bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolutely continuous spectrum for one-dimensional Schrödinger operators with slowly decaying potentials: Some optimal results
Authors: Christ Michael , Kiselev Alexander
Published: July 2002

The absolutely continuous spectrum of one-dimensional Schrödinger operators is proved to be stable under perturbation by potentials satisfying mild decay conditions. In particular, the absolutely continuous spectra of free and periodic Schrödinger operators are preserved under all perturbations

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This result is optimal in the power scale. Slightly more general classes of perturbing potentials are also treated. A general criterion for stability of the absolutely continuous spectrum of one-dimensional Schrödinger operators is established. In all cases analyzed, the main term of the asymptotic behavior of the generalized eigenfunctions is shown to have WKB form for almost all energies. The proofs rely on maximal function and norm estimates, and on almost everywhere convergence results for certain multilinear integral operators.
Deformations of canonical singularities
Authors: Kawamata Yujiro
Published: July 2002

We prove that small deformations of canonical singularities are canonical.
Targeted Destruction of DNA Replication Protein Cdc6 by Cell Death Pathways in Mammals and Yeast
Authors: Blanchard Frederic , Rusiniak Michael E. , Sharma Karuna , Sun Xiaolei , Todorov Ivan , Castellano M. Mar , Gutierrez Crisanto , Baumann Heinz , Burhans William C.
Published: July 2002

The highly conserved Cdc6 protein is required for initiation of eukaryotic DNA replication and, in yeast and Xenopus, for the coupling of DNA replication to mitosis. Herein, we show that human Cdc6 is rapidly destroyed by a p53-independent, proteasome-, and ubiquitin-dependent pathway during early stages of programmed cell death induced by the DNA-damaging drug adozelesin, or by a separate caspase-dependent pathway in cells undergoing apoptosis through an extrinsic pathway induced by tumor necrosis factor-α and cycloheximide. The proteasome-dependent pathway induced by adozelesin is conserved in the budding yeast Saccharomyces cerevisiae. The destruction of Cdc6 may be a primordial programmed death response that uncouples DNA replication from the cell division cycle, which is reinforced in metazoans by the evolution of caspases and p53.
GeneGenerator--a flexible algorithm for gene prediction and its application to maize sequences.
Authors: Kleffe J , Hermann K , Vahrson W , Wittig B , Brendel V
Published: July 2002

MOTIVATION: We developed GeneGenerator because of the need for a tool to predict gene structure without knowing in advance how to score potential exons and introns in order to obtain the best results, pertinent in particular to less well-studied organisms for which suitable training sets are small. GeneGenerator is a very flexible algorithm which for a given genomic sequence generates a number of feasible gene structures satisfying user-defined constraints. The specific implementation described in detail requires minimum scoring for translation start and donor and acceptor splice sites according to previously trained logitlinear models. In addition, potential exons and introns are required to exceed specified minimal lengths and threshold scores for coding or non-coding potential derived as log-likelihood ratios of appropriate Markov sequence models. RESULTS: A database of 46 non-redundant genomic sequences from maize is used for illustration. It is shown that the correct gene structures do not always maximize the considered target function. However, in most cases, the correct or nearly correct structures are found in a small set of high-scoring structures. A critical review of the generated structures sometimes allows the choices to be narrowed by considering additional variables such as predicted splice site strength or local optimality of splice site scores. Summary statistics for prediction accuracy over all 46 maize genes are derived under cross-validation and non-cross-validation training conditions for the Markov sequence models. The algorithm achieved exon sensitivity of 0.81 and specificity of 0.75 on an independent set of 14 novel maize genomic segments. AVAILABILITY: GeneGenerator runs under Borland-Pascal 7.0 using MS-DOS and C on UNIX work stations. The source code is available upon request. CONTACT: jkleffe@euler.grumed.fu-berlin-de
The cyclin B1 gene is actively transcribed during mitosis in HeLa cells
Authors: Sciortino Selvaggia , Gurtner Aymone , Manni Isabella , Fontemaggi Giulia , Dey Anup , Sacchi Ada , Ozato Keiko , Piaggio Giulia
Published: July 2002

In mammalian cells, the expression level of the cyclin B1 gene plays a critical role in the progression through mitosis. Here we demonstrate that the transcriptional activity of the human cyclin B1 promoter, as well as the rate of gene transcription, is high during mitosis. Indeed, the cyclin B1 promoter maintains an open chromatin configuration at the mitotic stage. Consistent with this, we show that the cyclin B1 promoter is occupied and bound to NF‐Y during mitosis in vivo. Our results provide the first example of RNA polymerase II‐dependent transcription during mitosis in mammalian cells.
An intervention resembling caloric restriction prolongs life span and retards aging in yeast
Authors: Jiang James C. , Jaruga Ewa , Repnevskaya Marina V. , Jazwinski S. Michal
Published: July 2002

