bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniqueness theorems in inverse spectral theory for one-dimensional Schrödinger operators
Authors: Gesztesy F. , Simon B.
Published: July 2002

New unique characterization results for the potential

V
(
x
)

V(x)

in connection with Schrödinger operators on

R

\Bbb R

and on the half-line

[
0
,
∞
)

[0,\infty )

are proven in terms of appropriate Krein spectral shift functions. Particular results obtained include a generalization of a well-known uniqueness theorem of Borg and Marchenko for Schrödinger operators on the half-line with purely discrete spectra to arbitrary spectral types and a new uniqueness result for Schrödinger operators with confining potentials on the entire real line.
Spectral element discretization of the Maxwell equations
Authors: Belgacem F. , Bernardi C.
Published: July 2002

We consider a variational problem which is equivalent to the electromagnetism system with absorbing conditions on a part of the boundary, and we prove that it is well-posed. Next we propose a discretization relying on a finite difference scheme for the time variable and on spectral elements for the space variables, and we derive error estimates between the exact and discrete solutions. Résumé. On considère un problème variationnel équivalent aux équations de l’électromagnétisme avec conditions aux limites absorbantes sur une partie de la frontière, qu’on prouve être bien posé. Puis on propose une discrétisation de ce problème par schéma aux différences finies en temps et éléments spectraux en espace, et on établit des estimations d’erreur entre solutions exacte et approchée.
Stu1p Is Physically Associated with β-Tubulin and Is Required for Structural Integrity of the Mitotic Spindle
Authors: Yin Hongwei , You Liru , Pasqualone Danielle , Kopski Kristen M. , Huffaker Tim C.
Published: July 2002

Formation of the bipolar mitotic spindle relies on a balance of forces acting on the spindle poles. The primary outward force is generated by the kinesin-related proteins of the BimC family that cross-link antiparallel interpolar microtubules and slide them past each other. Here, we provide evidence that Stu1p is also required for the production of this outward force in the yeast Saccharomyces cerevisiae. In the temperature-sensitive stu1–5mutant, spindle pole separation is inhibited, and preanaphase spindles collapse, with their previously separated poles being drawn together. The temperature sensitivity of stu1–5 can be suppressed by doubling the dosage of Cin8p, a yeast BimC kinesin–related protein. Stu1p was observed to be a component of the mitotic spindle localizing to the midregion of anaphase spindles. It also binds to microtubules in vitro, and we have examined the nature of this interaction. We show that Stu1p interacts specifically with β-tubulin and identify the domains required for this interaction on both Stu1p and β-tubulin. Taken together, these findings suggest that Stu1p binds to interpolar microtubules of the mitotic spindle and plays an essential role in their ability to provide an outward force on the spindle poles.
J-Express: exploring gene expression data using Java
Authors: Dysvik B. , Jonassen I.
Published: July 2002

Summary: J-Express is a Java application that allows the user to analyze gene expression (microarray) data in a flexible way giving access to multidimensional scaling, clustering, and visualization methods in an integrated manner. Specifically, J-Express includes implementations of hierarchical clustering, k-means, principal component analysis, and self-organizing maps. At present, it does not include methods for comparing two or more experiments for differentially expressed genes. The application is completely portable and requires only that a Java runtime environment 1.2 is installed on the system. Its efficiency allows interactive clustering of thousands of expression profiles on standard personal computers.

Availability: http://www.ii.uib.no/~bjarted/jexpress/

Contact: bjarted@ii.uib.no

* To whom correspondence should be addressed.
HOMSTRAD: adding sequence information to structure-based
alignments of homologous protein families
Authors: de Bakker P. I. W. , Bateman A. , Burke D. F. , Miguel R. N. , Mizuguchi K. , Shi J. , Shirai H. , Blundell T. L.
Published: July 2002

Summary: We describe an extension to the Homologous Structure Alignment Database (HOMSTRAD; Mizuguchi et al. , Protein Sci. , 7, 2469–2471, 1998a) to include homologous sequences derived from the protein families database Pfam (Bateman et al. , Nucleic Acids Res. , 28, 263–266, 2000). HOMSTRAD is integrated with the server FUGUE (Shi et al. , submitted, 2001) for recognition and alignment of homologues, benefitting from the combination of abundant sequence information and accurate structure-based alignments.

Availability: The HOMSTRAD database is available at: http://www-cryst.bioc.cam.ac.uk/homstrad/. Query sequences can be submitted to the homology recognition/alignment server FUGUE at: http://www-cryst.bioc.cam.ac.uk/fugue/.

