bluuebunny/crossref_metadata_2025 huggingface dataset:
Parsimonious modelling of water and suspended sediment flux from nested catchments affected by selective tropical forestry
Authors: Chappell N. A. , McKenna P. , Bidin K. , Douglas I. , Walsh R. P. D.
Published: July 2002

The ability to model the suspended sediment flux (SSflux) and associated water flow from terrain affected by selective logging is important to the establishment of credible measures to improve the ecological sustainability of forestry practices. Recent appreciation of the impact of parameter uncertainty on the statistical credibility of complex models with little internal state validation supports the use of more parsimonious approaches such as data–based mechanistic (DBM) modelling. The DBM approach combines physically based understanding with model structure identification based on transfer functions and objective statistical inference. Within this study, these approaches have been newly applied to rainfall–SSflux response. The dynamics of the sediment system, together with the rainfall–river flow system, were monitored at five nested contributory areas within a 44 ha headwater region in Malaysian Borneo. The data series analysed covered a whole year at a 5 min resolution, and were collected during a period some five to six years after selective timber harvesting had ceased. Physically based and statistical interpretation of these data was possible given the wealth of contemporary and past hydrogeomorphic data collected within the same region. The results indicated that parsimonious, three–parameter models of rainfall–river flow and rainfall–SSflux for the whole catchment describe 80 and 90% of the variance, respectively, and that parameter changes between scales could be explained in physically meaningful terms. Indeed, the modelling indicated some new conceptual descriptions of the river flow and sediment–generation systems. An extreme rainstorm having a 10 to 20 year return period was present within the data series and was shown to generate new mass movements along the forestry roads that had a differential impact on the monitored contributory areas. Critically, this spatially discrete behaviour was captured by the modelling and may indicate the potential use of DBM approaches for (i) predicting the differential effect of alternative forestry practices, (ii) estimating uncertainty in the behaviour of ungauged areas and (iii) forecasting river flow and SSflux in terrain with temporal changes in rainfall regime and forestry impacts.
Scrapie infections initiated at varying doses: an analysis of 117 titration experiments
Authors: McLean Angela R. , Bostock Christopher J.
Published: July 2002

An analysis of 117 titration experiments in the murine scrapie model is presented. The experiments encompass 30 years' work and a wide range of experimental conditions. To check that the experimental designs were reasonably consistent over time, comparisons were made of size, duration, source of inoculum, etc., in each experiment. These comparisons revealed no systematic trends that would render invalid comparisons across experiments. For 114 of the experiments it was possible to calculate the dose at which half of the challenged animals were infected (the ID
50
). These 114 experiments were then combined on the basis of relative dose (i.e. tenfold dilution relative to the ID
50
). This created a data set in which over 4000 animals were challenged with doses of scrapie ranging from four orders of magnitude below to five orders of magnitude above the ID
50
. Analysis of this data reveals that mean incubation periods rise linearly with logarithmic decreases in dose. A one unit increase in relative dose (i.e. a tenfold increase in actual dose) will, on average, decrease the incubation period by 25 days. At ID
50
the average incubation period in this data set is 300 days. Within a single dose, in a single experimental model, incubation periods have a distribution close to normal. Variability in incubation period also rises linearly as dose decreases. There is no age or sex effect upon the probability of infection, but female mice have incubation periods that are, on average, nine days shorter than their male counterparts and young mice have incubation periods that are longer by seven days. Although many of these patterns are apparent in the results of single titration curves, they can be more rigorously investigated by considering the outcome for thousands of mice.
Presence of the vomeronasal system in aquatic salamanders
Authors: Eisthen Heather L.
Published: July 2002

Previous reports have indicated that members of the proteid family of salamanders lack a vomeronasal system, and this absence has been interpreted as representing the ancestral condition for aquatic amphibians. I examined the anatomy of the nasal cavities, nasal epithelia, and forebrains of members of the proteid family, mudpuppies (
Necturus maculosus
), as well as members of the amphiumid and sirenid families (
Amphiuma tridactylum
and
Siren intermedia
). Using a combination of light and transmission electron microscopy, I found no evidence that mudpuppies possess a vomeronasal system, but found that amphiuma and sirens possess both vomeronasal and olfactory systems. Amphiumids and sirenids are considered to be outgroups relative to proteids; therefore, these data indicate that the vomeronasal system is generally present in salamanders and has been lost in mudpuppies. Given that the vomeronasal system is generally present in aquatic amphibians, and that the last common ancestor of amphibians and amniotes is believed to have been fully aquatic, I conclude that the vomeronasal system arose in aquatic tetrapods and did not originate as an adaptation to terrestrial life. This conclusion has important implications for the hypothesis that the vomeronasal organ is specialized for detection of non–volatile compounds.
Bacillus subtilis CodY represses early-stationary-phase genes by sensing GTP levels
Authors: Ratnayake-Lecamwasam Manoja , Serror Pascale , Wong Ka-Wing , Sonenshein Abraham L.
Published: July 2002

