bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrimination between Paralogs using Microarray Analysis: Application to the Yap1p and Yap2p Transcriptional Networks
Authors: Cohen Barak A. , Pilpel Yitzhak , Mitra Robi D. , Church George M.
Published: July 2002

Ohno [Ohno, S. (1970) in Evolution by Gene Duplication, Springer, New York] proposed that gene duplication with subsequent divergence of paralogs could be a major force in the evolution of new gene functions. In practice the functional differences between closely related homologues produced by duplications can be subtle and difficult to separate experimentally. Here we show that DNA microarrays can distinguish the functions of two closely related homologues from the yeast Saccharomyces cerevisiae, Yap1p and Yap2p. Although Yap1p and Yap2p are both bZIP transcription factors involved in multiple stress responses and are 88% identical in their DNA binding domains, our work shows that these proteins activate nonoverlapping sets of genes. Yap1p controls a set of genes involved in detoxifying the effects of reactive oxygen species, whereas Yap2p controls a set of genes over represented for the function of stabilizing proteins. In addition we show that the binding sites in the promoters of the Yap1p-dependent genes differ from the sites in the promoters of Yap2p-dependent genes and we validate experimentally that these differences are important for regulation by Yap1p. We conclude that while Yap1p and Yap2p may have some overlapping functions they are clearly not redundant and, more generally, that DNA microarray analysis will be an important tool for distinguishing the functions of the large numbers of highly conserved genes found in all eukaryotic genomes.
PREDICTING THE EFFECTS OF CHANGES IN WELFARE PAYMENTS ON THE PROBABILITIES OF RECEIVING ALTERNATE SOURCES OF INCOME: THE CASE OF HOMELESS PERSONS IN LOS ANGELES
Authors: Conroy* Stephen J.
Published: July 2002

This article investigates the role that changes in welfare payments are likely to have on the earnings behavior of homeless persons. Using a cross‐sectional random sample of 1,489 homeless persons in Los Angeles, the author analyzes the marginal effect of reducing public transfers on (a) the probability of earning and (b) the level of income from various traditional and nontraditional sources. This procedure allows the author to control for a number of important factors (including background, human capital, and social network variables) that may also influence the probability of earning income. Findings suggest that reducing government benefit income by $100 increases the probability of receiving income from traditional and nontraditional sources by 1.37% and 2.18% respectively. Among the latter are selling items on the streets and “other” (nonspecified) sources. It is concluded that welfare reform measures may in fact create additional societal costs as former welfare recipients turn to alternative forms of income.
Catalysis of serine oligopeptidases is controlled by a gating filter mechanism
Authors: Fülöp Vilmos , Szeltner Zoltán , Polgár László
Published: July 2002

Proteases have a variety of strategies for selecting substrates in order to prevent uncontrolled protein degradation. A recent crystal structure determination of prolyl oligopeptidase has suggested a way for substrate selection involving an unclosed seven‐bladed β‐propeller domain. We have engineered a disulfide bond between the first and seventh blades of the propeller, which resulted in the loss of enzymatic activity. These results provided direct evidence for a novel strategy of regulation in which oscillating propeller blades act as a gating filter during catalysis, letting small peptide substrates into the active site while excluding large proteins to prevent accidental proteolysis.
Internal phylogeny of the Chilopoda (Myriapoda, Arthropoda) using complete 18S rDNA and partial 28S rDNA sequences
Authors: Giribet Gonzalo , Carranza Salvador , Riutort Marta , Baguñà Jaume , Ribera Carles
Published: July 2002

The internal phylogeny of the ‘myriapod’ class Chilopoda is evaluated for 12 species belonging to the five extant centipede orders, using 18S rDNA complete gene sequence and 28S rDNA partial gene sequence data. Equally and differentially weighted parsimony, neighbour–joining and maximum–likelihood were used for phylogenetic reconstruction, and bootstrapping and branch support analyses were performed to evaluate tree topology stability. The results show that the Chilopoda constitute a monophyletic group that is divided into two lines, Notostigmophora (= Scutigeromorpha) and Pleurostigmophora, as found in previous morphological analyses. The Notostigmophora are markedly modified for their epigenic mode of life. The first offshoot of the Pleurostigmophora are the Lithobiomorpha, followed by the Craterostigmomorpha and by the Epimorpha s. str. (= Scolopendromorpha + Geophilomorpha), although strong support for the monophyly of the Epimorpha s. lat. (= Craterostigmomorpha + Epimorpha s. str.) is only found in the differentially weighted parsimony analysis.
How carotenoids protect bacterial photosynthesis
Authors: Cogdell Richard J. , Howard Tina D. , Bittl Robert , Schlodder Erberhard , Geisenheimer Irene , Lubitz Wolfgang
Published: July 2002

The essential function of carotenoids in photosynthesis is to act as photoprotective agents, preventing chlorophylls and bacteriochlorophylls from sensitizing harmful photodestructive reactions in the presence of oxygen. Based upon recent structural studies on reaction centres and antenna complexes from purple photosynthetic bacteria, the detailed organization of the carotenoids is described. Then with specific reference to bacterial antenna complexes the details of the photoprotective role, triplet–triplet energy transfer, are presented.
Intronless homing: site-specific endonuclease SegF of bacteriophage T4 mediates localized marker exclusion analogous to homing endonucleases of group I introns
Authors: Belle Archana , Landthaler Markus , Shub David A.
Published: July 2002