The yeast Saccharomyces cerevisiae has a finite life span that is measured by the number of daughter cells an individual produces. The 20 genes known to determine yeast life span appear to function in more than one pathway, implicating a variety of physiological processes in yeast longevity. Less attention has been focused on environmental effects on yeast aging. We have examined the role that nutritional status plays in determining yeast life span. Reduction of the glucose concentration in the medium led to an increase in life span and to a delay in appearance of an aging phenotype. The increase in life span was the more extensive the lower the glucose levels. Life extension was also elicited by decreasing the amino acids content of the medium. This suggests that it is the decline in calories and not a particular nutrient that is responsible, in striking similarity to the effect on aging of caloric restriction in mammals. The caloric restriction effect did not require the induction of the retrograde response pathway, which signals the functional status of the mitochondrion and determines longevity. Furthermore, deletion of RTG3, a downstream mediator in this pathway, and caloric restriction had an additive effect, resulting in the largest increase (123%) in longevity described thus far in yeast. Thus, retrograde response and caloric restriction operate along distinct pathways in determining yeast longevity. These pathways may be exclusive, at least in part. This provides evidence for multiple mechanisms of metabolic control in yeast aging. Inasmuch as caloric restriction lowers blood glucose levels, this study raises the possibility that reduced glucose alters aging at the cellular level in mammals.
A genetic model for human polyglutamine-repeat disease in Drosophila melanogaster
Authors: Bonini Nancy M.
Published: July 2002

To apply genetics to the problem of human polyglutamine–repeat disease, we recreated polyglutamine–repeat disease inDrosophila melanogaster. To do this, we expressed forms of the human gene encoding spinocerebellar ataxia type 3, also called Machado–Joseph disease (SCA–3/MJD). This gene is responsible for the most common form of human ataxia worldwide. Expression of a normal form of the MJD protein with 27 polyglutamines (MJDtr–Q27) had no phenotype. However, expression of a form of the protein with an expanded run of 78 glutamines (MJDtr–Q78) caused late onset progressive degeneration. In addition, the MJDtr–Q78 formed abnormal protein aggregates, or nuclear inclusions (NIs), whereas the control protein was cytoplasmic. These data indicate that the mechanisms of human polyglutamine–repeat disease are conserved toDrosophila. We are currently using this model to address potential mechanisms by which the mutant disease protein causes neural degeneration, as well as to define genes that can prevent polyglutamine–induced degeneration. By applying the power ofDrosophilagenetics to the problem of human polyglutamine–induced neural degeneration, we hope to identify ways to prevent and treat these diseases in humans.
Functionally independent components of early event-related potentials in a visual spatial attention task
Authors: Makeig Scott , Westerfield Marissa , Townsend Jeanne , Jung Tzyy-Ping , Courchesne Eric , Sejnowski Terrence J.
Published: July 2002

Spatial visual attention modulates the first negative–going deflection in the human averaged event–related potential (ERP) in response to visual target and non–target stimuli (the N1 complex). Here we demonstrate a decomposition of N1 into functionally independent subcomponents with functionally distinct relations to task and stimulus conditions. ERPs were collected from 20 subjects in response to visual target and non–target stimuli presented at five attended and non–attended screen locations. Independent component analysis, a new method for blind source separation, was trained simultaneously on 500 ms grand average responses from all 25 stimulus–attention conditions and decomposed the non–target N1 complexes into five spatially fixed, temporally independent and physiologically plausible components. Activity of an early, laterally symmetrical component pair (N1aRand N1aL) was evoked by the left and right visual field stimuli, respectively. Component N1aRpeakedca.9 ms earlier than N1aL. Central stimuli evoked both components with the same peak latency difference, producing a bilateral scalp distribution. The amplitudes of these components were not reliably augmented by spatial attention. Stimuli in the right visual field evoked activity in a spatio–temporally overlapping bilateral component (N1b) that peaked atca.180 ms and was strongly enhanced by attention. Stimuli presented at unattended locations evoked a fourth component (P2a) peaking near 240 ms. A fifth component (P3f) was evoked only by targets presented in either visual field. The distinct response patterns of these components across the array of stimulus and attention conditions suggest that they reflect activity in functionally independent brain systems involved in processing attended and unattended visuospatial events.
Electrostatics in protein–protein docking
Authors: Heifetz Alexander , Katchalski‐Katzir Ephraim , Eisenstein Miriam
Published: July 2002

A novel geometric‐electrostatic docking algorithm is presented, which tests and quantifies the electrostatic complementarity of the molecular surfaces together with the shape complementarity. We represent each molecule to be docked as a grid of complex numbers, storing information regarding the shape of the molecule in the real part and information regarding the electrostatic character of the molecule in the imaginary part. The electrostatic descriptors are derived from the electrostatic potential of the molecule. Thus, the electrostatic character of the molecule is represented as patches of positive, neutral, or negative values. The potential for each molecule is calculated only once and stored as potential spheres adequate for exhaustive rotation/translation scans. The geometric‐electrostatic docking algorithm is applied to 17 systems, starting form the structures of the unbound molecules. The results—in terms of the complementarity scores of the nearly correct solutions, their ranking in the lists of sorted solutions, and their statistical uniqueness—are compared with those of geometric docking, showing that the inclusion of electrostatic complementarity in docking is very important, in particular in docking of unbound structures. Based on our results, we formulate several “good electrostatic docking rules”: The geometric‐electrostatic docking procedure is more successful than geometric docking when the potential patches are large and when the potential extends away from the molecular surface and protrudes into the solvent. In contrast, geometric docking is recommended when the electrostatic potential around the molecules to be docked appears homogenous, that is, with a similar sign all around the molecule.
A depth‐dose measuring device using a multichannel scintillating fiber array for electron beam therapy
Authors: Aoyama Takahiko , Koyama Shuji , Tsuzaka Masatoshi , Maekoshi Hisashi
Published: July 2002