CodY, a highly conserved protein in the low G + C, gram-positive bacteria, regulates the expression of many Bacillus subtilisgenes that are induced as cells make the transition from rapid exponential growth to stationary phase and sporulation. This transition has been associated with a transient drop in the intracellular pool of GTP. Many stationary-phase genes are also induced during exponential-growth phase by treatment of cells with decoyinine, a GMP synthetase inhibitor. The effect of decoyinine on an early-stationary-phase gene is shown here to be mediated through CodY and to reflect a reduction in guanine nucleotide accumulation. CodY proved to bind GTP in vitro. Moreover, CodY-mediated repression of target promoters was dependent on a high concentration of GTP, comparable to that found in rapidly growing exponential-phase cells. Because a codY-null mutant was able to sporulate under conditions of nutrient excess, CodY also appears to be a critical factor that normally prevents sporulation under such conditions. Thus,B. subtilis CodY is a novel GTP-binding protein that senses the intracellular GTP concentration as an indicator of nutritional conditions and regulates the transcription of early-stationary-phase and sporulation genes, allowing the cell to adapt to nutrient limitation.
Specific targeting and constitutive association of histone deacetylase complexes during transcriptional repression
Authors: Li Jiwen , Lin Qiushi , Wang Weidong , Wade Paul , Wong Jiemin
Published: July 2002

Specific recruitment of corepressor complexes containing histone deacetylases (HDAC) by transcription factors is believed to play an essential role in transcriptional repression. Recent studies indicate that repression by unliganded nuclear hormone receptors and by the Mad family of repressors requires distinct HDAC-containing corepressor complexes. In this work, we show that unliganded TR specifically recruits only the closely related N-CoR and SMRT–HDAC3 complexes, whereas the Mad1 recruits only the Sin3–HDAC1/2 complex. Significantly, both the Sin3 and Mi-2/NURD complexes also exhibit constitutive association with chromatin and contribute to chromatin deacetylation in a nontargeted fashion. These results suggest that HDAC complexes can contribute to gene repression by two distinct mechanisms as follows: (1) specific targeting by repressors and (2) constitutive association with chromatin.
Structures of the two 3D domain‐swapped RNase A trimers
Authors: Liu Yanshun , Gotte Giovanni , Libonati Massimo , Eisenberg David
Published: July 2002

When concentrated in mildly acidic solutions, bovine pancreatic ribonuclease (RNase A) forms long‐lived oligomers including two types of dimer, two types of trimer, and higher oligomers. In previous crystallographic work, we found that the major dimeric component forms by a swapping of the C‐terminal β‐strands between the monomers, and that the minor dimeric component forms by swapping the N‐terminal α‐helices of the monomers. On the basis of these structures, we proposed that a linear RNase A trimer can form from a central molecule that simultaneously swaps its N‐terminal helix with a second RNase A molecule and its C‐terminal strand with a third molecule. Studies by dissociation are consistent with this model for the major trimeric component: the major trimer dissociates into both the major and the minor dimers, as well as monomers. In contrast, the minor trimer component dissociates into the monomer and the major dimer. This suggests that the minor trimer is cyclic, formed from three monomers that swap their C‐terminal β‐strands into identical molecules. These conclusions are supported by cross‐linking of lysyl residues, showing that the major trimer swaps its N‐terminal helix, and the minor trimer does not. We verified by X‐ray crystallography the proposed cyclic structure for the minor trimer, with swapping of the C‐terminal β‐strands. This study thus expands the variety of domain‐swapped oligomers by revealing the first example of a protein that can form both a linear and a cyclic domain‐swapped oligomer. These structures permit interpretation of the enzymatic activities of the RNase A oligomers on double‐stranded RNA.
Energy and dose rate dependence of BANG‐2 polymer‐gel dosimeter
Authors: Novotny Josef , Spevacek Vaelav , Dvorak Pavel , Novotny Josef , Cechak Tomas
Published: July 2002

The purpose of this study was to evaluate dependence of BANG‐2 polymer‐gel dosimeter sensitivity on different photon and electron energies as well as on different mean dose rates expressed as repetition rates for a standard clinically used linear accelerator. The sensitivity of the dosimeter was represented by the slope of calibration curve in the linear region measured for each modality. A calibration curve (in the linear region) based on five dosimeters (four irradiated and one background) was obtained for each photon and electron energy and different repetition rates. Dosimeter sensitivity dependence on energy was studied for 4, 6, and 18 MV x‐ray photons and for nominal electron energies 9, 12, 16, and 20 MeV. Dosimeter sensitivity dependence on mean dose rate was separately studied for electron and photon beams with the use of repetition rates 80, 160, 240, 320, and 400 MU min−1. Evaluation of dosimeters was performed on Siemens MAGNETOM EXPERT 1T scanner in the head coil. A multiecho sequence with 16 equidistant echoes was used for the evaluation of irradiated polymer‐gel dosimeters. The parameters of the sequence were as follows: TR 2000 ms, TE 22.5–360.0 ms, slice thickness 5 mm, FOV 255 mm, one acquisition. There was observed a trend in polymer‐gel dosimeter sensitivity dependence on the quality index of high energy x‐ray beams used and on mean electron energy absorbed in the center of the dosimeter. Polymer‐gel dosimeter sensitivity was decreasing with increasing photon or electron energy. There was observed no trend in polymer‐gel dosimeter sensitivity dependence on mean dose rate expressed as a repetition rate for both photon and electron beams.
Measurement of the presampled two‐dimensional modulation transfer function of digital imaging systems
Authors: Fetterly Kenneth A. , Hangiandreou Nicholas J. , Schueler Beth A. , Ritenour E. Russell
Published: July 2002

