bluuebunny/crossref_metadata_2025 huggingface dataset:
Multivariate Analysis, Description, and Ecological Interpretation of Weed Vegetation in the Summer Crop Fields of Anhui Province, China
Authors: QIANG Sheng
Published: October 2005

Abstract: Two surveys were conducted to investigate weed vegetation in a 153‐hm2 sampling area of summer crop fields from Anhui Province, China, through visual scoring of the level of weed infestation compared with summer crops on a seven‐class scale. In total, 155 sampling sites were selected in the field based on crops, tillage, rotation systems, geographical regions, and soil types across the province. Data on weed communities and environmental factors were collected and analyzed through principal component analysis (PCA) and canonical correspondence analysis (CCA), and the output was interpreted ecologically. Results showed that the main factors influencing the structure and distribution of weed communities in summer crop fields were the soil submersion period, latitude, and soil type and pH. The CCA indicated a significant relationship between weed dominance and soil submersion duration, latitude, and soil pH. From the result of the PCA and CCA ordination, the 155 sampling sites could be divided into three groups based on geographic and floristic composition, as well as weed abundance. The southern dry land group, which was characterized by a double‐cropping system in the hilly regions of southern and central Anhui Province with a continuous summer crop and an autumn dry land crop, was dominated by Galium aparine Linn. var. tenerum (Gren. et Godr) Robb., Avenafatua L., and Veronicapersica Poir. The northern dry land group, which had the same cropping system as the southern dry land group, was dominated by G. aparine var. tenerum, Galium tricorne Stokes, Descurainia sophia (L.) Schur., and Lithospermum arvense L. in the North Anhui Province, China. These two dry land groups could be combined into one large dry land group, in which the Galium weed vegetation type dominated. The third group was the paddy soil group, which was characterized by a continuous summer crop and double‐ or triple‐cropping systems of rice, and prevailed in the south and central areas of Anhui Province; Alopecurus aequalis Sobol. was the dominant weed in this group. Other main weeds in this group included Malachium aquaticum (L.) Fries, Stellaria alsine Grimm, Alopecurus japonicus Steud., and Lapsana apogonoides Maxim. Thus, the weed community distributions in this group were described as the Alopecurus weed vegetation type. The paddy soil group could be divided into two subgroups, one southern and one central paddy soil subgroup. A strategy for integrated weed management is suggested according to the weed distribution pattern. The present study serves as a good example of how a quantitative research method was used to associate a visual estimate of weed infestation with multivariate analyses, such as PCA and CCA, and how this method can be applied to the study of weed vegetation on arable land.

(Managing editor: Ya‐Qin HAN)
Regulation Mechanisms of Stomatal Oscillation
Authors: YANG Hui‐Min , ZHANG Jian‐Hua , ZHANG Xiao‐Yan
Published: October 2005

Abstract: Stomata function as the gates between the plant and the atmospheric environment. Stomatal movement, including stomatal opening and closing, controls CO2 absorption as the raw material for photosynthesis and water loss through transpiration. How to reduce water loss and maintain enough CO2 absorption has been an interesting research topic for some time. Simple stomatal opening may elevate CO2 absorption, but, in the meantime, promote the water loss, whereas simple closing of stomatal pores may reduce both water loss and CO2 absorption, resulting in impairment of plant photosynthesis. Both processes are not economical to the plant. As a special rhythmic stomatal movement that usually occurs at smaller stomatal apertures, stomatal oscillation can keep CO2 absorption at a sufficient level and reduce water loss at the same time, suggesting a potential improvement in water use efficiency. Stomatal oscillation is usually found after a sudden change in one environmental factor in relatively constant environments. Many environmental stimuli can induce stomatal oscillation. It appears that, at the physiological level, feedback controls are involved in stomatal oscillation. At the cellular level, possibly two different patterns exist: (i) a quicker responsive pattern; and (ii) a slower response. Both involve water potential changes and water channel regulation, but the mechanisms of regulation of the two patterns are different. Some evidence suggests that the regulation of water channels may play a vital and primary role in stomatal oscillation. The present review summarizes studies on stomatal oscillation and concludes with some discussion regarding the mechanisms of regulation of stomatal oscillation.