The development of a new depth‐dose measuring device for electron beam therapy is described. The device employs plastic scintillating fiber detectors inserted in a polymethylmethacrylate (PMMA) phantom in line along an incident electron beam. Output photons from a fiber, the number of which is proportional to the absorbed dose at each depth of the phantom, were converted to an electric signal with a photodiode. Each signal from the photodiode was transmitted to a personal computer through a multichannel analog–digital converter, and was processed to draw a depth‐dose curve on the computer display. A depth‐dose curve could be obtained in a measuring time of 5 s for each incident electron beam with an energy range between 4 and 21 MeV. The mean electron energies estimated using the curves and the depth‐scaling factor for PMMA were consistent with those obtained from conventional depth‐dose measurements using an ion chamber and a water phantom. The newly developed system, being simple and not time consuming, could be used routinely for quality assurance purposes in electron beam therapy.
A novel 675.2 nm diode laser densitometer for use with GafChromic films
Authors: Ertl Adolf , Kellermann Peer Oliver , Zehetmayer Martin , Schöggl A. , Kindl Peter , Maitz Ann H.
Published: July 2002

In this article we compare the accuracy of a diode laser densitometer emitting 675.2 nm to that of a commercial He–Ne laser densitometer emitting 632.8 nm for GafChromic MD‐55 film readout. A Leksell gamma unit (AB Elekta Stockholm, Sweden) Model B with a 14 and 8 mm collimator at the same isocenter (combined 11 mm collimator) was used to irradiate GafChromic MD‐55 films. Dose response curves, dose cross profile and FWHM were measured with a custom‐designed diode laser scanning device, emitting light at 675.2 nm. The same data were recorded with a commercial He–Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements were compared to dose cross profiles of a radiosurgery dose planning program (GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He–Ne laser densitometer, the custom‐designed diode laser scanning device showed better agreement with the calculated dose cross profile. For two axes, the full width half maxima (FWHM) of the diode laser scanning device was within 0.1 mm deviation compared to the data calculated by the dose planning program. The FWHM of the commercial He–Ne laser densitometer was less accurate (1.6 and 2.1 mm deviation). Our data show that a diode laser scanning device using a light source emitting 675.2 nm increases the accuracy of a GafChromic MD‐55 film readout. This greater accuracy may be related to the diode laser measuring the optical density close to maximum absorption of the GafChromic film MD‐55 (671–675 nm).
Neural network based algorithm to quantify joint space width in joints of the hand for arthritis assessment
Authors: Duryea J. , Jiang Y. , Zakharevich M. , Genant H. K.
Published: July 2002

Arthritis diseases are widespread with enormous societal costs. The two most common forms, rheumatoid arthritis and osteoarthritis, affect joints of the hand and cause narrowing of the joint spaces as the disease destroys the articular cartilage. Radiographic assessment is one of the most promising tools to detect subtle changes in joint space width (JSW), and therefore disease progression. Currently radiographic assessment of arthritis in joints of the hand is accomplished though semiquantitative subjective scoring systems which do not provide a quantitative measurement of the JSW. We describe here an automated method which calculates the average JSW of the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joint spaces for fingers 2 to 5 (index, middle, ring, and little) on digitized hand radiographs. The method was tested with a set of 54 hand radiographs on joints with mild to moderate rheumatoid arthritis. Performance was evaluated by comparing algorithm measured JSW to a gold standard determined from expertly hand‐drawn joint margins. The agreement was quantified by a measurement of root mean square deviation, 0.148 mm, 0.089 mm, and 0.114 mm for the MCP, PIP, and DIP joints, respectively. In addition, the algorithm measured JSW strongly correlated with the gold standard: (MCP), (PIP), and (DIP). This is an accurate and robust algorithm and should provide a more quantitative measure of disease progression than current methods.
Crossover from the exact factor to the Boltzmann factor
Authors: Prentis Jeffrey J. , Andrus Aaron E. , Stasevich Timothy J.
Published: July 2002

We derive the exact physical statistics of a system in thermal equilibrium with different environments—a gas, a spin, and a Boltzmann environment. The crossover from the exact factor to the Boltzmann factor is parametrized by scaled energy variables. The precise conditions that generate the Boltzmann factor emerge naturally. Such an analytic representation of the exact factor, the crossover, and the Boltzmann limit are not found in the standard model-free derivations of the Boltzmann factor.
Quantitative investigation of Fresnel reflection in the electromagnetism laboratory
Authors: Dekker M. , Kromminga A. J. , Van Baak D. A. , Pilskalns O. J. , Jacobs J. P.
Published: July 2002