Contact: homstrad@cryst.bioc.cam.ac.uk
A continuous dynamic beam model for swimming fish
Authors: Cheng J.–Y. , Pedley T. J. , Altringham J. D.
Published: July 2002

When a fish swims in water, muscle contraction, controlled by the nervous system, interacts with the body tissues and the surrounding fluid to yield the observed movement pattern of the body. A continuous dynamic beam model describing the bending moment balance on the body for such an interaction during swimming has been established. In the model a linear visco–elastic assumption is made for the passive behaviour of internal tissues, skin and backbone, and the unsteady fluid force acting on the swimming body is calculated by the 3D waving plate theory. The body bending moment distribution due to the various components, in isolation and acting together, is analysed. The analysis is based on the saithe (Pollachius virens), a carangiform swimmer. The fluid reaction needs a bending moment of increasing amplitude towards the tail and near–standing wave behaviour on the rear–half of the body. The inertial movement of the fish results from a wave of bending moment with increasing amplitude along the body and a higher propagation speed than that of body bending. In particular, the fluid reaction, mainly designed for propulsion, can provide a considerable force to balance the local momentum change of the body and thereby reduce the power required from the muscle. The wave of passive visco–elastic bending moment, with an amplitude distribution peaking a little before the mid–point of the fish, travels with a speed close to that of body bending. The calculated muscle bending moment from the whole dynamic system has a wave speed almost the same as that observed for EMG–onset and a starting instant close to that of muscle activation, suggesting a consistent matching between the muscle activation pattern and the dynamic response of the system in steady swimming. A faster wave of muscle activation, with a variable phase relation between the strain and activation cycle, appears to be designed to fit the fluid reaction and, to a lesser extent, the body inertia, and is limited by the passive internal tissues. Higher active stress is required from caudal muscle, as predicted from experimental studies on fish muscle. In general, the active force development by muscle does not coincide with the propulsive force generation on the tail. The stiffer backbone may play a role in transmitting force and deformation to maintain and adjust the movement of the body and tail in water.
Spectral tuning and the visual ecology of mantis shrimps
Authors: Cronin Thomas W. , Marshall N. Justin , Caldwell Roy L.
Published: July 2002

The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photic environments, from intertidal to deep water (> 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well–known pattern of decreasing λ
max
with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual λ
max
–values near 500 nm, independent of depth. Finally, the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.
Bidirectional action of the Igf2r imprint control element on upstream and downstream imprinted genes
Authors: Zwart Ronald , Sleutels Frank , Wutz Anton , Schinkel Alfred H. , Barlow Denise P.
Published: July 2002

Imprinting of the maternally-expressed Igf2r gene is controlled by an intronic imprint control element (ICE) known as Region2 that contains the promoter of the noncoding Air RNA, whose transcript overlaps the silenced paternal Igf2r promoter in an antisense orientation. Two novel imprinted genes, Slc22a2and Slc22a3 are described here that lie 110 and 155 kb 3′ toIgf2r and that are not overlapped by the Air transcript but are regulated by the Igf2r-ICE, as previously shown forIgf2r. These results identify a new cluster of imprinted genes whose repression by the bidirectional action of the Region2-ICE is independent of transcript overlap by the Air RNA.
The zinc-finger proto-oncogene Gfi-1b is essential for development of the erythroid and megakaryocytic lineages
Authors: Saleque Shireen , Cameron Scott , Orkin Stuart H.
Published: July 2002

Gfi-1 and Gfi-1b are novel proto-oncogenes identified by retroviral insertional mutagenesis. By gene targeting, we establish that Gfi-1b is required for the development of two related blood lineages, erythroid and megakaryocytic, in mice.Gfi-1b−/− embryonic stem cells fail to contribute to red cells of adult chimeras. Gfi-1b−/− embryos exhibit delayed maturation of primitive erythrocytes and subsequently die with failure to produce definitive enucleated erythrocytes. The fetal liver of mutant mice contains erythroid and megakaryocytic precursors arrested in their development. Myelopoiesis is normal. Therefore, Gfi-1b is an essential transcriptional regulator of erythroid and megakaryocyte development.
Improvement of mammographic mass characterization using spiculation measures and morphological features
Authors: Sahiner Berkman , Chan Heang‐Ping , Petrick Nicholas , Helvie Mark A. , Hadjiiski Lubomir M.
Published: July 2002

