bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Impedance Tomography Study of Biological Processes in a Single Cell
Authors: CHILCOTT TERRY C. , COSTER HANS G. L.
Published: February 2006

Abstract: An in vivo electrical impedance tomography (EIT) study of single plant cells of Chara corallina is reported. When these aquatic cells grow in alkaline conditions, proton‐translocating ATP synthases in the plasma membrane operate in reverse, utilizing ATP to translocate protons against an electrochemical gradient to the periplasm and creating localized acidic regions along the cell's cylindrical surface. These acidic regions, which appear as radial bands, ~ 5 mm long, between narrower alkaline bands, facilitate the uptake of bicarbonate, the plant's source of inorganic carbon for photosynthesis in the carbon dioxide‐depleted alkaline conditions. Our EIT study of cell ultrastructure in the acidic and alkaline regions provides evidence that the plasma membrane is folded in localized regions (e.g., charasomes) in the acidic bands. The very low frequency capacitance dispersions were very similar to those of double fixed‐charge structures. Such charge distributions are known to be present in the membrane‐bound F0 portion of the ATP synthase. The theoretical dependence of the fixed‐charge concentrations on pH in the proteins is shown to broadly account for the observed correlations between pH, membrane potential, conductance, and capacitance in these regions. In synthetically formed double fixed‐charge membranes, electric field‐induced dissociation of water into H+ and OH− occurs. This leads to the speculation that H+/OH− fluxes in ATP synthases located in the alkaline regions of Chara cells might also involve the electric field‐induced dissociation of water.
Some Design Concepts for Electrical Impedance Measurement
Authors: GOOVAERTS H. G. , FAES TH. J. C. , RAAIJMAKERS E. , HEETHAAR R. M.
Published: February 2006

Abstract: Design concepts for the implementation of two basic functions for measurement of electrical impedance are presented: current injection and voltage measurement. At relatively high frequencies, the application of an alternating current through the body or a body segment results in electromagnetic stray fields that reduce the amount of current actually injected into the tissue under study. It is shown that electrical isolation and small dimensions of the isolated section are indispensable in order to substantially reduce these stray currents. The paper describes a new wideband current source configuration driven by direct digital sine wave synthesis (DDS) presenting very low stray currents due to a symmetrical layout. Two implementations of the actual current source circuit are presented: (1) a voltage‐controlled system and (2) a current conveyor‐based circuit.

A wideband input amplifier with transformer coupling is described. The current source, amplifier, and (in case of tomography) multiplexer are also situated on an electrically isolated front end. The presented concepts are applied in a new electrical impedance tomograph (EIT) presently under construction in our department.
EIT Reconstruction of Static Images by a Genetic Algorithm Approach
Authors: OLMI R. , BINI M. , MANETTA S. , PRIORI S.
Published: February 2006

Abstract: A genetic algorithm (GA) approach is proposed for the reconstruction of static images in electrical impedance tomography (EIT). Genetic algorithms can be demonstrated to possess several advantages over more conventional “gradient‐based” techniques. In particular, they are implicitly parallel and realize a good compromise between “exploration” and “exploitation”, thus being more robust against the problem of false minima. The results of GA‐EIT in numerical experiments are presented, compared to those obtained by other, more established inversion methods, such as the modified Newton‐Raphson method and the double‐constraint method. The GA approach is relatively expensive in terms of computation time and resources, requiring (for example) from several minutes to tens of minutes on a Pentium Pro 200‐based machine for normal‐size EIT problems. This currently limits the applicability of GA‐EIT to the field of static imaging. However, in light of the development trend in the field of computing, an extension to real‐time dynamic imaging applications is not inconceivable in the near future.
The Duct Cell in Cystic Fibrosis
Authors: HARRIS ANN
Published: February 2006

Abstract: The pancreatic duct cell is central to the etiology of cystic fibrosis (CF) and is the site where pathology commences in utero. We have evaluated expression of the cystic fibrosis transmembrane conductance regulator gene (CFTR) through human development and shown it to be expressed from the early mid‐trimester, with highest levels in the most distal portion of the developing duct system and in centroacinar cells. The precise cause of pancreatic destruction in CF is thought to be the obstruction of pancreatic ducts with inspissated secretions. We have shown that the MUC6 mucin is a significant component of the material that obstructs the ducts and that the MUC6 gene shows a very similar pattern of expression to that of CFTR in the developing pancreas. These observations provide a starting point for investigating how mutations in CFTR lead to obstruction of the pancreatic ducts in CF.
Genomic Anomalies in Pancreatic Tumors Other Than Common Adenocarcinoma
Authors: SCARPA ALDO , ZAMBONI GIUSEPPE
Published: February 2006