We have developed an experimental apparatus that makes it possible for students to make detailed quantitative measurements of the Fresnel reflection coefficients for the reflection of light from a plane interface. The experiment is made possible by the linear polarization, and impressive power stability, exhibited by visible and near-infrared diode-laser modules, and it has been a very effective addition to our sophomore electromagnetism laboratories.
Predicting speech metrics in a simulated classroom with varied sound absorption
Authors: Bistafa Sylvio R. , Bradley John S.
Published: July 2002

By systematically varying the amount of sound absorption, and the location of the sound-absorbing material in a simulated classroom, it was possible to assess the accuracy of the prediction of speech metrics in quite simple acoustical environments. Predictions of speech level, early-to-late sound ratios (C50) and speech transmission index (STI) values were obtained analytically and with two hybrid ray-based computer programs, RAYNOISE 3.0 and ODEON 4.1. The RAYNOISE predictions were accomplished with a purely specular reflection model and also with a calibrated diffuse reflection model. ODEON uses a parameter called transition order, TO, to change the reflection procedure from purely specular to diffuse for reflections that have orders higher than TO. A parametric study was conducted to determine the best transition order for the ODEON prediction of speech metrics. It was found that the analytical predictions of speech level and C50 were on average accurate to about 1 just-noticeable difference (jnd), whereas the analytical predictions of STI were on average within 2 jnd’s. ODEON predictions of speech level, C50 and STI were on average within 2 jnd’s. RAYNOISE predictions of C50 and STI with the specular model were on average within 2 jnd’s. However, the RAYNOISE predictions of speech level, with both types of reflection models, and the RAYNOISE predictions of C50 and STI with the diffuse model had average errors greater than 2 jnd’s. The effects of the sound-absorption treatments on the measured speech metric values are also discussed.
A two-microphone dual delay-line approach for extraction of a speech sound in the presence of multiple interferers
Authors: Liu Chen , Wheeler Bruce C. , O’Brien William D. , Lansing Charissa R. , Bilger Robert C. , Jones Douglas L. , Feng Albert S.
Published: July 2002

This paper describes algorithms for signal extraction for use as a front-end of telecommunication devices, speech recognition systems, as well as hearing aids that operate in noisy environments. The development was based on some independent, hypothesized theories of the computational mechanics of biological systems in which directional hearing is enabled mainly by binaural processing of interaural directional cues. Our system uses two microphones as input devices and a signal processing method based on the two input channels. The signal processing procedure comprises two major stages: (i) source localization, and (ii) cancellation of noise sources based on knowledge of the locations of all sound sources. The source localization, detailed in our previous paper [Liu et al., J. Acoust. Soc. Am. 108, 1888 (2000)], was based on a well-recognized biological architecture comprising a dual delay-line and a coincidence detection mechanism. This paper focuses on description of the noise cancellation stage. We designed a simple subtraction method which, when strategically employed over the dual delay-line structure in the broadband manner, can effectively cancel multiple interfering sound sources and consequently enhance the desired signal. We obtained an 8–10 dB enhancement for the desired speech in the situations of four talkers in the anechoic acoustic test (or 7–10 dB enhancement in the situations of six talkers in the computer simulation) when all the sounds were equally intense and temporally aligned.
Individual acoustic variation in Belding’s ground squirrel alarm chirps in the High Sierra Nevada
Authors: McCowan Brenda , Hooper Stacie L.
Published: July 2002

The acoustic structure of calls within call types can vary as function of individual identity, sex, and social group membership and is important in kin and social group recognition. Belding’s ground squirrels (Spermophilus beldingi) produce alarm chirps that function in predator avoidance but little is known about the acoustic variability of these alarm chirps. The purpose of this preliminary study was to analyze the acoustic structure of alarm chirps with respect to individual differences (e.g., signature information) from eight Belding’s ground squirrels from four different lakes in the High Sierra Nevada. Results demonstrate that alarm chirps are individually distinctive, and that acoustic similarity among individuals may correspond to genetic similarity and thus dispersal patterns in this species. These data suggest, on a preliminary basis, that the acoustic structure of calls might be used as a bioacoustic tool for tracking individuals, dispersal, and other population dynamics in Belding’s ground squirrels, and perhaps other vocal species.
A backpropagation network model of the monaural localization information available in the bat echolocation system
Authors: Wotton Janine M. , Jenison Rick L.
Published: July 2002

The information echolocating bats receive is a combination of the properties of the sound they emit and the sound they receive at the eardrum. Convolving the emission and the external ear transfer functions produces the full spectral information contained in the echolocation combination. Spatially dependent changes in the magnitude spectra of the emission, external ear transfer functions, and the echolocation combination of Eptesicus fuscus could provide localization information to the bat. Principal component analysis was used to reduce the dimensionality of these complex spectral data sets. The first eight principal component weights were normalized, rotated, and used as the input to a backpropagation network model which examined the relative directionality of the emission, ear, and the echolocation combination. The model was able to localize more accurately when provided with the directional information of the echolocation combination compared to either the emission or ear information alone.
Improvements in an experimental thermoacoustically driven thermoacoustic refrigerator
Authors: Hofler Thomas J. , Adeff Jay A.
Published: July 2002