(Managing editor: Wei WANG)
Isolation of a Tomato Protease that May Be Involved in Proteolysis of 1‐Aminocyclopropane‐1‐Carboxylate Synthase
Authors: LI Jian‐Feng , QU Liang‐Hu , LI Ning
Published: October 2005

Abstract: 1‐aminocyclopropane‐1‐carboxylate (ACC) synthase is a principal enzyme that catalyses the committed step in phytohormone ethylene biosynthesis. Previous evidence indicates that the hypervariable C‐terminus of ACC synthase is most likely to be processed proteolytically in vivo. However, the protease responsible has not been identified thus far. In the present study, we detected proteolytic activity against ACC synthase (LeACS2) in tomato (Lycopersicon esculentum Mill.) fruit extract based on a newly established in vitro assay system. Purification of the protease through DEAE, gel filtration and Mono Q chromatography resulted in considerable enrichment of a 64‐kDa protein species. Subsequent biochemical analysis of the purified tomato protease revealed that the optimal conditions for its proteolytic activity were at pH 8.0 and at 37 °C. In addition, the protease activity was blocked completely by the metalloprotease inhibitor 1,10‐phenanthroline. The present study represents the first report on the isolation of an ACC synthase‐processing protease from plant tissues.

(Managing editor: Ping HE)
Possible Involvement of Anti‐Oxidant Enzymes in the Cross‐Tolerance of the Germination/Growth of Wheat Seeds to Salinity and Heat Stress
Authors: LEI Yan‐Bao , SONG Song‐Quan , FU Jia‐Rui
Published: October 2005

Abstract: The germination/growth of wheat (Triticum aestivum L. cv. Zimai 1) seeds and changes in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT), as well as in the content of thiobarbituric acid‐reactive substances (TBARS), in response to salt and heat stress, as well as cross‐stress, were investigated in the present study. With increasing temperature and decreasing water potential caused by NaCl solution, the germination percentage of seeds and the fresh weight of seedlings decreased markedly, SOD activity increased, activities of APX and CAT decreased distinctly, and the TBARS content increased gradually. Seeds pretreated at 33 °C for different times displayed increased tolerance to subsequent salt stress, enhanced SOD, APX, and CAT activities, and decreased TBARS content. Seeds pretreated at ‐0.8 MPa NaCl for different times displayed increased tolerance to subsequent heat stress and marked increases in SOD, APX, and CAT activities, which were associated with decreased TBARS content. It is considered that the common component in the cross‐tolerance of the germination and growth of wheat seeds to salinity and heat stress is the anti‐oxidant enzyme system.

(Managing editor: Ping HE)
Chlorophyll Fluorescence Detected Passively by Difference Reflectance Spectra of Wheat (Triticum aestivum L.) Leaf
Authors: ZHANG Yong‐Jiang , ZHAO Chun‐Jiang , LIU Liang‐Yun , WANG Ji‐Hua , WANG Ren‐Chao
Published: October 2005

Abstract: The chlorophyll fluorescence (CF) signature emitted from vegetation provides an abundance of information regarding photosynthetics activity and has been used as a powerful tool to obtain physiological information of plant leaves in a non‐invasive manner. CF is difficult to quantify because the CF signal is obscured by reflected light. In the present study, the apparent reflectance spectra of wheat (Triticum aestivum L.) leaves were measured under illuminations with and without filtering by three specially designed long‐wave pass edge filters; the cut‐off wavelengths of the three filters were 653.8, 678.2, and 694.1 nm at 50% of maximum transmittance. The CF spectra could be derived as the reflectance difference spectra of the leaves under illuminations with and without the long wave pass edge filters. The ratio of the reflectance difference at 685 and 740 nm (Dif685/Dif740) was linear correlated with the CF parameters (maximal photochemical efficiency Fv/Fm, and the yield of quantum efficiency) measured by the modulated fluorometer. In addition, the ratio reflected the water stress status of the wheat leaf, which was very high when water deficiency was serious. This method provides a new approach for detecting CF and the physiological state of crops.

