bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatics and the Gating Pore of Shaker Potassium Channels
Authors: Islas Leon D. , Sigworth Fred J.
Published: July 2002

Various experiments have suggested that the S4 segment in voltage-dependent Na+ and K+ channels is in contact with a solvent-accessible cavity. We explore the consequences of the existence of such a cavity through the electrostatic effects on the gating currents of Shaker K+ channels under conditions of reduced ionic strength S. We observe that ∼10-fold reductions of intracellular S produce reductions of the measured gating charge of ∼10%. These effects continue at even lower values of S. The reduction of gating charge when S is reduced by 10-fold at the extracellular surface is much smaller (∼2%). Shifts of the Q(V) curve because of a reduced S are small (<10 mV in size), which is consistent with very little fixed surface charge. Continuum electrostatic calculations show that the S effects on gating charge can be explained by the alteration of the local potential in an intracellular conical cavity of 20–24-Å depth and 12-Å aperture, and a smaller extracellular cavity of 3-Å depth and the same aperture. In this case, the attenuation of the membrane potential at low S leads to reduction of the apparent gating charge. We suggest that this cavity is made by a bundle of transmembrane helices, and that the gating charge movement occurs by translocation of charged residues across a thin septum of ∼3–7 Å thickness.
Voltage Dependence of the Apparent Affinity for External Na+ of the Backward-Running Sodium Pump
Authors: De Weer Paul , Gadsby David C. , Rakowski R.F.
Published: July 2002

The steady-state voltage and [Na+]o dependence of the electrogenic sodium pump was investigated in voltage-clamped internally dialyzed giant axons of the squid, Loligo pealei, under conditions that promote the backward-running mode (K+-free seawater; ATP- and Na+-free internal solution containing ADP and orthophosphate). The ratio of pump-mediated 42K+ efflux to reverse pump current, Ipump (both defined by sensitivity to dihydrodigitoxigenin, H2DTG), scaled by Faraday's constant, was −1.5 ± 0.4 (n = 5; expected ratio for 2 K+/3 Na+ stoichiometry is −2.0). Steady-state reverse pump current-voltage (Ipump-V) relationships were obtained either from the shifts in holding current after repeated exposures of an axon clamped at various Vm to H2DTG or from the difference between membrane I-V relationships obtained by imposing Vm staircases in the presence or absence of H2DTG. With the second method, we also investigated the influence of [Na+]o (up to 800 mM, for which hypertonic solutions were used) on the steady-state reverse Ipump-V relationship. The reverse Ipump-V relationship is sigmoid, Ipump saturating at large negative Vm, and each doubling of [Na+]o causes a fixed (29 mV) rightward parallel shift along the voltage axis of this Boltzmann partition function (apparent valence z = 0.80). These characteristics mirror those of steady-state 22Na+ efflux during electroneutral Na+/Na+ exchange, and follow without additional postulates from the same simple high field access channel model (Gadsby, D.C., R.F. Rakowski, and P. De Weer, 1993. Science. 260:100–103). This model predicts valence z = nλ, where n (1.33 ± 0.05) is the Hill coefficient of Na binding, and λ (0.61 ± 0.03) is the fraction of the membrane electric field traversed by Na ions reaching their binding site. More elaborate alternative models can accommodate all the steady-state features of the reverse pumping and electroneutral Na+/Na+ exchange modes only with additional assumptions that render them less likely.
Kinetics of Inward-Rectifier K+ Channel Block by Quaternary Alkylammonium Ions
Authors: Guo Donglin , Lu Zhe
Published: July 2002

We examined block of two inward-rectifier K+ channels, IRK1 and ROMK1, by a series of intracellular symmetric quaternary alkylammonium ions (QAs) whose side chains contain one to five methylene groups. As shown previously, the ROMK1 channels bind larger QAs with higher affinity. In contrast, the IRK1 channels strongly select TEA over smaller or larger QAs. This remarkable difference in QA selectivity between the two channels results primarily from differing QA unbinding kinetics. The apparent rate constant for binding (kon) of all examined QAs is significantly smaller than expected for a diffusion-limited process. Furthermore, a large (∼30-fold) drop in kon occurs when the number of methylene groups in QAs increases from three to four. These observations argue that between the intracellular solution and the QA-binding locus, there exists a constricted pathway, whose dimension (∼9 Å) is comparable to that of a K+ ion with a single H2O shell.
Molecular Regions Controlling the Activity of Cng Channels
Authors: Möttig Holger , Kusch Jana , Zimmer Thomas , Scholle Annette , Benndorf Klaus
Published: July 2002