The purpose of this work was to develop methods to measure the presampled two‐dimensional modulation transfer function (2D MTF) of digital imaging systems. A custom x‐ray “point source” phantom was created by machining 256 holes with diameter 0.107 mm through a 0.5‐mm‐thick copper plate. The phantom was imaged several times, resulting in many images of individual x‐ray “spots.” The center of each spot (with respect to the pixel matrix) was determined to subpixel accuracy by fitting each spot to a 2D Gaussian function. The subpixel spot center locations were used to create a 5× oversampled system point spread function (PSF), which characterizes the optical and electrical properties of the system and is independent of the pixel sampling of the original image. The modulus of the Fourier transform of the PSF was calculated. Next, the Fourier function was normalized to the zero frequency value. Finally, the Fourier transform function was divided by the first‐order Bessel function that defined the frequency content of the holes, resulting in the presampled 2D MTF. The presampled 2D MTF of a 0.1 mm pixel pitch computed radiography system and 0.2 mm pixel pitch flat panel digital imaging system that utilized a cesium iodide scintillator was measured. Comparison of the axial components of the 2D MTF to one‐dimensional MTF measurements acquired using an edge device method demonstrated that the two methods produced consistent results.
Morphometric texture analysis of spinal trabecular bone structure assessed using orthogonal radiographic projections
Authors: Ouyang Xiaolong , Majumdar Sharmila , Link Thomas M. , Lu Ying , Augat Peter , Lin John , Newitt David , Genant Harry K.
Published: July 2002

The measurement of bone microstructure as well as bone mineral density may improve the estimation of bone strength. Cubic specimens (N=26, 12 mm×12 mm×12 mm) of human cadaver vertebrae were cut along three orthogonal anatomic orientations, i.e., superior–inferior (SI), medial–lateral (ML), and anterior–posterior (AP). Contact radiographs of the bone cubes along all three orientations were obtained and then digitized by a laser scanner with pixel size of 50 μm×50 μm. The specimens were tested in compression along the 3 orthogonal orientations and the Young's modulus (YM) was calculated for each direction. Quantitative computed tomography (QCT) was used to obtain a measure of trabecular bone mineral density (BMD). Global gray level thresholding and local thresholding algorithms were used to extract the trabecular bone network. Apparent trabecular bone fraction (ABV/TV), mean intercept length (I.TH), mean intercept separation (I.SP), and number of nodes (N.ND) were measured from the extracted trabecular network. Fractal dimension (Fr.D) of the trabecular bone texture was also measured. Paired t‐tests showed that the mean values of each texture parameter (except ABV/TV) and of YM along the SI direction were significantly different from those along the ML and AP direction. However, the mean values along the ML and AP directions were not significantly different. Multivariate regression of YM as a function of the texture parameters and BMD showed that without adjusting for the effect of BMD, YM was significantly explained by all the texture parameters When BMD was included in the regression, although the variations in YM of ML, AP, and SI orientations could be explained by BMD alone, some of the texture parameters did improve the overall prediction of the biomechanical properties, while, some parameters such as ABV/TV and Fr.D in the ML orientation showed a more significant overall effect in explaining mechanical strength than did BMD. In conclusion, trabecular texture parameters correlated significantly with BMD and YM. Trabecular texture parameters from projectional radiographs reflect the anisotropy of trabecular structure. Quantitative radiographic assessment of trabecular structure using fine‐detail radiography can potentially improve the estimation of bone strength.
Dosimetry of a W‐188/Re‐188 beta line source for endovascular brachytherapy
Authors: Häfeli Urs O. , Roberts William K. , Meier Dominik S. , Ciezki Jay P. , Pauer Gayle J. , Lee Eric J. , Weinhous Martin S.
Published: July 2002

Purpose: The objective was to determine the dosimetry of a potential endovascular brachytherapy source consisting of a coiled tungsten wire mounted on the distal end of a drive wire and neutron‐activated to contain the parent–daughter nuclides tungsten‐188 and rhenium‐188 Methods: A coiled tungsten wire 40 mm in length was neutron‐activated by double‐neutron capture for 78 hours at to contain 925 MBq (25 mCi) of in equilibrium. The dose‐fall off from this source was determined using three independent methods: (a) Thermoluminescence dosimetry with small LiF‐100 rods, (b) Gafchromic film dosimetry, and (c) Bang gel dosimetry. In addition, a Monte Carlo simulation was performed to compute the beta‐dose. Results: Each of the three measurement methods recorded similar values for the dose fall‐off within the distances useful for endovascular brachytherapy. The Monte Carlo calculations closely approximated the measured results in the treatment range between 1 and 3 mm and may thus be useful for evaluating changing geometries in the development of catheters and source setups. A 2 min restenosis treatment delivering 20 Gy at a radius of 2 mm would require a source of 1384.8 MBq/cm (37.4 mCi/cm). Conclusions: The dose distribution from a source is similar to that of a ‐source. An added advantage of the source is that it can be used for at least two months and still provides fast treatment times because of the parent isotope's half‐life of 69 days. The additional gamma emission from the source is too small to impose a serious radiological hazard. The high atomic number and density of the source material allows direct fluoroscopic imaging without additional markers.
The thermodynamic cube: A mnemonic and learning device for students of classical thermodynamics
Authors: Pate Stephen F.
Published: July 2002