A thermoacoustically (heat) driven, thermoacoustic refrigerator apparatus, having a novel topology, has produced significant cooling power and efficiency. It has achieved a cooling temperature span of 60 °C, and 91 W of cooling power at a span of 25 °C, with an overall COP of 0.15. These numbers were produced with a porous carbon refrigerator stack and a driver stack comprised of stainless steel wire mesh disks. While easy to fabricate, the wire mesh stack is known to produce poor efficiency with the commercially available wire sizing. New modifications currently being fabricated include: a stainless steel foil roll stack for the driver, a plastic film roll stack for the refrigerator, as well as improved heat exchangers. Substantial increases in amplitude, cooling power, and overall COP are anticipated as a result of these modifications. [Work supported by Office of Naval Research.]
Time analysis of immersed waveguides using the finite element method
Authors: Hladky-Hennion Anne-Christine , Bossut Régis , de Billy Michel
Published: July 2002

The propagation of acoustic waves in immersed waveguides has been previously studied with the help of the finite element method, using the ATILA code [A. C. Hladky-Hennion et al., J. Sound Vib. 200, 519–530 (1997)]. But this method, which is a modal analysis, essentially concerns the case of rectilinear, infinite, and uniform waveguides. Thus this paper deals with another way of solving the problem of wave propagation along waveguides, with the help of a time analysis using finite elements. First, the theoretical formulation is presented for immersed structures. Then, Plexiglas and brass wedge guides, of different apex angles, are considered. When immersed in water, these wedges generate either propagating or radiating wedge waves. The finite element results, using a time analysis, are compared to the previous finite element results, using a modal analysis and to the experiments, leading to a good agreement. Thus the approach can be easily extended to other waveguides whatever their cross sections.
Information entropy of humpback whale song
Authors: Suzuki Ryuji , Buck John R. , Tyack Peter L.
Published: July 2002

Many theories of nonhuman animal communication posit a first-order Markov model in which the next signal depends only on the current one. Such a model precludes a hierarchical structure to the communication signal. Information theory and signal processing provide quantitative techniques to estimate the underlying complexity of an arbitrary signal or symbol sequence. These techniques are applied to humpback whale songs and demonstrate that any first-order Markov model fails to attain the underlying bound of complexity in these songs. Humpback songs are symbolized into alphabet sequences using spectrograms and self-organizing neural nets [Walker, unpublished]. The entropy of the song sequence is measured with a first-order parametric Markov model, and with a nonparametric sliding window method [Kontoyiannis et al., IEEE Trans. Info. Theory 44, 1319–1327 (1998)]. Preliminary analyses suggest that the entropy of the first-order Markov model is significantly higher than that of the nonparametric model, meaning that any first-order Markov source cannot reasonably model humpback songs. Furthermore, it is found that the symbolized song statistics are locally but not globally stationary, implying that these songs possess a hierarchical structure. [Work supported by NSF Ocean Sciences.]
Model-based approach to envelope and positive instantaneous frequency estimation of signals with speech applications
Authors: Kumaresan Ramdas , Rao Ashwin
Published: July 2002

An analytic signal s(t) is modeled over a T second duration by a pole-zero model by considering its periodic extensions. This type of representation is analogous to that used in discrete-time systems theory, where the periodic frequency response of a system is characterized by a finite number of poles and zeros in the z-plane. Except, in this case, the poles and zeros are located in the complex-time plane. Using this signal model, expressions are derived for the envelope, phase, and the instantaneous frequency of the signal s(t). In the special case of an analytic signal having poles and zeros in reciprocal complex conjugate locations about the unit circle in the complex-time plane, it is shown that their instantaneous frequency (IF) is always positive. This result paves the way for representing signals by positive envelopes and positive IF (PIF). An algorithm is proposed for decomposing an analytic signal into two analytic signals, one completely characterized by its envelope and the other having a positive IF. This algorithm is new and does not have a counterpart in the cepstral literature. It consists of two steps. In the first step, the envelope of the signal is approximated to desired accuracy using a minimum-phase approximation by using the dual of the autocorrelation method of linear prediction, well known in spectral analysis. The criterion that is optimized is a waveform flatness measure as opposed to the spectral flatness measure used in spectral analysis. This method is called linear prediction in spectral domain (LPSD). The resulting residual error signal is an all-phase or phase-only analytic signal. In the second step, the derivative of the error signal, which is the PIF, is computed. The two steps together provide a unique AM-FM or minimum-phase/all-phase decomposition of a signal. This method is then applied to synthetic signals and filtered speech signals.
Multimode radiation from an unflanged, semi-infinite circular duct
Authors: Joseph Phillip , Morfey Christopher L.
Published: July 2002

Theoretical expressions for sound radiation from a single incident duct mode, arriving at the open end of a semi-infinite circular unflanged duct with rigid walls, are used to obtain numerical results for (1) the single-mode sound power transmission coefficient, and (2) the multimode far-field directivity factor. For the multimode calculations the modes are assumed incoherent, and a weighting model is adopted which includes, as special cases, equal power per mode (above cutoff), and excitation by incoherent monopoles or axial dipoles uniformly distributed over a duct cross section. High-frequency asymptotic features of the results are explored in detail and analytical approximations are given. The findings have practical application to sound power measurement from tall exhaust stacks.
Analysis and perception of spectral 1/f characteristics of amplitude and period fluctuations in normal sustained vowels
Authors: Aoki Naofumi , Ifukube Tohru
Published: July 2002