The α subunits of CNG channels of retinal photoreceptors (rod) and olfactory neurons (olf) are proteins that consist of a cytoplasmic NH2 terminus, a transmembrane core region (including the segments S1–S6), and a cytoplasmic COOH terminus. The COOH terminus contains a cyclic nucleotide monophosphate binding domain NBD) that is linked by the C-linker (CL) to the core region. The binding of cyclic nucleotides to the NBD promotes channel opening by an allosteric mechanism. We examined why the sensitivity to cGMP is 22 times higher in olf than in rod by constructing chimeric channels and determining the [cGMP] causing half maximum channel activity (EC50). The characteristic difference in the EC50 value between rod and olf was introduced by the NH2 terminus and the core-CL region, whereas the NBD showed a paradoxical effect. The difference of the free energy difference Δ(ΔG) was determined for each of these three regions with all possible combinations of the other two regions. For rod regions with respect to corresponding olf regions, the open channel conformation was destabilized by the NH2 terminus (Δ(ΔG) = −1.0 to −2.0 RT) and the core-CL region (Δ(ΔG) = −2.0 to −2.9 RT), whereas it was stabilized by the NBD (Δ(ΔG) = 0.3 to 1.1 RT). The NH2 terminus deletion mutants of rod and olf differed by Δ(ΔG) of only 0.9 RT, whereas the wild-type channels differed by the much larger value of 3.1 RT. The results show that in rod and olf, the NH2 terminus, the core-CL region, and the NBD differ by characteristic Δ(ΔG) values that do not depend on the specific composition of the other two regions and that the NH2 terminus generates the main portion of Δ(ΔG) between the wild-type channels.
Allosteric Regulation of Bk Channel Gating by Ca2+ and Mg2+ through a Nonselective, Low Affinity Divalent Cation Site
Authors: Zhang X. , Solaro C.R. , Lingle C.J.
Published: July 2002

The ability of membrane voltage to activate high conductance, calcium-activated (BK-type) K+ channels is enhanced by cytosolic calcium (Ca2+). Activation is sensitive to a range of [Ca2+] that spans over four orders of magnitude. Here, we examine the activation of BK channels resulting from expression of cloned mouse Slo1 α subunits at [Ca2+] and [Mg2+] up to 100 mM. The half-activation voltage (V0.5) is steeply dependent on [Ca2+] in the micromolar range, but shows a tendency towards saturation over the range of 60–300 μM Ca2+. As [Ca2+] is increased to millimolar levels, the V0.5 is strongly shifted again to more negative potentials. When channels are activated by 300 μM Ca2+, further addition of either mM Ca2+ or mM Mg2+ produces similar negative shifts in steady-state activation. Millimolar Mg2+ also produces shifts of similar magnitude in the complete absence of Ca2+. The ability of millimolar concentrations of divalent cations to shift activation is primarily correlated with a slowing of BK current deactivation. At voltages where millimolar elevations in [Ca2+] increase activation rates, addition of 10 mM Mg2+ to 0 Ca2+ produces little effect on activation time course, while markedly slowing deactivation. This suggests that Mg2+ does not participate in Ca2+-dependent steps that influence current activation rate. We conclude that millimolar Mg2+ and Ca2+ concentrations interact with low affinity, relatively nonselective divalent cation binding sites that are distinct from higher affinity, Ca2+-selective binding sites that increase current activation rates. A symmetrical model with four independent higher affinity Ca2+ binding steps, four voltage sensors, and four independent lower affinity Ca2+/Mg2+ binding steps describes well the behavior of G-V curves over a range of Ca2+ and Mg2+. The ability of a broad range of [Ca2+] to produce shifts in activation of Slo1 conductance can, therefore, be accounted for by multiple types of divalent cation binding sites.
Utrophin Binds Laterally along Actin Filaments and Can Couple Costameric Actin with Sarcolemma When Overexpressed in Dystrophin-deficient Muscle
Authors: Rybakova Inna N. , Patel Jitandrakumar R. , Davies Kay E. , Yurchenco Peter D. , Ervasti James M.
Published: July 2002

Dystrophin is widely thought to mechanically link the cortical cytoskeleton with the muscle sarcolemma. Although the dystrophin homolog utrophin can functionally compensate for dystrophin in mice, recent studies question whether utrophin can bind laterally along actin filaments and anchor filaments to the sarcolemma. Herein, we have expressed full-length recombinant utrophin and show that the purified protein is fully soluble with a native molecular weight and molecular dimensions indicative of monomers. We demonstrate that like dystrophin, utrophin can form an extensive lateral association with actin filaments and protect actin filaments from depolymerization in vitro. However, utrophin binds laterally along actin filaments through contribution of acidic spectrin-like repeats rather than the cluster of basic repeats used by dystrophin. We also show that the defective linkage between costameric actin filaments and the sarcolemma in dystrophin-deficientmdx muscle is rescued by overexpression of utrophin. Our results demonstrate that utrophin and dystrophin are functionally interchangeable actin binding proteins, but that the molecular epitopes important for filament binding differ between the two proteins. More generally, our results raise the possibility that spectrin-like repeats may enable some members of the plakin family of cytolinkers to laterally bind and stabilize actin filaments.
Centrosome Reorientation in Wound-Edge Cells Is Cell Type Specific
Authors: Yvon Anne-Marie C. , Walker Jonathan W. , Danowski Barbara , Fagerstrom Carey , Khodjakov Alexey , Wadsworth Patricia
Published: July 2002