The “thermodynamic cube,” a mnemonic device for learning and recalling thermodynamic relations, is introduced. The cube is an extension of the familiar “thermodynamic square” seen in many textbooks. The cube reproduces the functions of the usual thermodynamic squares and incorporates the Euler relations which are not as well known.
Acoustic scattering by a circular cylinder parallel with another of small radius
Authors: Roumeliotis John A. , Ziotopoulos Agissilaos-Georgios P. , Kokkorakis Gerassimos C.
Published: July 2002

The scattering of a plane acoustic wave by an infinite penetrable or impenetrable circular cylinder, parallel with another one, also penetrable or impenetrable, of acoustically small radius, is considered. The method of separation of variables, in conjunction with translational addition theorems for cylindrical wave functions, is used. Analytical expressions are obtained for the scattered pressure field and the various scattering cross sections, for normal incidence. Numerical results are given for penetrable and impenetrable cylinders.
Optimal focusing by spatio-temporal inverse filter. II. Experiments. Application to focusing through absorbing and reverberating media
Authors: Aubry J.-F. , Tanter M. , Gerber J. , Thomas J.-L. , Fink M.
Published: July 2002

To focus ultrasonic waves in an unknown heterogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. (In most applications of ultrasound, medical imaging, medical therapy, nondestructive testing, the first step consists of focusing a broadband ultrasound beam deeply inside the medium to be investigated.) Focusing in a homogeneous medium simply requires to compensate for the varying focus–array elements geometrical distances. Nevertheless, heterogeneities in the medium, in terms of speed of sound, density, or absorption, may strongly degrade the focusing. Different techniques have been developed in order to correct such aberrations induced by heterogeneous media (time reversal, speckle brightness, for example). In the companion to this paper, a new broadband focusing technique was investigated: the spatio-temporal inverse filter. Experimental results obtained in various media, such as reverberating and absorbing media, are presented here. In particular, intraplate echoes suppression and high-quality focusing through a human skull, as well as hyper-resolution in a reverberating medium, will be shown. It is important to notice that all these experiments were performed with fully programmable multichannel electronics whose use is required to fully exploit the spatio-temporal technique.
Harmonic amplitude distribution in a wideband ultrasonic wavefront after propagation through human abdominal wall and breast specimens
Authors: Liu Dong-Lai , Waag Robert C.
Published: July 2002

The amplitude characteristics of ultrasonic wavefront distortion produced by transmission through the abdominal wall and breast is described. Ultrasonic pulses were recorded in a two-dimensional aperture after transmission through specimens of abdominal wall or breast. After the pulse arrival times were corrected for geometric path differences, the pulses were temporally Fourier transformed and two-dimensional maps of harmonic amplitudes in the measurement aperture were computed. The results indicate that, as the temporal frequency increases, the fluctuation in harmonic amplitudes increases but the spatial scale of the fluctuation decreases. The normalized second-order and third-order moments of the amplitude distribution also increase with temporal frequency. The wide range variation of these distribution characteristics could not be covered by the Rayleigh, Rician, or K-distribution because of their limited flexibility. However, the Weibull distribution and especially the generalized K-distribution provide better fits to the data. In the fit of the generalized K-distribution, a decrease of its parameter α with increasing temporal frequency was observed, as predicted by analysis based on a phase screen model.
A recursive Green’s function technique for acoustic scattering from heterogeneous objects
Authors: Jensen Michael A.
Published: July 2002

A fast, efficient algorithm for computing acoustic fields scattered by inhomogeneous objects in an otherwise homogeneous space is presented. The algorithm, called the Recursive Green’s Function Method (RGFM), constructs the domain Green’s function by recursively combining known Green’s functions from smaller subdomains. The fields on the scatterer surface are then computed using a boundary integral formulation. Proper implementation of the RGFM results in a storage requirement of O(N) and computational costs of O(N3/2) and O(N2) for two- and three-dimensional problems, respectively, where N is the total number of discrete points in the inhomogeneous region. Results are compared with those obtained from exact solutions to show the accuracy of the method.
Modulation rate detection and discrimination by normal-hearing and hearing-impaired listeners
Authors: Grant Ken W. , Summers Van , Leek Marjorie R.
Published: July 2002

