscous fluid; and the time-dependent diffusion equation (TDDE) for waves in the interstitial gas in a porous solid. The impulse-response solution for each of the three equations is developed and all are shown to be strictly causal, with no arrivals prior to the activation of the source. However, the VWE is nonphysical in that it predicts instantaneous arrivals, which are associated with infinitely fast, propagating Fourier components in the Green’s function. Stokes’ equation and the TDDE are well behaved in that they do not predict instantaneous arrivals. Two of the equations, the VWE and Stokes’ equation, satisfy the Kramers-Kronig dispersion relations, while the third, the TDDE, does not satisfy Kramers-Kronig, even though its impulse-response solution is causal and physically realizable. The Kramers-Kronig relations are predicated upon the (mathematical) existence of the complex compressibility, a condition which is not satisfied by the TDDE because the Fourier transform of the complex compressibility is not square-integrable.
On the statistical errors in the estimate of acoustical energy density by using two microphones in a one dimensional field
Authors: Pascal Jean-Claude , Thomas Jean-Hugh , Li Jing-Fang
Published: October 2008

It was recently shown that the statistical errors of the measurement in the acoustic energy density by the two microphone method in waveguide have little variation when the losses of coherence between microphones increase. To explain these intervals of uncertainty, the variance of the measurement is expressed in this paper as a function of the various energy quantities of the acoustic fields—energy densities and sound intensities. The necessary conditions to reach the lower bound are clarified. The results obtained are illustrated by an example of a one-dimensional partially coherent field, which allows one to specify the relationship between the coherence functions of the pressure and particle velocity and those of the two microphone signals.
Bubble growth by rectified diffusion at high gas supersaturation levels
Authors: Ilinskii Yurii A. , Wilson Preston S. , Hamilton Mark F.
Published: October 2008

For high gas supersaturation levels in liquids, on the order of 300% as predicted in capillaries of marine mammals following a series of dives [D. S. Houser, R. Howard, and S. Ridgway, J. Theor. Biol. 213, 183–195 (2001)], standard mathematical models of both static and rectified diffusion are found to underestimate the rate of bubble growth by 10%–20%. The discrepancy is demonstrated by comparing predictions based on existing mathematical models with direct numerical solutions of the differential equations for gas diffusion in the liquid and thermal conditions in the bubble. Underestimation of bubble growth by existing mathematical models is due to the underlying assumption that the gas concentration in the liquid is given by its value for a bubble of constant equilibrium radius. This assumption is violated when high supersaturation causes the bubble to grow too fast in relation to the time scale associated with diffusion. Rapid bubble growth results in an increased gas concentration gradient at the bubble wall and therefore a growth rate in excess of predictions based on constant equilibrium bubble radius.
A quantitative analysis of signal reproduction from cylinder recordings measured via noncontact full surface mapping
Authors: Nascè Antony , Hill Martyn , McBride John W. , Boltryk Peter J.
Published: October 2008

Sound reproduction via a noncontact surface mapping technique has great potential for sound archives, aiming to digitize content from early sound recordings such as wax cylinders, which may otherwise be “unplayable” with a stylus. If the noncontact techniques are to be considered a viable solution for sound archivists, a method for quantifying the quality of the reproduced signal needs to be developed. In this study, a specially produced test cylinder recording, encoded with sinusoids, provides the basis for the first quantitative analysis of signal reproduction from the noncontact full surface mapping method. The sampling and resolution of the measurement system are considered with respect to the requirements for digital archiving of cylinder recordings. Two different methods of audio signal estimation from a discrete groove cross section are described and rated in terms of signal-to-noise ratio and total harmonic distortion. Noncontact and stylus methods of sound reproduction are then compared using the same test cylinder. It is shown that noncontact methods appear to have distinct advantages over stylus reproduction, in terms of reduced harmonic distortion and lower frequency modulation.
Is ecological segregation in a pair of sympatric coregonines supported by divergent feeding efficiencies?
Authors: Ohlberger Jan , Mehner Thomas , Staaks Georg , Hölker Franz
Published: October 2008