We are developing new computer vision techniques for characterization of breast masses on mammograms. We had previously developed a characterization method based on texture features. The goal of the present work was to improve our characterization method by making use of morphological features. Toward this goal, we have developed a fully automated, three‐stage segmentation method that includes clustering, active contour, and spiculation detection stages. After segmentation, morphological features describing the shape of the mass were extracted. Texture features were also extracted from a band of pixels surrounding the mass. Stepwise feature selection and linear discriminant analysis were employed in the morphological, texture, and combined feature spaces for classifier design. The classification accuracy was evaluated using the area under the receiver operating characteristic curve. A data set containing 249 films from 102 patients was used. When the leave‐one‐case‐out method was applied to partition the data set into trainers and testers, the average test for the task of classifying the mass on a single mammographic view was 0.83±0.02, 0.84±0.02, and 0.87±0.02 in the morphological, texture, and combined feature spaces, respectively. The improvement obtained by supplementing texture features with morphological features in classification was statistically significant For classifying a mass as malignant or benign, we combined the leave‐one‐case‐out discriminant scores from different views of a mass to obtain a summary score. In this task, the test value using the combined feature space was 0.91±0.02. Our results indicate that combining texture features with morphological features extracted from automatically segmented mass boundaries will be an effective approach for computer‐aided characterization of mammographic masses.
Forward dose perturbation at high atomic number interfaces in kilovoltage x‐ray beams
Authors: Das Indra J.
Published: July 2002

High atomic number materials such as lead, used for field shaping and shielding normal tissues in kilovoltage beams could produce significant dose enhancement in the forward direction contrary to our normal belief with respect to the attenuation of photon beams. Such a dose enhancement has not been studied in kilovoltage beams, which is investigated in this study. Using a Siemens orthovoltage unit (60–240 kVp) and a thin window (5 μm) parallel plate ion chamber, forward dose perturbation factor (FDPF) was measured at interfaces created by high‐ and low‐ materials. The FDPF is defined as the ratio of doses with and without an interface ( where is the dose at an interface and is the dose in a homogeneous medium). Results indicate that dose enhancement (FDPF>1) as high as 20‐fold can be observed for a thin (⩾0.02 mm) Pb sheet in contact with soft tissue. The magnitude of FDPF is relatively independent of field size and falls off exponentially with Pb thickness. The typical photon beam attenuation takes place at a thickness >1 mm. This intense dose enhancement is localized within 250 μm of the interface. The FDPF is energy dependent but saturates above 140 kVp, unlike the backscatter dose perturbation that peaks around 200 kVp. The FDPF varies inversely with the thickness of high and distance between the surface and high‐ medium. The FDPF falls off rapidly to a level of photon transmission usually predicted by exponential attenuation when distance is increased. In conclusion, with kilovoltage beam, a high‐ medium placed in contact with soft tissue may not attenuate radiation dose unless adequate thickness and proper distance between the surface and high‐ medium is used. The localized intense dose enhancement (≈20‐fold) created by the high‐ interface could be exploited for clinical use.
Determination of scatter factor parameters and electron disequilibrium for monoenergetic photon beams
Authors: McDonough James , Bloch Peter , Bjärngard Bengt E.
Published: July 2002

The tissue‐phantom‐ratio (TPR) is expressed as the product of the phantom scatter factor (SF), an electron disequilibrium factor, and an attenuation factor, equal to the zero‐area TPR. The scatter factor, as a function of depth d and field size s, has been described by two parameters a and w, We have determined the parameters a and w for 20 monoenergetic photon beams between 1 and 20 MeV. Pencil‐beam energy‐deposition kernels were obtained using Monte Carlo simulations. The kernels were used to calculate broad‐beam depth‐dose data, which were converted to TPR and fitted to the equation above using an iterative search over space. The parameter a is nearly equal to the attenuation coefficient for all energies while the parameter w increases with energy. The resulting a and w compare favorably to values determined for clinical photon beams, as a function of the measured attenuation coefficient. With the scatter factor determined, we isolated the electron disequilibrium factor for each monoenergetic beam. It can be characterized as a quadratic function of the depth. The coefficients of the quadratic function can be related to the range of the most energetic secondary electron produced.
The rolling motion of an eccentrically loaded wheel
Authors: Theron W. F. D.
Published: July 2002

This article discusses the rolling motion on a rough plane of a wheel whose center of mass does not coincide with the axis; for example, when a heavy particle is fixed to the rim of a rigid hoop. In cases with large eccentricity, the resulting motion is surprisingly complex, with four phases being identified, namely rolling (without slipping), spinning, skidding, and “hopping,” by which is meant that the wheel actually leaves the plane. The main result of this analysis is the identification of the conditions that are required for hopping to occur. A second result is that faster than gravity accelerations occur when the mass of the particle is greater than the mass of the hoop. Massless hoops are briefly discussed as a special case of the general results.
Relative motion of orbiting bodies
Authors: Butikov Eugene I.
Published: July 2002

A problem of relative motion of orbiting bodies is investigated on the example of the free motion of any body ejected from the orbital station that stays in a circular orbit around the earth. An elementary approach is illustrated by a simulation computer program and supported by a mathematical treatment based on approximate differential equations of the relative orbital motion.
Measuring air resistance in a computerized laboratory
Authors: Takahashi Ken , Thompson D.
Published: July 2002