Abstract: In recent years enormous advances have been made in the understanding of the molecular mechanisms governing pancreatic ductal adenocarcinoma. However, little is known about other pancreatic neoplasms, which include intraductal papillary mucinous (IPMT), serous cystic (SCT), mucinous cystic (MCT), solid pseudopapillary (SPT), acinar and islet cell tumors. In addition, the study of tumors grouped under the unfortunate term of periampullary cancers will help distinguish the pathogenetic features of these neoplasms, often confused with pancreatic head neoplasms. The available data suggest that the less common pancreatic tumor types do not generally follow the same molecular pathway as the more common ductal carcinoma. IPMT seems to contain chromosomal anomalies similar to those found in ductal cancers, whereas papilla of Vater and duodenal cancers show genetic anomalies resembling those of gastrointestinal malignancies. The application of genome‐wide screening techniques uo these less common pancreatic tumors will undoubtedly play a central role in unraveling the complexity behind their pathology.
The HCN Gene Family: Molecular Basis of the Hyperpolarization‐Activated Pacemaker Channels
Authors: SANTORO BINA , TIBBS GARETH R.
Published: February 2006

ABSTRACT: The molecular basis of the hyperpolarization‐activated cation channels that underlie the anomalous rectifying current variously termed Ih, Iq, or If is discussed. On the basis of the expression patterns and biophysical properties of the newly cloned HCN ion channels, an initial attempt at defining the identity and subunit composition of channels underlying native Ih is undertaken. By comparing the sequences of HCN channels to other members of the K channel superfamily, we discuss how channel opening may be coupled to membrane hyperpolarization and to direct binding of cyclic nucleotide. Finally, we consider some of the questions in cardiovascular physiology and neurobiology that can be addressed as a result of the demonstration that Ih is encoded by the HCN gene family.
Whole heart action potential duration restitution properties in cardiac patients: a combined clinical and modelling study
Authors: Nash Martyn P. , Bradley Chris P. , Sutton Peter M. , Clayton Richard H. , Kallis Panny , Hayward Martin P. , Paterson David J. , Taggart Peter
Published: February 2006

Steep action potential duration (APD) restitution has been shown to facilitate wavebreak and ventricular fibrillation. The global APD restitution properties in cardiac patients are unknown. We report a combined clinical electrophysiology and computer modelling study to: (1) determine global APD restitution properties in cardiac patients; and (2) examine the interaction of the observed APD restitution with known arrhythmia mechanisms. In 14 patients aged 52–85 years undergoing routine cardiac surgery, 256 electrode epicardial mapping was performed. Activation–recovery intervals (ARI; a surrogate for APD) were recorded over the entire ventricular surface. Mono‐exponential restitution curves were constructed for each electrode site using a standard S1–S2 pacing protocol. The median maximum restitution slope was 0.91, with 27% of all electrode sites with slopes < 0.5, 29% between 0.5 and 1.0, and 20% between 1.0 and 1.5. Eleven per cent of restitution curves maintained slope > 1 over a range of diastolic intervals of at least 30 ms; and 0.3% for at least 50 ms. Activation–recovery interval restitution was spatially heterogeneous, showing regional organization with multiple discrete areas of steep and shallow slope. We used a simplified computer model of 2‐D cardiac tissue to investigate how heterogeneous APD restitution can influence vulnerability to, and stability of re‐entry. Our model showed that heterogeneity of restitution can act as a potent arrhythmogenic substrate, as well as influencing the stability of re‐entrant arrhythmias. Global epicardial mapping in humans showed that APD restitution slopes were organized into regions of shallow and steep slopes. This heterogeneous organization of restitution may provide a substrate for arrhythmia.
Correlation of α‐skeletal actin expression, ventricular fibrosis and heart function with the degree of pressure overload cardiac hypertrophy in rats
Authors: Stilli Donatella , Bocchi Leonardo , Berni Roberta , Zaniboni Massimiliano , Cacciani Francesca , Chaponnier Christine , Musso Ezio , Gabbiani Giulio , Clément Sophie
Published: February 2006

We have analysed alterations of α‐skeletal actin expression and volume fraction of fibrosis in the ventricular myocardium and their functional counterpart in terms of arrhythmogenesis and haemodynamic variables, in rats with different degrees of compensated cardiac hypertrophy induced by infra‐renal abdominal aortic coarctation. The following coarctation calibres were used: 1.3 (AC1.3 group), 0.7 (AC0.7) and 0.4 mm (AC0.4); age‐matched rats were used as controls (C group). One month after surgery, spontaneous and sympathetic‐induced ventricular arrhythmias were telemetrically recorded from conscious freely moving animals, and invasive haemodynamic measurements were performed in anaesthetized animals. After killing, subgroups of AC and C rats were used to evaluate in the left ventricle the expression and spatial distribution of α‐skeletal actin and the amount of perivascular and interstitial fibrosis. As compared with C, all AC groups exhibited higher values of systolic pressure, ventricular weight and ventricular wall thickness. AC0.7 and AC0.4 rats also showed a larger amount of fibrosis and upregulation of α‐skeletal actin expression associated with a higher vulnerability to ventricular arrhythmias (AC0.7 and AC0.4) and enhanced myocardial contractility (AC0.4). Our results illustrate the progressive changes in the extracellular matrix features accompanying early ventricular remodelling in response to different degrees of pressure overload that may be involved in the development of cardiac electrical instability. We also demonstrate for the first time a linear correlation between an increase in α‐skeletal actin expression and the degree of compensated cardiac hypertrophy, possibly acting as an early compensatory mechanism to maintain normal mechanical performance.
Chemoreflex sympathoexcitation was not altered by the antagonism of glutamate receptors in the commissural nucleus tractus solitarii in the working heart–brainstem preparation of rats
Authors: Braga Valdir A. , Machado Benedito H.
Published: February 2006