The reorientation of the microtubule organizing center during cell migration into a wound in the monolayer was directly observed in living wound-edge cells expressing γ-tubulin tagged with green fluorescent protein. Our results demonstrate that in CHO cells, the centrosome reorients to a position in front of the nucleus, toward the wound edge, whereas in PtK cells, the centrosome lags behind the nucleus during migration into the wound. In CHO cells, the average rate of centrosome motion was faster than that of the nucleus; the converse was true in PtK cells. In both cell lines, centrosome motion was stochastic, with periods of rapid motion interspersed with periods of slower motion. Centrosome reorientation in CHO cells required dynamic microtubules and cytoplasmic dynein/dynactin activity and could be prevented by altering cell-to-cell or cell-to-substrate adhesion. Microtubule marking experiments using photoactivation of caged tubulin demonstrate that microtubules are transported in the direction of cell motility in both cell lines but that in PtK cells, microtubules move individually, whereas their movement is more coherent in CHO cells. Our data demonstrate that centrosome reorientation is not required for directed migration and that diverse cells use distinct mechanisms for remodeling the microtubule array during directed migration.
Clustering of non-polar contacts in proteins.
Authors: Drabl√∏s F
Published: July 2002

MOTIVATION: Hydrophobic or non-polar contacts in proteins are important for protein folding, protein stability and protein-protein interactions. In particular, in the interior of a protein, in the hydrophobic core, a large number of such contacts are found. The residues involved in these contacts often form a tightly packed cluster of atoms. It is useful for the understanding of protein structure to be able to identify and analyse such clusters. RESULTS: Tools for hierarchical cluster analysis of non-polar contacts in proteins are described. These tools allow for efficient identification of clusters of non-polar interactions in proteins, both internal clusters and clusters involved in protein-protein contacts. The non-polar contacts are represented by a dendrogram structure, which is a simple approach for flexible identification of clusters by visual inspection. The tools are demonstrated on the structure of crambin, the structure of the complex between human growth hormone and the human growth hormone binding protein, and a pair of lipase/esterase structures. AVAILABILITY: On request from the author.
Serum bactericidal activity of levofloxacin against Streptococcus pneumoniae
Authors: Shah P. M.
Published: July 2002

The objective of this study was to determine the serum bactericidal activity (SBA) of levofloxacin against Streptococcus pneumoniae strains with various degrees of susceptibility to penicillin and cefotaxime. Serum samples of volunteers ( n = 12) who had received levofloxacin 500 mg as a single po dose were provided in blinded fashion. SBA was determined, using the microdilution method, in Todd–Hewitt broth supplemented with lysed horse blood inoculated with an overnight culture diluted to yield a final concentration of approximately 10 5 cfu/mL. The serum bactericidal titre was defined as the highest dilution of serum showing no growth (>99.9% reduction of inoculum). The duration of SBA ranged from 0.75 to 6.3 h (mean 3.85 h), and was independent of the susceptibility of the strains to penicillin and cefotaxime. In conclusion, a single po dose of 500 mg levofloxacin achieved serum concentrations which were bactericidal against penicillin-resistant S. pneumoniae for a mean period of 3.85 h.
Interactions between proteins implicated in exocytosis and voltage–gated calcium channels
Authors: Seagar Michael , Lévêque Christian , Charvin Nathalie , Marquèze Beatrice , Martin–Moutot Nicole , Andrée Boudier Jeanne , Boudier Jean–Louis , Shoji-Kasai Yoko , Sato Kazuki , Takahashi Masami
Published: July 2002

Neurotransmitter release from synaptic vesicles is triggered by voltage–gated calcium influx through P/Q–type or N–type calcium channels. Purification of N–type channels from rat brain synaptosomes initially suggested molecular interactions between calcium channels and two key proteins implicated in exocytosis: synaptotagmin I and syntaxin 1. Co–immunoprecipitation experiments were consistent with the hypothesis that both N– and P/Q–type calcium channels, but not L–type channels, are associated with the 7S complex containing syntaxin 1, SNAP–25, VAMP and synaptotagmin I or II. Immunofluorescence confocal microscopy at the frog neuromuscular junction confirmed that calcium channels, syntaxin 1 and SNAP–25 are co–localized at active zones of the presynaptic plasma membrane where transmitter release occurs. Experiments with recombinant proteins were performed to map synaptic protein interaction sites on the α
1
A subunit, which forms the pore of the P/Q–type calcium channel.
In vitro
–translated
35
S–synaptotagmin I bound to a site located on the cytoplasmic loop linking homologous domains II and III of the α
1
A subunit. This direct link would target synaptotagmin, a putative calcium sensor for exocytosis, to a microdomain of calcium influx close to the channel mouth. Cysteine string proteins (CSPs) contain a J–domain characteristic of molecular chaperones that co–operate with Hsp70. They are located on synaptic vesicles and thought to be involved in modulating the acticity of presynaptic calcium channels. CSPs were found to bind to the same domain of the calcium channel as synaptotagmin, and also to associate with VAMP. CSPs may act as molecular chaperones in association with Hsp70 to direct assembly or dissociation of multi–protein complexes at the calcium channel.
Indirect and direct evidence for DNA double–strand breaks in hypermutating immunoglobulin genes
Authors: Jacobs Heinz , Rajewsky Klaus , Fukita Yosho , Bross Linda
Published: July 2002