Two kinds of fluctuations are always observed in the steady parts of normal sustained vowels. One is amplitude fluctuation, defined as the cyclic changes of maximum peak amplitudes. The other is period fluctuation, defined as the cyclic changes of pitch periods. The primary purpose of this paper is to present quantitative descriptions of amplitude and period sequences obtained from normal sustained vowels. These fluctuation sequences consisted of maximum peak amplitudes or pitch periods extracted successively from 512 consecutive pitch periods in the steady part. Results of the frequency analysis indicated that their frequency characteristics seemed to be subject to the spectral 1/f power law. In order to investigate the possibility that the frequency characteristics of the fluctuation sequences influence the voice quality of sustained vowels, psychoacoustic experiments were conducted. Amplitude and period sequences evaluated in the experiments were spectral 1/f0 (white noise), 1/f, 1/f2, and 1/f3 sequences, respectively. The experimental results indicated that the subjective voice quality of synthesized sustained vowels could reflect the differences in the frequency characteristics of the fluctuation sequences.
The use of complex material constants to model losses in piezoelectric
Authors: Mukherjee Binu K. , Yang Guomao , Sherritt Stewart G.
Published: July 2002

Complex material constants are now being used to accurately model the dynamic response of piezoelectric materials. A simple physical model of piezoelectric materials will be used to show how complex material constants can be conveniently used to characterize losses in the dielectric, elastic, and piezoelectric response of piezoelectric materials. The same model is also used to explain why the material constants are also a function of frequency, temperature, and applied signal strength. Theoretical attempts to understand the loss mechanisms and experimental methods to measure the various functional dependencies will be reviewed. [Funding support from the U.S. Office of Naval Research is gratefully acknowledged.]
Shock wave–inertial microbubble interaction: A theoretical study based on the Gilmore formulation for bubble dynamics
Authors: Zhu Songlin , Zhong Pei
Published: July 2002

The Gilmore formulation for bubble dynamics coupled with zeroth-order gas diffusion were used to investigate theoretically the cavitation activity produced by a modified XL-1 lithotripter [J. Acoust. Soc. Am. 105, 1997–2009 (1999)]. The model calculation confirms many of the basic features in bubble dynamics observed experimentally, in particular the strong secondary shock wave emission generated by in situ lithotripter shock wave–inertial microbubble interaction. In addition, shock wave–inertial microbubble interaction produced by a Dornier HM-3, the most commonly used clinical lithotripter, was evaluated. It was shown that the forced collapse of inertial microbubbles with strong secondary shock wave emission could be produced consistently, provided that an appropriate preceding shock wave and interpulse delay were used. Further, it was demonstrated that truncation of the tensile stress of the lithotripter shock wave could significantly reduce the large expansion of the bubble following shock wave-inertial microbubble interaction, which may alleviate the risk for vascular injury during shock wave exposure.
A class of chaotic bird calls?
Authors: Fletcher N. H.
Published: July 2002

Evidence is presented that the basic vocalized sound produced by some cockatoos, specifically the Australian sulfur-crested cockatoo (Cacatua galerita) and the gang-gang cockatoo (Callocephalon fimbriatum), has a chaotic acoustic structure rather than the harmonic structure characteristic of most birdsongs. These findings support those of Fee et al. [Nature (London) 395(3), 67–71 (1999)] on nonlinear period-doubling transitions in the song of the zebra finch (Taeniopygia guttata). It is suggested that syllables with chaotic structure may be a feature of the songs of many birds.
Rheology of Aluminum Dilaurate in Toluene
Authors: Gaskins Frederick H. , Brodnyan John G. , Philippoff Wladimir
Published: July 2002

The stress-optical properties of aluminum dilaurate-toluene solutions were investigated over a wide range in shear rates, D. Flow curves of 1, 2, and 3 wt-% of the aluminum soap dispersed in toluene displaced the type of behavior previously reported by Weber and Bauer: i.e., Newtonian behavior at low shear rates, pronounced shear thinning at D greater than 10−2 sec−1, and dependence of apparent shear stress, τ, on length-to-radius ratio, L/R, of the capillary tubes used at high shear rates. Flow birefringence behavior was similar. For example, at low shear rates the degree of birefringence, Δn, increased in proportion to D and the extinction angle, χ, was nearly 45°. Above a critical shear rate, Δn, increased overproportionally, finally leveling out at a high value. Simultaneously χ decreased equally rapidly to about 1°. Despite these dramatic changes in dependence of τ, Δn and χ on D, the stress-optical coefficient remained constant over the entire range of variables. Elastic recoverable shear strains, or simply “recoverable shears,” s, were calculated from the variance of τ with L/R. These were found to be in good agreement with data obtained from normal stress measurements in a Weissenberg Rheogoniometer. At low shear stress s increased linearly with τ. Above a critical shear stress the recoverable shear increased rapidly with small increases in τ finally leveling off at a value of approximately 300 shear units and remaining constant with additional increases in shear stress. This behavior is similar to that observed with polyethylene in the region where melt fracture occurs. In these experiments, however, the transition takes place in a rotational instrument under continuous shear in which no “entrance effects” can be postulated as causing melt fracture. During the progress of this investigation it was ascertained that the rotational viscometer could be used to determine elasticity in aluminum soap solutions under dynamic conditions. Quantitative evaluation of the results produced data which correlated with dynamic test data obtained by a variety of techniques. The authors believe that this is a unique and novel method for measuring the dynamic rheological properties of viscoelastic materials.
Hydrodynamic Interaction Effects in Rigid Dumbbell Suspensions. I. Kinetic Theory
Authors: Bird R. B. , Warner H. R.
Published: July 2002

