bluuebunny/crossref_metadata_2025 huggingface dataset:
The operational characteristics of a stopped-flow system for ESR studies
Authors: J C Kertesz  , W Wolf
Published: July 2002

A stopped-flow system was designed which allows precise control of flow variables during chemical generation of free radical species in the cavity of an ESR spectrometer. This equipment is applicable to both continuous and stopped-flow studies. It may be used to determine the kinetics of disappearance of short-lived intermediates with lifetimes in the millisecond range. The capability for the generation of accurate kinetic data is provided by the usage of rapid-action solenoid valves. A method for measuring their response times is described. Other features include components for oxygen and temperature measurement and an automated system for triggering repetitive kinetic experiments in conjunction with signal-averaging techniques. The advantages and improvements of this stopped-flow technique over previous such methods are discussed.
On trace identities and universal eigenvalue estimates for some partial differential operators
Authors: Harrell Evans , Stubbe Joachim
Published: July 2002

In this article, we prove and exploit a trace identity for the spectra of Schrödinger operators and similar operators. This identity leads to universal bounds on the spectra, which apply to low-lying eigenvalues, eigenvalue asymptotics, and to partition functions (traces of heat operators). In many cases they are sharp in the sense that there are specific examples for which the inequalities are saturated. Special cases corresponding to known inequalities include those of Hile and Protter and of Yang.
Computational space reduction and parallelization of a new clustering approach for large groups of sequences.
Authors: Trelles O , Andrade M A , Valencia A , Zapata E L , Carazo J M
Published: July 2002

MOTIVATION: The explosive growth of the biological sequences databases stimulated by genome projects has modified the framework of several applications in the biological sequence analysis area. In most cases, this new scenario is characterized by studies on large sets of sequences, suggesting the need for effective and automatic methods for their clustering. A more effective clustering of the database could be followed by the application of common family analysis schemes to the groups so formed. RESULTS: In this work, we present a new strategy to reduce the computational cost associated with the clustering of large sets of sequences which are expected to contain several families. The strategy is based on the grouping of the sequences into families by using a dynamic threshold on a pairwise sequence similarity criterion. Routine clustering of large data sets can now be done very efficiently. The method developed here achieves a computational space reduction of about an order of magnitude over more traditional ones of all-versus-all comparisons. The outcome of this approach produces family groupings that reproduce closely already accepted biological results. Our work includes a parallel implementation for distributed memory multiprocessors with a dynamic scheduling strategy for performance optimization. AVAILABILITY: By anonymous ftp at ftp.ac.uma.es (/pub/ots/pCluster directory), or from our Web site http://www.cnb. uam.es/www/software/software_index.html CONTACT: ots@ac.uma.es
A metadata approach to query interoperation between molecular biology databases.
Authors: Cheung K H , Nadkarni P M , Shin D G
Published: July 2002

MOTIVATION: Molecular biology databases have been proliferating rapidly. Their heterogeneity and complexity pose a great challenge to efforts in database interoperation. To minimize the efforts of interoperating heterogeneous databases, it is useful to develop a system that lets a user of a particular genomic database access another related database as if the latter is structurally similar to the former. RESULTS: We extend a structurally simple model-the entity-attribute-value (EAV) model-to describe uniformly metadata relating to individual databases. Such metadata, which are necessary for performing database comparisons, include descriptions of primitive database objects (including entities, attributes, domain values and entity relationships) and specification of correspondences among the database objects. We show how to decompose SQL queries and map them from one database to another based on the EAV representation of the basic database objects. A prototype system is implemented to demonstrate query interoperation between two chromosome map databases. AVAILABILITY: Freely available (Cold Fusion source code and an Access database containing the mapping knowledge) upon request from the author. CONTACT: kei.cheung@yale.edu
Mixups in the Warehouse: Centralized and Decentralized Multi‐Plant Firms
Authors: Hunnicutt Lynn
Published: July 2002

Single‐plant firms choose quantity/quality levels to maximize profits. Multi‐plant firms face this decision and must also choose how many decision makers to have. This article presents two case studies and a model of a multi‐plant firm in which overhead costs are lower with one decision maker (centralization), but the mass of information and the need for timely decisions make occasional mixups unavoidable. Multiple decision makers (decentralization) solves the mixup problem. Standardization—treating different outlets similarly in response to costly mixups—appears in the case studies, and is demonstrated as a result in the model.
The role of charge separation in the response of electrochemical systems
Authors: Baker Daniel R. , Verbrugge Mark W.
Published: July 2002