The generation of a diverse antigen receptor repertoire is fundamental for the functionality of the adaptive immune system. While the V(D)J recombination process that generates the primary antigen receptor repertoire is understood in great detail, it is still unclear by which mechanism immunoglobulin (Ig) genes are further diversified by somatic hypermutation. Using mouse strains that carry a non–functional, predefined V
H
D
H
J
H
gene segment in their IgH locus we demonstrate DNA double–strand breaks (DSBs) in and around V
H
D
H
J
H
in B cells undergoing somatic hypermutation. The generation of these DSBs depends on transcriptional activity, and their distribution along the V
H
D
H
J
H
segment parallels that of point mutations in the hypermutation domain. Furthermore, similar to hot spots of somatic hypermutation, 50–60% of all DSBs occur preferentially at RGYW motifs. DSBs may transiently dissociate the Ig promoter from the intronic enhancer to block further transcription and to initiate an error–prone nonhomologous DSB repair pathway. In accord with this model large deletions are frequently produced, along with point mutations, in a V
H
D
H
J
H
segment inserted together with its promoter into the IgH locus in inverted orientation. Our data suggest that DSBs are reaction intermediates of the mechanism underlying somatic hypermutation.
Functional analysis of
Plasmodium falciparum
merozoite antigens: implications for erythrocyte invasion and vaccine development
Authors: Cowman Alan F. , Baldi Deborah L. , Duraisingh Manoj , Healer Julie , Mills Kerry E. , O'Donnell Rebecca A. , Thompson Jennifer , Triglia Tony , Wickham Mark E. , Crabb Brendan S.
Published: July 2002

Malaria is a major human health problem and is responsible for over 2 million deaths per year. It is caused by a number of species of the genus
Plasmodium
, and
Plasmodium falciparum
is the causative agent of the most lethal form. Consequently, the development of a vaccine against this parasite is a priority. There are a number of stages of the parasite life cycle that are being targeted for the development of vaccines. Important candidate antigens include proteins on the surface of the asexual merozoite stage, the form that invades the host erythrocyte. The development of methods to manipulate the genome of
Plasmodium
species has enabled the construction of gain–of–function and loss–of–function mutants and provided new strategies to analyse the role of parasite proteins. This has provided new information on the role of merozoite antigens in erythrocyte invasion and also allows new approaches to address their potential as vaccine candidates.
A filtering method for signal equalization in region‐of‐interest fluoroscopy
Authors: Robert Normand , Komljenovic Philip T , Rowlands J. A.
Published: July 2002

A method to significantly reduce the exposure area product in fluoroscopy using a pre‐patient region‐of‐interest (ROI) attenuator is presented. The attenuator has a thin central region and a gradually increasing thickness away from the center. It is shown that the unwanted brightening artifact caused by the attenuator can be eliminated by attenuating the low spatial frequencies in the detected image using digital image processing techniques. An investigation of the best image processing method to correct for the presence of the attenuator is undertaken. The correction procedure selected is suitable for use with real‐time image processors and the ROI attenuator can be permitted to move during image acquisition. Images of an anthropomorphic chest phantom acquired in the presence of the ROI attenuator using an x‐ray image intensifier/video chain are corrected to illustrate the clinical feasibility of our approach.
Inertial forces and the Hall effect
Authors: Johnson B. L.
Published: July 2002

We demonstrate that inertial forces give rise to a phenomenon similar to the Hall effect in metals and semiconductors. This phenomenon is useful for illustrating the structure of the Hall effect, since the Hamiltonian for the rotating reference frame problem has most of the same features as that for the problem of charges moving under a magnetic field. In addition, we investigate the quantum regime of a rotating system. We find that there exists an analog of the integer quantum Hall effect at extreme rotation rates, but of a qualitatively different nature. An analog of the fractional quantum Hall effect will not occur. The similarities and differences between the inertial-force and magnetic versions of the Hall effect are good pedagogical illustrations for the classical and quantum Hall regimes.
Dynamic behavior of multistep cracked beams with varying cross section
Authors: Li Q. S.
Published: July 2002

An analytical method for free-vibration analysis of a multistep nonuniform cracked beam is presented. Special solutions for five different types of nonuniform beams are given first. The procedure for determining the fundamental solutions that satisfy the normalization conditions is proposed. The problem of free vibration of a multistep beam, each step beam being nonuniform and having an arbitrary number of cracks and concentrated masses, can be conveniently solved based on the fundamental solutions and recurrence formulas developed in this paper. The eigenvalue equation of such a multistep cracked beam with any kind of two end supports can be established from a determinant of order 2.
Intracochlear pressure measurements related to cochlear tuning
Authors: Olson Elizabeth S.
Published: July 2002

Pressure in turn one of the scala tympani (s.t.) was measured close to the basilar membrane (b.m.) and at additional positions as the pressure sensor approached and/or withdrew from the b.m. The s.t. pressure measured within about 100 μm of the b.m. varied rapidly in space at frequencies around the region’s best frequency. Very close to the b.m. the s.t. pressure was tuned and scaled nonlinearly with sound level. The scala vestibuli (s.v.) pressure was measured at one position close to the stapes within seconds of the s.t. pressure and served primarily as a reference pressure. The driving pressure across the organ of Corti and the b.m. velocity were derived from the pressure data. Both were tuned and nonlinear. Therefore, their ratio, the specific acoustic impedance of the organ of Corti complex, was relatively untuned, and only subtly nonlinear. The impedance was inspected specifically for negative resistance (amplification) and resonance. Both were detected in some instances; taken as a whole, the current results constrain the possibilities for these qualities.
Pulse propagation in randomly fluctuating media
Authors: Dacol Dalcio K.
Published: July 2002

