bluuebunny/crossref_metadata_2025 huggingface dataset:
Scatterer size estimation in pulse-echo ultrasound using focused sources: Theoretical approximations and simulation analysis
Authors: Bigelow Timothy A. , O’Brien William D.
Published: July 2004

The speckle in ultrasound images has long been thought to contain information related to the tissue microstructure. Many different investigators have analyzed the frequency characteristics of the backscattered signals to estimate the scatterer acoustic concentration and size. Previous work has been mostly restricted to unfocused or weakly focused ultrasound sources, thus limiting its implementation with diagnostically relevant fields. Herein, we derive equations capable of estimating the size of a scatterer for any reasonably focused source provided that the velocity potential field in the focal region can be approximated as a three-dimensional Gaussian beam, scatterers are a sufficient distance from the source, and the field is approximately constant across the scatterer. The calculations show that, when estimating the scatterer size, correcting for focusing requires a generalized attenuation-compensation function that includes both attenuation and focusing along the beam axis. The Gaussian approximation is validated by comparing the ideal velocity potential field for three spherically focused sources with f-numbers of 1, 2, and 4 to the Gaussian approximation for frequencies from 2 to 14 MHz. The theoretical derivations are evaluated by simulating the backscatter by using spherically focused sources (f-numbers of 1, 2, and 4) adjacent to attenuating media (0.05 to 1 dB/cm/MHz) that contain scatterers with Gaussian impedance distributions. The generalized attenuation-compensation function yielded results accurate to 7.2% while the traditional attenuation-compensation functions that neglected focusing had errors as high as 103%.
Directionality of dog vocalizations
Authors: Frommolt Karl-Heinz , Gebler Alban
Published: July 2004

The directionality patterns of sound emission in domestic dogs were measured in an anechoic environment using a microphone array. Mainly long-distance signals from four dogs were investigated. The radiation pattern of the signals differed clearly from an omnidirectional one with average differences in sound-pressure level between the frontal and rear position of 3–7 dB depending from the individual. Frequency dependence of directionality was shown for the range from 250 to 3200 Hz. The results indicate that when studying acoustic communication in mammals, more attention should be paid to the directionality pattern of sound emission.
Tracking sperm whale (Physeter macrocephalus) dive profiles using a towed passive acoustic array
Authors: Thode Aaron
Published: July 2004

A passive acoustic method is presented for tracking sperm whale dive profiles, using two or three hydrophones deployed as either a vertical or large-aperture towed array. The relative arrival times between the direct and surface-reflected acoustic paths are used to obtain the ranges and depths of animals with respect to the array, provided that the hydrophone depths are independently measured. Besides reducing the number of hydrophones required, exploiting surface reflections simplifies automation of the data processing. Experimental results are shown from 2002 and 2003 cruises in the Gulf of Mexico for two different towed array deployments. The 2002 deployment consisted of two short-aperture towed arrays separated by 170 m, while the 2003 deployment placed an autonomous acoustic recorder in tandem with a short-aperture towed array, and used ship noise to time-align the acoustic data. The resulting dive profiles were independently checked using single-hydrophone localizations, whenever multipath reflections from the ocean bottom could be exploited to effectively create a large-aperture vertical array. This technique may have applications for basic research and for real-time mitigation for seismic airgun surveys.
Phenomenological detectors for crack echo families in elastic solids
Authors: Asraf Daniel E. , Gustafsson Mats G.
Published: July 2004

The potential performance of low-complexity phenomenological detectors for crack echo families in elastic solids is evaluated. Ultrasonic echoes from a strip-like crack residing in an isotropic elastic solid with coarse microstructure are considered and the achieved detector performance is compared to the theoretical upper bounds (constrained only by the underlying physics) obtained by means of a recently presented physics-based optimal detector. A phenomenological signal model for the scattering process is formulated based on the time-domain impulse-response method and used to derive detectors of low numerical complexity which are dependent on a small number of parameters. The proposed detectors are compared in terms of receiver operating characteristic curves, which are computed by means of Monte Carlo simulations for the case of a strip-like crack with uncertain angular orientation. The minimum probability of error criterion is used to optimize the detector parameters for the simulation study and shown to be useful even for small training data sets. These results show that the proposed detectors have close to optimal performance in particular for the case of high signal-to-noise ratios.
Transient modeling of Lamb waves generated in viscoelastic materials by surface bonded piezoelectric transducers
Authors: Duquenne Laurent , Moulin Emmanuel , Assaad Jamal , Grondel Sébastien
Published: July 2004

In order to help optimize health monitoring systems based on Lamb wave propagation, a hybrid finite element–normal mode expansion modeling technique has been developed. This technique allows one to predict the Lamb waves generated in a structure as a function of the transducer parameters (size, location, material, etc.). The present paper shows how this hybrid modeling, initially valid for nonlossy materials and harmonic excitation, can be extended to lossy (viscoelastic) materials and transient excitation. For this purpose, simplifying assumptions have been proposed and validity conditions have been established and verified. Moreover, numerical results concerning Lamb wave generation have been successfully compared to experimental ones. As a result, the method has proved to be pertinent and practically unrestrictive.
Objective evaluation of chamber-music halls in Europe and Japan
Authors: Hidaka Takayuki , Nishihara Noriko
Published: July 2004