To elucidate the effect of charge layers on the behavior of electrochemical systems comprising microgeometries, we investigate microhemisphere and microdisc electrodes. A binary electrolyte is examined, consistent with virtually all battery and fuel–cell electrolytes. The transport–controlled current density response is shown to be governed by two dimensionless groups: the first group, δ, corresponds to a Debye length divided by the electrode radius, while the second, σ, characterizes the charge density on the electrode surface relative to the salt concentration. In many cases of practical interest, δ is very small, and the modelling equations approach a singularity; the resulting equation system is thus not amenable to numerical solution. We have used an asymptotic analysis to deal with this problem, so that our model calculations cover the full range of δ–values that are of interest. The asymptotics are given for more general electrode shapes, including hemispheres and discs.
Athila4 of Arabidopsis and Calypso of Soybean Define a Lineage of Endogenous Plant Retroviruses
Authors: Wright David A. , Voytas Daniel F.
Published: July 2002

The Athila retroelements of Arabidopsis thaliana encode a putative envelope gene, suggesting that they are infectious retroviruses. Because most insertions are highly degenerate, we undertook a comprehensive analysis of the A. thaliana genome sequence to discern their conserved features. One family (Athila4) was identified whose members are largely intact and share >94% nucleotide identity. As a basis for comparison, related elements (the Calypsoelements) were characterized from soybean. ConsensusCalypso and Athila4 elements are 12–14 kb in length and have long terminal repeats of 1.3–1.8 kb. Gag and Pol are encoded on a single open reading frame (ORF) of 1801 (Calypso) and 1911 (Athila4) amino acids. Following the Gag-Pol ORF are noncoding regions of ∼0.7 and 2 kb, which, respectively, flank the env-like gene. Theenv-like ORF begins with a putative splice acceptor site and encodes a protein with a predicted central transmembrane domain, similar to retroviral env genes. RNA of Athilaelements was detected in an A. thaliana strain with decreased DNA methylation (ddm1). Additionally, a PCR survey identified related reverse transcriptases in diverse angiosperm genomes. Their ubiquitous nature and the potential for horizontal transfer by infection implicates these endogenous retroviruses as important vehicles for plant genome evolution.
Short‐chain dehydrogenase/reductase (SDR) relationships: A large family with eight clusters common to human, animal, and plant genomes
Authors: Kallberg Yvonne , Oppermann Udo , Jörnvall Hans , Persson Bengt
Published: July 2002

The progress in genome characterizations has opened new routes for studying enzyme families. The availability of the human genome enabled us to delineate the large family of short‐chain dehydrogenase/reductase (SDR) members. Although the human genome releases are not yet final, we have already found 63 members. We have also compared these SDR forms with those of three model organisms: Caenorhabditis elegans, Drosophila melanogaster, and Arabidopsis thaliana. We detect eight SDR ortholog clusters in a cross‐genome comparison. Four of these clusters represent extended SDR forms, a subgroup found in all life forms. The other four are classical SDRs with activities involved in cellular differentiation and signalling. We also find 18 SDR genes that are present only in the human genome of the four genomes studied, reflecting enzyme forms specific to mammals. Close to half of these gene products represent steroid dehydrogenases, emphasizing the regulatory importance of these enzymes.
Determination of the voltage applied to x‐ray tubes from the bremsstrahlung spectrum obtained with a silicon PIN photodiode
Authors: Silva Marcia C. , Herdade Silvio B. , Lammoglia Patrı́cia , Costa Paulo R. , Terini Ricardo A.
Published: July 2002

This work describes a methodology for the obtainment of the electron accelerating potential (kVp) applied to an x‐ray tube, through the determination of the end point of the energy spectrum of the radiation emitted by the tube. The measurements have been performed utilizing alternatively two silicon PIN photodiodes, directly irradiated by the x‐ray beam. Both were operated at room temperature, with low bias, so avoiding the drawbacks presented by photomultiplier tubes and germanium detectors. The energy calibration of the system was performed with X‐ and ‐emitter radioactive sources, which makes the method absolute. Each kVp value was determined by means of a linear regression in the end of the spectrum, to give, simultaneously, a good fit of the straight line to the experimental data and a low standard deviation for the kVp value. Results of the measurements carried out with an x‐ray tube connected to a three‐phase generator, using additional filtration between 1.5 and 4.0 mm of Cu, are presented. This filtration was used in order to minimize the contribution of low energy photons and to reduce pulse pile‐up. Errors determined for the values of kVp are between 0.06 and 0.16 kV, in the potential range from 50 to 100 kV. As an example, the methodology has been applied in the verification of the secondary calibration of a voltage divider, utilized, by its turn, in the tertiary calibration of noninvasive kVp meters. All intrinsic sources of errors involved in the process are discussed and evaluated.
Cone beam volume CT image artifacts caused by defective cells in x‐ray flat panel imagers and the artifact removal using a wavelet‐analysis‐based algorithm
Authors: Tang Xiangyang , Ning Ruola , Yu Rongfeng , Conover David
Published: July 2002