All genetic markers from phage T2 are partially excluded from the progeny of mixed infections with the related phage T4 (general, or phage exclusion). Several loci, including gene 56 of T2, are more dramatically excluded, being present in only ∼1% of the progeny. This phenomenon is referred to as localized marker exclusion. Gene 69 is adjacent to gene 56 of T4 but is absent in T2, being replaced by completely nonhomologous DNA. We describe SegF, a novel site-specific DNA endonuclease encoded by gene 69, which is similar to GIY–YIG homing endonucleases of group I introns. Interestingly, SegF preferentially cleaves gene 56 of T2, both in vitro and in vivo, compared with that of phage T4. Repair of the double-strand break (DSB) results in the predominance of T4 genes56 and segF in the progeny, with exclusion of the corresponding T2 sequences. Localized exclusion of T2 gene 56is dependent on full-length SegF and is likely analogous to group I intron homing, in which repair of a DSB results in coconversion of markers in the flanking DNA. Phage T4 has many optional homing endonuclease genes similar to segF, whereas similar endonuclease genes are relatively rare in other members of the T-even family of bacteriophages. We propose that the general advantage enjoyed by T4 phage, over almost all of its relatives, is a cumulative effect of many of these localized events.
Angular measurement of the Cobalt‐60 emitted radiation spectrum from a radiosurgery irradiator
Authors: Drzymala R. E. , Sohn J. W. , Guo C. , Sobotka L. G. , Purdy J. A.
Published: July 2002

The photon energy spectrum emanating from a Leksell Gamma Knife, Model 23004B, was measured between 0.250 and 3.5 MeV with the sources exposed. Measurements were made using a 2×2 inch NaI detector enclosed in a lead‐shielded apparatus having a inch diameter measurement aperture, which reduced the amount of radiation received by the crystal. All measurements were made one meter above the floor within a quadrant toward one side of the Gamma Knife couch. The measured spectra displayed the expected doublet of photon peaks at energies of 1.17 and 1.33 MeV. These peaks appeared in spectra beginning at ∼50 degrees, as one proceeds from a point directly lateral to the source enclosure (0 degrees) toward the foot of the couch (90 degrees). The average photon energy of the spectrum shifts to lower values as the doublet decreases in magnitude with increasing angle until almost vanishing at an angle equal to 90 degrees. Inserting a 16 cm diameter plastic sphere phantom, provided with the Gamma Knife, into the radiation beams increases the low energy photon emissions appearing in the spectrum, especially for measurements at the foot of the couch. Implications for the design of shielding a treatment room containing the Gamma Knife, Model B, and estimation of the radiation exposure to personnel during an emergency procedure in the treatment room with the sources exposed are discussed.
Fitted dosimetric parameters of high dose‐rate sources according to the AAPM TG43 formalism
Authors: Lliso F. , Pérez‐Calatayud J. , Carmona V. , Ballester F. , Lluch J. L. , Serrano M. A. , Limami Y. , Casal E.
Published: July 2002

The purpose of this study is to find fitted functional forms to the anisotropy function, and the radial dose function, in order to characterize dose‐rate distributions around all the high‐intensity sources currently in use. Dosimetry data are at present available as tables for: the microSelectron HDR (“classic” and “new” design models), the PDR source, and the VariSource HDR source, expressed in terms of the AAPM Task Group No. 43 recommendations. There is only one paper out which introduces a functional form to fit the anisotropy function, but only for symmetric sources with respect to the transverse axis. However, dosimetric data of the HDR and PDR sources mentioned above cannot be reproduced with these functional forms. In our study and published data are fitted with functional forms in such a way that appropriate limits are reached for both functions and the maximum fit error approaches the data uncertainty. The average fit error is less than 1% in all cases. These functional forms make handling data easier within the treatment planning system, avoiding the use of tabulated data.
Description and dosimetric verification of the PEREGRINE Monte Carlo dose calculation system for photon beams incident on a water phantom
Authors: Hartmann Siantar C. L. , Walling R. S. , Daly T. P. , Faddegon B. , Albright N. , Bergstrom Paul , Bielajew A. F. , Chuang C. , Garrett D. , House R. K. , Knapp D. , Wieczorek D. J. , Verhey L. J.
Published: July 2002

PEREGRINE is a three‐dimensional Monte Carlo dose calculation system written specifically for radiotherapy. This paper describes the implementation and overall dosimetric accuracy of PEREGRINE physics algorithms, beam model, and beam commissioning procedure. Particle‐interaction data, tracking geometries, scoring, variance reduction, and statistical analysis are described. The BEAM code system is used to model the treatment‐independent accelerator head, resulting in the identification of primary and scattered photon sources and an electron contaminant source. The magnitude of the electron source is increased to improve agreement with measurements in the buildup region in the largest fields. Published measurements provide an estimate of backscatter on monitor chamber response. Commissioning consists of selecting the electron beam energy, determining the scale factor that defines dose per monitor unit, and describing treatment‐dependent beam modifiers. We compare calculations with measurements in a water phantom for open fields, wedges, blocks, and a multileaf collimator for 6 and 18 MV Varian Clinac 2100C photon beams. All calculations are reported as dose per monitor unit. Aside from backscatter estimates, no additional, field‐specific normalization is included in comparisons with measurements. Maximum discrepancies were less than either 2% of the maximum dose or 1.2 mm in isodose position for all field sizes and beam modifiers.
Dosimetry characteristics of the Plus and 12i Gammamed PDR sources
Authors: Pérez‐Calatayud J. , Ballester F. , Serrano‐Andrés M. A. , Puchades V. , Lluch J. L. , Limami Y. , Casal F.
Published: July 2002