By dropping spherical party balloons onto a sonic motion sensor we show that the force associated with the air resistance is proportional to both the square of the velocity and to the cross-sectional area of the balloon. These results are in agreement with those expected for the value of the Reynolds number used, R≈104.
Effects of frequency and level on auditory stream segregation
Authors: Rose Marina M. , Moore Brian C. J.
Published: July 2002

This study examined the effect of center frequency and level on the perceptual grouping of rapid tone sequences. The sequence ABA-ABA- ⋯ was used, where A and B represent sinusoidal tone bursts (10-ms rise/fall, 80-ms steady state, 20-ms interval between tones) and - represents a silent interval of 120 ms. In experiment 1, tone A was fixed in frequency at 62, 125, 250, 500, 1000, 2000, 4000, 6000, or 8000 Hz. Both tones had a level of approximately 40 dB SL. Tone B started with a frequency well above that of tone A, and its frequency was swept toward that of tone A so that the frequency separation between them decreased in an exponential manner. Subjects were required to indicate when they could no longer hear the tones A and B as two separate streams, but heard only a single stream with a “gallop” rhythm. This changeover point between percepts is called the fission boundary. The separation between tones A and B at the fission boundary was roughly independent of the frequency of tone A when expressed as the difference in number of equivalent rectangular bandwidths (ERBs) between A and B, but varied more with frequency when the difference was expressed in barks or cents. In experiment 2, the center frequency was fixed at 250, 1000, or 4000 Hz, and the level of the A and B tones was 40, 55, 70, or 85 dB SPL. The frequency separation of the A and B tones at the fission boundary tended to increase slightly with increasing level, in a manner consistent with the broadening of the auditory filter with increasing level. The results support the “peripheral channeling” explanation of stream segregation advanced by Hartmann and Johnson [Music Percept. 9, 155–184 (1991)], and indicate that the perception of fusion or fission in alternating-tone sequences depends partly upon the degree of overlap of the excitation patterns evoked by the successive sounds in the cochlea, as assumed in the theory of Beauvois and Meddis [J. Acoust. Soc. Am. 99, 2270–2280 (1996)].
Intelligibility of bandpass speech: Effects of truncation or removal of transition bands
Authors: Warren Richard M. , Bashford James A. , Lenz Peter W.
Published: July 2002

An intelligibility of over 90% was reported for keywords in “everyday” 1/3-octave sentences centered on 1500 Hz and having steep transition band slopes of 100 dB/octave [Warren et al., Percept. Psychophys. 57, 175–182 (1995)]. A subsequent study by Warren and Bashford [J. Acoust. Soc. Am. 106, L47–L52 (1999)] found that it was not the 1/3-octave passband, but the transition bands that were chiefly responsible for this high intelligibility: When the passband and transition bands were segregated using filter slopes of 1000 dB/octave, the isolated passband had an intelligibility score of only 24%, while the pair of transition bands had a score of over 80%. In the present study, experiment 1 examined the distribution of information along the transition bands’ slopes by truncation at graded downpoints: Truncation at downpoints of 40 dB or more produced no significant change in intelligibility. Experiment 2 closed the gap separating the transition bands so that their slopes intersected at 1500 Hz. This triangular band had a negligible passband (as defined conventionally by 3-dB downpoints) and an intelligibility score of 60%; truncation at downpoints of 50 dB or more produced no significant change in intelligibility. Experiment 3 determined the intelligibilities of rectangular bands (1000-dB/octave slopes) centered on 1500 Hz. Their bandwidths ranged from 3 to 12 semitones in 1-semitone steps, resulting in intelligibility scores increasing monotonically from 14% to 94%. Calculations based upon experiments 2 and 3 showed that the triangular band truncated at 30-dB downpoints had half the intelligibility of a rectangular band having the same frequency range.
Children’s perception of speech in multitalker babble
Authors: Fallon Marianne , Trehub Sandra E. , Schneider Bruce A.
Published: July 2002

Children 5, 9, and 11 years of age and young adults attempted to identify the final word of sentences recorded by a female speaker. The sentences were presented in two levels of multitalker babble, and participants responded by selecting one of four pictures. In a low-noise condition, the signal-to-noise ratio (SNR) was adjusted for each age group to yield 85% correct performance. In a high-noise condition, the SNR was set 7 dB lower than the low-noise condition. Although children required more favorable SNRs than adults to achieve comparable performance in low noise, an equivalent decrease in SNR had comparable consequences for all age groups. Thus age-related differences on this task can be attributed primarily to sensory factors.
Distortion-product source unmixing: A test of the two-mechanism model for DPOAE generation
Authors: Kalluri Radha , Shera Christopher A.
Published: July 2002