Modulation detection and modulation rate discrimination thresholds were obtained at three different modulation rates (fm=80, 160, and 320 Hz) and for three different ranges of modulation depths (m): full (100%), mid (70%–80%), and low (40%–60%) with both normal-hearing (NH) and hearing-impaired (HI) subjects. The results showed that modulation detection thresholds increased with modulation rate, but significantly more so for HI than for NH subjects. Similarly, rate discrimination thresholds (Δr) increased with increases in fm and decreases in modulation depth. When compared to NH subjects, rate discrimination thresholds for HI subjects were significantly worse for all rates and for all depths. At the fastest modulation rate with less than 100% modulation depth, most HI subjects could not discriminate any change in rate. When valid thresholds for rate discrimination were obtained for HI subjects, they ranged from 2.5 semitones (Δr=12.7 Hz, fm=80 Hz, m=100%) to 8.7 semitones (Δr=214.5 Hz, fm=320 Hz, m=100%). In contrast, average rate discrimination thresholds for NH subjects ranged from 0.9 semitones (Δr=4.2 Hz, fm=80 Hz, m=100%) to 4.7 semitones (Δr=103.5 Hz, fm=320 Hz, m=60%). Some of the differences in temporal processing between NH and HI subjects, especially those related to modulation detection, may be accounted for by differences in signal audibility, especially for high-frequency portions of the modulated noise. However, in many cases, HI subjects encountered great difficulty discriminating a change in modulation rate even though the modulation components of the standard and test stimuli were detectable.
Perceptual rating and acoustic analysis of tracheo-esophageal voice
Authors: Festen Joost M. , Verdonck Irma M.
Published: July 2002

Perceptual analysis of tracheo-esophageal (TE) voice shows a large variability among listeners and is time consuming. Therefore, an acoustic analysis procedure has been developed that can handle these often very irregular signals. The analysis is based on moderate, comfortable, and strong phonations of a sustained vowel /a/ and includes sound-pressure level, fundamental frequency, frequency stability, spectral shape, and other measures. As an evaluation of the acoustic analysis an experiment was conducted to collect perceptual ratings for the same phonations. Ratings were given by naive listeners on scales like pitch, noisiness, strength, and deviance. Relations between the acoustic parameters and the perceptual evaluation will be discussed.
Stretching of Elastic Tubes over Rotationally Symmetric Mandrels
Authors: Wessling R. A. , Alfrey T.
Published: July 2002

The pattern of biaxial stretching which occurs when a thin-walled elastic tube is drawn slowly over a rotationally symmetric mandrel is analyzed. Acceleration terms are neglected in the balance of forces and the friction is assumed to be simple Coulombic. The particular case of the conical mandrel is treated in detail. Solutions are obtained for both Mooney-Rivlin and Hookean elastic material properties and the results are compared with experiment.
The Stretching of a Viscous Tube over a Conical Mandrel
Authors: Wessling R. A.
Published: July 2002

The theoretical analysis of mandrel processes has been extended to cases involving viscous materials. An exact solution is obtained for the Newtonian fluid. The results show that a wide range of biaxial stretching patterns can be obtained by controlling the surface friction, input and take-off velocity and the temperature gradient. Conditions necessary for uniform biaxial stretching are shown.
Steady Flow and Dynamic Oscillatory Experiments on Polymer Melts
Authors: Huseby T. W. , Blyler L. L.
Published: July 2002

We compare experimental results for tube flow of polymer melts with those computed from Pao's theory. We further present a correlation scheme for the behavior of bulk polymer melts in steady flow and dynamic oscillatory experiments. The correlation is not limited to low shear rates, but is theoretically valid for all frequencies and shear rates. The steady flow shear viscosity is expected to equal or exceed the dynamic viscosity at all frequencies and shear rates. Similarly, the correlation predicts that G exceeds or equals G′ over the entire frequency range. At low shear rates τ12 should correlate with G″ and P11−P22 is given by 2G′. Limited agreement between the experimental results and computed curves for tube flow is observed. The correlation scheme appears to represent the behavior of certain polymer solutions very well but quantitative agreement is not obtained for a linear polyethylene melt. We propose that changes in the relaxation spectrum of the polymer melt subjected to steady shearing can account for the discrepancies.
Viscoelastic Tests Under Finite Strain and Variable Strain Rate
Authors: Flowers Ronald J. , Lianis George
Published: July 2002

In this paper we present the results of uniaxial, equal biaxial, and unequal homogeneous biaxial tension of viscoelastic materials under isothermal conditions and compare them with predictions based on the approximate constitutive equations of Refs. 1 and 2. Theoretical expressions for uniaxial and equal biaxial constant and logarithmic stretch-rates and for unequal homogeneous biaxial single-step and double-step relaxation and constant stretch-rate are developed and compared with experimental results for a styrene-butadiene rubber (SBR); agreement is found to be satisfactory. The uniaxial and equal biaxial constant stretch results for very short ramp times are used to predict the behavior of actual single-step relaxation tests and to study the effects of fast motion on the constitutive equations of Refs. 1 and 2.
Multiple Step, Nonlinear Creep of Polyurethane Predicted from Constant Stress Creep by Three Integral Representations
Authors: Nolte K. G. , Findley W. N.
Published: July 2002