The changes in thoracic sympathetic nerve activity, heart rate and frequency of phrenic nerve discharge in response to chemoreflex activation before and after bilateral microinjections of glutamate receptor antagonists into the comissural nucleus tractus solitarii (cNTS) were evaluated in the working heart–brainstem preparation of rats. Microinjections of kynurenic acid (KYN, 250 mm), (+/−)‐α‐methyl‐4‐carboxyphenylglycine (MCPG, 100 mm), or KYN plus MCPG into the cNTS were performed in three different groups. These microinjections into the cNTS did not affect the increase in the thoracic sympathetic nerve activity elicited by chemoreflex activation (KYN, 54 ± 3 versus 51 ± 2%, n= 11; MCPG, 48 ± 5 versus 54 ± 5%, n= 7; and KYN plus MCPG, 57 ± 6 versus 55 ± 3%, n= 5). The increase in the frequency of the phrenic nerve discharge in response to chemoreflex activation was also not affected by KYN (0.28 ± 0.02 versus 0.30 ± 0.04 Hz), MCPG (0.27 ± 0.03 versus 0.27 ± 0.04 Hz), or KYN plus MCPG (0.30 ± 0.04 versus 0.20 ± 0.03 Hz). The bradycardic response to chemoreflex activation was significantly reduced after microinjection of KYN at 2 (−220 ± 16 versus−50 ± 6 beats min−1) and 10 min (−220 ± 16 versus−65 ± 9 beats min−1) and after microinjection of KYN plus MCPG into the NTS it was abolished at 2 (−192 ± 14 versus−2 ± 1 beats min−1) and 10 min (−192 ± 14 versus−4 ± 2 beats min−1). These data support the hypothesis that the neurotransmission of the sympathoexcitatory and respiratory components of the chemoreflex in the cNTS involves neurotransmitters other than l‐glutamate and also the concept that the parasympathetic component of this reflex is mediated by l‐glutamate.
Modeling extreme ultraviolet∕H2O oxidation of ruthenium optic coatings
Authors: Hollenshead Jeromy , Klebanoff Leonard
Published: February 2006

A mathematical model of extreme ultraviolet (EUV)-induced oxidation of a ruthenium (Ru)-coated EUV optic is presented. The model describes the key processes that contribute to the growth of the oxide within the optic when exposed to EUV radiation in the presence of water vapor. These processes include the adsorption and thermal desorption of water to and from the Ru surface, molecular diffusion of water across the optic surface, and the dissociation of the water by both direct EUV ionization and secondary electron excitation. Oxygen produced by dissociation may associatively desorb from the surface or may diffuse into the Ru subsurface where it can react to form an oxide. The presence of oxygen in the Ru coating, whether as oxide or atomic oxygen, reduces the reflectivity of the optic and the overall throughput of the EUV lithographic system. The model predicts oxide thickness over time, which may later be used to estimate the reflectively loss attributable to the oxide in any given EUV environment. Model predictions for EUV-induced oxide growth provide a good description of the oxide growth observed in available electron-beam experiments. The model is also used to estimate oxygen penetration into the Ru coating under various conditions of water partial pressure, EUV power, and temperature. The model predicts reduced oxidation with higher temperatures and for substrates that bind water less tightly than ruthenium.
Scanning capacitance microscopy: Quantitative carrier profiling down to nanostructures
Authors: Giannazzo F. , Raineri V. , Mirabella S. , Impellizzeri G. , Priolo F. , Fedele M. , Mucciato R.
Published: February 2006

We addressed the issues related to quantitative carrier profiling by scanning capacitance microscopy (SCM) on doped layers with different dimensions, starting from thick (∼5μm) uniformly B-doped Si layers, down to Si∕Si1−xGex∕Si quantum wells with nanometric width. We preliminarly discussed the influence of the SCM hardware on the quantification, by comparing the analyses performed on Si calibration standards with two different atomic force microscopes, i.e., DI3100 by Veeco and XE-100 by PSIA, equipped with different SCM sensors. Furthermore, both concentration and spatial resolution are demonstrated by measurements on specially designed samples containing B-doped quantum wells of Si0.75Ge0.25 layers strained between Si films. Measurements were taken both on cross-sectioned samples and on beveled ones. A SCM spatial resolution of 1nm with a concentration sensitivity from 5% to 10% was demonstrated by quantitative majority carrier profiling on the B-doped Si∕Si0.75Ge0.25∕Si heterostructures.
Characterization of metal oxide semiconductor field effect transistor dosimeters for application in clinical mammography
Authors: Benevides Luis A. , Hintenlang David E.
Published: February 2006