Some of the sympatric species pairs commonly described in temperate freshwater fishes provide evidence for ecological specialization driven by competition for food resources as a potential prerequisite of subsequent sympatric speciation. In the postglacial Lake Stechlin (Germany), two sympatric coregonines coexist, common vendace ( Coregonus albula ) and endemic dwarf-sized Fontane cisco ( Coregonus fontanae ). The species segregate vertically along the light intensity and prey density gradients of their pelagic environment. Accordingly, we hypothesized that the species might show differences in their foraging efficiency associated with these environmental gradients. We investigated the feeding behaviour by measuring the functional response of both species to Daphnia magna at various prey densities (0.25–8 individuals·L–1) and light intensities (0.005–5 lx) at a deep blue light spectrum to simulate their natural habitat. Decreasing light intensity and prey density significantly depressed consumption rates in both species. Overall, we observed only weak differences in feeding behaviour, which indicates that the species are functionally similar, coexisting planktivores.
Anguilla marmorata larval migration plasticity as revealed by otolith microstructural analysis
Authors: Réveillac Elodie , Feunteun Eric , Berrebi Patrick , Gagnaire Pierre-Alexandre , Lecomte-Finiger Raymonde , Bosc Pierre , Robinet Tony
Published: October 2008

The oceanic early-life history of Anguilla marmorata was examined in the southwestern Indian Ocean in Mayotte, Mauritius, and Réunion islands through otolith microstructural analysis. The study of the hatching dates, the first feeding check diameter (FFD), the leptocephalus (LD) and metamorphosis (MD) durations, the age at recruitment (AR), and the leptocephalus otolith growth rate (OGR) of glass eels revealed great variations in early-life traits and relationships between them. An agglomerative nesting analysis discriminated three early-life histories, differently represented according to the locality: (i) fast migrants with short LD, short MD, young AR, large FFD, and high OGR dominated in Réunion and Mayotte; (ii) midspeed migrants with intermediate LD, MD, AR, FFD, and OGR dominated in Mauritius; (iii) slow migrants with long LD, long MD, old AR, small FFD, and low OGR were recorded only in Mauritius. All possible strategies were not observed and therefore not successful at the sampling time. However, several were simultaneously expressed, which suggests larval migration plasticity at the population level. This evidence is crucial information regarding both the species dispersal capabilities and the evolution from short-migratory tropical species towards long-migratory temperate ones in the genus Anguilla .
Overcompensatory response of a smallmouth bass (Micropterus dolomieu) population to harvest: release from competition?
Authors: Zipkin Elise F. , Sullivan Patrick J. , Cooch Evan G. , Kraft Clifford E. , Shuter Brian J. , Weidel Brian C.
Published: October 2008

An intensive seven-year removal of adult, juvenile, and young-of-the-year smallmouth bass ( Micropterus dolomieu ) from a north temperate lake (Little Moose Lake, New York, USA) resulted in an increase in overall population abundance, primarily due to increased abundance of immature individuals. We developed a density-dependent, stage-structured model to examine conditions under which population control through harvest could result in the increase of a targeted species. Parameter values were derived from a 54-year data set collected from another north temperate lake (Lake Opeongo, Ontario, Canada) smallmouth bass population. Sensitivity analyses identified the demographic conditions that could lead to increased abundance in response to harvest. An increase in population abundance with harvest was most likely to occur when either (i) per capita recruitment at low levels of spawner abundance was large, juvenile survivorship was high, and maturation of age-4 and older juveniles was moderately high or (ii) per capita recruitment at low levels of spawner abundance was slightly lower, yet the maturation rate of age-3 juveniles and adult survivorship were high. Our modeling results together with empirical evidence further demonstrate the importance of overcompensation as a substantial factor to consider in efforts to regulate population abundance through harvest.
A modelling study of Norway lobster (Nephrops norvegicus) larval dispersal in southern Portugal: predictions of larval wastage and self-recruitment in the Algarve stock
Authors: Marta-Almeida Martinho , Dubert Jesus , Peliz Álvaro , dos Santos Antonina , Queiroga Henrique
Published: October 2008

A set of simulations using a validated and realistic parameterization of a numerical model was conducted for the south and southwest Portuguese regions as an attempt to understand larval dispersal patterns in the Norway lobster ( Nephrops norvegicus ). Larvae were introduced in the model as Lagrangian particles with five different behavioural scenarios concerning their ability to migrate vertically. Growth rate was temperature dependent and the larvae were tracked individually. The end point of the simulations was the position of the larvae when they reached competency at age 1. Age 1.25 was also considered to simulate a possible delay in settling due to lack of an appropriate substrate. The results showed that the majority of the larvae reached age 1 near the hatching area along the southern shelf, while low exchange of larvae between the south and the west coasts was observed, especially for behavioural scenarios where larvae remained in relatively shallow waters. Scenarios where larvae performed diurnal vertical migration and delayed settlement until age 1.25 indicated a tendency for westward motion because of interactions with the Mediterranean undercurrent. Self-recruitment to the Algarve stock was estimated at 0.2% to 0.5%, raising the concern that this stock may be experiencing recruitment limitation.
Cyclic performance of frames with prestressed steel–concrete composite beams
Authors: Xue Weichen , Li Kun , Zheng Renguang , Li Liang
Published: October 2008