A macromolecular solution is represented by the simple model of rigid dumbbells suspended in a Newtonian fluid with Brownian motion included; hydrodynamic interaction is taken into account. The expressions for the “diffusion equation” and the stress tensor are given. Example results using the equations for the rigid dumbbell suspension modified to include the hydrodynamic interaction effect are obtained for two flows: steady shearing flow and small-amplitude oscillatory motion.
Effects of the low-surface-energy component on the viscosity of poly(ether ether ketone) and polytetrafluoroethylene blends
Authors: Chan Chi-Ming , Nixon Allen , Venkatraman Subbu
Published: July 2002

The effects of a low-surface-energy component, polytetrafluoroethylene (PTFE), on the apparent viscosity of poly(ether ether ketone) (PEEK) were studied. Blends of PEEK and PTFE were prepared by using a twin-counter-rotating-screw extruder (ZSE). One percent and five percent by weight of PTFE were used. The apparent viscosity of the blends as a function of apparent shear rate was determined by a capillary rheometer. The observed reduction in the apparent viscosity is attributed to the migration and accumulation of the low-surface-energy component (PTFE) at the interface between the die wall and the melt. The enrichment of PTFE on the surface of the extrudates was confirmed by x-ray photoelectron spectroscopy. Surface enrichment of PTFE and viscosity reduction are enhanced with an increase in shear rate and PTFE concentration in the blend.
The Considère condition and rapid stretching of linear and branched polymer melts
Authors: McKinley Gareth H. , Hassager Ole
Published: July 2002

We analyze the onset of “necking” and subsequent filament failure during the transient uniaxial elongation of viscoelastic fluid samples in extensional rheometers. In the limit of rapid elongation (such that no molecular relaxation occurs), the external work applied is all stored elastically and the Considère criterion originally developed in solid mechanics can be used to quantitatively predict the critical Hencky strain to failure. By comparing the predictions of the Doi–Edwards model for linear homopolymer melts with those of the “Pom-Pom” model recently proposed by McLeish and Larson [J. Rheol. 42, 81–110 (1998)] for prototypical branched melts we show that the critical strain to failure in rapid elongation of a rubbery material is intimately linked to the molecular topology of the chain, especially the degree of chain branching. The onset of necking instability is monotonically shifted to larger Hencky strains as the number of branches is increased. Numerical computations at finite Deborah numbers also show that there is an optimal range of deformation rates over which homogeneous extensions can be maintained to large strain. We also consider other rapid homogeneous stretching deformations, such as biaxial and planar stretching, and show that the degree of stabilization afforded by inclusion of material with long-chain branching is a sensitive function of the imposed mode of deformation.
Optoelectronic Properties of MoS2 in Proximity to Carrier Selective Metal Oxides
Authors: Lattyak Colleen , Vehse Martin , Gonzalez Marco A. , Pareek Devendra , Gütay Levent , Schäfer Sascha , Agert Carsten
Published: March 2022

Transition metal dichalcogenides are an exciting class of new absorber materials for photovoltaic applications due to their unique optoelectronic properties in the single to few‐layer regime. In recent years, these materials have been intensively studied, often utilizing conventional substrates such as sapphire and silicon dioxide on silicon. This study investigates the optical properties of molybdenum disulfide (MoS2) mono‐, bi‐, and multilayer films prepared by flake exfoliation and atomic layer deposition (ALD). These films are transferred to different photovoltaic relevant carrier‐selective contacts, such as titanium oxide, titanium–titanium oxide, molybdenum oxide, and silicon–silicon dioxide reference substrates. Raman and photoluminescence (PL) spectra of single‐crystalline exfoliated MoS2 flakes and ALD‐grown MoS2 films on different substrates are compared in order to investigate the influence of the different contact materials on the corresponding optical transitions in MoS2. It is demonstrated that the different substrates influence the Raman and PL spectra of MoS2 layers due to doping and charge transfer effects, and similar effects are observed in both the exfoliated single‐crystalline flakes and ALD‐grown MoS2 layers.
Wide‐Bandgap Organic–Inorganic Lead Halide Perovskite Solar Cells
Authors: Tong Yao , Najar Adel , Wang Le , Liu Lu , Du Minyong , Yang Jing , Li Jianxun , Wang Kai , Liu Shengzhong (Frank)
Published: March 2022