This paper tests key predictions of the “two-mechanism model” for the generation of distortion-product otoacoustic emissions (DPOAEs). The two-mechanism model asserts that lower-sideband DPOAEs constitute a mixture of emissions arising not simply from two distinct cochlear locations (as is now well established) but, more importantly, by two fundamentally different mechanisms: nonlinear distortion induced by the traveling wave and linear coherent reflection off pre-existing micromechanical impedance perturbations. The model predicts that (1) DPOAEs evoked by frequency-scaled stimuli (e.g., at fixed f2/f1) can be unmixed into putative distortion- and reflection-source components with the frequency dependence of their phases consistent with the presumed mechanisms of generation; (2) The putative reflection-source component of the total DPOAE closely matches the reflection-source emission (e.g., low level stimulus-frequency emission) measured at the same frequency under similar conditions. These predictions were tested by unmixing DPOAEs into components using two completely different methods: (a) selective suppression of the putative reflection source using a third tone near the distortion-product frequency and (b) spectral smoothing (or, equivalently, time-domain windowing). Although the two methods unmix in very different ways, they yield similar DPOAE components. The properties of the two DPOAE components are consistent with the predictions of the two-mechanism model.
Time-domain simulation of damped impacted plates. II. Numerical model and results
Authors: Lambourg Christophe , Chaigne Antoine , Matignon Denis
Published: July 2002

A time-domain model for the flexural vibrations of damped plates was presented in a companion paper [Part I, J. Acoust. Soc. Am. 109, 1422-1432 (2001)]. In this paper (Part II), the damped-plate model is extended to impact excitation, using Hertz’s law of contact, and is solved numerically in order to synthesize sounds. The numerical method is based on the use of a finite-difference scheme of second order in time and fourth order in space. As a consequence of the damping terms, the stability and dispersion properties of this scheme are modified, compared to the undamped case. The numerical model is used for the time-domain simulation of vibrations and sounds produced by impact on isotropic and orthotropic plates made of various materials (aluminum, glass, carbon fiber and wood). The efficiency of the method is validated by comparisons with analytical and experimental data. The sounds produced show a high degree of similarity with real sounds and allow a clear recognition of each constitutive material of the plate without ambiguity.
On the stability of long-range sound propagation through a structured ocean
Authors: Wolfson Michael A. , Tomsovic Steven
Published: July 2002

Several acoustic experiments show a surprising degree of stability in wave fronts propagating over multi-megameter ranges through the ocean’s sound channel despite the presence of random-like, sound-speed fluctuations. Previous works have pointed out the existence of chaos in simplified ray models incorporating structure inspired by the true ocean environment. A “predictability horizon” has been introduced beyond which stable wavefronts cease to exist and point-wise, detailed comparisons between even the most sophisticated models and experiment may be limited for fundamental reasons. By applying one of the simplified models it is found that, for finite ranges, the fluctuations of the ray stabilities are very broad and consistent with log-normal densities. A fraction of the ray density retains a much more stable character than the typical ray. This may be one of several possible mechanisms leading to greater than anticipated sound-field stability. The log-normal ray stability density may underlie the recent, experimentally determined, log-normal density of wave-field intensities [Colosi et al., J. Acoust. Soc. Am. 105, 3202–3218 (1999)].
Silencer consisting of two-stage Helmholtz resonator with auto-tuning control
Authors: Nagaya Kosuke , Hano Yasudide , Suda Akihisa
Published: July 2002

A Helmholtz resonator has advantages over other noise control methods in that it does not require energy to function and it can be applied to high-frequency noise. In this article, a noise reduction method based on a Helmholtz resonator is discussed in reference to application to a blower. However, as the frequency of noise generated by a blower, although high, varies over time, the Helmholtz resonator is ineffectual if applied directly. In order to reduce varying high-frequency noise, a new type of silencer, comprised of a two-stage rotary auto-tuning resonator, is proposed. A fast Fourier transform (FFT) analysis of noise obtained by a noise meter is used for control. The frequencies of the peak intensities obtained by the FFT vary according to the variations in source frequency. Two significant peaks in the frequency domain are considered, the cost functions of which are taken, allowing for frequency variation. The silencer is tuned by minimizing the cost function. The system and control algorithm are presented in this report, along with the results of experimental tests that were conducted on a typical blower in order to verify the effectiveness of the system and method.
Guided waves energy velocity in absorbing and non-absorbing plates
Authors: Bernard A. , Lowe M. J. S. , Deschamps M.
Published: July 2002