The application of x‐ray flat panel imagers (FPIs) in cone beam volume CT (CBVCT) has attracted increasing attention. However, due to a deficient semiconductor array manufacturing process, defective cells unavoidably exist in x‐ray FPIs. These defective cells cause their corresponding image pixels in a projection image to behave abnormally in signal gray level, and result in severe streak and ring artifacts in a CBVCT image reconstructed from the projection images. Since a three‐dimensional (3‐D) back‐projection is involved in CBVCT, the formation of the streak and ring artifacts is different from that in the two‐dimensional (2‐D) fan beam CT. In this paper, a geometric analysis of the abnormality propagation in the 3D back‐projection is presented, and the morphology of the streak and ring artifacts caused by the abnormality propagation is investigated through both computer simulation and phantom studies. In order to calibrate those artifacts, a 2D wavelet‐analysis‐based statistical approach to correct the abnormal pixels is proposed. The approach consists of three steps: (1) the location‐invariant defective cells in an x‐ray FPI are recognized by applying 2‐D wavelet analysis on flat‐field images, and a comprehensive defective cell template is acquired; (2) based upon the template, the abnormal signal gray level of the projection image pixels corresponding to the location‐invariant defective cells is replaced with the interpolation of that of their normal neighbor pixels; (3) that corresponding to the isolated location‐variant defective cells are corrected using a narrow‐windowed median filter. The CBVCT images of a CT low‐contrast phantom are employed to evaluate this proposed approach, showing that the streak and ring artifacts can be reliably eliminated. The novelty and merit of the approach are the incorporation of the wavelet analysis whose intrinsic multi‐resolution analysis and localizability make the recognition algorithm robust under variable x‐ray exposure levels between 30% and 70% of the dynamic range of an x‐ray FPI.
Investigation of a direct conversion flat panel imager for portal imaging
Authors: Pang G. , Lee D. L. , Rowlands J. A.
Published: July 2002

Flat‐panel based x‐ray imaging is an emerging new technology that could be used to significantly improve the quality of on‐line portal imagers. There are two types of flat panel imagers: direct and indirect conversion. Previous experimental work on flat panel detectors for portal imaging application used indirect‐conversion imagers. In this paper, a direct‐conversion amorphous‐selenium flat panel imager is investigated for application in portal imaging. The imager has an active imaging area of i.e., each with dimensions The spatial frequency dependent detective quantum efficiency of the imager has been measured for a 6 MV beam and found to be amongst the best area detectors investigated for on‐line portal imaging. Effects of changing pixel size, as well as possible improvements to both the image quality and convenience of operation are discussed. Comparison with an indirect conversion flat panel imager is also included.
Adult patient doses in interventional neuroradiology
Authors: Gkanatsios Nikolaos A. , Huda Walter , Peters Keith R.
Published: July 2002

We investigated radiation doses to 149 adult patients who underwent interventional neuroradiologic procedures, consisting of 132 patients who had diagnostic imaging examinations and 17 patients who had therapeutic procedures. The interventional procedures were carried out on a biplane system capable of performing fluoroscopy and digital subtraction angiography (DSA). The x‐ray imaging system was interfaced to a patient dosimetry system, which computed surface (skin) doses based on the selected radiographic technique factors in each of the radiographic and fluoroscopic imaging modes. For each patient, an assessment was made of the maximum surface dose received during the procedure, which predicts the possibility of inducing deterministic effects. Knowledge of the surface doses, beam quality and x‐ray cross sectional area permitted the computation of the total energy imparted to each patient. Energy imparted values were converted to effective dose, which provides an estimate of the stochastic radiation risk to the patient. The median surface dose for the frontal plane during diagnostic imaging examinations was 1.3 Gy, with a maximum surface dose of 5.1 Gy. The median surface dose for the frontal plane during therapeutic procedures was 2.8 Gy with a maximum surface dose of 5.0 Gy. Ratios of the lateral to frontal median surface doses were 0.47 for diagnostic examinations and 0.68 for interventional procedures. The median energy imparted was 1.8 J during fluoroscopy, and 4.3 J during radiography, showing that on average, 66% of the patient exposure comes from radiographic imaging (DSA). For diagnostic examinations, the median patient effective dose was 33 mSv, with a maximum of 152 mSv. For therapeutic procedures, the median patient effective dose was 74 mSv, with a maximum of 156 mSv. In interventional neuroradiology, surface doses could induce deterministic effects, and the corresponding effective doses are noticeably higher than those normally encountered in diagnostic radiology.
Monte Carlo calculation of single‐beam dose profiles used in a gamma knife treatment planning system
Authors: Cheung Joel Y. C. , Yu K. N. , Yu C. P. , Ho Robert T. K.
Published: July 2002