In this study a complete set of dosimetric data for the Plus and 12i Gammamed PDR (pulsed dose rate) sources is presented. These data have been calculated using the Monte Carlo simulation code GEANT3. Absolute dose rate distributions in water around these sources were calculated and are presented in form of conventional two dimensional (2D) Cartesian look‐up tables. All dosimetric quantities recommended by the AAPM Task Group 43 report have been also calculated. These quantities are dose rate constant, radial dose function, anisotropy function and anisotropy factor. The dose rate distribution of the 12i source was compared with the corresponding data for the microselectron PDR source showing large differences between both sources.
Estimation of a photon energy spectrum for a computed tomography scanner
Authors: Ruth Christopher , Joseph Peter M.
Published: July 2002

Estimated photon energy spectra are derived from transmission measurements using aluminum, copper, and sodium iodide absorbers. Two spectral models are proposed. One is based on a previously published model that analyzes the electron's penetration into the anode, and the production and attenuation of bremsstrahlung photons. The second model does not include details regarding the underlying physics, but treats the spectrum as a sum of delta functions. A nonlinear regularization method is used to overcome ill conditioning in the second model. Both models fit the transmission data to an accuracy of 0.30%, which is consistent with the experimental error. A quantitative comparison of the models is made by calculating the average and variance (over the derived energy spectra) of several relevant mass attenuation coefficients. The maximum variation in the average and variance was 1.5% and 3.2%, respectively, indicating that the spectra exhibit similar attenuation and beam hardening properties. The spectra were tested with a simulation that predicts scanner CT numbers for phantom measurements consisting of dilutions of sodium iodide in a water equivalent background. The agreement between simulation and experiment ranged from 1.5% at 220 HU to 4.4% at 1700 HU.
Signal, noise, and detective quantum efficiency of a‐Si:H flat‐panel imagers
Authors: Siewerdsen Jeffrey H.
Published: July 2002

Flat‐panel imagers based upon the technology of thin‐film amorphous silicon transistors and photodiodes are under investigation for a wide variety of medical imaging applications. This thesis presents quantitative empirical and theoretical investigations of the imaging performance of such imaging systems. Performance was evaluated in terms of imager signal size, spatial resolution, noise characteristics, and signal‐to‐noise ratio for a wide variety of imaging system configurations and exposure conditions relevant to medical imaging. A theoretical model based upon cascaded systems analysis allowed prediction of imager signal, noise, and detective quantum efficiency (DQE), and theoretical results were found to agree well with empirical measurements. The empirical and theoretical analyses yielded quantification of the performance of existing imager designs, allowed investigation of the potential performance of future flat‐panel imaging systems, and provided a methodology for identifying optimal imager configurations for various applications and imaging tasks. There is every indication that flat‐panel imagers could provide performance superior to that of existing clinical imaging technologies. For example, in general x‐ray radiography, mammography, and radiotherapy portal imaging, such systems could provide DQE exceeding 60%, 80%, and 1.5%, respectively, approximately twice that of film‐based systems. However, for applications involving very low exposures per image, e.g., real‐time fluoroscopy, flat‐panel imagers may suffer from reduced signal‐to‐noise ratio. The analyses developed in this thesis provide a general description of imager signal and noise as well as a means of identifying strategies for improved imager performance.
Virtual light field projection for CT‐simulation
Authors: Lu Hsiao‐Ming , Chin Lee
Published: July 2002

We report a method to project a virtual light field over the patient during CT‐simulations of external beam radiotherapy. It can be used to perform all the tasks associated with the physical light field of a conventional simulator. The system consists of a three‐dimensional sonic digitizer interfacing with a window‐based software on a personal computer. The digitizer can provide the three‐dimensional coordinates of any point in space accessible by the digitizer probe. When these coordinates are transformed into the beam's eye view, the position of the digitized point relative to the beam can readily be displayed. Thus, the system establishes a virtual light field in space, which can be “seen” only by the digitizer probe. For any digitized point, the system can immediately show, by the beam's eye view display, whether the point is inside the field, outside of the field, or on the field border. Moreover, this virtual field projection allows one to evaluate external target coverage (or external normal tissue sparing) conveniently and interactively. By simply digitizing the concerned area and viewing its position in the beam's eye view display, one can immediately assess the coverage and if necessary, modify the treatment field accordingly. The system also provides an efficient and essential procedure in CT‐simulations for marking treatment portals on the patient. By cruising the digitizer probe on the patient's skin surface under visual and audio guidances, one can promptly find the projection of the field center, field corners, etc., on the patient. Measurements have been performed to study the accuracy of the GP‐12 sonic digitizer using rigid phantoms. Based on the measured data, the overall accuracy of the portal localization system is estimated to be ±2 mm. The system has been in clinical use for our CT simulator.
3D reconstruction of the cerebral arterial network from stereotactic DSA
Authors: Coste Eric , Vasseur Christian , Rousseau Jean
Published: July 2002