Pulse propagation in a weakly and randomly inhomogeneous medium is studied using a time-domain progressive wave equation. An eikonal-like approximated solution to the wave equation derived from the path integral representation is used to obtain the time-dependent statistics of pulses propagating through this random medium. This approach yields both a simple way of producing simulations of time series as well as their statistical properties.
Coupled guided acoustic modes in water-filled thin-walled tubes
Authors: Maze G. , Cheeke J. D. N. , Li X. , Wang Z.
Published: July 2002

Recent results [J. D. N. Cheeke et al., J. Acoust. Soc. Am. 104, 3678 (1998)] reported a 20% decrease in group velocity for flexural mode circumferential waves propagating around water-filled thin-walled stainless-steel tubes. In the present work, the full theory of such modes is developed to explain the structure modes which originates from the coupling between the water filler and stainless tube. Calculated values of the group velocity for the first two coupled modes are in excellent agreement with experiment. The results are of interest for the physics of acoustic waves in fluid-loaded structures and have potential application for liquid level detection.
Surrogate analysis for detecting nonlinear dynamics in normal vowels
Authors: Tokuda Isao , Miyano Takaya , Aihara Kazuyuki
Published: July 2002

Normal vowels are known to have irregularities in the pitch-to-pitch variation which is quite important for speech signals to be perceived as natural human sound. Such pitch-to-pitch variation of vowels is studied in the light of nonlinear dynamics. For the analysis, five normal vowels recorded from three male and two female subjects are exploited, where the vowel signals are shown to have normal levels of the pitch-to-pitch variation. First, by the false nearest-neighbor analysis, nonlinear dynamics of the vowels are shown to be well analyzed by using a relatively low-dimensional reconstructing dimension of 4⩽d⩽7. Then, we further studied nonlinear dynamics of the vowels by spike-and-wave surrogate analysis. The results imply that there exists nonlinear dynamical correlation between one pitch-waveform pattern to another in the vowel signals. On the basis of the analysis results, applicability of the nonlinear prediction technique to vowel synthesis is discussed.
Optical and atomic force microscopic studies on sonoporation
Authors: Ross Joel P. , Cai Xiane , Chiu Jen-Fu , Yang J. , Wu Junru
Published: July 2002

Optical and atomic force microscopies were used for investigating morphological changes of Jurkat lymphocytes, which showed sonoporation after being exposed to a vibrating Mason horn tuned to 21.4 kHz for 2 min. The tip of the Mason horn had a diameter of 400 μm and its transverse vibration amplitude was 7.8 μm. It was found that immediately after sonification, some cells became irregular in shape but still more or less maintained their sizes, and other cells appeared to be much smaller than their normal sizes.
An acoustic boundary element method using analytical/numerical matching
Authors: Epstein Ronald J. , Bliss Donald B.
Published: July 2002

Analytical/numerical matching (ANM) is a hybrid scheme combining a low-resolution global numerical solution with a high-resolution local solution to form a composite solution. ANM is applied to a harmonically oscillating body to calculate the radiated acoustic field and the associated fluid loading. The approach utilizes overlapping smoothed dipoles, and local corrections to calculate the dipole strength distribution along the surface of the body. A smoothing length scale is introduced that is larger than the smallest physical scale, and smaller than the largest physical scale. The global low-resolution solution is calculated numerically using smoothed dipole solutions to the wave equation, and converges quickly. Local corrections are done with high-resolution local analytical solutions. The global numerical solution is asymptotically matched to the local analytical solutions via a matching solution. The matching solution cancels the global solution in the near field, and cancels the local solution in the far field. The method is very robust, offering insensitivity to node location. ANM provides high-resolution calculations from low-resolution numerics with analytical corrections, while avoiding the usual subtleties involving singular integral equations, and their numerical implementation. The method is applied to calculate the radiated acoustic field and surface pressure of various flat plate configurations in two dimensions. An oscillating rigid flat plate, a forced elastic flat plate, plane-wave diffraction, and mechanical impedance calculations are addressed.
Ultrasonic anisotropic phase velocity determination with the Radon transformation
Authors: Kebaili A. , Schmitt D. R.
Published: July 2002

Coplanar arrays of small longitudinal ultrasonic transducers acquire a set of waveforms which are initially plotted as an amplitude image in the offset-time domain. This amplitude image is then mapped to the intercept time-horizontal slowness (τ−p) domain via a slant-stack Radon transformation. The shape of the locus of these arrivals in τ−p space directly provides information on the propagation angle-dependent phase velocities in an anisotropic medium. The method is applied to an isotropic acrylic and an anisotropic laminate with orthorhombic symmetry. The method allows determination of the phase velocities over an 80° range of propagation angles. The acrylic is isotropic with a phase velocity of 2780 m/s which differs little from that determined in a conventional pulse transmission. The phase velocities versus propagation angle were measured in three planes of symmetry and in one off-symmetry plane in the laminate. Anisotropies of up to 22% over an 80° range of propagation angles were found in the planes perpendicular to the layering. The plane containing the layering was only weakly anisotropic with velocities dependent on the weave of the fiber mats.
Two-tone rate suppression boundaries of cochlear ganglion neurons in chickens following acoustic trauma
Authors: Chen Lin , Trautwein Patricia G. , Powers Nicholas , Salvi Richard J.
Published: July 2002