This paper presents a study of the cyclic performance of moment-resisting frames with prestressed steel–concrete composite beams subjected to cyclic displacement reversals. The failure patterns, failure mechanism, hysteretic model, ductility, energy dissipation capacity, stiffness degradation, and deformation-restoring capacity of two composite frames are discussed. Larger slip could be observed along the beam span of the frame with the common composite beam in comparison with the prestressed composite beam. A four-linear hysteretic model with descending branches and two pinching pivot points is proposed for the two composite frames. Tests show that both the test frames failed in a beam side-sway mechanism within the plane of the frame, and the frame with the prestressed composite beam develops relatively high deformation restoring capacity. The applied prestressing in the composite beam has a small contribution to cyclic behavior of the composite frame. Studies also show that more energy is dissipated by the frame with the prestressed composite beam than that with the common composite beam.
Equivalent mechanical models of tuned liquid dampers with different tank geometries
Authors: Deng X. , Tait M. J.
Published: October 2008

This paper focuses on the development of equivalent mechanical models for tuned liquid dampers (TLDs) with rectangular, vertical-cylindrical, horizontal-cylindrical, and hyperboloid (conical) tank shapes under external excitation in the transverse direction. Potential flow theory is utilized to obtain the free-surface response amplitude and the corresponding velocity of the sloshing liquid and Lagrange’s equations are used to determine the generalized properties. Morison’s equation and the virtual work method are used to estimate an equivalent viscous damping ratio based on the screen loss coefficient. The equivalent mechanical properties derived in this paper model the fundamental sloshing mode only and are restricted to small response amplitudes. Subsequently, the equivalent mechanical properties including effective mass, natural frequency, and damping ratio of the TLDs, having different tank geometries, are compared. It is found that the effective mass values for horizontal-cylindrical and hyperboloid TLDs are larger than the effective mass values for vertical-cylindrical and rectangular TLDs. The increased effective mass values for horizontal-cylindrical and hyperboloid TLDs can result in improved tuned liquid damper performance given the same total liquid mass as that of rectangular or vertical-cylindrical TLDs.
Observed evidence of subgrade moisture influence on pavement longitudinal profile
Authors: Bae Abraham , Stoffels Shelley M. , Antle Charles E. , Lee Seung Woo
Published: October 2008

The relationship between subgrade moisture parameters and pavement profile was explored for 34 asphalt pavements of the seasonal monitoring program (SMP) in the long-term pavement performance (LTPP) program. Volumetric moisture content was quantified in terms of the moisture index (MI), representing moisture as reasonably related to subgrade performance. Using power spectral density (PSD), roughness was evaluated in 21 individual wavebands. From statistical analysis, it was concluded that subgrade moisture significantly affects roughness in the wavebands of 14.9 to 31.2 m and 24.0 to 31.2 m for nonfreezing sites, and in the waveband of 14.9 to 24.0 m for freezing sites. At nonfreezing sites, as the magnitude and variation of moisture increase, pavement surface profile deteriorates quickly. At freezing sites, it was found that moisture variation by freezing contributes to roughness deterioration. Moreover, it was found that pavement thickness and the percent passing the top 0.002 mm of subgrade are significant factors accelerating roughness progression at nonfreezing and freezing sites, respectively.
Mechanical performance and crack retardation study of a fiberglass-grid-reinforced asphalt concrete system
Authors: Lee S. Joon
Published: October 2008

This paper presents constitutive design considerations for a semi-rigid, resin-impregnated fiberglass grid that enhances the mechanical performance of an asphalt concrete overlay and provides a pattern to retard crack propagation. An acrylic polymer resin covers the grid-structured fiberglass strands, thus making their viscoelastic nature compatible with the asphalt materials. The remarkable temperature susceptibility of the resin is observed using time–temperature superposition. The grid tensile strength of 100 kN/m was qualified using standard measurements. Three-point bending and cyclic fatigue loading mechanical tests affirm the retardation performance of the grid-reinforced system in terms of crack propagation. The retardation mechanism is affected by synchronizing the cracking pattern with the flexural stress–strain profile through image analysis. A National Center for Asphalt Technology full-scale road testing program provides assessment of the grid-reinforced pavements. A visual inspection of the grid extracted from the traffick zone showed fair condition of the pavement.
Influence of longitudinal reinforcement strength on one-way slab deflection
Authors: Tang Jijun , Lubell Adam S.
Published: October 2008