Five high‐sensitivity metal oxide semiconductor field effect transistor dosimeters in the TN‐502 and 1002 series (Thomson Nielsen Electronics Ltd., 25B, Northside Road, Ottawa, ON K2H8S1, Canada) were evaluated for use in the mammography x‐ray energy range as a tool to assist in the documentation of patient specific average glandular dose. The dosimeters were interfaced with the Patient Dose Verification System, model No. TN‐RD 15, which consisted of a dosimeter reader and up to four dual bias power supplies. Two different dual bias power supplies were evaluated in this study, model No. TN‐RD 22 in high‐sensitivity mode and a very‐high sensitivity prototype. Each bias supply accommodates up to five dosimeters for 20 dosimeters per system. Sensitivity of detectors, defined as the , was measured free in air with the bubble side of the dosimeter facing the x‐ray field with a constant exposure. All dosimeter models’ angular response showed a marked decrease in response when oriented between 120° and 150° and between at 190° and 220° relative to the incident beam. Sensitivity was evaluated for , , and target‐filter combinations. The individual dosimeter model sensitivity was for TN‐502RDS(micro); for TN‐1002RD; for TN‐1002RDI; for TN‐1002RDM (micro); and for TN‐1002RDS (micro). The energy response is presented and is observed to vary with dosimeter model, generally increasing with tube potential through the mammography energy range. An intercomparison of the high‐sensitivity mode of TN‐RD‐22 was made to the very‐high sensitivity bias power supply using a target‐filter. The very‐high sensitivity‐bias power supply increased dosimeter response by for dosimeter models TN‐1002RD and TN‐1002RDM. The responses of all dosimeter models were found to be linear for tube potentials of between 24 and . Dosimeters showed a reproducibility varying from 15.5% to 31.8% depending on the model of dosimeter. Micro MOSFETS model Nos. TN‐1002RDS and TN‐1002RDM used in conjunction with their respective high‐sensitivity and ultrahigh‐sensitivity bias supplies provided the highest sensitivity response of the models evaluated. Either micro MOSFETS model No. TN‐1002RDS or TN‐1002RDM used in conjunction with the appropriate bias supply provide the best choice for clinical mammography applications. Under these conditions, MOSFET dosimeters can provide a viable option as a dosimeter in the mammography energy range . The clinical application of MOSFET dosimeters must take into account the energy dependence and reproducibility to ensure accurate measurements.
Wall correction factors, , for thimble ionization chambers
Authors: Buckley Lesley A. , Rogers D. W. O.
Published: February 2006

The EGSnrc Monte Carlo user‐code CSnrc is used to calculate wall correction factors, , for thimble ionization chambers in photon and electron beams. CSnrc calculated values of give closer agreement with previous experimental results than do the values from the standard formalism used in current dosimetry protocols. A set of values, computed at the reference depth in water, is presented for several commonly used thimble chambers. These values differ from the commonly used values by up to 0.8% for megavoltage photon beams, particularly for nominal beam energies below . The sleeve effect, which is not currently taken into account by the TG‐51 dosimetry protocol, is computed to be up to 0.3% and is in some cases larger than the correction itself. In electron beams, where dosimetry protocols assume a wall correction of unity, CSnrc calculations show values of up to 0.6% at the reference depth, depending on the wall material. is shown to be sensitive to the depth of measurement, varying by 2.5% for a graphite‐walled cylindrical Farmer‐like chamber between a depth of and in a electron beam.
Development of the two Korean adult tomographic computational phantoms for organ dosimetry
Authors: Lee Choonsik , Lee Choonik , Park Sang‐Hyun , Lee Jai‐Ki
Published: February 2006

Following the previously developed Korean tomographic phantom, KORMAN, two additional whole‐body tomographic phantoms of Korean adult males were developed from magnetic resonance (MR) and computed tomography (CT) images, respectively. Two healthy male volunteers, whose body dimensions were fairly representative of the average Korean adult male, were recruited and scanned for phantom development. Contiguous whole body MR images were obtained from one subject exclusive of the arms, while whole‐body CT images were acquired from the second individual. A total of 29 organs and tissues and 19 skeletal sites were segmented via image manipulation techniques such as gray‐level thresholding, region growing, and manual drawing, in which each of segmented image slice was subsequently reviewed by an experienced radiologist for anatomical accuracy. The resulting phantoms, the MR‐based KTMAN‐1 (Korean Typical MAN‐1) and the CT‐based KTMAN‐2 (Korean Typical MAN‐2), consist of voxels with a voxel resolution of for both phantoms. Masses of segmented organs and tissues were calculated as the product of a nominal reference density, the prevoxel volume, and the cumulative number of voxels defining each organs or tissue. These organs masses were then compared with those of both the Asian and the ICRP reference adult male. Organ masses within both KTMAN‐1 and KTMAN‐2 showed differences within 40% of Asian and ICRP reference values, with the exception of the skin, gall bladder, and pancreas which displayed larger differences. The resulting three‐dimensional binary file was ported to the Monte Carlo code MCNPX2.4 to calculate organ doses following external irradiation for illustrative purposes. Colon, lung, liver, and stomach absorbed doses, as well as the effective dose, for idealized photon irradiation geometries (anterior‐posterior and right lateral) were determined, and then compared with data from two other tomographic phantoms (Asian and Caucasian), and stylized ORNL phantom. The armless KTMAN‐1 can be applied to dosimetry for computed tomography or lateral x‐ray examination, while the whole body KTMAN‐2 can be used for radiation protection dosimetry.
An image quality comparison of standard and dual‐side read CR systems for paediatric radiology
Authors: Monnin P. , Holzer Z. , Wolf R. , Neitzel U. , Vock P. , Gudinchet F. , Verdun F. R.
Published: February 2006