The room acoustical parameters reverberation time, RT; early decay time, EDT; clarity, C80; time gravity, Tg; bass ratio, BR; strength, G; initial time delay gap, ITDG; interaural cross-correlation coefficient, IACCE, the where binaural quality index BQI equals [1-IACCE3]; and stage support, ST1 were measured in 18 major chamber-music halls in Austria, Germany, the Netherlands, Czech Republic, Switzerland, and Japan, employing procedures in accordance with ISO 3382 (1997). In combination with the architectural data, the intrinsic objective parameters for the acoustics of chamber-music halls and their variation range were examined. The results of these studies reveal four pertinent orthogonal parameters: RT, G, ITDG, BQI. General design guidelines for a chamber-music hall are presented.
Non-Gaussian statistics and temporal variations of the ultrasound signal backscattered by blood at frequencies between 10 and 58 MHz
Authors: Cloutier Guy , Daronat Michel , Savéry David , Garcia Damien , Durand Louis-Gilles , Foster F. Stuart
Published: July 2004

Very little is known about the blood backscattering behavior and signal statistics following flow stoppage at frequencies higher than 10 MHz. Measurements of the radio frequency (rf) signals backscattered by normal human blood (hematocrit=40%, temperature=37 °C) were performed in a tube flow model at mean frequencies varying between 10 and 58 MHz. The range of increase of the backscattered power during red blood cell (RBC) rouleau formation was close to 15 dB at 10 and 36 MHz, and dropped, for the same blood samples, below 8 dB at 58 MHz. Increasing the frequency from 10 to 58 MHz raised the slope of the power changes at the beginning of the kinetics of aggregation, and could emphasize the non-Gaussian behavior of the rf signals interpreted in terms of the K and Nakagami statistical models. At 36 and 58 MHz, significant increases of the kurtosis coefficient, and significant reductions of the Nakagami parameter were noted during the first 30 s of flow stoppage. In conclusion, increasing the transducer frequency reduced the magnitude of the backscattered power changes attributed to the phenomenon of RBC aggregation, but improved the detection of rapid growth in aggregate sizes and non-Gaussian statistical behavior.
Periodogram based tests for distortion product otoacoustic emissions
Authors: Craigmile Peter F. , King Wayne M.
Published: July 2004

Distortion product otoacoustic emissions (DPOAEs) are an important nonbehavioral measure of cochlear function, which provides a close analogue of the behavioral pure-tone audiogram. DPOAEs are sinusoidal distortion products (DPs) produced by nonlinearities in the healthy cochlea. Detection of DPs is accomplished in the Fourier domain with a periodogram based test. The test compares the power in the DP periodogram bin to a noise estimate derived from a certain number of the surrounding bins. Statistical properties of this test to date have only been examined by constructing receiver operator characteristics curves derived from DPOAE measurements in normal and hearing impaired individuals. In this paper the null distribution of this order-statistic based test is explicitly derived, and via simulations intended to mimic the nonwhite features of real-ear noise measurements, the power of the test is demonstrated. These simulations demonstrate that a local F test is more powerful than this DPOAE test, with critical values that are easier to calculate. Although the power of both tests increase with an increasing number of bins, the improvement is negligible at around four bins. Since the power of both tests decrease at lower DP frequencies, it is not recommended to use a large number of bins.
Limits to the role of a common fundamental frequency in the fusion of two sounds with different spatial cues
Authors: Darwin C. J. , Hukin R. W.
Published: July 2004

Two experiments establish constraints on the ability of a common fundamental frequency (F0) to perceptually fuse low-pass filtered and complementary high-pass filtered speech presented to different ears. In experiment 1 the filter cut-off is set at 1 kHz. When the filters are sharp, giving little overlap in frequency between the two sounds, listeners report hearing two sounds even when the sounds at the two ears are on the same F0. Shallower filters give more fusion. In experiment 2, the filters’ cut-off frequency is varied together with their slope. Fusion becomes more frequent when the signals at the two ears share low-frequency components. This constraint mirrors the natural filtering by head-shadow of sound sources presented to one side. The mechanisms underlying perceptual fusion may thus be similar to those underlying auditory localization.
Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds
Authors: Middlebrooks John C.
Published: July 2004

Interactions among the multiple channels of a cochlear prosthesis limit the number of channels of information that can be transmitted to the brain. This study explored the influence on channel interactions of electrical pulse rates and temporal offsets between channels. Anesthetized guinea pigs were implanted with 2-channel scala-tympani electrode arrays, and spike activity was recorded from the auditory cortex. Channel interactions were quantified as the reduction of the threshold for pulse-train stimulation of the apical channel by sub-threshold stimulation of the basal channel. Pulse rates were 254 or 4069 pulses per second (pps) per channel. Maximum threshold reductions averaged 9.6 dB when channels were stimulated simultaneously. Among nonsimultaneous conditions, threshold reductions at the 254-pps rate were entirely eliminated by a 1966-μs inter-channel offset. When offsets were only 41 to 123 μs, however, maximum threshold shifts averaged 3.1 dB, which was comparable to the dynamic ranges of cortical neurons in this experimental preparation. Threshold reductions at 4069 pps averaged up to 1.3 dB greater than at 254 pps, which raises some concern in regard to high-pulse-rate speech processors. Thresholds for various paired-pulse stimuli, pulse rates, and pulse-train durations were measured to test possible mechanisms of temporal integration.
Spectral estimation for characterization of acoustic aberration
Authors: Varslot Trond , Angelsen Bjørn , Waag Robert C.
Published: July 2004