The authors present an automatic algorithm for 3D reconstruction of cerebral blood vessels by digital subtracted angiography. The patient is localized by a stereotactic method. The reconstruction algorithm includes two steps: first vessel extraction then 2D matching and reconstruction. Accurate vessel skeletons are generated by a combination of mathematical morphological algorithms and adaptive filters. The 3D reconstruction algorithm is based on the reconstruction of vessels center lines. For that purpose, three different projections of the vascular network are used. Reconstruction is computed segment by segment (a curved line between two nodes). For each segment point, the algorithm defines all epipolar solutions on the other views. These epipolar solutions are sorted and pooled by 2D continuity and 3D proximity criteria resulting in a 3D graph. Optimal 3D segment is defined by a recursive algorithm that looks up the better path in the 3D graph. The algorithms have been implemented on a Compatible‐PC computer in C language. More than 95% of static copper phantom was reconstructed in 5 min and with 1 mm 3D accuracy. 70% of arteries (from carotid to the seventh node) of a true patient arterial network were reconstructed is less than 30 min.
Full breast digital mammography with an amorphous silicon‐based flat panel detector: Physical characteristics of a clinical prototype
Authors: Vedantham Srinivasan , Karellas Andrew , Suryanarayanan Sankararaman , Albagli Douglas , Han Sung , Tkaczyk Eric J. , Landberg Cynthia E. , Opsahl‐Ong Beale , Granfors Paul R. , Levis Ilias , D'Orsi Carl J. , Hendrick R. Edward
Published: July 2002

The physical characteristics of a clinical prototype amorphous silicon‐based flat panel imager for full‐breast digital mammography have been investigated. The imager employs a thin thallium doped CsI scintillator on an amorphous silicon matrix of detector elements with a pixel pitch of 100 μm. Objective criteria such as modulation transfer function (MTF), noise power spectrum, detective quantum efficiency (DQE), and noise equivalent quanta were employed for this evaluation. The presampling MTF was found to be 0.73, 0.42, and 0.28 at 2, 4, and 5 cycles/mm, respectively. The measured DQE of the current prototype utilizing a 28 kVp, Mo–Mo spectrum beam hardened with 4.5 cm Lucite is ∼55% at close to zero spatial frequency at an exposure of 32.8 mR, and decreases to ∼40% at a low exposure of 1.3 mR. Detector element nonuniformity and electronic gain variations were not significant after appropriate calibration and software corrections. The response of the imager was linear and did not exhibit signal saturation under tested exposure conditions.
An edge spread technique for measurement of the scatter‐to‐primary ratio in mammography
Authors: Cooper Virgil N. , Boone John M. , Seibert J. Anthony , Pellot‐Barakat Claire J.
Published: July 2002

An experimental measurement technique that directly measures the magnitude and spatial distribution of scatter in relation to primary radiation is presented in this work. The technique involves the acquisition of magnified edge spread function (ESF) images with and without scattering material present. The ESFs are normalized and subtracted to yield scatter‐to‐primary ratios (SPRs), along with the spatial distributions of scatter and primary radiation. Mammography is used as the modality to demonstrate the ESF method, which is applicable to all radiographic environments. Sets of three images were acquired with a modified clinical mammography system employing a flat panel detector for 2, 4, 6, and 8 cm thick breast tissue equivalent material phantoms composed of 0%, 43%, and 100% glandular tissue at four different kV settings. Beam stop measurements of scatter were used to validate the ESF methodology. There was good agreement of the mean SPRs between the beam stop and ESF methods. There was good precision in the ESF‐determined SPRs with a coefficient of variation on the order of 5%. SPRs ranged from 0.2 to 2.0 and were effectively independent of energy for clinically realistic kVps. The measured SPRs for 2, 4, and 6 cm 0% glandular phantoms imaged at 28 kV were 0.21±0.01, 0.39±0.01, and 0.57±0.02, respectively. The measured SPRs for 2, 4, and 6 cm 43% glandular phantoms imaged at 28 kV were 0.20±0.01, 0.35±0.02, and 0.53±0.02, respectively. The measured SPRs for 2, 4, and 6 cm 100% glandular phantoms imaged at 28 kV were 0.22±0.02, 0.42±0.03, and 0.88±0.08, respectively.
Speed of light measurement for the myriad
Authors: James Mary B. , Ormond Robert B. , Stasch Aric J.
Published: July 2002

We discuss a time-of-flight measurement of the speed of light which is inexpensive to build, has an experimental design completely accessible to students with a rudimentary knowledge of interference, and consistently produces values for c with errors of less than 1%. Students at the sophomore level can use the same apparatus to achieve uncertainties on the order of 0.25%.
Bound states of a finite periodic potential
Authors: Sprung D. W. L. , Sigetich J. D. , Wu Hua , Martorell J.
Published: July 2002