The CSA A23.3 standard for reinforced concrete design provides both an implicit check of deflection control based on minimum member thickness requirements and a direct computation method for deflection. This paper reports on an analytical study that compared maximum span-to-depth ratios from the implicit deflection provisions against ratios determined from direct deflection calculations. Emphasis was placed on the deflection performance of lightly reinforced one-way slabs, including those with high-strength steel reinforcement. The results indicated that maximum span-to-depth ratios should decrease as the span length increases, as the design load increases or as the cracking moment decreases. In contrast to the current implicit provisions, the design strength of the longitudinal reinforcement did not have a significant effect on the minimum slab thickness required to satisfy common deflection criterion. Design aids were proposed, with implications for design presented through a case study of a multispan one-way slab system.
Assessment of overtopping reliability and benefits of a flood detention dam
Authors: Yanmaz A. Melih , Gunindi M. Engin
Published: October 2008

There is a growing tendency to assess safety levels of existing dams and to design new dams using probabilistic approaches according to project characteristics and site-specific conditions. This study is a probabilistic assessment of the overtopping reliability of a dam, which will be designed for flood detention purpose, and will compute the benefits that can be gained as a result of the implementation of this dam. In a case study, a bivariate flood frequency analysis was carried out using a five-parameter bivariate gamma distribution. A family of joint return period curves relating the runoff peak discharges to the runoff volumes at the dam site was derived. A number of hydrographs were also obtained under a joint return period of 100 years to observe the variation of overtopping tendency. The maximum reservoir elevation and overtopping reliability were determined by performing a probabilistic reservoir routing based on Monte Carlo simulations.
A preliminary study of the mechanical properties of asphalt mixture containing bottom ash
Authors: Goh Shu Wei , You Zhanping
Published: October 2008

This paper shows a preliminary study of asphalt mixtures containing bottom ash with a primary focus on the permanent deformation. The objectives of this study are (i) perform literature reviews on the mechanical properties of asphalt mixtures containing bottom ash; (ii) evaluate the effects of using bottom ash as the mineral filler for the asphalt mixture through the flow number and dynamic modulus tests; and (iii) use the test results to evaluate the pavement permanent deformation using the Mechanistic–empirical pavement design guide (MEPDG) analysis. It was found that the asphalt mixture using bottom ash uses higher asphalt content due to the higher absorption. The replacement with bottom ash in the asphalt mixture generates a lower dynamic modulus as compared to the control mixtures. Additionally, results from MEPDG analysis show mixtures with bottom ash have higher rutting potential.
ABDUS SALAM AT IMPERIAL COLLEGE
Authors: KIBBLE TOM
Published: October 2008

It is a privilege, as well as a great pleasure, for me to talk about Abdus Salam at Imperial College. He is someone to whom I owe a great personal debt. I have always felt that I was very fortunate to have found myself joining his group in 1959, less than three years after he first set it up. It was a very exciting place to be, and a very exciting time in theoretical physics.
Particle Colliders for High Energy Physics
Authors: Edwards D. A. , Edwards H. T.
Published: October 2008

The purpose of this article is to outline the development of particle colliders from their inception just over a half-century ago, expand on today's achievements, and remark on the potential of coming years. There are three main sections, entitled "Past," "Present," and "Future." "Past" starts with the electron and electron–positron colliders of the 1950s, continues through the proton rings at CERN, and concludes with LEP. Technology development enters the section Present, "which includes not only the major colliders in both the lepton and baryon worlds, but also recognition of the near-immediate entry of the Large Hadron Collider. "Future" looks at the next potential steps, the most prominent of which is an electron–positron partner to the LHC, but there are other very interesting propositions undergoing exploration that include muon storage and even conceivably departure from reliance on radio frequency acceleration.
Medical Applications of Accelerators
Authors: Eickhoff Hartmut , Linz Ute
Published: October 2008

Particle accelerators play an essential role in the field of medical applications. A large variety of systems is in use for diagnostic purposes, such as the production of radioactive tracers for imaging or x-ray radiography. The dominant application, however, is related to the treatment of cancer patients. This article puts emphasis on cancer treatment, presenting the status and developments of the corresponding technical systems, and gives a brief overview of the biophysical properties and medical aspects of these treatments.
Industrial Accelerators
Authors: Hamm Robert W.
Published: October 2008