The following three integral representations for nonlinear creep were considered: a product form of the multiple integral representation, a second-order memory representation, and an integral form of the modified superposition principle which is equivalent to a first-order memory representation. The latter two representations were derived by limiting the memory capability of the multiple integral representation. These three representations required information from constant stress creep tests only to predict the creep resulting from multiple-step loading programs. The three representations were applied to the creep of polyurethane resulting from multiple-step loadings of combined tension and torsion. The second-order memory representation and the modified superposition principle predicted the multiple-step creep behavior more satisfactorily than the product form of the multiple integral representation.
Prediction of the Bagley End Correction Factor and Die Swell for Capillary Flow of an Oldroyd Rate Type Fluid
Authors: Balmer Robert T.
Published: July 2002

The significance of the Bagley capillary end correction factor and capillary die swell are analytically investigated for a fluid obeying the quasilinear Oldroyd rate type constitutive equation which incorporates the Jaumann differential operator. The Goddard and Miller integration technique is used, under the assumption that the fluid enters the capillary with a fully developed velocity profile, to invert the constitutive equation and to produce an explicit relation for the pressure drop in the capillary. The inlet stress field decay in the capillary is shown to produce both nonlinear die swell behavior and nonlinear pressure drop behavior with increasing L/D. The theory is substantiated, in part, with experimental results.
Microstructure of Melt Blended Polymer Systems
Authors: Starita Joseph M.
Published: July 2002

Two thermodynamically incompatible polymers were melt blended. The resulting microstructure and, consequently, the physical properties were dependent on the blending conditions and the rheological properties of the components. In this study the blending conditions were held constant while the rheological properties were varied and correlated with dispersion characteristics of the phases and the physical properties of the composite. A series of five atactic polystyrenes (weight average molecular weight from 75,000 to 400,000) and five linear polyethylenes (weight average molecular weight from 43,000 to 347,000) were used. The blending was done over a range of composition ratios in a normal stress extruder. Viscosity and normal stress of each pure component were measured in torsional flow. The mixed extrudates were examined by light interference microscopy, scanning electron microscopy, and solvent leaching. The nature and the fineness of the microstructure were interpreted in terms of the composition ratios, mixing history, and the melt rheological properties of the components. It was concluded that the fineness of the minor phase in a shear mixing process is a function of the difference between both the viscous and elastic behavior of the components.
Velocity Descriptions in the Die Exit Region for a Polymer Solution: Influence of Die Entry Instabilities
Authors: Rama Murthy A. V.
Published: July 2002

A Laser Doppler Anemometer and a capillary rheometer are used to study the nature of emerging jets of liquid paraffin and a highly elastic solution of Separan Ap30. In particular, the effect of die entry instabilities reported earlier for the polymer solution is studied. Velocity profile measurements are made in the ranges 550⩽γ⩽2176 sec−1, L/D=26.3, for liquid paraffin and 24.5⩽γ⩽489 sec−1, 26.3⩽L/D⩽52.6, for the polymer solution. Surface velocity measurements for the polymer solution in the above range show that the propagation of spiralling instabilities results in a transverse wave-like phenomenon which causes distortion of the jet diameter at die swell. The distortion increases with increasing shear rates and decreasing tube L/D ratios. Data for L/D=26.3 are presented and the results for the polymer solution are discussed in relation to the reported extrudate distortions in polymer melts. A mechanism for the occurrence of matte and sharkshin extrudates is proposed.
Rheological Behavior and Flow Patterns Around Agitators in Polymer Solutions
Authors: White James L. , Chankraiphon Sirikalaya , Ide Yoshiaki
Published: July 2002

Flow patterns around agitators of varying design have been determined for the systems: polystyrene/styrene, polybutadiene/styrene, and (butadiene-styrene)-copolymer/styrene at several concentrations. Normal stress coefficients and shear viscosities have been determined in the same concentration range. Three regimes of flow are observed for most agitator types: (1) centrifugal force dominated at low concentrations, (2) vortex patterns or stagnant regions near the agitator of intermediate concentrations, (3) normal stress dominated at high concentrations. It is argued that this behavior may be represented by the dimensionless group Ψ10/2ρR2 where Ψ10 is the zero shear normal stress coefficient, R the radius of the agitator, and ρ the solution density. This is the ratio of viscoelastic to inertial forces. It is found that the transformations of regimes (1) to (2) and (2) to (3) occur in agitators of the same diameter at the same concentrations in any particular solution. The critical concentrations for different solutions correlates with the same value of Ψ1/2ρR2.
On 1D instabilities in simple shear and extensional flows as predicted by some Maxwell-like constitutive equations
Authors: Kwon Y. , Leonov A. I.
Published: July 2002

One-dimensional (1D) instabilities, some of them of new type, were found in simple shear and simple elongation for Giesekus, Leonov, and Larson viscoelastic constitutive equations (CEs) with single relaxation mode. Whereas 1D instabilities in shear flow were found for all three CEs, only the Larson model manifested some 1D instabilities (and even nonexistence of solution) in simple extensional flows.
Viscoelastic flow past a confined cylinder of a polyisobutylene solution
Authors: Baaijens Hans P. W. , Peters Gerrit W. M. , Baaijens Frank P. T. , Meijer Han E. H.
Published: July 2002