We locate the bound states for a one-dimensional potential which consists of N identical cells, by the transfer matrix method. Our expressions involve only the Bloch phase and a scattering phase, both of which are properties of the single cell. The method applies to an arbitrary but nonoverlapping potential shape, and thereby emphasizes generic properties over specific details. It gives useful qualitative insight without tedious calculations. We discuss the evolution of the bound states as the intercell spacing is varied, and the occurrence of surface states as bound states in a forbidden zone.
Active attenuation of the wave transmission through an L-plate junction
Authors: Kessissoglou Nicole J.
Published: July 2002

Active control is applied to an L-shaped plate in order to attenuate the flexural energy transmission from one plate to the other. The coupled plates are simply supported along two parallel sides, and free at the other two ends. Point forces are used to generate the primary and secondary excitation of the plates. The flexural wave coefficients are determined from the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction of the two plates. Bending, shearing, and longitudinal effects are taken into consideration at the corner junction. Under broadband frequency control at a discrete location in plate 2, both the control shaker and the error sensor are optimally located to achieve the best control performance. Results show that when the control force and error sensor are arbitrarily located, the control performance is dependent on the excitation frequency. When both the control force and error sensor are optimally located with respect to the primary shaker location in a symmetrical arrangement, the control performance is both maximized and independent of the excitation frequency. Using single-frequency control to attenuate the total vibrational response of the coupled plates, the error sensor location is strongly mode dependent. It is shown that using a single, properly located control force and a single, properly located error sensor, global attenuation of the L-shaped plate can be achieved.
Comparison of in situ and laboratory acoustic measurements on Lough Hyne marine sediments
Authors: Best Angus I. , Huggett Quentin J. , Harris Andrew J. K.
Published: July 2002

Compressional wave velocity and attenuation were measured at frequencies of 200–1500 Hz on seafloor sediments at Lough Hyne, Ireland, using a mini-boomer source and hydrophone array. Velocity and attenuation were also measured in the laboratory at 200–800 kHz on a 1 m long sediment core taken from the site. The in situ results indicate an average sediment phase velocity of about 1600 m/s and sediment quality factor of 10–20. The laboratory core measurements give an average phase velocity of 1793±26 m/s and quality factor of 16±5. The poorly sorted, Lough Hyne sediments are highly attenuating and highly dispersive when compared to values published in the literature for well-sorted, marine sediments such as clean sands and marine clays. The results are consistent with the few published data for poorly sorted sediments, and indicate that intrinsic attenuation is highest when the mass ratio of mud (clay+silt) to sand grade particles is close to unity. It is proposed that compliance heterogeneities are most abundant when mud and sand grade particles are present in roughly equal proportions, and that the observations support local viscous fluid flow as the most likely loss mechanism.
Circular concentric Helmholtz resonators
Authors: Selamet A. , Radavich P. M. , Dickey N. S. , Novak J. M.
Published: July 2002

The effect of specific cavity dimensions of circular concentric Helmholtz resonators is investigated theoretically, computationally, and experimentally. Three analytical models are employed in this study: (1) A two-dimensional model developed to account for the nonplanar wave propagation in both the neck and the cavity; (2) a one-dimensional solution developed for the limit of small cavity length-to-diameter ratio, l/d, representing a radial propagation in the cavity; and (3) a one-dimensional closed-form solution for configurations with large l/d ratios which considers purely axial wave propagation in the neck and the cavity. For low and high l/d, the resonance frequencies determined from the two-dimensional approach are shown to match the one-dimensional predictions. For cavity volumes with l/d>0.1, the resonance frequencies predicted by combining Ingard’s end correction with one-dimensional axial wave propagation are also shown to agree closely with the results of the two-dimensional model. The results from the analytical methods are then compared with the numerical predictions from a three-dimensional boundary element method and with experiments. Finally, these approaches are employed to determine the wave suppression performance of circular Helmholtz resonators in the frequency domain.
Hearing deficits measured in some Tursiops truncatus, and discovery of a deaf/mute dolphin
Authors: Ridgway Sam H. , Carder Donald A.
Published: July 2002

Eight bottlenose dolphins Tursiops truncatus (four male, four female) were trained to respond to 100-ms tones. Three male dolphins (ages 23, 26, and 34) exhibited hearing disability at four higher frequencies—70, 80, 100, and 120 kHz even at 111–135 dB re:1 μPa. Two females (ages 32 and 35) responded to all frequencies as did a male (age 7) and a female (age 11). One female (age 33) responded to all tones at 80 kHz and below; however, she failed to respond at 100 or 120 kHz. One young female dolphin (age 9) exhibited no perception of sound to behavioral or electrophysiological tests. This young female was not only deaf, but mute. The dolphin was monitored periodically by hydrophone and daily by trainers (by ear in air) for 7 years until she was age 16. The animal never whistled or made echolocation pulses or made burst pulse sounds as other dolphins do.
Steady-state spectra of diapason class stops of the Newberry Memorial organ, Yale University
Authors: Harrison J. M. , Thompson-Allen N.
Published: July 2002