The accuracy of single‐beam dose profiles used in the algorithm of the Gamma Knife treatment planning system (Leksell GammaPlan®) is verified. EGS4 Monte Carlo calculation was employed to calculate the dose distributions of single‐beams in a spherical water phantom with diameter 160 mm. The beams were directed to the center of the phantom. Collimators of 4, 8, 14, and 18 mm sizes were studied. The single‐beam dose profiles provided by Elekta (Manufacturer of Leksell Gamma Knife®) were excellently consistent with the results of Monte Carlo for the 4, 14, and 18 mm collimators. The maximum discrepancy was less than 3% at all radial distances. For the 8 mm collimator, the maximum discrepancy was 8% in the relative dose in the radial distance range from 4.3 mm to 5.2 mm. Excellent agreement in dose profiles along x, y, and z axes for all collimator helmets by summing over all 201 sources was observed between the cases using the default single‐beam dose profiles and the calculated Monte Carlo results, except for the 8 mm collimator helmet along z axis. Such difference may however be too small to give a clinical significance.
A method to check the accuracy of dose computation using quality index: Application to scatter contribution in high energy photon beams
Authors: Caneva S. , Rosenwald J. C. , Zefkili S.
Published: July 2002

Computerized dose calculation verification is a relevant component of radiotherapy treatment planning quality assurance. The usual procedure is to compare measurements to computations for several standard situations. As cases become more complex, special test phantoms and beam arrangements must be used, and an experimental procedure must be carefully established. In this paper we follow a new methodology to prepare a set of reference data that may be used to verify the accuracy of dose calculations involving changes in the scatter component of photon beams. The advantage of this methodology is that local measurements are not required. A quantitative evaluation of dose modifications was performed by means of correction factors (CF). For this purpose, three geometrical configurations were designed (asymmetric, symmetric, and reference) where the primary component was kept constant and the scatter component was varied by changing the height (h) of lateral columns. Measurements were performed in polystyrene phantoms for seven photon beam energies. CF were derived as the ratio of the absolute dose measured at the point of interest to the absolute dose for the reference configuration, for the asymmetric and symmetric configurations, respectively. They were expressed as a function of beam quality (QI). We have verified that, for all configurations studied, CF decrease with QI. For CF remain practically constant, whatever machine technology is used [the mean values of CF for the asymmetric and symmetric cases are (0.2% 1 s.d.) and (0.4% 1 s.d.)]. We have developed a test protocol and we have chosen those configurations corresponding to because they both present greater values of the CF and lower standard deviations. The direct application of the method is straightforward. The user can reproduce on his local TPS the three experimental configurations described in the test protocol, and then compute CF which can be compared to our reference data set for any beam quality.
Monte Carlo calculations and experimental measurements of dosimetry parameters of a new source
Authors: Li Zuofeng , Palta Jatinder R. , Fan Jay J.
Published: July 2002

Permanent prostate implantation using (iodine) or (palladium) sources is a popular treatment option in the management of early prostate cancer. As sources of new designs are developed and marketed for application in permanent prostate implantations, their dosimetric characteristics must be carefully determined in order to maintain the accuracy of patient treatment. This report presents the results of experimental measurements and Monte Carlo calculations of the dosimetric parameters performed for a newly available seed source. The measurements were performed in a large scanning water phantom using a diode detector. The positioning of the source and detector was achieved by a computer‐controlled positioning mechanism in the scanning water phantom. The dose rate constant in water for the new source was determined from measurements with the diode detector calibrated with sources of known air‐kerma strength. The radial dose function values for the source were measured using the diode detector. Monte Carlo photon transport calculations were then used to calculate the dosimetric parameters of dose rate constant, radial dose function, and anisotropy function using an accurate geometric model of the source. The measured dose rate constant of 0.693 cGy/U‐hr compares well with the Monte Carlo calculated value of 0.677 cGy/U‐hr. These results are further compared with data on existing sources.
Two novel special relativistic effects: Space dilatation and time contraction
Authors: Field J. H.
Published: July 2002

The conventional discussion of the observed distortions of space and time in special relativity (the Lorentz–Fitzgerald contraction and time dilatation) is extended by considering observations, from a stationary frame, of: (i) objects moving with constant velocity and uniformly illuminated during a short time τL (their “luminous proper time”) in their rest frame; these may be called “transient luminous objects” and (ii) a moving, extended, array of synchronized “equivalent clocks” in a common inertial frame. Application of the Lorentz transformation to (i) shows that such objects, observed from the stationary frame with coarse time resolution in a direction perpendicular to their direction of motion, are seen to be at rest but longer in the direction of the relative velocity v by a factor 1/1−(v/c)2 (space dilatation) and to (ii) that the moving equivalent clock at any fixed position in the rest frame of the stationary observer is seen to be running faster than a similar clock at rest by the factor 1/1−(v/c)2 (time contraction). All four space–time “effects” of special relativity are simply classified in terms of the projective geometry of space–time, and the close analogy of these effects to linear spatial perspective is pointed out.
Isolating the auditory system from acoustic noise during functional magnetic resonance imaging: Examination of noise conduction through the ear canal, head, and body
Authors: Ravicz Michael E. , Melcher Jennifer R.
Published: July 2002