An objective analysis of image quality parameters was performed for a computed radiography (CR) system using both standard single‐side and prototype dual‐side read plates. The pre‐sampled modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) for the systems were determined at three different beam qualities representative of pediatric chest radiography, at an entrance detector air kerma of . The NPS and DQE measurements were realized under clinically relevant x‐ray spectra for pediatric radiology, including x‐ray scatter radiations. Compared to the standard single‐side read system, the MTF for the dual‐side read system is reduced, but this is offset by a significant decrease in image noise, resulting in a marked increase in DQE in the low spatial frequency range. Thus, for the same image quality, the new technology permits the CR system to be used at a reduced dose level.
Lateral distribution of ultrasound velocity in horizontal layers of human teeth
Authors: John Christoph
Published: February 2006

The speed of ultrasound at 20MHz differs inside human teeth depending on which tissues are involved. At least two out of four dental tissues exhibit variations in the longitudinal velocity (cL). The aim of this in vitro study is to describe the laterally varying propagation velocity of tangentially propagating longitudinal waves. At a distance of 5mm from the crown reference, the cL is determined using longitudinal sections and a pulse-echo technique. Several graphs are combined to account for the corono-apical decrease in cL and the laterally varying cL distribution along horizontally adjacent relative tooth width portions. The laterally increasing cL of 21 specimens at radial locations rises from 2900to4000m∕s. A mathematical evaluation reveals an optimal horizontal formula of the form cL(5mm)=a+bX2ln(X), where X is the standardized lateral parameter relative to individual tooth width w, which is compensated for offsets. Individual residuals and a,b coefficients of the corresponding approximations are provided. Individual mean errors range from 7m∕s(SD=6m∕s)to92m∕s(SD=79m∕s). The lower contour of the envelope curve of all cL distributions is described by taking up a formerly introduced equation [J. Acoust. Soc. Am. 116, 545 (2004)].
Autocorrelation in meter induction: The role of accent structure
Authors: Toiviainen Petri , Eerola Tuomas
Published: February 2006

The performance of autocorrelation-based meter induction was tested with two large collections of folk melodies, consisting of approximately 13 000 melodies for which the correct meters were available. The performance was measured by the proportion of melodies whose meter was correctly classified by a discriminant function. Furthermore, it was examined whether including different melodic accent types would improve the classification performance. By determining the components of the autocorrelation functions that were significant in the classification it was found that periodicity in note onset locations was the most important cue for the determination of meter. Of the melodic accents included, Thomassen's melodic accent was found to provide the most reliable cues for the determination of meter. The discriminant function analyses suggested that periodicities longer than one measure may provide cues for meter determination that are more reliable than shorter periodicities. Overall, the method predicted notated meter with an accuracy reaching 96% for binary classification and 75% for classification into nine categories of meter.
Wind-induced noise in a screened microphone
Authors: van den Berg G. P.
Published: February 2006

To reduce the effect of wind on a microphone, wind screens are used, usually made of foam or cloth. Although this measure to reduce wind noise is well known and widely used, it lacks a theoretical explanation. One possible explanation was the turbulent wake in the air flow behind the wind screen, another the pressure variations due to turbulence inherent in outdoor wind. In the present paper it is shown that atmospheric turbulence is indeed the cause of outdoor microphone wind noise, and the knowledge that is available in atmospheric boundary layer physics can be used to model the effects of atmospheric turbulence on a bare or screened microphone. A wind screen can be seen as a first order low pass filter for pressure variations due to atmospheric turbulence. Induced wind noise is thus determined by (average) wind speed and wind screen diameter, but also by factors related to frictional and thermal turbulence (roughness length and atmospheric stability). This approach leads to predicted spectral values of the induced “sound” pressure that match experimental data. The result can be used to obtain proper outdoor ambient wind related sound levels by correcting measured sound levels with calculated wind-induced pressure levels.
Longitudinal vibration frequencies of steadily whirling rods
Authors: Shum W. S. , Entwistle R. D.
Published: February 2006