Steady-state line spectra of the C’s (C2 to C9) of eight diapasons of the Newberry Memorial organ were investigated using DAT records made in the hall. To better represent what a listener hears, the SPL spectra were transformed to loudness levels (LL’s), and adjusted to accommodate masking between the harmonics. The way the LL transformation altered the levels of the harmonics was shown in detail for C2, C4, and C6. The transformed LL spectral envelopes had essentially identical and well-known “diapason type” contours from C4 to C6. These envelopes differed from those at C2, C3 and C7, C8, and C9. Hence, no common diapason pattern was found over the entire frequency range. However, the spectral envelopes of the seven diapason at C2, for example, were similar, and constituted the “typical diapason” envelope at C2. The advisability of assuming a “typical diapason envelope” for all diapason sounds was discussed. The spectral envelopes at C7 and C8 of the diapason and also of chorus reed stops of the organ were similar. Since diapason type pipes were used for C7 and C8 of the reed stops (as is typical) it is not surprising that they sound similar to these notes of diapason stops.
Acoustical finite-difference time-domain simulations of subwavelength geometries
Authors: De Poorter John , Botteldooren Dick
Published: July 2002

Accurate simulation of wave propagation around subwavelength geometries using standard finite-difference time-domain (FDTD) techniques require a fine spatial and temporal sampling resulting in high computational costs. In this paper an extension to this standard FDTD technique is proposed by means of quasi-stationary solutions on a subwavelength scale. The FDTD equations in the region near the subwavelength geometry are extended with some correction terms of which the magnitude is extracted from the quasi-stationary pressure distribution around these geometries. These pressure distributions can be calculated from the Laplace equation. Using this new technique, FDTD simulations can be based on a more coarse grid, thus reducing computational cost considerably. The accuracy of this technique is mainly determined by the accuracy of the Laplace solutions. This technique was tested with success on the simulation of resonators. It was also shown that the new FDTD equations can be extended to include viscosity effects.
Spectral properties of fricatives in Parkinson’s Disease
Authors: McRae Paul , Tjaden Kris
Published: July 2002

Consonant imprecision is one of the most prominent speech characteristics of Parkinson’s Disease (PD). Few studies have characterized the nature of the imprecision for sound classes other than stop consonants, however. Research further suggests that consonant imprecision may improve with slowed speaking rate, perhaps as a result of increased articulatory displacements [M. P. Caliguiri, Brain Lang. 35, 493–502 (1989)]. In the current study, nine speakers with PD and nine age and gender matched neurologically healthy speakers read the Farm Passage at habitual and slow reading rates. Spectral moments were used to describe /s/ and /∫/ fricatives occurring in the word initial position of the reading passage. For both the habitual and slow rate conditions, moment coefficients for speakers with PD were compared to moment coefficients for the healthy speakers to characterize between group differences in fricative productions. Within each speaker group, moment coefficients for the habitual rate condition were compared to moment coefficients for the slow rate condition to evaluate the effects of slowed speaking rate on fricative productions.
Snell’s law of refraction and sound rays for a moving medium
Authors: Hohenwarter D. , Jelinek F.
Published: July 2002

Fermat’s principle of least time is used to calculate a new law of refraction for a stratified medium moving horizontally with different temperatures in each layer. This new law of refraction includes velocity of sound, wind speed, and the angle between the vectorial sum of sound velocity and the wind speed. This new equation is compared with the usual approximations for the different refraction laws of a moving medium occasionally mentioned in literature as ‘‘Snell’s law for a moving media.’’ The sound rays in a moving thermically stratified medium are refracted more or less (dependent on either upwind or downwind sound propagation), then calculated according to the ‘‘Snell’s law.’’ For upward-oriented sound rays and a moderate thermical stratification with high wind speeds, the difference in the angle of refraction between the new refraction law and the usual approximation is roughly 3 degrees and neglectable for grazing incidence. The sound ray trajectories expressed as analytical equations for a constant sound velocity combined with a wind speed profile proportional to height; the results are shown in a figure. Furthermore, the sound ray trajectories for a linear sound speed profile combined with a linear height-dependent wind speed profile are calculated and shown graphically.
A study of loss in piezoelectric ceramic resonators
Authors: Pastore Robert , Ballato Arthur , Cui H. L.
Published: July 2002

Piezoelectric resonators and filters are important components in many military and commercial communication systems. Standard piezoelectric materials such as quartz have low coupling values and are quite expensive to fabricate. Newer materials like piezoceramics have been developed that are cheaper, have higher values of coupling constant, but can be considerably more lossy than single-crystal materials. The purpose of this work is to explore loss mechanisms through the use of complex elastic coefficients in the piezoelectric constitutive relations and the differential equations for a simple one-dimensional (1-D) resonator. Results will be presented that show how the complex elastic coefficients modify the acoustic wave velocity, the coupling constant, and the resonant frequencies of the resonator. An equivalent circuit model of a resonator will also be presented with and without loss to compare with the calculated results. An experiment has been designed to better characterize loss in devices by applying an exponentially decaying sine wave. In theory this type of signal should be able to excite the complex resonance of the device. Results will be presented for thickness-excited PZT resonators, and the results will be compared to the circuit models and the 1-D calculations.
Mass, momentum, and energy transfer by the propagation of acoustic solitary waves
Authors: Sugimoto N.
Published: July 2002