Approaches were examined for reducing acoustic noise levels heard by subjects during functional magnetic resonance imaging (fMRI), a technique for localizing brain activation in humans. Specifically, it was examined whether a device for isolating the head and ear canal from sound (a “helmet”) could add to the isolation provided by conventional hearing protection devices (i.e., earmuffs and earplugs). Both subjective attenuation (the difference in hearing threshold with versus without isolation devices in place) and objective attenuation (difference in ear-canal sound pressure) were measured. In the frequency range of the most intense fMRI noise (1–1.4 kHz), a helmet, earmuffs, and earplugs used together attenuated perceived sound by 55–63 dB, whereas the attenuation provided by the conventional devices alone was substantially less: 30–37 dB for earmuffs, 25–28 dB for earplugs, and 39–41 dB for earmuffs and earplugs used together. The data enabled the clarification of the relative importance of ear canal, head, and body conduction routes to the cochlea under different conditions: At low frequencies (⩽500 Hz), the ear canal was the dominant route of sound conduction to the cochlea for all of the device combinations considered. At higher frequencies (>500 Hz), the ear canal was the dominant route when either earmuffs or earplugs were worn. However, the dominant route of sound conduction was through the head when both earmuffs and earplugs were worn, through both ear canal and body when a helmet and earmuffs were worn, and through the body when a helmet, earmuffs, and earplugs were worn. It is estimated that a helmet, earmuffs, and earplugs together will reduce the most intense fMRI noise levels experienced by a subject to 60–65 dB SPL. Even greater reductions in noise should be achievable by isolating the body from the surrounding noise field.
On the annoyance caused by impulse sounds produced by small, medium-large, and large firearms
Authors: Vos Joos
Published: July 2002

A laboratory study was designed in which the annoyance was investigated for 14 different impulse sound types produced by various firearms ranging in caliber from 7.62 to 155 mm. Sixteen subjects rated the annoyance for the simulated conditions of (1) being outdoors, and (2) being indoors with the windows closed. In the latter case, a representative outdoor-to-indoor reduction in sound level was applied. It was anticipated that the presumed additional annoyance caused by the “heaviness” of the impulse sounds might be predicted from the difference between the C-weighted sound exposure level (CSEL; LCE) and the A-weighted sound exposure level (ASEL; LAE). In the outdoor rating conditions, the annoyance was almost entirely determined by ASEL. The explained variance, r2, in the mean ratings by ASEL was 0.95. In the indoor rating conditions, however, the explained variance in the annoyance ratings by (outdoor) ASEL was significantly increased from r2=0.87 to r2=0.97 by adding the product (LCE−LAE)(LAE−α) as a second variable. In combination with a 12-dB adjustment for small firearms, the present results showed that for the entire set of impulse sounds rated indoors with windows closed, the rating sound level, Lr, is given by Lr=LAE+12 dB+β(LCE−LAE)(LAE−α), with α=45 dB and β=0.015 dB−1. For the outdoor rating condition, the optimal parameter values were equal to α=57 dB and, again, β=0.015 dB−1. In validation studies, in which the effects of the present rating procedure will be compared to field data, it has to be determined to what extent the constants α and β have to be adjusted.
Response to “Comment on ‘Reducing seat dip attenuation”’ [J. Acoust. Soc. Am. 110, 1260 (2001)]
Authors: Davies W. J. , Cox T. J.
Published: July 2002

This letter responds to Klepper’s comments [J. Acoust. Soc. Am. 110, 1260 (2001)] on the subject paper, which is concerned with ameliorating seat dip attenuation in auditoria by introducing a pit under the seats. Klepper asks what the effect of the pit will be on seat absorption and reverberation times. A little evidence is presented to support the idea that low-frequency absorption in an auditorium will increase with a pit. It is further speculated that reverberation times could be predicted by using a coupled space model. Klepper’s suggestion of an experiment to answer his questions is supported.
A predictive model of noise for Delhi
Authors: Kumar Krishan , Jain Vinod K. , Rao Dwivedula N.
Published: July 2002

Noise levels have been measured at several sites spread throughout Delhi. Based on these observations and taking into account the specific site characteristics, a linear regression model has been fitted to predict the noise levels for Delhi. It is found that noise levels are primarily determined by vehicular traffic. The residential areas have considerably lower noise levels than commercial areas. The results indicate that the vegetation has a role in attenuation of noise levels.
An exemplar-based account of emergent phonetic categories
Authors: Lacerda Francisco
Published: July 2002

This paper describes how an exemplar-based model can be used to study the early stages of language acquisition and phonetic category formation. The paper discusses in particular how a (conceptually) very simple model, inspired by Edelmans notion of Neural Darwinism, may account for the emergence of phonetic categories arising from the interaction between ambient language input and limited memory-representation resources. It presents an explicit attempt to demonstrate how phonetic categorization may emerge ‘‘spontaneously’’ from exposure to natural infant-directed speech data. The results suggest that phonetic categories may emerge if the auditory input is statistically correlated with one (or several) other sensory inputs. The perceptual-magnet effect is also discussed in the light of the present model. According to the model, the perceptual-magnet effect can be seen as a consequence of distributed memory representations. [Work supported by The Bank of Sweden Tercentenary Foundation, grant 94-0435.]
Environmental acoustic influences on array beam response
Authors: Carey William , Reese James , Bucker Homer
Published: July 2002