Spectral estimation based on acoustic backscatter from a motionless stochastic medium is described for characterization of aberration in ultrasonic imaging. The underlying assumptions for the estimation are: The correlation length of the medium is short compared to the length of the transmitted acoustic pulse, an isoplanatic region of sufficient size exists around the focal point, and the backscatter can be modeled as an ergodic stochastic process. The motivation for this work is ultrasonic imaging with aberration correction. Measurements were performed using a two-dimensional array system with 80×80 transducer elements and an element pitch of 0.6 mm. The f number for the measurements was 1.2 and the center frequency was 3.0 MHz with a 53% bandwidth. Relative phase of aberration was extracted from estimated cross spectra using a robust least-mean-square-error method based on an orthogonal expansion of the phase differences of neighboring wave forms as a function of frequency. Estimates of cross-spectrum phase from measurements of random scattering through a tissue-mimicking aberrator have confidence bands approximately ±5° wide. Both phase and magnitude are in good agreement with a reference characterization obtained from a point scatterer.
Using finite element method for the determination of elastic moduli by resonant ultrasound spectroscopy
Authors: Plesek Jiri , Kolman Radek , Landa Michal
Published: July 2004

Resonant ultrasound spectroscopy is a recent experimental/numerical method for the determination of moduli of elastic materials. Generally, all 21 elastic components of the elastic tensor can be determined by the numerical procedure based on the knowledge of a mechanical spectrum of a specimen. This involves the solution of a demanding inverse problem. Presently, Levenberg–Marquardt’s (LM) algorithm with the Ritz method for the solution of eigenfrequencies is usually applied. The LM method is based on the modified Newton–Raphson procedure, where all the eigenfrequencies and eigenvectors must be known for the computation of relevant gradients. Finite element method offers an analogous but more general optimization. The tested specimen, for instance, can be made of a composite material consisting of several layers with different material properties; the form of the specimen can be of a more complex shape, etc. In the present work, the elastic moduli are optimized by the fixed point iteration method, which requires only the lowest few eigenfrequencies to be known. The proposed algorithm is verified by test examples and suitable convergence criteria are established.
Time domain holography: Forward projection of simulated and measured sound pressure fields
Authors: de La Rochefoucauld Ombeline , Melon Manuel , Garcia Alexandre
Published: July 2004

In this article, the fundamental principles of forward projecting time domain acoustic pressure fields are summarized. Four different numerical approaches are presented and compared both with simulated and measured signals. The approaches differ in their definition domain: Frequency/time and space/wave vector domains. The simulated source is a planar baffled piston excited with a Gaussian pulsed velocity. The pressure radiated by two different real sources has been measured: The first source is made up of two baffled loudspeakers (a Gaussian white noise can be radiated by a third loudspeaker). The second one is a baffled aluminum plate excited by a short impact at its center. The influence of parameters such as the sound source radius, the array size, the number of microphones and the propagation distance is studied. Finally, results concerning the optimization of the sampling of the sound field are presented.
Analysis and design of conical concentric tube resonators
Authors: Kar T. , Munjal M. L.
Published: July 2004

The concept of perforate impedance and its exploitation for acoustic attenuation through several elements including concentric tube resonators, is common in practice. Variable cross-sectional area ducts are often used for better performance at lower frequencies (like in horns), whereas concentric tube resonators are often used to provide attenuation at relatively higher frequencies. A combination of the two leads to conical concentric-tube resonators. Using a one-dimensional control volume approach, a mathematical model is presented that accounts for waves in an incompressible mean flow in the center tube, wave propagation in the cavity, and an acoustic coupling between the two due to the impedance of the perforate. The matrizant model results have been validated for self consistency. In the sections dealing with discussion and parametric study, the effect of the moving medium has been neglected so as to bring out clearly the physical effect of the variable area ducts. A few notable effects have been found that include an effective length shorter than the geometric length for an inhomogeneous duct. Some useful features like the absence of pass bands are noticed in the transmission loss spectrum. Finally, results of a parametric study are presented for use by the noise control engineers.
Frequency dependence of acoustic properties of aqueous glucose solutions in the VHF/UHF range
Authors: Akashi Naoyuki , Kushibiki Jun-ichi , Dunn Floyd
Published: July 2004