Under the groundswell of calls for the industrialization of perovskite solar cells (PSCs), wide‐bandgap (>1.7 eV) mixed halide perovskites are equally or more appealing in comparison with typical bandgap perovskites when the former's various potential applications are taken into account. In this review, the progress of wide‐bandgap organic–inorganic hybrid PSCs—concentrating on the compositional space, optimization strategies, and device performance—are summarized and the issues of phase segregation and voltage loss are assessed. Then, the diverse applications of wide‐bandgap PSCs in semitransparent devices, indoor photovoltaics, and various multijunction tandem devices are discussed and their challenges and perspectives are evaluated. Finally, the authors conclude with an outlook for the future development of wide‐bandgap PSCs.
Superior Piezoelectricity in Bismuth Titanate‐Based Lead‐Free High‐Temperature Piezoceramics via Domain Engineering
Authors: Xie Xinchun , Zhou Zhiyong , Liang Ruihong , Dong Xianlin
Published: March 2022

High‐temperature piezoelectric materials are widely needed in electromechanical sensors, actuators, and transducers that are exposed to high‐temperature conditions. Bismuth layer‐structured bismuth titanate (Bi4Ti3O12, BIT) ferroelectrics have a high Curie temperature of 675 °C but suffer from poor electrical properties, especially the piezoelectricity. Here, a giant piezoelectric coefficient d33 of 40.2 pC N−1 is obtained in the Bi3.97Ce0.03Ti2.98(WNb)0.01O12 ceramics with a high Curie temperature of 657 °C, the highest value reported to date in BIT‐based piezoceramics. Electrical property and microstructural analysis reveal that the high piezoelectricity benefits from the preferential orientation of ferroelectric domains, the irreversibility of ferroelectric domain reorientation, and the high density of ferroelectric domain walls. Besides, excellent thermal stability of piezoelectric constant (d33 = 36.7 pC N−1 at 500 °C, <10% variations in the range of room temperature to 500 °C), high electrical resistivity (ρ > 107 Ω cm at 500 °C), and low loss (tanδ < 1.5% at 500 °C) are also obtained in the Bi3.97Ce0.03Ti2.98(WNb)0.01O12 ceramics. This work not only penetrates the origins of outstanding piezoelectricity of BIT‐based ceramics but also offers prospects for brand‐new tactics to exploit high‐performance high‐temperature piezoceramics.
Over‐Potential Tailored Thin and Dense Lithium Carbonate Growth in Solid Electrolyte Interphase for Advanced Lithium Ion Batteries
Authors: Qin Nan , Jin Liming , Lu Yanyan , Wu Qiang , Zheng Junsheng , Zhang Cunman , Chen Zonghai , Zheng Jim P.
Published: March 2022

A stable solid electrolyte interphase (SEI) is highly desired to prevent parasitic reactions during normal operation of lithium‐ion batteries (LIBs). Lithium carbonate (Li2CO3) is one of the most significant components for smooth SEI passivation layers; while the formation mechanism and special distribution of the Li2CO3 layer has not yet been illustrated. Here, an over‐potential tailored Li2CO3 growth mechanism based on the typical hard carbon anode is demonstrated. With an increase in the over‐potential, the size of Li2CO3 decreases gradually as the amount increases. When the over‐potential is large (potential at 0.01 V), a Li2CO3‐rich thin and dense inorganic layer with the average thickness of 4.4 nm in the SEI is constructed. The special SEI the completely wraps the boundaries of the anode enables a larger Li‐ion de‐solvation energy barrier and a lower Li‐ion diffusion energy barrier, which supports low self‐discharge behavior and a fast kinetic rate at the anode. More generally, this Li2CO3 growth mechanism is also applicable to commercialized graphite anodes and similar results are also obtained. Therefore, this work provides a new insight into the Li2CO3 growth mechanism in SEIs, as well as a guideline for the design of stable artificial SEIs.
Reaction rate enhancement of three‐phase hydrogenation using the Taylor flow reactor
Authors: Horie Takafumi , Hirai Kenta , Kumagai Norihisa , Taniya Keita , Ichihashi Yuichi , Ohmura Naoto , Matsuda Keigo , Matsumoto Hideyuki , Sakurai Makoto , Watabe Yoshihide
Published: March 2022

A gas–liquid–solid three‐phase reaction was conducted in a Taylor flow reactor to improve the apparent reaction rate by enhancing the mass transfer rate of the gas component to the surface of the solid catalyst through the liquid. Hydrogenation of α‐methyl styrene (AMS) was the model reaction. The reactor was an aluminum tube with a length of 300 mm and an inner diameter of 4 mm. A thin alumina layer was formed on the inner wall and palladium was used as the catalyst. Hydrogen and AMS were introduced into a T‐joint installed at the upper stream of the reactor to form a gas–liquid Taylor flow. The AMS conversion obtained using the Taylor flow was higher than that obtained without the flow. To examine the effect of the hydrogen absorption promotion by the circulating flow in the AMS slug, the total flow rate of the reactants was varied whereas the length of the gas and liquid slugs was maintained. Although the absorption increased owing to the faster surface renewal, only a slight improvement was observed. Conversely, when the total flow rate was fixed and the ratio of the gas slug length to the liquid slug length was increased, the apparent reaction rate improved significantly. These results indicate that diffusion in the thin liquid film directly toward the solid catalyst on the reactor wall was dominant for enhancing the reaction rate.