Experimental data (environmental propagation loss and beam response) obtained in the Levantine Basin of the Mediterranean Sea are presented and compared to calculations performed with a multilayer, normal-mode computer model. The comparisons show good agreement between measured propagation loss and computer calculations. Beam response data show that the primary source of signal gain degradation is the bifurcated and broadened beam response. The degraded response pattern results from the combined effects of acoustic pressure field variations and motional array shape deformation. Calculations performed with the multilayer, normal-mode model show similar degraded response patterns caused by array tilting. These results indicate that system response and performance characteristics can be calculated for a specific sound channel as a function of the array shape and motion.
Archaeological acoustic study of chirped echo from the Mayan pyramid at Chichén Itzá
Authors: Lubman David
Published: July 2002

Handclaps evoke impressive chirped echoes from the unusually narrow limestone staircases of the Mayan pyramid at Chichén Itzá, located in Mexico’s northern Yucatan. This highly conspicuous acoustical feature, apparently ignored in the archaeological literature, may provide important clues to Mayan cultural practices of the time. Inspection and ray acoustic modeling provide a simple physical explanation for the chirped echo—the ‘‘picket fence effect’’ due to periodic sound reflections from staircases. The authors argue that chirped echoes were always present, and are not spurious artifacts of reconstruction. It is suggested that the Maya must have noticed and may have exploited his acoustical feature in ceremonies at their sacred site. Is the chirped echo an acoustical design flaw, or intentional acoustical engineering by a perceptive stone age people? The author suggests that the simple acoustical engineering required for intentional design falls well within Mayan capabilities. In seeking a cultural motivation for intentional design, it is speculated that the chirped echo may be intended to imitate the primary call of the Mayan sacred bird, the resplendent quetzal. Recorded sound samples show that the two sounds do bear uncanny resemblance. The quetzal hypothesis also provides a credible explanation for the unusually short staircase treads.
Laboratory measurements of current flow using cross correlation on acoustic backscattering from suspended sediments
Authors: van Unen Robert F. , Thorne Peter D. , Cox Henk , Kamminga Sicco D.
Published: July 2002

The application of acoustic backscattering, for measuring near-bed high-resolution profiles of suspended sediment concentration and particle size, has advanced substantially in recent years. To interpret these suspension observations and link them with the hydrodynamics, similarly detailed flow observations would be advantageous. In the present work backscattering from suspensions of marine sediments has been investigated to examine the potential of using the backscattered signal to also measure high-resolution near-bed vertical profiles of horizontal current flow. The approach adopted has been to attempt to utilize the temporal coherence in the suspension field, and to employ cross correlation of the backscattered signal between pairs of horizontally separated transducers to measure current profiles. To investigate this technique a series of laboratory measurements have been conducted for a variety of experimental arrangements, and the outcome from these measurements is reported in the present work. An examination of the suspension field has been conducted, and cross correlations between pairs of transducers investigated. Using cross-correlation time lags, current profiles have been calculated, and the results assessed using laser Doppler flow measurements. Comparison of the acoustic cross-correlation flow measurements with the Doppler reference measurements show a high degree of agreement, and strongly support the use of the cross-correlation approach to accurately measure vertical profiles of the mean horizontal current.
The velocity of ultrasound propagation through brain tissue at low ultrasound frequencies
Authors: Zoric Igor , Ivancevic Bojan , Jambrosic Kristian
Published: July 2002

The acoustic properties of the brain tissue have been in the focus of much scientific research. These properties determine the possibilities of the application and development of the ultrasound methods, as well as the development of the equipment used by the neurosurgeon during the resection of the brain tissue. The results of the measurements of these acoustic properties done at megahertz frequency range have been published. Although the velocity of ultrasound wave propagation does not directly influence the distribution of the ultrasound field within the cranium, it enables the determination of the specific resistance, which has an important role in the distribution of the ultrasound field within the cranium. Using the published results and the conditions of the measurements that have been done, the velocity of ultrasound propagation for the frequency range at which cavitation ultrasonic surgical aspirators work has been estimated. After that the measurement of the velocity of the propagation has been done at the frequency of 24 kHz. The values of both the estimated and the measured velocities of the ultrasound propagation prove the validity of the assumptions on which the estimation is based on.
Effect of the acceleration on vehicle noise emission
Authors: Lelong Joel , Michelet Roger
Published: July 2002