The bioultrasonic spectroscopy system was employed for measurements of velocity and attenuation coefficient of glucose solutions in the VHF/UHF range. The relation between the slope of the square of velocity and the relaxation parameters, and the relation between the frequency exponent on attenuation coefficient and the relaxation parameters are investigated. In order to carry out numerical calculations, a model for a single relaxation process is employed, wherein the attenuation coefficient is expressed as (A/(1+(f/fα)2)+B)f2 where fα is the attenuation relaxation frequency, and A and B are constants. The numerical calculations show that the slope of the square of the velocity is determined uniquely by the velocity relaxation frequency fv and v∞2−v02 where v0 is the zero-frequency velocity and v∞ is the infinite-frequency velocity, and that the frequency exponent on the attenuation coefficient is determined uniquely by fα and A/B. For experimental considerations, the velocities and the attenuation coefficients of 5, 15, and 25% concentration aqueous solutions of glucose were measured in the frequency range 20 to 700 MHz. The data for the 5 and 15% aqueous solutions can be explained using the single relaxation model. However, the data for the 25% aqueous solution suggest the existence of multirelaxation processes.
Influence of dispersed-phase elasticity on steady-state deformation and breakup of droplets in simple shearing flow of immiscible polymer blends
Authors: Lerdwijitjarud Wanchai , Sirivat Anuvat , Larson Ronald G.
Published: July 2004

The effect of dispersed-phase elasticity on steady-state deformation and breakup of isolated droplets for polybutadiene/poly(dimethyl siloxane) blends in simple shearing flow is investigated systematically for values of the dispersed-phase Weissenberg number (Wid) ranging up to around 3, where the Weissenberg number is defined as the ratio of the first normal stress difference to twice the shear stress at the imposed shear rate. The dependence on droplet elasticity of steady-state morphology for 10%-dispersed phase blends is also studied. The polybutadiene droplet phase is an elastic “Boger” fluid prepared by dissolving a high-molecular-weight polybutadiene into a low-molecular-weight Newtonian polybutadiene melt. To isolate the contribution of droplet elasticity, all experiments were done at a fixed viscosity ratio of around unity, achieved by adjusting the temperature appropriately for each blend. When the droplet elasticity increases, the steady-state deformation of isolated droplets decreases for fixed capillary number. The critical capillary number for breakup (Cacrit) increases linearly with the Weissenberg number of the droplet phase (Wid) up to a value of Wid of around unity. When Wid is greater than unity, Cacrit seems to approach an asymptotic value of 0.95 for high values of Wid. For 10%-dispersed phase blends, the steady-state capillary number (Cass) calculated from a volume-averaged droplet diameter is less than the Cacrit for isolated droplets for the same blend. Cass increases monotonically with the first normal stress difference of the droplet phase. Droplet widening in the vorticity direction is not observed even at droplet Weissenberg numbers much in excess of those for which widening is observed in blends of melts, suggesting that widening is strongly influenced by factors other than the first normal stress difference, such as shear thinning or second normal stress differences.
Director reorientation of a side-chain liquid crystalline polymer under extensional flow
Authors: Cormier Ryan J. , Schmidt Claudia , Callaghan Paul T.
Published: July 2004

When a nematic liquid crystal is subject to deformational flow, rotational torques arising from the Leslie viscosities lead to director realignment. In the case when a magnetic field is present these torques compete with the alignment torque associated with magnetic anisotropy. Under purely extensional flow, this competition results in a sudden director flip at a critical rate of strain given by ε̇c=χaB02/(μ0|α3+α2|), where χa is the anisotropy of the magnetic susceptibility per unit volume of the liquid crystalline polymer, and α2 and α3 are viscosity coefficients arising from the anisotropic (or viscous) part of the stress tensor in the Leslie–Ericksen velocity equation. Using a four-roll mill placed in the 7 T magnet of a nuclear magnetic resonance (NMR) spectrometer, we have observed the orientation of the director, as a function of strain rate, for a flow aligning liquid crystalline polymer consisting of a polysiloxane backbone and mesogenic 4-methoxyphenyl-4′-butenyloxybenzoate side chains, the temperature being 348 K, just a few degrees below the nematic to isotropic transition. Director orientations were obtained using H2 NMR spectral splittings from a probe molecule species comprising <10% methyl-(sulfoxide)-d6. A distinct director flip is observed at a value of strain rate measured by NMR velocimetry to be 0.037 s−1. From this value we determine |α2+α3|/χa∼107×107 Pa s.
Broad frequency range characterization of molten polymers
Authors: He Chunxia , Wood-Adams Paula , Dealy John M.
Published: July 2004

We report a technique for obtaining the continuous retardation spectrum or relaxation spectrum over a very broad range of relaxation times. The major challenge is to obtain reliable data at the long-time end of the spectrum. It is often not practical to use low-frequency oscillatory shear to obtain the necessary data because of the very long time required for the measurements. Polyolefins pose special problems in long-time characterization, because time-temperature superposition is not very useful. Information about the long-time behavior can be obtained by means of creep experiments, but now another problem arises. If we use a stress sufficiently large to yield precise data, the strain may go beyond the limit of linear viscoelastic behavior before steady state is achieved. This problem can be addressed by eliminating the stress well before nonlinearity becomes a problem and tracking the resulting recovery. Using a method proposed by Meissner, the combined creep and recovery data can be used to construct the entire creep curve. The final challenge is to combine the data from the oscillatory shear and creep experiments to obtain a composite linear spectrum. We propose a new method for accomplishing this. Retardation spectra are inferred from both sets of data and compared to reveal the range of times over which both techniques provide reliable data and the range in which each technique is uniquely reliable. The two spectra can then be combined to form a composite spectrum, which can be used to calculate any linear material function. This procedure is demonstrated for two branched polypropylenes whose terminal zones could not be accessed by means of oscillatory shear. For each of these materials, we found that the spectra obtained by the two experimental techniques superposed perfectly within the region of overlapping experimental windows, making it possible to construct a reliable composite spectrum valid over a wide range of times. The composite continuous spectrum is more directly related to molecular structure than rheological properties, such as the complex modulus, which involve integrals of the spectrum.
A model for post-flow induced crystallization: General equations and predictions
Authors: Zheng R. , Kennedy P. K.
Published: July 2004