(Managing editor: Ping HE)
Lack of Evidence for 3/4 Scaling of Metabolism in Terrestrial Plants
Authors: LI Hai‐Tao , HAN Xing‐Guo , WU Jian‐Guo
Published: October 2005

Abstract: Scaling, as the translation of information across spatial, temporal, and organizational scales, is essential to predictions and understanding in all sciences and has become a central issue in ecology. A large body of theoretical and empirical evidence concerning allometric scaling in terrestrial individual plants and plant communities has been constructed around the fractal volume‐filling theory of West, Brown, and Enquist (the WBE model). One of the most thought‐provoking findings has been that the metabolic rates of plants, like those of animals, scale with their size as a 3/4 power law. The earliest, single most‐important study cited in support of the application of the WBE model to terrestrial plants claims that whole‐plant resource use in terrestrial plants scales as the 3/4 power of total mass, as predicted by the WBE model. However, in the present study we show that empirical data actually do not support such a claim. More recent studies cited as evidence for 3/4 scaling also suffer from several statistical and data‐related problems. Using a forest biomass dataset including 1 266 plots of 17 main forest types across China, we explored the scaling exponents between tree productivity and tree mass and found no universal value across forest stands. We conclude that there is not sufficient evidence to support the existence of a single constant scaling exponent for the metabolism‐biomass relationship for terrestrial plants.

(Managing editor: Ya‐Qin HAN)
The Drosophilatweety family: molecular candidates for large‐conductance Ca2+‐activated Cl− channels
Authors: Suzuki Makoto
Published: October 2005

Calcium‐activated chloride currents (ICl(Ca)) can be recorded in almost all cells, but the molecular identity of the channels underlying this Cl− conductance is still incompletely understood. Here, I report that tweety, a gene located in Drosophilaflightless, possesses five or six transmembrane segments, and that a human homologue of tweety (hTTYH3) is a novel large‐conductance Ca2+‐activated Cl− channel, while the related gene, hTTYH1, is a swelling‐activated Cl− current. hTTYH3 is expressed in excitable tissues, including the heart, brain and skeletal muscle, whereas hTTYH1 is expressed mainly in the brain. Expression of hTTYH3 in CHO cells generated a unique Cl− current activated by an increase in the intracellular Ca2+ concentration. The hTTYH3‐induced Cl− current had a linear current–voltage (I–V) relationship, a large single‐channel conductance (260 pS) and the anion permeability sequence I− > Br− > Cl−. Like native Ca2+‐activated Cl− channels, the hTTYH3 channel showed complex gating kinetics and voltage‐dependent inactivation, and was dependent on micromolar intracellular Ca2+ concentration. Expression in CHO cells of an hTTYH1 splice variant that lacks the C‐terminal glutamate‐rich domain of hTTYH1 (hTTYH1sv) generated a swelling‐activated Cl− current. I conclude that investigation of the tweety family will provide important information about large‐conductance Cl− channel molecules.
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Model for the Atmospheric Boundary Layer Under Various Thermal Stratifications
Authors: Alinot Cédric , Masson Christian
Published: October 2005