Past researchers suggested that “static instabilities” exist at certain rotational speeds of whirling rods. This paper shows these instabilities are an artefact of the material constitutive laws that are being used well outside their range of applicability. An alternative approach is developed where strains due to rotation are separated from the superimposed vibration. This enables the generally predicted lowering of longitudinal natural frequencies with rotational speed shown to be simply a result of the bulk changes in the geometry of whirling rods. Steady-state equations of whirling rods are formulated in Lagrangian coordinates. Due to the nonlinear nature of the governing equations, an original numerical method is applied to solve the problem. Numerical results are compared with analytical results obtained from the linearized uniaxial model. There is close agreement between these two models at low angular velocities. However, at high angular velocities, discrepancies between them arise, confirming that the nonlinear strain-displacement relationship has significant effect on the results and the inferred “static instabilities.” This approach first solves the “static” problem of the deformed geometry of a highly strained whirling rod before longitudinal natural modes are determined by classical methods. Furthermore, conditions for existence and uniqueness of solutions are derived.
Comment on “The cochlear amplifier as a standing wave: ‘Squirting’ waves between rows of outer hair cells?” [J. Acoust. Soc. Am. 116, 1016–1024 (2004)]
Authors: LePage Eric L.
Published: February 2006

Bell and Fletcher [J. Acoust. Soc. Am. 116, 1016–1024 (2004)] proposed that one of the functions of activity of the outer hair cells (OHCs) might be a fluid-pumping action generating lateral fluid flow in the gap between the reticular membrane and the tectorial membrane and they supplied mathematical and descriptive justification for their theory which drew heavily upon the postulation (Gold, 1948) of the need for an active mechanism in the mammalian cochlea. In the 1970s there had been considerable speculation about how the inner hair cell (IHC) stereocilia are stimulated, whether they are stimulated in proportion to basilar membrane displacement or velocity or both, and whether the velocity dependence is due to subtectorial fluid flow. In 1977 experiments were conducted to investigate the possibility of subtectorial fluid flows using a dye as tracer. The work was not reported because it had been conducted at a time when visual observation of cochlear function had fallen out of favor in comparison with the more sensitive techniques thought necessary to observe submicroscopic phenomena, and secondly because it yielded a negative result. The essential details of those experiments are reported here to note for the record the extent to which this elaborate idea has already been tested.
Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I. Experiment
Authors: Tarnopolsky Alex Z. , Fletcher Neville H. , Hollenberg Lloyd C. L. , Lange Benjamin D. , Smith John , Wolfe Joe
Published: February 2006

The didjeridu, or yidaki, is a simple tube about 1.5m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers’ vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1–3kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player’s lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of “circular breathing” and combined playing and vocalization are shown.
Vocal tract resonances and the sound of the Australian didjeridu (yidaki) II. Theory
Authors: Fletcher N. H. , Hollenberg L. C. L. , Smith J. , Tarnopolsky A. Z. , Wolfe J.
Published: February 2006

The didjeridu (didgeridoo) or yidaki of the Australian Aboriginal people consists of the narrow trunk of a small Eucalypt tree that has been hollowed out by the action of termites, cut to a length of about 1.5m, smoothed, and decorated. It is lip-blown like a trumpet and produces a simple drone in the frequency range 55to80Hz. Interest arises from the fact that a skilled player can make a very wide variety of sounds with formants rather like those of human vowels, and can also produce additional complex sounds by adding vocalization. An outline is given of the way in which the whole system can be analyzed using the harmonic-balance technique, but a simpler approach with lip motion assumed shows easily that upper harmonics of the drone with frequencies lying close to impedance maxima of the vocal tract are suppressed, so that formant bands appear near impedance minima of the vocal tract. This agrees with experimental findings. Simultaneous vibration of the player’s lips and vocal folds is shown to generate multiple sum and difference tones, and can be used to produce subharmonics of the drone. A brief discussion is given of player preference of particular bore profiles.
A structurally guided method for the decomposition of expression in music performance
Authors: Windsor W. Luke , Desain Peter , Penel Amandine , Borkent Michiel
Published: February 2006

A method for separating, profiling, and quantifying the contributions of different structural components to expressive musical performance is described. The method is demonstrated through its application to a set of expert piano performances of a short piece from the classical period. The results show that the output of the method aids in the understanding of how the different structural components in a piece of music combine in the generation of an expressive performance. A second demonstration applies the method to performances at different tempi to illustrate its effectiveness in pinpointing the structural features responsible for small but statistically significant differences between performances. The method is compared with other approaches to the analysis and modeling of musical performance, and a number of potential applications are identified.
Characterization of scatterer motion in a reverberant medium
Authors: Conti Stéphane G. , de Rosny Julien , Roux Philippe , Demer David A.
Published: February 2006

Recently, an acoustic technique has been proposed to measure the scattering strength and the dynamics of weak moving scatterers in a reverberant cavity: diffusing reverberant acoustic wave spectroscopy (DRAWS). Both parameters are obtained from the correlations of the reverberated-scattered transient pressure fields for different scatterers positions. This technique is based on a diffusive field theory [de Rosny et al., Phys. Rev. Lett., 90, 094302 (2003)]. Here, a more systematic approach of the DRAWS technique properties is presented. Moreover, an important extension is proposed using the fourth-order moment of the field, or the variance of the correlation estimator. Contrary to the correlations (second-order moment) that allow the measurement of the scattering cross section, its variance (fourth-order moment) is shown to be mainly sensitive to the scatterer displacement. The robustness of DRAWS is discussed using different configurations: a computer simulation of a moving scatterer in a two-dimensional cavity. Experiments were also carried out with a 23-mm-diameter copper sphere moved by stepping motors in 16liters of water, and finally a human walking in a 125-m3 reverberant room.
Viscous scattering of a pressure wave: Calculation of the fluid tractions on a biomimetic acoustic velocity sensor
Authors: Homentcovschi Dorel , Miles Ronald N.
Published: February 2006