In urban areas, traffic noise, considered as one of the most important public nuisances, is generated by stop–go traffic. Irregular urban traffic is directly linked to traffic regulation devices, which are the cause of frequent accelerations/decelerations of vehicles, depending on driving behavior. In order to predict sound levels at the time of conception, traffic regulation devices, measurements of acceleration passby noise, are necessary. Urban streets are synonymous with complex acoustical environments (presence of reverberant obstacles and multiple sources of noise): carrying out of in situ vehicle noise emissions measurements is impossible. Measuring vehicles’ noise emissions on test tracks can overcome this difficulty, therefore resulting in a better understanding of the acceleration effect on vehicle noise emission. The method described in this paper is based on simultaneous measurements of kinematical data (speeds, accelerations), mechanical parameters (gear ratio, engine speed), and acoustical levels (LA max). First results obtained on cars show significant differences between acceleration levels and cruise levels obtained at same speeds. The level of increase depends on the acceleration value, the gear ratio, and the engine speed. These first results have been compared to existing published results. [Work supported by French Research Program on Ground Transportation (PREDIT).]
Gap detection by early-deafened cochlear-implant subjects
Authors: Busby P. A. , Clark G. M.
Published: July 2002

Two studies investigating gap-detection thresholds were conducted with cochlear-implant subjects whose onset of profound hearing loss was very early in life. The Cochlear Limited multiple-electrode prosthesis was used. The first study investigated the effects of pulse rate (200, 500, and 1000 pulses/s) and stimulus duration (500 and 1000 ms) on gap thresholds in 15 subjects. Average gap thresholds were 1.8 to 32.1 ms. There was essentially no effect of pulse rate and for almost all subjects, no effect of stimulus duration. For two subjects, performance was poorer for the 1000-ms stimulus duration. The second study investigated the relationships between gap thresholds, subject variables, and speech-perception scores. Data from the first study were combined with those from previous studies [Busby et al., Audiology 31, 95–111 (1992); Tong et al., J. Acoust. Soc. Am. 84, 951–962 (1988)], providing data from 27 subjects. A significant negative correlation was found between age at onset of deafness and gap thresholds and most variability in gap thresholds was for the congenitally deaf subjects. Significant negative correlations were found between gap thresholds and word scores for open-set Bamford–Kowal–Bench (BKB) sentences in the auditory–visual condition and lipreading enhancement scores for the same test.
Influence of circumferential partial coating on the acoustic radiation from a fluid-loaded shell
Authors: Cuschieri J. M. , Feit D.
Published: July 2002

Acoustic compliant coatings are a common approach to mitigate the radiation and scattering of sound from fluid-loaded submerged structures. An acoustic compliant coating is a coating that decouples an acoustic source from the surrounding acoustic medium; that is, it provides an acoustic impedance mismatch (different density and speed of sound product). Such a coating is distinct from an ordinary compliant coating in that it may not be resilient in the sense of low stiffness, but still provides an acoustic impedance mismatch. Ideally, the acoustic coating is applied uniformly over the entire surface of the fluid-loaded structure to minimize the acoustic radiation and scattering. However, in certain instances, because of appendages, it may not be practically possible to completely cover the surface of a fluid-loaded structure to decouple it from the adjacent acoustic medium. Furthermore, there may be some inherent advantages to optimizing the distribution of the coating around areas from which the acoustic radiation appears to be dominant. This would be analogous to the application of damping treatment to a vibrating structure in areas where the vibration levels are highest. In the case of the acoustic radiation the problem is more complex because of the coupling between the acoustic fluid and the structure. In this paper, the influence of a partial coating on the acoustic radiation from a fluid-loaded, cylindrical shell of infinite extent and excited by either a line force or an incident plane acoustic wave is examined. The solution to the response and scattered pressure is developed following the procedure used by the authors in previous work on the scattering from fluid-loaded plates and shells. The coating is assumed to be normally reacting providing a decoupling layer between the acoustic medium and the structure; that is, it does not add mass or stiffness to the base structure. The influence of added mass or stiffness of the coating can be included as an added inhomogeneity and treated separately in the solution.
The effect of parametric variations of cochlear implant processors on speech understanding
Authors: Loizou Philipos C. , Poroy Oguz , Dorman Michael
Published: July 2002

This study investigated the effect of five speech processing parameters, currently employed in cochlear implant processors, on speech understanding. Experiment 1 examined speech recognition as a function of stimulation rate in six Med-El/CIS-Link cochlear implant listeners. Results showed that higher stimulation rates (2100 pulses/s) produced a significantly higher performance on word and consonant recognition than lower stimulation rates (<800 pulses/s). The effect of stimulation rate on consonant recognition was highly dependent on the vowel context. The largest benefit was noted for consonants in the /uCu/ and /iCi/ contexts, while the smallest benefit was noted for consonants in the /aCa/ context. This finding suggests that the /aCa/ consonant test, which is widely used today, is not sensitive enough to parametric variations of implant processors. Experiment 2 examined vowel and consonant recognition as a function of pulse width for low-rate (400 and 800 pps) implementations of the CIS strategy. For the 400-pps condition, wider pulse widths (208 μs/phase) produced significantly higher performance on consonant recognition than shorter pulse widths (40 μs/phase). Experiments 3–5 examined vowel and consonant recognition as a function of the filter overlap in the analysis filters, shape of the amplitude mapping function, and signal bandwidth. Results showed that the amount of filter overlap (ranging from −20 to −60 dB/oct) and the signal bandwidth (ranging from 6.7 to 9.9 kHz) had no effect on phoneme recognition. The shape of the amplitude mapping functions (ranging from strongly compressive to weakly compressive) had only a minor effect on performance, with the lowest performance obtained for nearly linear mapping functions. Of the five speech processing parameters examined in this study, the pulse rate and the pulse width had the largest (positive) effect on speech recognition. For a fixed pulse width, higher rates (2100 pps) of stimulation provided a significantly better performance on word recognition than lower rates (<800 pps) of stimulation. High performance was also achieved by jointly varying the pulse rate and pulse width. The above results indicate that audiologists can optimize the implant listener’s performance either by increasing the pulse rate or by jointly varying the pulse rate and pulse width.
The Strain-Energy Function for Elastomers
Authors: Rivlin R. S. , Sawyers K. N.
Published: July 2002