About half of the particle accelerators produced worldwide are used for industrial applications. These commercial systems utilize a wide range of accelerator technologies and cover numerous applications over a broad range of business segments. While this is not a high profile business, these "industrial accelerators" have a significant impact on people's lives and the world's economy, as many products contain parts that have been processed by charged particle beams. Wide scale adoption of many of these processing tools has resulted in the rapid growth of the business of producing and selling them. This paper is a review of the current status of industrial accelerators worldwide, including the technologies, the applications, the vendors and the sizes of the markets.
Development of Superconducting RF Technology
Authors: Furuya Takaaki
Published: October 2008

The development of superconducting RF cavity technology started in the 1960s, aiming for continuous wave operation of high gradient linacs with excellent electric power efficiency. After continuous efforts for more than four decades, the initial achievable field gradient of only 2 MV/m was gradually improved and approached the theoretical upper limit of 50 MV/m on Nb cavities. At each stage of this development, many applications have been extended in various fields. This article will review those advances and applications of the superconducting RF cavities.
Differential expression of the regulated catecholamine secretory pathway in different hereditary forms of pheochromocytoma
Authors: Eisenhofer Graeme , Huynh Thanh-Truc , Elkahloun Abdel , Morris John C. , Bratslavsky Gennady , Linehan W. Marston , Zhuang Zhengping , Balgley Brian M. , Lee Cheng S. , Mannelli Massimo , Lenders Jacques W. M. , Bornstein Stefan R. , Pacak Karel
Published: October 2008

Pheochromocytomas in patients with von Hippel-Lindau (VHL) syndrome and multiple endocrine neoplasia type 2 (MEN 2) differ in the types and amounts of catecholamines produced and the resulting signs and symptoms. We hypothesized the presence of different processes of catecholamine release reflecting differential expression of components of the regulated secretory pathway among the two types of hereditary tumors. Differences in catecholamine secretion from tumors in patients with VHL syndrome ( n = 47) and MEN 2 ( n = 32) were examined using measurements of catecholamines in tumor tissue, urine, and plasma, the last of which was under baseline conditions in all subjects and in a subgroup of patients who received intravenous glucagon to provoke catecholamine release. Microarray and proteomics analyses, quantitative PCR, and Western blotting were used to assess expression of tumor tissue secretory pathway components. The rate constant for baseline catecholamine secretion was 20-fold higher in VHL than in MEN 2 tumors (0.359 ± 0.094 vs. 0.018 ± 0.009 day−1), but catecholamine release was responsive only to glucagon in MEN 2 tumors. Compared with tumors from MEN 2 patients, those from VHL patients were characterized by reduced expression of numerous components of the regulated secretory pathway (e.g., SNAP25, syntaxin, rabphilin 3A, annexin A7, calcium-dependent secretion activator). The mutation-dependent differences in expression of secretory pathway components indicate a more mature regulated secretory pathway in MEN 2 than VHL tumors. These data provide a unique mechanistic link to explain how variations in the molecular machinery governing exocytosis may contribute to clinical differences in the secretion of neurotransmitters or hormones and the subsequent presentation of a disease.
Both TASK-3 and TREK-1 two-pore loop K channels are expressed in H295R cells and modulate their membrane potential and aldosterone secretion
Authors: Brenner Tanja , O'Shaughnessy Kevin M.
Published: October 2008

The rate of aldosterone synthesis by adrenal glomerulosa cells relies on the selective permeability of the glomerulosa cell to K+ions. In rodent and bovine adrenal glomerulosa cells, this background potassium current is provided by a two-pore loop potassium (K2P) channel: largely TASK-3 in the rat and TREK-1 in the cow. The nature of the K2P channel in the human adrenal cortex is not known, and we have addressed this issue here using the H295R human adrenal cell line. We show that these cells express mRNA and protein for both TASK-3 and TREK-1 K2P channels. Using a potentiometric dye (FMP), we also show that TASK-3 and TREK-1 channel modulators can affect the membrane potential of H295R cells. Transfecting H295R cells with TASK-3 or TREK-1 dominant-negative mutants (TASK-3 G95E or TREK-1 G144E) produced depolarization of H295R cells and altered K-stimulated aldosterone secretion. Finally, transfection of a constitutively active mutant of Gαqinto H295R cells (GTPase-deficient Gαq-QL) depolarized them and increased basal aldosterone secretion. Taken together, our data support both TASK-3 and TREK-1 as being functionally operational in the H295R cell line. This suggests that human adrenal glomerulosa cells may utilize both of these K2P channels for their background potassium current.