The purpose of the present study was to examine the effects of acoustic trauma and hair cell loss and regeneration on the two-tone rate suppression (TTRS) boundaries of cochlear ganglion neurons in chickens. Chickens were exposed for 48 hours to a 525-Hz, 120-dB SPL tone which destroyed the hair cells and tectorial membrane in a crescent-shaped patch along the abneural side of the basilar papilla. Afterwards, TTRS boundaries were recorded from cochlear ganglion neurons at 0–1, 5, 14, and 28 days postexposure. Acoustic trauma reduced the percentage of neurons with TTRS boundaries below CF (TTRSb) (52.6% to 8.2%) and above CF (TTRSa) (88.4% to 46.6%). In addition, the exposure reduced TTRS boundary slopes, elevated best suppression threshold (BST), and increased the frequency separation between the tips of the TTRS boundaries and CF. All the TTRS measures started to recover by 5 days postexposure and by 14 days and 28 days postexposure, most measures had recovered to normal levels. However, the BST, TTRS slopes, and the frequency separation of TTRSb boundaries from CF were still slightly abnormal near the exposure frequency. In addition, the percentage of neurons with TTRS below CF was reduced significantly. The partial recovery of TTRS boundaries is presumably due to the regeneration of hair cells and the lower honeycomb layer of the tectorial membrane. The residual TTRS deficits observed 28 days postexposure were most closely associated with the missing upper fibrous layer of the tectorial membrane.
Comments on “The attenuation and dispersion of sound in water containing multiply interacting air bubbles” [J. Acoust. Soc. Am. 99, 3412–3430 (1996)]
Authors: Ye Zhen
Published: July 2002

The new dispersion relation for acoustic wave propagation in bubbly media introduced by C. Feuillade [J. Acoust. Soc. Am. 99, 3412–3430 (1996)] is rederived from a self-consistent approach, and examined through numerical examples. A few concerns are raised with regard to the validity of the assumptions that lead to the new dispersion relation.
Structural intensity of acoustically excited waves in a fluid-loaded elastic plate
Authors: Means Steven L. , Goodman Ralph R.
Published: July 2002

When an acoustic plane wave is incident on an elastic plate, energy propagates within the plate, as well as being reflected from and transmitted through the plate. The present study determines the structural intensity as a function of incident angle at different depths along the cross section. It is found that most peaks, but not all, in the structural intensity may be identified as free waves of the fluid–plate system yielding a form of “numerical spectroscopy.” It is also found that for particular frequencies and angles of incidence the direction of the structural intensity parallel to the plane of the plate is opposite than what would normally be expected. Various studies are performed to gain physical insight into this phenomenon.
Ground effect for A-weighted noise in the presence of turbulence and refraction
Authors: Attenborough Keith , Li Kai Ming
Published: July 2002

Closed-form approximations, of ground effect for continuous A-weighted noise from a point source near to finite impedance ground, obtained by Li et al. [J. Acoust. Soc. Am. 88, 1170–1172 (1990)] and Makarewicz [J. Acoust. Soc. Am. 82, 1706–1711 (1987); 88, 1172–1175 (1990)], are extended to take account of more general models for ground impedance including revised variable-porosity, thin-layer, and rough porous ground where the roughness is small compared with incident wavelengths. The influences of both turbulence and weak atmospheric refraction within the illuminated zone are included. Approximate relationships between optimum ground effect for A-weighted noise, ground parameters, source spectrum, source height, and receiver height are predicted and explored. For low source heights and noise sources with A-weighted spectra with low peak frequencies, it is possible to indicate ground surface parameters that will give significantly higher excess attenuation than those typical of grass-covered ground. It is predicted that, in the illuminated zone, the optimum ground effect parameters are fairly robust to weak refraction effects.
The longitudinal vibration response of a curved fiber used for laser ultrasound surgical therapy
Authors: Makarov S. N. , Ochmann M. , Desinger K.
Published: July 2002

A theoretical study of the longitudinal vibration response of a bent fiber used as an active element of a medical applicator for Laser Ultrasound Surgical Therapy (LUST) is presented. The fiber cross section (∅300–1000 μm) is much smaller than the longitudinal wavelength (λ=15–20 cm). Wave propagation in the bent fiber is described by the governing second-order equations of motion which neglect the flexure effect. The range of the validity of those equations is discussed. In contrast to numerous works on bent rods, the case of an arbitrary continuous curvative distribution along the fiber is investigated. A simple analytical formula for the transfer function, i.e., the ratio of displacements at the working end of the fiber divided by those at the driven end, is obtained. The transfer function depends on frequency, fiber length, output impedance, loss factor, and the mean-square curvative of the fiber. The behavior of this function is investigated applied to some fibers whose lengths are of the order 1 m. The driven frequency is of about 10–50 kHz. If the displacement at the driven end of the fiber is known, the power output of the applicator can be found from the known values of the tissue impedance and the transfer function.
Detection of narrow-band signals in spherically invariant noise
Authors: Izzo Luciano , Tanda Mario
Published: July 2002