The aim of this work is to model the flow-enhanced crystallization and the flow-induced morphological changes of semi-crystalline materials during and after shearing flow. A FENE-P dumbbell model and a rigid dumbbell model are used to describe the molecular chain conformation and the orientation evolution for the amorphous phase and the semi-crystalline phase, respectively. The effect of flow on crystallization is considered by relating excess free energy and flow-induced orientation to crystallization kinetics. The crystallization of the material couples back to influence the solidification rheology of the crystallizing system. An isotactic polypropylene is used as an example to illustrate model predictions. We predict a pronounced effect of short-term shear treatments in accelerating nucleation and changing rheological behavior. Results are compared with available experimental data.
Monte Carlo simulation of steady extensional flows
Authors: Li Xianfeng , Denn Morton M.
Published: July 2004

An efficient nonequilibrium Monte Carlo method using the Bond fluctuation model is used to simulate uniaxial and planar extension of dilute polymer solutions. The time scale is obtained from the stress relaxation of a fully stretched chain and can be related to the longest relaxation time of a real molecule, while the length scale is taken to be the statistical Kuhn segment length. The method leads to τ1∼N2.16 and D∼N−1.02 for a freely draining chain with an excluded volume constraint, where τ1, N, and D are the longest relaxation time, chain length, and diffusion coefficient, respectively. The finite extensibility of the bond causes extension thinning following the coil-stretch transition. The Monte Carlo predictions for the transient extension of isolated DNA molecules in a planar extensional flow agree reasonably well with published experimental measurements and Brownian dynamics simulations. “Molecular individualism” is observed in the unraveling of the polymer chain.
Visualization of individual DNA molecules in a small-scale coating flow
Authors: Duggal Rajat , Pasquali Matteo
Published: July 2004

Individual DNA molecules in an ultradilute solution were observed with a fluorescence microscope as they flow between a scaled-down rotating roll and a stationary glass knife. The roll picks up a thin layer of liquid from a pool and drags it to the knife, establishing a bead delineated by two menisci. At low roll speed the flow is premetered and there is a large recirculation. The DNA experiences nearly rectilinear shear flow at the minimum gap position where there is a zero velocity surface. We report the mean and the distribution of fractional extension of DNA molecules and show that the mean fractional extension asymptotes to 0.5, in agreement with the results of Smith et al. [D. E. Smith et al., Science 283, 1724 (1999)]. Interestingly, no polymer distortion is observed at the two menisci. At high roll speed, capillarity is not strong enough to drive backflow; the big recirculation under the coverslip breaks into two smaller recirculations and two separation surfaces arise upstream and downstream of the location of the minimum gap. At the upstream separation surface, most DNA molecules are extended parallel to the knife as they traverse the field of view. We report the distribution of DNA extension and shape in this flow region. Slow, nodular recirculations are present under the upstream and downstream free surfaces. Notably, most DNA molecules stretch axially as they move in these slow recirculating regions.
Silencing the Jasmonate Cascade: Induced Plant Defenses and Insect Populations
Authors: Kessler André , Halitschke Rayko , Baldwin Ian T.
Published: July 2004

We transformed the native tobacco,
Nicotiana attenuata
, to silence its lipoxygenase, hydroperoxide lyase, and allene oxide synthase genes in order to inhibit oxylipin signaling, known to mediate the plant's direct and indirect defenses. When planted into native habitats, lipoxygenase-deficient plants were more vulnerable to
N. attenuata
's adapted herbivores but also attracted novel herbivore species, which fed and reproduced successfully. In addition to highlighting the value of genetically silencing plants to study ecological interactions in nature, these results show that lipoxygenase-dependent signaling determines host selection for opportunistic herbivores and that induced defenses influence herbivore community composition.
That's My Hand! Activity in Premotor Cortex Reflects Feeling of Ownership of a Limb
Authors: Ehrsson H. Henrik , Spence Charles , Passingham Richard E.
Published: July 2004

When we look at our hands, we immediately know that they are part of our own body. This feeling of ownership of our limbs is a fundamental aspect of self-consciousness. We have studied the neuronal counterparts of this experience. A perceptual illusion was used to manipulate feelings of ownership of a rubber hand presented in front of healthy subjects while brain activity was measured by functional magnetic resonance imaging. The neural activity in the premotor cortex reflected the feeling of ownership of the hand. This suggests that multisensory integration in the premotor cortex provides a mechanism for bodily self-attribution.
FORMATION OF TRANSPORT BARRIER BY SHEARING
Authors: KIM EUN-JIN
Published: July 2004