This paper presents a study of the velocity of the propagation of energy in guided waves in plates. The motivation of the work comes from the practical observation that the conventional approach to predicting the velocities of pulses or wave packets, that is, the simple group velocity calculation, breaks down when the guided waves are attenuative. The conventional approach is therefore not valid for guided waves in absorbing materials or for leaky waves. The paper presents a theoretical derivation of an expression to predict the energy velocity of guided waves in an isotropic plate, based on the integration of the Poynting energy vectors. When applied to modes with no attenuation, it is shown analytically from this expression that the energy velocity is always identical to the group velocity. On the other hand, when applied to attenuative modes, numerical integration of the expression to yield the true energy velocity shows that this can differ quite significantly from the group velocity. Experimental validation of the expression is achieved by measuring the velocity of wave packets in an absorbing plate, under such conditions when the energy velocity differs substantially from the group velocity. Excellent agreement is found between the predictions and the measurements. The paper also shows the Poynting vectors in the various model studies, and some interesting phenomena relating to their directions.
Heat transfer from transverse tubes adjacent to a thermoacoustic stack
Authors: Mozurkewich George
Published: July 2002

The goal of this work was to test the usefulness of the time-average steady-flow equivalent (TASFE) approximation for the analysis of heat exchangers for thermoacoustic engines. The TASFE approximation assumes that the heat transfer in an acoustic standing wave with zero mean flow is equivalent to averaging the corresponding steady-flow correlation over a sinusoidal distribution of gas speeds. The experiment tested three simple heat-exchanger configurations located immediately adjacent to the hot end of a thermoacoustic stack. Two configurations consisted of bare, parallel, water-carrying tubes oriented transverse to the mean acoustic flow. A third configuration consisted of a single layer of woven copper screen soldered to transverse tubes. Experiments with pure helium and with a mixture of helium and argon found qualitative, and sometimes quantitative, agreement with expectations of the TASFE approximation at both large and small acoustic amplitudes. In addition, large heat transfer with zero temperature difference between the heat exchanger and the stack was observed and interpreted.
Theoretical and experimental examination of near-field acoustic levitation
Authors: Nomura Hideyuki , Kamakura Tomoo , Matsuda Kazuhisa
Published: July 2002

A planar object can be levitated stably close to a piston sound source by making use of acoustic radiation pressure. This phenomenon is called near-field acoustic levitation [Y. Hashimoto et al., J. Acoust. Soc. Am. 100, 2057–2061 (1996)]. In the present article, the levitation distance is predicted theoretically by numerically solving basic equations in a compressible viscous fluid subject to the appropriate initial and boundary conditions. Additionally, experiments are carried out using a 19.5-kHz piston source with a 40-mm aperture and various aluminum disks of different sizes. The measured levitation distance agrees well with the theory, which is different from a conventional theory, and the levitation distance is not inversely proportional to the square root of the surface density of the levitated disk in a strict sense.
Acoustic identification of female Steller sea lions (Eumetopias jubatus)
Authors: Campbell Gregory S. , Gisiner Robert C. , Helweg David A. , Milette Linda L.
Published: July 2002

Steller sea lion (Eumetopias jubatus) mothers and pups establish and maintain contact with individually distinctive vocalizations. Our objective was to develop a robust neural network to classify females based on their mother-pup contact calls. We catalogued 573 contact calls from 25 females in 1998 and 1323 calls from 46 females in 1999. From this database, a subset of 26 females with sufficient samples of calls was selected for further study. Each female was identified visually by marking patterns, which provided the verification for acoustic identification. Average logarithmic spectra were extracted for each call, and standardized training and generalization datasets created for the neural network classifier. A family of backpropagation networks was generated to assess relative contribution of spectral input bandwidth, frequency resolution, and network architectural variables to classification accuracy. The network with best overall generalization accuracy (71%) used an input representation of 0–3 kHz of bandwidth at 10.77 Hz/bin frequency resolution, and a 2:1 hidden:output layer neural ratio. The network was analyzed to reveal which portions of the call spectra were most influential for identification of each female. Acoustical identification of distinctive female acoustic signatures has several potentially important conservation applications for this endangered species, such as rapid survey of females present on a rookery.
Theory of compressional and shear waves in fluidlike marine sediments
Authors: Buckingham Michael J.
Published: July 2002

An unconsolidated, saturated marine sediment consists of a more or less loose assemblage of mineral grains in contact, with seawater in the interstices. It is postulated that the two-phase medium possesses no skeletal frame, implying that the elastic rigidity modulus of the material is zero. A theory of wave propagation in such a sediment is developed, in which the medium is treated as a fluid that supports a specific form of intergranular dissipation. Two important equations emerge from the analysis, one for compressional wave propagation and the second describing transverse disturbances. For the type of dissipation considered, which exhibits hysteresis or memory, the shear equation admits a wavelike solution, and is thus a genuine wave equation, even though the sediment shows no elastic rigidity. In effect, the medium possesses a “dissipative” rigidity, which is capable of supporting shear. This behavior is distinct from that of a viscous fluid, for which the shear equation is diffusionlike in character, giving rise to critically damped disturbances rather than propagating waves. The new theory predicts an attenuation coefficient for both compressional and shear waves that scales with the first power of frequency, in accord with published data. The wave theory is combined with a model of the mechanical properties of marine sediments to yield expressions relating the compressional and shear wave speeds to the grain size, the porosity, and the density of the medium. These expressions show compelling agreement with a number of measurements from the literature, representing a variety of sediment types ranging from clay to coarse sand.
The influence of belt and tread band stiffness on the tire noise generation mechanisms
Authors: Kropp Wolfgang , Larsson Krister , Barrelet Stephane
Published: July 2002