This paper deals with noncoherent discrete-time detection of a narrow-band signal subject to slow and nonselective fading and embedded in correlated non-Gaussian noise modeled as a spherically invariant random process whose modulating random variable is continuous. At first, an asymptotic sufficient statistic for an arbitrary fading law is derived; then, the asymptotically optimum detector for Rayleigh-distributed amplitude fluctuations is synthesized. The detection structure implementation requires the knowledge, but for a scale factor, of the correlation function of the noise, but is independent of the distribution function of the modulating random variable. The performance of the asymptotically optimum detector synthesized for Rayleigh fading is assessed via computer simulations. The results show that the performance degradation with respect to the fully optimum performance is scarcely significant, even for low values of the sample size. Moreover, in highly non-Gaussian noise the proposed detector largely outperforms the fully optimum detector synthesized under the correlated Gaussian noise assumption.
Comments on “A consonance-based approach to the harpsichord tuning of Domenico Scarlatti” [J. Acoust. Soc. Am. 101, 2332–2337 (1997)]
Authors: Sloane Carl
Published: July 2002

Issue is taken with the finding that Domenico Scarlatti probably used a harpsichord tuning with no wolf fifth. Arguments indicating that he used a tuning with a substantial wolf are presented.
Response to “Comments on ‘A consonance-based approach to the harpsichord tuning of Domenico Scarlatti’ ” [J. Acoust. Soc. Am. 103, 1680 (1998)]
Authors: Sankey John , Sethares William A.
Published: July 2002

This Letter briefly responds to Carl Sloane’s arguments regarding Scarlatti’s use of wolf fifths. It is believed that the historical record is sufficiently unclear that firm conclusions are not possible.
Acoustic simulation for a loudspeaker using FEM/BEM
Authors: Ikonen Veijo , Suutala Antti , Pohjolainen Seppo
Published: July 2002

Although the theory of acoustics is well known, computers and numerical methods have not been effectively utilized in the field. Formulating a sufficiently good physical model is often difficult. The wave equation for pressure can easily be derived, but the boundary conditions are not so obvious. The structure of the walls of an acoustic cavity and the behavior of surface materials can be quite complex. In addition, under the influence of an acoustic field the structures can start vibrating, and this vibration is then coupled to the acoustic field. Mathematically this leads to a system of two partial differential equations. This paper studies the problem of computing an internal acoustic field of a loudspeaker box. The acoustic properties of walls, made of MDF, are taken into account by using the impedance boundary condition. The coupling between the structure and the fluid is also considered. Both finite-element and boundary- element methods (FEM/BEM with SYSNOISE) are used for numerical computations and the results are compared with each other and with analytical solutions. When the wavelength is decreased, the element grid must be refined and the number of equations becomes very large. This is why partial differential equation models are more suitable in low frequencies.
Dynamic mechanical measurements on violin wood and audience evaluations of violin tone quality
Authors: Fitzgerald Edwin R. , Hutchins Carleen M. , Hutchins Morton A.
Published: July 2002

At the 125th Acoustical Society of America meeting in Ottawa, Canada, values of complex shear compliance (J*=J′−iJ″), modulus (G*=1/J*), and shear wave velocity and attenuation, measured over a continuous frequency range from 10 to 10 000 Hz at 20 °C and 50% RH, were described for samples of spruce and maple wood used in the construction of six violins. Four wood samples were measured for each violin, viz., samples of spruce and maple with and without cross grain. Relation of the violin wood dynamic mechanical properties to plate tuning of the violins also was discussed. Following these presentations, two members of the Ottawa Symphony orchestra each played two short pieces on each of the six violins, and the audience was asked for written comments on the tone quality of each violin. The evaluations display some variations as to the violin(s) with the best tone, but one of the six was rated as good or best tone by none, and the worst tone by many. The dynamic mechanical shear properties of this violin’s wood differ in several respects from those of the other violins. Similar property differences for this wood relative to the others also exist in extensional moduli determined from flexural vibrations.
Mathematical model of echo-location of fish-eating flying bats
Authors: Stulov Anatoli
Published: July 2002

The ability of flying bats Vespertillionidae to detect fish under the water surface using echo-location is surprised, because only one-thousandth of the acoustical pulse energy penetrates into water. Supposing the fish (air bubble) reflects the whole signal backwards, the bat must detect the echo-signal which is a million times less than the transmitted one. This fantastic level of the perception sensitivity of the flying bat lies on the bound of its ability. It seems incredible that the main method of getting food is provided for by the maximum effort of bat senses. The method of the bat echo-location is explained here in terms of the interaction of the frequency-modulated acoustical pulse with the air bubble under the water surface. It was shown that in the presence of the bubble the amplitude of the echo reflected by the water surface depends on the signal frequency. In the usual range of the echo-location, 50–100 kHz (the resonance frequency of the bubble lies near 1 kHz), there are at least four regions of frequency for which the amplitude of the signal reflected back to the bat varies up to 25%. Thus, the bat can detect fish in water easily.
Acoustic pulse diagnostics of relaxation media
Authors: Maksimov German A. , Larichev Vladimir A.
Published: July 2002