We review the effect of shearing on transport and the formation of transport barriers. The focus is primarily on laboratory plasmas where the formation of transport barriers (the L–H transition) is thought to originate from the turbulence regulation due to both (coherent) mean and (random) zonal flows. We provide quantitative discussion on the reduction of turbulent transport by these flows and elucidate their roles in the barrier formation.
A CRYSTAL STRUCTURE STUDY OF La1-xCaxMnO3 NANOPARTICLES
Authors: DUAN YINGWEN , LI JIANGONG
Published: July 2004

Using a sol-gel method, La 1-x Ca x MnO 3(0≤x≤0.5) nanoparticles with nearly the same average grain size of about 21 nm and different Ca contents, La 0.8 Ca 0.2 MnO 3 nanoparticles with various average grain sizes were prepared. Crystal structure was investigated by X-ray diffraction. Increasing Ca content and decreasing grain size can lead to the average Mn–O bond lengths decrease and Mn–O–Mn bond angles increase. The crystal symmetry changes from orthorhombic to cubic as x≥0.3 for the La 1-x Ca x MnO 3(0≤x≤0.5) nanoparticles with nearly the same average grain size and D~16 nm for the La 0.8 Ca 0.2 MnO 3 nanoparticles with various grain sizes. Small-size effect and surface effect may be the reasons of the lattice distortion and structure transition.
MEAN-FIELD AND FLUCTUATION ANALYSIS OF A FORCED TURBULENCE SIMULATED BY THE LATTICE BOLTZMANN METHOD
Authors: SAKIKAWA WATARU , NARIKIYO OSAMU
Published: July 2004

On the basis of the lattice Boltzmann method for the Navier–Stokes equation, we have done a numerical experiment of a forced turbulence in real space and time. Our new findings are summarized into two points. Firstly, in the analysis of the mean-field behavior of the velocity field using the exit-time statistics, we have verified Kolmogorov's scaling and Taylor's hypothesis at the same time. Secondly, in the analysis of the intermittent velocity fluctuations using a non-equilibrium probability distribution function and the wavelet denoising, we have clarified that the coherent vortices sustain the power-law velocity correlation in the non-equilibrium state.
CYLINDRICAL HIERARCHY FOR DEFORMING NECKLACES
Authors: BEREG SERGEY
Published: July 2004

Recently, Guibas et al.10 studied deformable necklaces — flexible chains of balls, called beads, in which only adjacent balls can intersect. In this paper, we investigate the problem of covering a necklace by cylinders. We consider several problems under different optimization criteria. We show that optimal cylindrical cover of a necklace with n beads in ℝ3 by k cylinders can be computed in polynomial time. We also study a bounding volume hierarchy based on cylinders.
TETRIS IS HARD, EVEN TO APPROXIMATE
Authors: BREUKELAAR RON , DEMAINE ERIK D. , HOHENBERGER SUSAN , HOOGEBOOM HENDRIK JAN , KOSTERS WALTER A. , LIBEN-NOWELL DAVID
Published: July 2004

In the popular computer game of Tetris, the player is given a sequence of tetromino pieces and must pack them into a rectangular gameboard initially occupied by a given configuration of filled squares; any completely filled row of the gameboard is cleared and all filled squares above it drop by one row. We prove that in the offline version of Tetris, it is [Formula: see text]-complete to maximize the number of cleared rows, maximize the number of tetrises (quadruples of rows simultaneously filled and cleared), minimize the maximum height of an occupied square, or maximize the number of pieces placed before the game ends. We furthermore show the extreme inapproximability of the first and last of these objectives to within a factor of p1-ε, when given a sequence of p pieces, and the inapproximability of the third objective to within a factor of 2-ε, for any ε>0. Our results hold under several variations on the rules of Tetris, including different models of rotation, limitations on player agility, and restricted piece sets.
EFFICIENT CONSTRUCTION OF LOW WEIGHTED BOUNDED DEGREE PLANAR SPANNER
Authors: LI XIANG-YANG , WANG YU
Published: July 2004

Given a set V of n points in a two-dimensional plane, we give an O(n log n)-time centralized algorithm that constructs a planar t-spanner for V, for [Formula: see text] such that the degree of each node is bounded from above by [Formula: see text], where 0<α<π/2 is an adjustable parameter. Here Cdel is the spanning ratio of the Delaunay triangulation, which is at most [Formula: see text]. We also show, by applying the greedy method in Ref. [14], how to construct a low weighted bounded degree planar spanner with spanning ratio ρ(α)2(1+∊) and the same degree bound, where ∊ is any positive real constant. Here, a structure is called low weighted if its total edge length is proportional to the total edge length of the Euclidean minimum spanning tree of V. Moreover, we show that our method can be extended to construct a planar bounded degree spanner for unit disk graphs with the adjustable parameter α satisfying 0<α<π/3. Previously, only centralized method6 of constructing bounded degree planar spanner is known, with degree bound 27 and spanning ratio t≃10.02. The distributed implementation of this centralized method takes O(n2) communications in the worst case. Our method can be converted to a localized algorithm where the total number of messages sent by all nodes is at most O(n).
DETERMINATION OF THE PARAMETERS OF CANCELLOUS BONE USING LOW FREQUENCY ACOUSTIC MEASUREMENTS
Authors: BUCHANAN JAMES L. , GILBERT ROBERT P. , KHASHANAH KHALDOUN
Published: July 2004