This paper considers the mass, momentum, and energy transfer accompanied by the propagation of the acoustic solitary wave in a gas-filled tube. As was demonstrated previously [J. Acoust. Soc. Am. 99, 1971–1976 (1996); Phys. Rev. Lett. 83, 4053–4056 (1999)], the propagation of the solitary waves is made possible by connecting a periodic array of Helmholtz resonators axially with the tube. The solitary wave can convey the mass, momentum, and energy steadily with a constant speed that is subsonic but nearly equal to the linear sound speed. It is emphasized that the quantities transferred are of first order in magnitude. Formulating the basic equations in the conservation form, the total amount of the mass, momentum, and energy transferred is obtained by using the solitary-wave solutions. It has the upper bounds determined by the limiting solitary wave, which are proportional to the size of the resonator and the inverse of its natural frequency. In evaluating the energy transfer, a clear distinction should be made between the gas-dynamic energy and the acoustic energy. The former, which contains the first-order quantity whereas the latter begins with the quadratic ones, is to be used to determine the energy transfer in the form of heat (internal energy) associated with the mass transfer.
Spatial-temporal correlation of a diffuse sound field
Authors: Rafaely Boaz
Published: July 2002

The spatial correlation function of the sound in a diffuse field is a quantity widely used in many reverbrant room acoustic applications. Although results for the spatial and temporal correlation for pure-tone and band-limited diffuse fields have already been developed, these have not been generalized for other signal types. This work presents a generalized derivation of the diffuse field spatial-temporal correlation which can be used for stationary random signals with given power spectral density. It is shown that the spatial-temporal correlation depends entirely on the temporal correlation of the signal exiting the diffuse field, or alternatively on its power spectral density. A simulation using the plane wave model is presented for tonal and broadband diffuse sound fields.
Stresses in Dilute Solutions of Bead-Nonlinear-Spring Macromolecules. III. Friction Coefficient Varying with Dumbbell Extension
Authors: Tanner R. I.
Published: July 2002

The examination of the mechanics of dumbbell suspensions is extended to include the increase of the friction coefficient with molecular extension, both in weak flows and in strong flows. The most interesting result occurs in steady elongational flows where a “hysteresis” loop is found, so that in a certain range of elongation rates two elongational viscosities are possible, the one occurring depending on the previous history of the elongation rate. This result is of interest because it increases the plausibility of those explanations of turbulent drag reduction which depend on maintaining the molecules in an extended, highly dissipative configuration. The hysteresis loop is also of interest in that it represents an effectively infinite memory of a selective type which is not compatible with the usual hypotheses about fading memory usually associated with the simple fluid concepts of continuum mechanics, although our dilute solution model is clearly a simple fluid. No hysteresis loop was found in steady shearing flows, but an increase in viscosity above the zero-shear viscosity is predicted at intermediate shear rates.
The nematic dumbbell model
Authors: Maffettone P. L. , Marrucci G.
Published: July 2002

Flexible polymeric chains (Kuhn chains) made up of nematogenic moieties are considered here. The simplest approach to the dynamics of such a system, in both the isotropic and the nematic phases, is that of modeling the chain as an elastic dumbbell where the ‘‘spring’’ law also accounts for the nematic interaction. The constitutive equation of this ‘‘nematic dumbbell model’’ is thereby derived. The rheological predictions so obtained are qualitatively compared with the most prominent features of LCP rheology as well as with previous theoretical results.
Determination of molecular weight distributions of linear flexible polymers from linear viscoelastic material functions
Authors: Mead D. W.
Published: July 2002

Numerical and analytical methods are developed to invert the double reptation mixing rule to determine the molecular weight distribution (MWD). An analytic method involving Mellin transforms is developed for the case of a single exponential monodisperse relaxation function. A general analytic solution for the MWD is generated for a step-function monodisperse relaxation function. Numerical methods are developed for more general multiple time constant monodisperse relaxation functions. Both analytical and numerical methods are simple, robust, and capable of appropriately handling error-infected experimental data. The power-law relaxation modulus associated with broad MWD commercial polymer is analytically inverted to generate the corresponding molecular weight distribution. MWDs calculated from rheological data for polybutadiene and polypropylene are in close agreement with the corresponding GPC data and are very sensitive to small amounts of high molecular weight material present. The fundamental origins of this sensitivity lie in the intrinsically nonlinear nature of the dependence of rheological properties on molecular weight. The quality of the results suggest that the ‘‘double reptation’’ mixing rule captures an essential feature of the physics of entangled polydisperse polymeric systems.
Direct‐Writing of Multi‐Functional Photo‐Reduced Graphene Oxide Fabric (rGOf) at the Liquid‐Air Interface with Tunable Porosity
Authors: Shi HaoTian Harvey , Hong Sung Hwa , Naguib Hani E.
Published: May 2022