The investigation of propagation of acoustic fields in different media is an important source of information about nonideal properties of these media. For study of small-amplitude acoustic waves, the most essential of the nonideal properties are the dissipative–dispersive properties, which are characterized by the frequency dependence of the absorption factor and the phase velocity. These properties can be described in terms of relaxation processes, which arise in the field of acoustic waves. Conventional ways to determine the relaxation times spectrum (RTS) parameters are acoustic spectroscopic measurements of temperature–frequency dependence of absorption and phase velocity of sound in the medium. Currently, such problems can be solved by applying the pulse methods of measurements. In the report the possibilities of acoustic pulse diagnostics of relaxation media are discussed. Parameters of media (such as five moments of RTS) are defined which can be determined experimentally by methods of pulse acoustic diagnostics. The criteria for a pulse excitation source and its registration distances are obtained which provide the most efficient pulse acoustic diagnostics. The comparison of developed approach with the first experiments is fulfilled.
Applications of two frequency insonification techniques to oceanic bubble sizing
Authors: Phelps Andy D. , Simpson Matt D. , Leighton Timothy G.
Published: July 2002

This work presents the results from using a combination frequency acoustic technique to measure the near-surface bubble population in both the open sea and surf zone. The benefits of using a combination frequency technique are that the collected data are more accurate and less prone to ambiguities than linear backscatter measurements. The technique monitors the appearance of sum-and-difference signals generated by the nonlinear interaction of two sound fields: one high-frequency signal scattering geometrically from the bubble surface and the other used to excite the bubble into resonant pulsation. The work details the calibration of the apparatus necessary to relate the measured heights of the sum-and-difference terms to actual numbers of bubbles, and describes the experimental procedure for the collection of the oceanic data. The collected data are verified using simultaneous measurements of the dispersive sound speed and attenuation, which can be compared with estimates calculated from the measured bubble population. The results from a number of trials are presented, with both time-averaged and time-variant measures of the local population demonstrated. [Work supported by the Natural Environment Research Council.]
Monitoring air–sea exchange using ambient sound
Authors: Nystuen Jeffrey A.
Published: July 2002

Wave breaking and precipitation are important processes contributing to the exchange of momentum, heat, water, and gas at the air–sea interface. These processes are also principal generators of high-frequency (over 1 kHz) underwater ambient sound. Furthermore, the bubbles generated by the breaking waves and raindrop splashes can be stirred downward into the ocean mixed layer forming an effective sound absorption layer. When present this layer modifies the ambient sound field, and can thus be detected using passive acoustics. Using the passive sound field as the exploratory tool, more conventional measurements of salinity, temperature, bubbles, wind, and surface waves will be examined. Anomalies in near-surface salinity are explained by acoustically derived rainfall and wind-speed measurements. Acoustically derived rainfall measurements suggest that rain affects the surface wave field. Enhanced injection of bubbles into the mixed layer by rain in the presence of high wind is indicated by changes to the shape of the underwater sound spectrum. [Work supported by ONR Ocean Acoustics and NSF.]
Mechanisms for biological effects of ultrasound
Authors: Carstensen Edwin L.
Published: July 2002

At least three physical processes have the potential to produce therapeutic benefits through ultrasound exposure. These include heating, cavitation, and a related group of second-order mechanical effects that involve radiation forces and streaming on a macroscopic or microscopic scale. In most applications of ultrasound in physical therapy, deep heating is the postulated rationale for its use. Hyperthermia as an adjunct to cancer therapy requires sophisticated control of ultrasonic heating. At higher levels, ultrasound can be used to destroy precisely selected tissues obviating the need for surgical intervention. In this application, nonlinear propagation can be used to selectively increase the absorption parameters of the target tissues. At low amplitudes the response of bubbles is dominated by the acoustic pressure. At a critical acoustic pressure, however, the inertia of the surrounding medium becomes controlling. At this threshold acoustic pressure a 10% or 20% increase in acoustic pressure leads to an increase in the collapse pressure in the bubble by orders of magnitude. Radiation forces can be detected by auditory and tactile sensors. Macroscopic acoustic streaming may alter transport across biological membranes and microscopic streaming exerts stresses on the membranes and the cytoplasmic and nuclear contents of cells.
The study of long-term sensitivity changes in backplate electret type condenser microphones
Authors: Miura Kenzo , Yasuno Yoshinobu
Published: July 2002

The estimation of the lifetime of a usual electret condenser microphone (ECM) using an electret foil as a diaphragm has already been reported by authors. On the other hand, backplate electret type condenser microphones (BECMs) used for mobile telephones, recently, and the backplate that is laminated with electret foil has been examined and studied concerning the estimation of sensitivity changes over a long time span. Heat acceleration tests for electret foil on the backplate were taken, and from the results, the surface charge decay of backplate electret was estimated. As the thickness of the diaphragm in a BECM is thinner than the usual ECM, sensitivity increasing because of looseness of diaphragm tension was expected to become larger than the usual ECM. Therefore, heat acceleration tests for the diaphragm only were taken and estimates of the levels of sensitivity increasing by the looseness of the results. The charge decay characteristics on the electret surface and the characteristics of tension looseness in the diaphragm had both results taken together. The long-term sensitivity changes of BECMs were estimated and compared with the sensitivity of BECM samples that were left for about 10 years at room temperature.