Viscoelastic constitutive equations are evaluated using the benchmark problem of the planar flow past a confined cylinder for a well-characterized solution of 5%(w/w) polyisobutylene in tetradecane. The ratio of channel height to cylinder diameter is equal to two. We compare finite element simulations with point-wise measured velocities and stresses obtained by means of laser Doppler anemometry and a flow-induced birefringence technique, respectively. The Deborah number (De) ranges from 0.25 to 2.32. In the case of the geometry with a symmetrically confined cylinder, computations were made with a generalized Newtonian model and with both a single- and a four-mode Phan-Thien and Tanner (PTT) model. All model parameters were determined in simple shear flow. A similar analysis is presented in case of an asymmetrically confined cylinder (with De=1.87). Impressively good agreement was found between the predictions of the four-mode PTT model and the measured velocities and stresses. The agreement was even excellent in the geometry with the asymmetrically confined cylinder.
Powder diffraction analysis of substituted sulfonylurea
Authors: PuLan Yu , Shuang Ding , YuanYuan Qiao , XinKan Yao , HaiYue Zhang , ShaoFan Lin
Published: July 2002

The crystal structure of a series of substituted sulfonylureas were studied in this paper by means of powder diffraction, and the cell dimensions of each compound were refined by a least squares analysis. The cell parameters were in good agreement with those obtained from single crystal data. © 2002 International Centre for Diffraction Data.
Emotion in Second Language Writing
Authors: Uzun Kutay
Published: March 2022

Emotions have been a point of interest for psychology researchers for decades and equally so for second language acquisition (SLA) researchers, although the content of SLA research has typically been limited to negative emotions for most of that time. The broaden‐and‐build theory of positive emotions has given rise to emotion studies in SLA research in the first quarter of the 21st century, this time with increased focus on both negative and positive emotions. Even though the immediate context of L2 writing seems to have fallen behind emotion research in comparison to the more holistic studies in SLA, research has significant implications for the teaching and learning of L2 writing. In this entry, the emotional domain of L2 writing is presented, drawing from studies in both psychology and SLA.
Natural Language Processing Tools for Second Language Writing Research
Authors: Uzun Kutay
Published: March 2022

The developments in computer science and linguistics have enabled L2 writing researchers to process texts computationally, allowing for the generation of data that would either be impossible or highly time‐consuming if attempted manually. To this end, numerous pieces of software utilizing natural language processing (NLP) have been developed for the creation of textual indices, error correction, and evaluating learner texts. However, the immense potential of NLP technologies for the analysis of learner texts is yet to be explored. In this respect, this entry reviews NLP, its functions, current use, and prospects for the future of L2 writing research and teaching.
Sentence Boundaries in Academic Writing: Helping L2 Students Develop Sentence Fluency in Secondary School
Authors: Maamuujav Undarmaa , Olson Carol Booth , Scarcella Robin
Published: March 2022

To communicate well in an academic context, students in secondary school need to have comprehensive knowledge of sentence structures, types, and functions. This includes the ability to coordinate and subordinate sentences, choose among a variety of structures, and make syntactic choices appropriate for the academic genre and audience. Knowledge of syntax allows students to convey complex ideas with meaningful transitions and communicate coherently with an effective academic tone. Such knowledge also helps students to avoid making sentence boundary errors, which readers can find distracting. Despite the critical importance of teaching students command of sentence boundaries, there is little pedagogical research on them. In this entry, we focus on sentence boundary issues in L2 writing in a secondary context, providing a synopsis of recent research on this topic and exploring pedagogical approaches to help L2 writers build syntactic knowledge and use this knowledge to convey their ideas successfully in academic writing.
The Neurophysiology of Second Language Learning
Authors: Hardacre Bahiyyih , Güvendir Emre
Published: March 2022

Neuroplasticity in humans is characterized by the extraordinary ability of the human brain to adapt in response to environmental stimuli, cognitive demand, or behavioral experience. Cognitive brain research in recent decades, especially the past 20 years, has revealed that neuroplastic changes in response to experience can produce beneficial effects on cognition. Research has also shown that second language learning is mediated by changes in the brain, and that brain plasticity is involved in the successful adult second language learning outcomes. This entry examines the current literature on neurophysiology of second language learning and discusses implications and recommendations for second language pedagogy.
The Role of Social Interaction on Brain Development and Language Acquisition
Authors: Güvendir Emre , Hardacre Bahiyyih
Published: March 2022

Previously, scientists thought that human brain development was genetically pre‐established, and that it would follow a biologically predetermined pathway as it grew. However, with the recent technological and scientific developments in brain research, scientists have observed that infants' early social and emotional experiences and interactions influence early brain development and how the pathways in the brain are wired. Research has shown that, like nutrients, establishing interactions with conspecifics and objects is vital for the developing brain, and having a variety of experiences causes the brain to develop in different ways. This entry examines current literature and discusses implications for early childhood development, suggesting it is a favorable time to expose a child to an L2.
Language Teacher Educator Identity
Authors: Yazan Bedrettin
Published: March 2022