A brief introduction to a theoretical model is presented which describes a smooth tire rolling on a rough road surface. The model is limited to a two-dimensional contact between tire and road. It includes the vibration properties of the tire, the nonlinear contact, and the sound radiation. It is also taking into account the influence of the acoustic properties of the road surface. The model is applied to determine the sound radiated due to the tire vibrations and the local deformations of the tread band. A parameter study is presented which shows the influence of the bending stiffness of the belt and the stiffness of the tread band on the noise generation and radiation mechanisms. The study also considers the influence of the surface roughness of the road. In this way it is possible to quantify which part of the roughness spectrum is leading to sound generation via tire vibration and which part of the roughness spectrum is involved in the local deformation of the tread band.
Phase conjugation in the ocean: Experimental demonstration of an acoustic time-reversal mirror
Authors: Kuperman W. A. , Hodgkiss William S. , Song Hee Chun , Akal T. , Ferla C. , Jackson Darrell R.
Published: July 2002

An experiment conducted in the Mediterranean Sea in April 1996 demonstrated that a time-reversal mirror (or phase conjugate array) can be implemented to spatially and temporally refocus an incident acoustic field back to its origin. The experiment utilized a vertical source–receiver array (SRA) spanning 77 m of a 125-m water column with 20 sources and receivers and a single source/receiver transponder (SRT) colocated in range with another vertical receive array (VRA) of 46 elements spanning 90 m of a 145-m water column located 6.3 km from the SRA. Phase conjugation was implemented by transmitting a 50-ms pulse from the SRT to the SRA, digitizing the received signal and retransmitting the time reversed signals from all the sources of the SRA. The retransmitted signal then was received at the VRA. An assortment of runs was made to examine the structure of the focal point region and the temporal stability of the process. The phase conjugation process was extremely robust and stable, and the experimental results were consistent with theory.
Observation of acoustic streaming near Albunex® spheres
Authors: Gormley Gerard , Wu Junru
Published: July 2002

Using Albunex® spheres (a contrast agent for ultrasonic imaging), a specially designed microscopic device, a video peak storage technique and micron-size Latex spheres as tracers, acoustic streaming patterns around a single and a pair of Albunex® spheres of a few tens micrometer radius in a 160-kHz ultrasonic standing wave field have been recorded. The spatial peak pressure amplitude of the standing wave was estimated to be of the order of 0.5 MPa with optical interferometry. The acoustic streaming velocity was in the range of 50–100 μm/s.
The neural network classification of false killer whale (Pseudorca crassidens) vocalizations
Authors: Murray Scott O. , Mercado Eduardo , Roitblat Herbert L.
Published: July 2002

This study reports the use of unsupervised, self-organizing neural network to categorize the repertoire of false killer whale vocalizations. Self-organizing networks are capable of detecting patterns in their input and partitioning those patterns into categories without requiring that the number or types of categories be predefined. The inputs for the neural networks were two-dimensional characterization of false killer whale vocalizations, where each vocalization was characterized by a sequence of short-time measurements of duty cycle and peak frequency. The first neural network used competitive learning, where units in a competitive layer distributed themselves to recognize frequently presented input vectors. This network resulted in classes representing typical patterns in the vocalizations. The second network was a Kohonen feature map which organized the outputs topologically, providing a graphical organization of pattern relationships. The networks performed well as measured by (1) the average correlation between the input vectors and the weight vectors for each category, and (2) the ability of the networks to classify novel vocalizations. The techniques used in this study could easily be applied to other species and facilitate the development of objective, comprehensive repertoire models.
Two phase effects in roughness perception
Authors: Pressnitzer Daniel , McAdams Stephen
Published: July 2002

The respective influences of spectral and temporal aspects of sound in roughness perception are examined by way of phase manipulations. In a first experiment, the phase of the central component of three-component signals is shown to modify perceived roughness, for a given amplitude spectrum, regardless of whether it modifies the waveform envelope. A second experiment shows that the shape of the waveform envelope, for a given amplitude spectrum and a given modulation depth, also influences perceived roughness. We interpret both of these results by considering the envelope of an internal representation that is deduced from the physical signal by taking into account peripheral auditory processing. The results indicate that the modulation depth of such an internal representation is not the only determinant of roughness, but that an effect of temporal asymmetry is also to be taken into account.
The mechanical waveform of the basilar membrane. III. Intensity effects
Authors: de Boer Egbert , Nuttall Alfred L.
Published: July 2002