In the paper we give a method for calculating the tractions (local forces) of the fluid motion determined by an incoming plane pressure wave on an artificial hair cell transducer structure. The sensing element of the transducer is a standing high aspect ratio cilium in the shape of a narrow thin curved beam (tape-like), which can be easily fabricated in micro-/nanotechnology. The method is based on considering the system of partial differential equations describing the motion of the compressible viscous fluid in an acoustic linearized approximation, and representation of the velocity field as a viscous acoustic single-layer potential. The boundary conditions, stating the cancellation of the velocity components on the solid beam, yield a two-dimensional (2-D) system of three integral equations over the beam’s surface for the traction components. In the case of a narrow cilium, the system of integral equations furnishes a system of two 1-D integral equations over the symmetry curve of the structure for obtaining the tangential and normal components of the traction. This system is solved numerically by a finite (boundary) element method. The numerical code written for solving the problem was applied to some particular structures. The last structure is similar to the trichobothrium of a spider Cupiennius salei. The results obtained show that the curvature of the hair is enhancing sensitivity to flows directed normal to the main shaft of the hair confirming the assertion of Barth et al. [Philos. Trans. R. Soc. London, Ser. B 340, 445–461 (1993)].
Acoustic measurement of lubricant-film thickness distribution in ball bearings
Authors: Zhang Jie , Drinkwater Bruce W. , Dwyer-Joyce Rob S.
Published: February 2006

An oil-film thickness monitoring system capable of providing an early warning of lubrication failure in rolling element bearings has been developed. The system is used to measure the lubricant-film thickness in a conventional deep groove ball bearing (shaft diameter 80mm, ball diameter 12.7mm). The measurement system comprises a 50MHz broadband ultrasonic focused transducer mounted on the static outer raceway of the bearing. Typically the lubricant-films in rolling element bearings are between 0.1–1.0μm in thickness and so are significantly smaller than the ultrasonic wavelength. A quasistatic spring model is used to calculate oil-film thickness from the measured reflection coefficient data. An accurate triggering system has been developed to enable multiple reflection coefficient measurements to be made as the contact ellipse sweeps over the measurement location. Experiments are described in which the loading conditions and rotational speed are varied. Lubricant-film thickness distributions measured ultrasonically are described and are shown to agree well with the predictions from classical elastohydrodynamic (EHD) lubrication theory, particularly at high radial loads and low rotary speeds. A range of parameters affecting the performance of the measurement are discussed and the limits of operation of the measurement technique defined.
Elastoacoustic model with uncertain mechanical properties for ultrasonic wave velocity prediction: Application to cortical bone evaluation
Authors: Macocco Karina , Grimal Quentin , Naili Salah , Soize Christian
Published: February 2006

The axial transmission technique can measure the longitudinal wave velocity of an immersed solid. An elementary model of the technique is developed with a set of source and receivers placed in a semi-infinite fluid coupled at a plane interface with a semi-infinite solid. The acoustic fluid is homogeneous. The solid is homogeneous, isotropic, and linearly elastic. The work is focused on the prediction of the measured velocity (apparent velocity) when the solid is considered to have random material properties. The probability density functions of the random variables modeling each mechanical parameter of the solid are derived following the maximum entropy principle. Specific attention is paid to the modeling of Poisson’s ratio so that the second-order moments of the velocities remain finite. The stochastic solver is based on a Monte Carlo numerical simulation and uses an exact semianalytic expression of the acoustic response derived with the Cagniard–de Hoop method. Results are presented for a solid with the material properties of cortical bone. The estimated mean values and confidence regions of the apparent velocity are presented for various dispersion levels of the random parameters. A sensibility analysis with respect to the source and receivers locations is presented.
A closed form solution for the dynamic response of finite ribbed plates
Authors: Lin Tian Ran , Pan Jie
Published: February 2006

A simple and closed form solution for the vibration response of finite ribbed plates to point force/moment excitations is presented in this paper. This solution shows that input mobilities of finite ribbed plates are bounded by the input mobilities of the uncoupled plate and beam that form the ribbed plate. It is found that point force input mobilities of a finite ribbed plate are controlled by the plate bending stiffness when the excitation force is more than a quarter wavelength away from the beam. The input mobilities are mainly dominated by the beam flexural stiffness when the force acts on or very close to the beam, and when the beam flexural stiffness is far greater than the plate bending stiffness. A similar result is found in the moment excitation case when the moment axis is perpendicular to the beam neutral axis (bending moment excitation). In contrast, the input mobilities of the ribbed plate do not vary much from that of the corresponding uncoupled plate when the moment axis parallels to the beam’s neutral axis (torsional moment excitation) where the input mobilities are mainly dominated by the plate bending stiffness. The reductions in plate kinetic energy due to beam insertions are discussed.
Framework for wind noise studies
Authors: Raspet Richard , Webster Jeremy , Dillion Kevin
Published: February 2006