This entry discusses the concept of language teacher educator (TE) identity by considering the multiplicity of TESOL practitioners engaged in teacher education practices and the lack of institutionalized support and preparation for teacher educators in TESOL. It shares the main research considerations to capture the complexities involved in negotiating and constructing a language teacher educator identity which is situated at the intersection of individual aspirations and contextual constraints at meso and macro levels. The entry also provides pedagogical ideas to support language teacher educators with identity‐oriented activities to be integrated into formal coursework and mentoring structures. Such activities can help teacher educators explore the relationship between learning, identity, and practice in their professional lives.
Teacher Leadership
Authors: Reinders Hayo
Published: March 2022

The quality of leadership is one of the most significant factors in educational success, but the skills necessary for taking on responsibility for self and others are not usually taught and supported. In this entry we look at the current role of leadership in language education, review common types of leadership, and consider the attributes individuals display in leadership roles. We conclude with a number of implications for pre‐service and in‐service language teacher training, as well as the broader TESOL field.
Nitric Oxide Delivering Surfaces: An Overview of Functionalization Strategies and Efficiency Progress
Authors: Beurton Jordan , Boudier Ariane , Barozzi Seabra Amedea , Vrana Nihal Engin , Clarot Igor , Lavalle Philippe
Published: March 2022

An overview on the design of nitric oxide (NO) delivering surfaces for biomedical purposes is provided, with a focus on the advances of the past 5 years. A localized supply of NO is of a particular interest due to the pleiotropic biological effects of this diatomic compound. Depending on the generated NO flux, the surface can mimic a physiological release profile to provide an activity on the vascular endothelium or an antibacterial activity. Three requirements are considered to describe the various strategies leading to a surface delivering NO. Firstly, the coating must be selected in accordance with the properties of the substrate (nature, shape, dimensions…). Secondly, the releasing and/or generating kinetics of NO should match the targeted biological application. Currently, the most promising structures are developed to provide an adaptable NO supply driven by pathophysiological needs. Finally, the biocompatibility and the stability of the surface must also be considered regarding the expected residence time of the device. A critical point of view is proposed to help readers in the design of the NO delivering surface according to its expected requirement and therapeutic purpose.
Zero‐Strain High‐Capacity Silicon/Carbon Anode Enabled by a MOF‐Derived Space‐Confined Single‐Atom Catalytic Strategy for Lithium‐Ion Batteries
Authors: Chen Bingjie , Chen Lu , Zu Lianhai , Feng Yutong , Su Qingmei , Zhang Chi , Yang Jinhu
Published: March 2022

Developing zero‐strain electrode materials with high capacity is crucial for lithium‐ion batteries (LIBs). Here, a new zero‐strain composite material made of ultrasmall Si nanodots (NDs) within metal organic framework‐derived nanoreactors (Si NDs⊂MDN) through a novel space‐confined catalytic strategy is reported. The unique Si NDs⊂MDN anode features a low strain (<3%) and a high theoretical lithium storage capacity (1524 mAh g‐1) which far surpasses the traditional single‐crystal counterparts that suffer from a low capacity delivery. The zero‐strain property is evidenced by substantial characterizations including ex/in situ transmission electron microscopy and mechanical simulations. The Si NDs⊂MDN exhibits superior cycling stability and high reversible capacity (1327 mAh g‐1 at 0.1 A g‐1 after 100 cycles) in half‐cells and high energy density (366 Wh kg‐1 after 300 cycles) in a full cell. This study reports a new catalog of zero‐strain electrode material with significantly improved capacity beyond the traditional single‐crystal zero‐strain materials.
Uncovering a Vital Band Gap Mechanism of Pnictides
Authors: Chen Jindong , Wu Qingchen , Tian Haotian , Jiang Xiaotian , Xu Feng , Zhao Xin , Lin Zheshuai , Luo Min , Ye Ning
Published: March 2022

Pnictides are superior infrared (IR) nonlinear optical (NLO) material candidates, but the exploration of NLO pnictides is still tardy due to lack of rational material design strategies. An in‐depth understanding structure–performance relationship is urgent for designing novel and eminent pnictide NLO materials. Herein, this work unravels a vital band gap mechanism of pnictides, namely P atom with low coordination numbers (2 CN) will cause the decrease of band gap due to the delocalization of non‐bonding electron pairs. Accordingly, a general design paradigm for NLO pnictides, ionicity–covalency–metallicity regulation is proposed for designing wide‐band gap NLO pnictides with maintained SHG effect. Driven by this idea, millimeter‐level crystals of MgSiP2 are synthesized with a wide band gap (2.34 eV), a strong NLO performance (3.5 x AgGaS2), and a wide IR transparency range (0.53–10.3 µm). This work provides an essential guidance for the future design and synthesis of NLO pnictides, and also opens a new perspective at Zintl chemistry important for other material fields.