It has been shown that the strain-energy function for an incompressible isotropic elastic material must be expressible as a function of two strain invariants I1, I2 which are elementary symmetric functions of the squares of the principal extension ratios λ1, λ2, λ3. Valanis and Landel have proposed a strain-energy function of the form f(λ1)+f(λ2)+f(λ3). It is shown how such a strain-energy function can be expressed explicitly as a function of I1 and I2. Also, necessary and sufficient conditions are derived for any function of I1 and I2 to be expressible in the form proposed by Valinis and Landel. It is shown how the results of problems which have been solved using the general form of the strain-energy function can be conveniently specialized to the case when the Valanis-Landel strain-energy function is valid.
ABIN1 is a signal‐induced autophagy receptor that attenuates NF‐κB activation by recognizing linear ubiquitin chains
Authors: Shinkawa Yutaka , Imami Koshi , Fuseya Yasuhiro , Sasaki Katsuhiro , Ohmura Koichiro , Ishihama Yasushi , Morinobu Akio , Iwai Kazuhiro
Published: February 2022

Linear ubiquitin chains play pivotal roles in immune signaling by augmenting NF‐κB activation and suppressing programmed cell death induced by various stimuli. A20‐binding inhibitor of NF‐κB 1 (ABIN1) binds to linear ubiquitin chains and attenuates NF‐κB activation and cell death induction. Although interactions with linear ubiquitin chains are thought to play a role in ABIN1‐mediated suppression of NF‐κB and cell death, the underlying molecular mechanisms remain unclear. Here, we show that upon stimulation by Toll‐like receptor (TLR) ligands, ABIN1 is phosphorylated on Ser 83 and functions as a selective autophagy receptor. ABIN1 recognizes components of the MyD88 signaling complex via interaction with linear ubiquitin chains conjugated to components of the complex in TLR signaling, which leads to autophagic degradation of signaling proteins and attenuated NF‐κB signaling. Our current findings indicate that phosphorylation and linear ubiquitination also play a role in downregulation of signaling via selective induction of autophagy.
NOX4 regulates TGFβ‐induced proliferation and self‐renewal in glioblastoma stem cells
Authors: García‐Gómez Pedro , Golán Irene , S. Dadras Mahsa , Mezheyeuski Artur , Bellomo Claudia , Tzavlaki Kalliopi , Morén Anita , Carreras‐Puigvert Jordi , Caja Laia
Published: February 2022

Glioblastoma (GBM) is the most aggressive and common glioma subtype, with a median survival of 15 months after diagnosis. Current treatments have limited therapeutic efficacy; thus, more effective approaches are needed. The glioblastoma tumoural mass is characterised by a small cellular subpopulation – glioblastoma stem cells (GSCs) – that has been held responsible for glioblastoma initiation, cell invasion, proliferation, relapse and resistance to chemo‐ and radiotherapy. Targeted therapies against GSCs are crucial, as is understanding the molecular mechanisms that govern the GSCs. Transforming growth factor β (TGFβ) signalling and reactive oxygen species (ROS) production are known to govern and regulate cancer stem cell biology. Among the differentially expressed genes regulated by TGFβ in a transcriptomic analysis of two different patient‐derived GSCs, we found NADPH oxidase 4 (NOX4) as one of the top upregulated genes. Interestingly, when patient tissues were analysed, NOX4 expression was found to be higher in GSCs versus differentiated cells. A functional analysis of the role of NOX4 downstream of TGFβ in several patient‐derived GSCs showed that TGFβ does indeed induce NOX4 expression and increases ROS production in a NOX4‐dependent manner. NOX4 downstream of TGFβ regulates GSC proliferation, and NOX4 expression is necessary for TGFβ‐induced expression of stem cell markers and of the transcription factor nuclear factor erythroid 2‐related factor 2 (NRF2), which in turn controls the cell’s antioxidant and metabolic responses. Interestingly, overexpression of NOX4 recapitulates the effects induced by TGFβ in GSCs: enhanced proliferation, stemness and NRF2 expression. In conclusion, this work functionally establishes NOX4 as a key mediator of GSC biology.