Morgan and Raspet [J. Acoust. Soc. Am. 92, 1180–1183 (1992)] performed simultaneous wind velocity and wind noise measurements and determined that the wind noise spectrum is highly correlated with the wind velocity spectrum. In this paper, two methods are developed for predicting the upper limits of wind noise pressure spectra from fluctuating velocity spectra in the inertial range. Lower limits on wind noise are estimated from two theories of the pressure fluctuations that occur in turbulence when no wind screen or microphone is present. Empirical results for the self-noise of spherical and cylindrical windscreens in substantially nonturbulent flows are also presented. Measurements of the wind velocity spectra and wind noise spectra from a variety of windscreens are described and compared to the theoretical predictions. The wind noise data taken at the height of the anemometer lies between the upper and lower limits and the predicted self-noise is negligible. The theoretical framework allows windscreen reduction to be evaluated in terms of the turbulent inflow properties and establishes practical upper limits on wind noise reduction for varying wind conditions.
Confirmation of the Biot theory for water-saturated sands at high frequencies and effects of scattering on the attenuation of sound waves
Authors: Ohkawa Keiichi
Published: February 2006

Sound attenuation caused by the absorption and scattering of energy is studied. The Biot theory is used to predict the absorption coefficient. The scattering attenuation applies the experimental result. The calculated attenuation coefficient is the sum of absorption and scattering components, and is in excellent agreement with data collected during the sediment acoustics experiment in 1999. This implies that the frequency dependence of the attenuation coefficient due to the fluid viscosity follows f1∕2 in the high-frequency range, as the Biot theory predicts. This also suggests that, at high frequencies, the attenuation coefficient is not linear in f.
The effect of intertalker speech rate variation on acoustic vowel space
Authors: Tsao Ying-Chiao , Weismer Gary , Iqbal Kamran
Published: February 2006

The present study aimed to examine the size of the acoustic vowel space in talkers who had previously been identified as having slow and fast habitual speaking rates [Tsao, Y.-C. and Weismer, G. (1997) J. Speech Lang. Hear. Res. 40, 858–866]. Within talkers, it is fairly well known that faster speaking rates result in a compression of the vowel space relative to that measured for slower rates, so the current study was completed to determine if the same differences in the size of the vowel space occur across talkers who differ significantly in their habitual speaking rates. Results indicated that there was no difference in the average size of the vowel space for slow vs fast talkers, and no relationship across talkers between vowel duration and formant frequencies. One difference between the slow and fast talkers was in intertalker variability of the vowel spaces, which was clearly greater for the slow talkers, for both speaker sexes. Results are discussed relative to theories of speech production and vowel normalization in speech perception.
A phase reconstruction algorithm for Lamb wave based structural health monitoring of anisotropic multilayered composite plates
Authors: Rajagopalan Jagannathan , Balasubramaniam Krishnan , Krishnamurthy C. V.
Published: February 2006

Platelike structures, made of composites, are being increasingly used for fabricating aircraft wings and other aircraft substructures. Continuous monitoring of the health of these structures would aid the reliable operation of aircrafts. This paper considers the use of a Lamb wave based structural health monitoring (SHM) system to identify and locate defects in large multilayered composite plates. The SHM system comprises of a single transmitter and multiple receivers, coupled to one side of the plate that send and receive Lamb waves. The proposed algorithm processes the data collected from the receivers and generates a reconstructed image of the material state of the composite plate. The algorithm is based on phased addition in the frequency domain to compensate for the dispersion of Lamb waves. In addition, small deviations from circularity of the slowness curves of Lamb wave modes, due to anisotropy, are corrected for by assuming that the phase and group velocity directions coincide locally. Experiments were performed on an anisotropic multilayered composite plate containing a single defect. Reconstruction of the defect is carried out using data for a weakly anisotropic Lamb wave mode as a proof of concept of the proposed algorithm.
Effect of age on detection of gaps in speech and nonspeech markers varying in duration and spectral symmetry
Authors: Pichora-Fuller M. Kathleen , Schneider Bruce A. , Benson Nancy J. , Hamstra Stanley J. , Storzer Edward
Published: February 2006

Gap detection thresholds for speech and analogous nonspeech stimuli were determined in younger and older adults with clinically normal hearing in the speech range. Gap detection thresholds were larger for older than for younger listeners in all conditions, with the size of the age difference increasing with stimulus complexity. For both ages, gap detection thresholds were far smaller when the markers before and after the gap were the same (spectrally symmetrical) compared to when they were different (spectrally asymmetrical) for both speech and nonspeech stimuli. Moreover, gap detection thresholds were smaller for nonspeech than for speech stimuli when the markers were spectrally symmetrical but the opposite was observed when the markers were spectrally asymmetrical. This pattern of results may reflect the benefit of activating well-learned gap-dependent phonemic contrasts. The stimulus-dependent age effects were interpreted as reflecting the differential effects of age-dependent losses in temporal processing ability on within- and between-channel gap detection.