The Biot model is widely used to model poroelastic media. Several authors have studied its applicability to cancellous bone. In this article the feasibility of determining the Biot parameters of cancellous bone by acoustic interrogation using frequencies in the 5–15 kHz range is studied. It is found that the porosity of the specimen can be determined with a high degree of accuracy. The degree to which other parameters can be determined accurately depends upon porosity.
ON THE USE OF THE REASSIGNED WAVELET TRANSFORM FOR MODE IDENTIFICATION
Authors: TAROUDAKIS MICHAEL I. , TZAGKARAKIS GEORGE
Published: July 2004

This paper is concerned with the use of the reassigned wavelet transform for mode identification in shallow water acoustic propagation. Mode identification is important for inverse procedures in underwater acoustics. An efficient way to recognize the modal structure of the acoustic field when a single hydrophone is available is to refer to the time frequency analysis of the recorded signal using wavelet transform. However, the standard wavelet transform in some cases may result in an obscure representation of the dispersion curves. Thus, a reassigned process is proposed which brings important improvements in the time frequency representation of the signal. This is achieved by moving the calculation point of the scalogram in the center of gravity of the energy concentration, associated with each one of the propagating modes. This argument is supported by two illustrative examples corresponding to propagation of low frequency tomographic signals, in shallow water.
SCATTERING NEAR A PLANE INTERFACE USING A GENERALIZED METHOD OF IMAGES APPROACH
Authors: COATANHAY ARNAUD , CONOIR JEAN-MARC
Published: July 2004

A new method for predicting the scattered acoustic field due to a plane wave incident upon an infinitely long cylinder lying near an penetrable plane interface is presented. The method generalizes the method of images which is restricted to rigid and soft plane interfaces. Validity domains, physical interpretations, simulations and numerical results are described for sedimentary medium-fluid plane interfaces. And, they are well compared with high frequency asymptotic results based on the Geometrical Theory of Diffraction(G.T.D.).
A MODAL METHOD FOR COUPLED FLUID-STRUCTURE INTERACTION ANALYSIS
Authors: LI SHENG , ZHAO DEYOU
Published: July 2004

A modal method is developed for solving, analyzing, and controlling vibration and sound radiation of coupled fluid-structure systems. The method recasts the coupled equation of a coupled fluid-structure system in the classical matrix structural dynamic equation by modeling the acoustic load vector as direct linear function of the acceleration, velocity, and displacement vector. With the Rayleigh damping assumption of the coupled fluid-structure system the resulting equation can be uncoupled via a transformation to modal coordinates and analyzed by solving independent equations of single degree of freedom system. The modal radiation efficiencies, effect of modal interaction on sound radiation, mode shapes, and modal control of the coupled fluid-structure system are presented and discussed. Numerical example of the vibration and sound radiation of a fluid-loaded stiffened plate is presented solely as a vehicle to demonstrate the method. The comparisons in terms of computed sound power of the present method with the standard coupling method and available published results show a very good agreement. The mode shapes and the self- and mutual-radiation efficiencies of modes of the fluid-loaded stiffened plate are given and discussed. The study of the effect of modal interaction on sound power shows that the power radiated by a single mode is to increase total radiated power and the interaction of modes may lead to an increase or a decrease or no change in the total radiated power. Numerical results also show that the modal control achieves good reductions in the mean square velocity and the sound power of the fluid-loaded stiffened plate.
PARALLEL ALGORITHMS FOR ADAPTIVE MATCHED-FIELD PROCESSING ON DISTRIBUTED ARRAY SYSTEMS
Authors: CHO KILSEOK , GEORGE ALAN D. , SUBRAMANIYAN RAJ , KIM KEONWOOK
Published: July 2004

Matched-field processing (MFP) localizes sources more accurately than plane-wave beamforming by employing full-wave acoustic propagation models for the cluttered ocean environment. The minimum variance distortionless response MFP (MVDR–MFP) algorithm incorporates the MVDR technique into the MFP algorithm to enhance beamforming performance. Such an adaptive MFP algorithm involves intensive computational and memory requirements due to its complex acoustic model and environmental adaptation. The real-time implementation of adaptive MFP algorithms for large surveillance areas presents a serious computational challenge where high-performance embedded computing and parallel processing may be required to meet real-time constraints. In this paper, three parallel algorithms based on domain decomposition techniques are presented for the MVDR–MFP algorithm on distributed array systems. The parallel performance factors in terms of execution times, communication times, parallel efficiencies, and memory capacities are examined on three potential distributed systems including two types of digital signal processor arrays and a cluster of personal computers. The performance results demonstrate that these parallel algorithms provide a feasible solution for real-time, scalable, and cost-effective adaptive beamforming on embedded, distributed array systems.
Oxidative DNA damage and DNA repair enzyme expression are inversely related in murine models of fatty liver disease
Authors: Gao Daqing , Wei Chiming , Chen Lei , Huang Jiawen , Yang Shiqi , Diehl Anna Mae
Published: July 2004