Mechanical responses in the basal turn of the guinea-pig cochlea were measured with broad-band noise stimuli and expressed as input–output cross-correlation functions. The experiments were performed over the full range of stimulus intensities in order to try to understand the influence of cochlear nonlinearity on frequency selectivity, tuning, signal compression and the impulse response. The results are interpreted within the framework of a nonlinear, locally active, three-dimensional model of the cochlea. The data have been subjected to inverse analysis in order to recover the basilar-membrane (BM) impedance, a parameter function that, when inserted into the (linearized version of that) model, produces a model response that is similar to the measured response. This paper reports details about intensity effects for noise stimulation, in particular, the way the BM impedance varies with stimulus intensity. In terms of the underlying cochlear model, the decrease of the “activity component” in the BM impedance with increasing stimulus level is attributed to saturation of transduction in the outer hair cells. In the present paper this property is brought into a quantitative form. According to the theory [the EQ-NL theorem, de Boer, Audit. Neurosci. 3, 377–388 (1997)], the BM impedance is composed of two components, both intrinsically independent of stimulus level. One is the passive impedance Zpass and the other one is the “extra” impedance Zextra. The latter impedance is to be multiplied by a real factor γ (0⩽γ⩽1) that depends on stimulus level. This concept about the composition of the BM impedance is termed the “two-component theory of the BM impedance.” In this work both impedances are entirely derived from experimental data. The dependence of the factor γ on stimulus level can be derived by using a unified form of the outer-hair-cell transducer function. From an individual experiment, the two functions Zpass and Zextra are determined, and an approximation (Zpass+γZextra) to the BM impedance constructed. Next, the model response (the “resynthesized” response) corresponding to this “artificial” impedance is computed. The same procedure is executed for several stimulus-level values. For all levels, the results show a close correspondence with the original experimental data; this includes correct prediction of the compression of response amplitudes, the reduction of frequency selectivity, the shift in peak frequency and, most importantly, the preservation of timing in the impulse response. All these findings illustrate the predictive power of the underlying model.
Flow of Polymer Melts in Extruders. Part I. The Effect of Transverse Flow and of a Superposed Steady Temperature Profile
Authors: Zamodits H. J. , Pearson J. R. A.
Published: July 2002

Steady flow in the metering section of relatively narrow channel extruders can be regarded as a special case of curvilineal viscometric flow (as defined by Coleman, Markovitz, and Noll). It is shown that under these conditions the behavior of simple fluids can be adequately described from knowledge of a single shear stress function. To specify this function an extended form of the power-law relationship is used, as it agrees well with viscometric measurements on polymer melts over a range of shear rates. The equations of motion and energy are solved taking into account the effect of transverse flow in the channel and of a superposed steady temperature profile. Results of the numerical computations are presented in terms of dimensionless parameters, and comparison is made with experimental results. The marked effect on non-Newtonian fluid behavior on extruder output at low back pressures and on the shape of the screw characteristics is emphasized. The importance of temperature effects is measured by the magnitude of the (dimensionless) Brinkman number. Output versus pressure characteristics are calculated for a range of Brinkman numbers, and it is shown that the predicted temperature profiles in the channel approximate experimentally observed profiles. The results provide a rational basis for extruder design and for predicting the effect of geometrical parameters, operating conditions, and melt rheology on extruder performance.
On the Concept of the Deborah Number
Authors: Huilgol R. R.
Published: July 2002

After examining the earlier definitions of the Deborah number and their usefulness relative to some kinematical histories, it is shown that a new definition is necessary. This new characterization is related to the rate at which a kinematic history is executed. Properties which make this characterization attractive are given.
Review of questionnaire to AIHA accredited laboratories for the analysis of silica
Authors: Smith Deane K.
Published: July 2002

X-ray powder diffraction is one of the two principal methods used for the routine analysis of free SiO2 for monitoring silica in the industrial workplace. During late 1996 and early 1997, a questionnaire was prepared and distributed to all the analytical laboratories on the American Industrial Hygiene Association (AIHA) list of accredited facilities that indicated they did analyses for silica. This report is based on the responses to that questionnaire with comments from the author on the responses and recommendations that suggest themselves from the responses.
Advancing Communication and Decision-making for Older Adults Discharged to Skilled Nursing Facilities—Not Where but Why?
Authors: Shi Sandra , Keeney Tamra , Ritchie Christine
Published: September 2022

This Viewpoint addresses the active role that clinicians can take in communicating with older patients in postacute care as they reflect and make decisions regarding their future.