A multi‐functional photo‐reduced graphene oxide fabric (rGOf) created through a laser direct‐write technique at the solution surface is presented. Taking advantage of the amphiphilic nature of graphene oxide (GO) and the rapid self‐assembly of GO sheets at the liquid‐air interface, a piece of rGOf can be easily produced without any binder or supporting material in an ambient environment. Without any added processing complexity or stringent sample requirements, this accessible technique creates rGOf that exhibits tuneable microscale porosity, which enables efficient surface functionalization and active material coating. Parameters, such as the GO concentration, stabilization time, laser power, printing speed, laser focus, and post‐processing steps, can lead to vastly different rGOf morphologies. The rGOf can be made into self‐standing film or transfer printed onto any desirable substrate. Herein, it is demonstrated that the rGOf platform holds tremendous potential in Joule heating, temperature sensing, humidity sensing, tactile sensing, and ammonia sensing applications.
Confined PdMo Ultrafine Nanowires in CNTs for Superior Oxygen Reduction Catalysis
Authors: He Qianqian , Xu Tengfei , Li Jiajie , Wang Jialong , Jin Chunqiao , Chen Qian , Gu Xiaokang , Wang Xingguo , Wei Juntian , Duan Huiping , Gong Yongji
Published: May 2022

One‐dimensional (1D) ultrafine nanowires of different materials, especially noble metals, present an enticing prospect for catalyst applications due to their numerous active sites exposed. However, the controllable synthesis and stability issues hinder their practical applications. Herein, single‐walled carbon nanotubes (SWCNTs) are adopted as the template to synthesize and stabilize ultrafine nanowires of metals. Furthermore, the oxygen reduction reaction (ORR) is employed as an application demonstration. Impressively, the as prepared PdMo nanowires exhibit a half‐wave potential of 0.923 V and the mass activity is 35 times and 130 times higher than those of commercial Pt/C and Pd/C catalysts, respectively. Because of the protection, a superior ORR durability with 50 000 cycles can be achieved. Density functional theory (DFT) calculations reveal that the SWCNTs surface can be activated by the encapsulated PdMo NWs to achieve the exclusive adsorption of O2and the following reduction reaction. In addition, PdMo NWs@SWCNTs demonstrate excellent catalytic performance as the cathode of lithium‐oxygen batteries. The cell can reach a high discharge capacity of over 10 000 mAh g−1, better than most of the former reported catalytic electrodes. The tailored design PdMo NWs@SWCNTs show widespread applications in various energy storage & conversion fields.
Thermo‐responsive topological metamorphosis in covalent‐and‐supramolecular polymer architectures
Authors: Wang Yongming , Zhang Hao , Zhang Zhaoming , Zhao Jun , Bai Ruixue , Liu Yuhang , Zhang Xinhai , Yan Xuzhou
Published: May 2022

Topological metamorphosis represents a powerful approach to modulate the properties of polymers. However, it still remains a major challenge to achieve the tunability of bulk mechanical properties via topological transformation in supramolecular polymer systems. Herein, we couple the covalent polymer and supramolecular polymer in a single system—referred to as covalent‐and‐supramolecular polymer (CSP)—to realize a thermo‐responsive macromolecular metamorphosis. The CSP is able to topologically switch from grafted polymer to cross‐linked network by taking advantage of synergistic dynamic covalent interactions and host–guest interactions. Benefiting from the topologically structural transformation, brittleness intrinsically evolves into toughness in our CSP architectures with minimum change of their molecular compositions from furan–maleimide to anthracene–maleimide linkers. Our work demonstrates that supramolecular polymers are a promising platform to design smart materials not only due to their inherent stimuli‐responsive properties but also because of their abilities in determining bulk mechanical properties of polymers with alterable topological structures.
Rapid One‐Pot Aerobic Oxidative N‐α‐C(sp3)‐H Functionalization of Arylmethylamines to Access Tetrasubstituted Imidazoles
Authors: Kadu Vikas D. , Khadul Siddheshwar P. , Kothe Gokul J. , Mali Ganesh A.
Published: May 2022

A simple copper catalyzed “one‐pot” process has been developed for synthesis of polysubstituted imidazoles via direct oxidative N‐α‐C(sp3)‐H functionalization of arylmethylamines. The readily available arylmethylamines as a substrate have afforded tetrasubstituted imidazoles products up to 94% yields under mild and environmentally benign conditions. The explored substrates scope with 1,2‐diketones and α‐hydroxyketones have shown great utility for synthesis of tetrasubstituted imidazoles.
S,O‐Ligand Promoted meta‐C−H Arylation of Anisole Derivatives via Palladium/Norbornene Catalysis
Authors: Sukowski Verena , van Borselen Manuela , Mathew Simon , Fernández‐Ibáñez M. Ángeles
Published: May 2022

Reversing the conventional site‐selectivity of C−H activation processes provides new retrosynthetic disconnections to otherwise unreactive bonds. Here, we report a new catalytic system based on palladium/norbornene and an S,O‐ligand for the meta‐C−H arylation of aryl ethers that significantly outperforms previously reported systems. We demonstrate the unique ability of this system to employ alkoxyarene substrates bearing electron donating and withdrawing substituents. Additionally, ortho‐substituted aryl ethers are well tolerated, overcoming the “ortho constraint”, which is the necessity to have a meta‐substituent on the alkoxyarene to achieve high reaction efficiency, by enlisting novel norbornene mediators. Remarkably, for the first time the monoarylation of alkoxyarenes is achieved efficiently enabling the subsequent introduction of a second, different aryl coupling partner to rapidly furnish unsymmetrical terphenyls. Further insight into the reaction mechanism was achieved by isolation and characterization of some Pd‐complexes—before and after meta C−H activation—prior to evaluation of their respective catalytic activities.