Mitochondrial generation of reactive oxygen species (ROS) is increased in mice with fatty livers induced by genetic obesity, chronic consumption of ethanol, or methionine/choline-deficient diets. Both nuclear and mitochondrial (mt) DNA are targets for ROS-induced damage and accumulate hydroxylated bases, such as 8-hydroxy-2′-deoxyguanosine (8-oxoG) and base substitution of adenine with 8-oxoG (A*8-oxoG), that introduce mutations that promote cancer as well as cell death. The mammalian homolog of the bacterial DNA mismatch repair enzyme MutY (MYH) removes A*8-oxoG from nuclear and mtDNA, reduces 8-oxoG accumulation, and restores genomic stability after ROS exposure. Cumulative damage to mtDNA occurs as fatty liver disease progresses. Therefore, differences in hepatic MYH activity may influence the severity of fatty liver disease. To evaluate this hypothesis, we compared mtH2O2 production, MYH expression, oxidative DNA damage, and hepatocyte death in healthy mice and different mouse models of fatty liver disease. The results show that diverse causes of steatohepatitis increase mtROS production, limit repair of mtDNA, and oxidatively damage DNA. However, there are important differences in the DNA repair response to oxidant stress among mouse models of fatty liver disease. Independent of the degree of mtROS generation, models with the least MYH exhibit the greatest accumulation of 8-oxoG and the most hepatocyte death. These findings raise the intriguing possibility that inherited or acquired differences in DNA repair enzyme activity may underlie some of the interindividual differences in fatty liver disease outcomes.
Modulatory influences on antegrade and retrograde tonic reflexes in the colon and rectum
Authors: Ng Clinton , Danta Mark , Prott Gillian , Badcock Caro-Anne , Kellow John , Malcolm Allison
Published: July 2004

Tonic reflexes in the colon and rectum are likely to be important in health and in disorders of gastrointestinal function. The aim of this study was to evaluate the fasting and postprandial “colorectal” and “rectocolic” reflexes in response to 2-min isobaric distensions of the colon and rectum, accounting for enteric sensation, compliance, and distending balloon volume. In 14 healthy fasting subjects, a dual barostat assembly was positioned (descending colon and rectum). A 2-min phasic distension was performed in the colon and rectum in random order while the opposing balloon volume was recorded. Sensation (phasic distension) and compliance (ramp distension) were also determined. The experiment was repeated postprandially. Colonic distension resulted in significant rectal tonic contraction in the fasting (rectal volume change: −35.4 ± 8.4 ml, P < 0.01) and postprandial (−22.2 ± 8.4 ml, P < 0.01) states. After adjustment for colonic sensitivity, for compliance, and for distending balloon volume, the rectal volume change remained significant; the extent of the tonic response, however, correlated significantly with increasing pain score ( P < 0.01). In contrast, rectal distension did not produce a significant tonic response in the colon (fasting: −6.5 ± 7.3 ml; postprandial: 2.7 ± 7.3 ml), either unadjusted or adjusted for rectal sensitivity, compliance, and distending balloon volume. In conclusion, the colorectal reflex, but not the rectocolic reflex, can be readily demonstrated both before and after a meal in response to a 2-min isobaric distension in the colon and rectum, respectively. Although the presence of the colorectal reflex does not depend on colonic sensitivity or the volume of the distending colonic balloon, these factors modulate the reflex, especially in the fasting state.
Theoretical considerations in the dynamic closed-loop baroreflex and autoregulatory control of total peripheral resistance
Authors: Aljuri Nikolai , Cohen Richard J.
Published: July 2004

The most important goal of this study is to enhance our understanding of the crucial functional relationships that determine the behavior of the systemic circulation and its underlying physiological regulatory mechanisms with minimal modeling. To the present day, much has been said about the indirect hydraulic effects of right atrial pressure (PRA) via cardiac output (CO) on arterial pressure (Pa) through the heart and pulmonary circulation or the direct regulatory effects of PRAon Pathrough the cardiopulmonary baroreflex; however, very little attention has been given to the hydraulic influence that PRAexerts directly through the systemic circulation. The experimental data reported by Guyton et al. in 1957 demonstrated that steady-state PRAand the rate at which blood passes through the systemic circulation are locked in a functional relationship independent of any consequence of altered PRAon cardiac function. With this in mind, we emphasize the analytic algebraic analysis of the systemic circulation composed of arteries, veins, and its underlying physiological regulatory mechanisms of baroreflex and autoregulatory modulation of total peripheral resistance (TPR), where the behavior of the system can be analytically synthesized from an understanding of its minimal elements. As a result of this analysis, we present a novel mathematical method to determine short-term TPR fluctuations, which accounts for the entirety of observed Pafluctuations, and propose a new cardiovascular system identification method to delineate the actual actions of the physiological mechanisms responsible for the dynamic couplings between CO, Pa, PRA, and TPR in an individual subject.