This paper presents a numerical method for predicting the atmospheric boundary layer under stable, neutral, or unstable thermal stratifications. The flow field is described by the Reynolds’ averaged Navier-Stokes equations complemented by the k‐ϵ turbulence model. Density variations are introduced into the momentum equation using the Boussinesq approximation, and appropriate buoyancy terms are included in the k and ϵ equations. An original expression for the closure coefficient related to the buoyancy production term is proposed in order to improve the accuracy of the simulations. The resulting mathematical model has been implemented in FLUENT. The results presented in this paper include comparisons with respect to the Monin-Obukhov similarity theory, measurements, and earlier numerical solutions based on k‐ϵ turbulence models available in the literature. It is shown that the proposed version of the k‐ϵ model significantly improves the accuracy of the simulations for the stable atmospheric boundary layer. In neutral and unstable thermal stratifications, it is shown that the version of the k‐ϵ models available in the literature also produce accurate simulations.
Blade Three-Dimensional Dynamic Stall Response to Wind Turbine Operating Condition
Authors: Schreck S. , Robinson M.
Published: October 2005

To further reduce the cost of wind energy, future turbine designs will continue to migrate toward lighter and more flexible structures. Thus, the accuracy and reliability of aerodynamic load prediction has become a primary consideration in turbine design codes. Dynamically stalled flows routinely generated during yawed operation are powerful and potentially destructive, as well as complex and difficult to model. As a prerequisite to aerodynamics model improvements, wind turbine dynamic stall must be characterized in detail and thoroughly understood. The current study analyzed turbine blade surface pressure data and local inflow data acquired by the NREL Unsteady Aerodynamics Experiment during the NASA Ames wind tunnel experiment. Analyses identified and characterized two key dynamic stall processes, vortex initiation and vortex convection, across a broad parameter range. Results showed that both initiation and convection exhibited pronounced three-dimensional kinematics, which responded in systematic fashion to variations in wind speed, turbine yaw angle, and radial location.
A Parallelized Coupled Navier-Stokes/Vortex-Panel Solver
Authors: Schmitz Sven , Chattot Jean-Jacques
Published: October 2005

A Navier-Stokes solver, CFX V5.6, is coupled with an in-house developed Vortex-Panel method for the numerical analysis of wind turbines. The Navier-Stokes zone is confined to the near-field around one wind turbine blade, the Vortex-Panel method models the entire vortex sheet of a two-bladed rotor and accounts for the far-field. This coupling methodology reduces both numerical diffusion and computational cost. The parallelized coupled solver (PCS) is applied to the NREL Phase VI rotor configuration under no-yaw conditions. Fully turbulent flow is assumed using the k - ϵ and k - ω turbulence models. Results obtained are very encouraging for fully attached flow. For separated and partially stalled flow, results are in good agreement with experimental data. Discrepancies observed between the turbulence models are attributed to different prediction of the onset of separation. This is revealed by two-dimensional (2D) results of the S809 airfoil.
Utility Scale Twist-Flap Coupled Blade Design
Authors: Wetzel Kyle K.
Published: October 2005

This paper reports an investigation of the use of off-axis carbon fibers in the all-carbon spar cap of a 37-m wind turbine rotor blade to induce twist-flap coupling. Many studies have been published on the structure of wind turbine rotor blades incorporating off-axis fibers; none has studied optimizing the blade structure simultaneously considering the angle of off-axis material, the fraction of off-axis material, constraints on cross-fiber and in-plane shear strength, constraints on tip deflection, and blade cost. A parametric study has been conducted varying the angle of off-axis fibers from 5° to 25° and varying the volume fraction of off-axis fibers in the spar cap from 10% to 90%. In all configurations, the remainder of the spar cap material is 0° carbon fiber. The spar cap thickness has been adjusted in each blade to simultaneously minimize the weight of carbon material, and hence the blade cost, while satisfying constraints on carbon fiber strain and tip deflection. The study also examines the cross-fiber strain and stress and the in-plane shear stress in the 0° and off-axis carbon layers. The conclusion of this study is that the optimal angle for most cost-effectively achieving twist-flap coupling—considering constraints on fiber strain, cross-fiber strength, in-plane shear strength, and tip deflection—is closer to 7.5° than the 20° that has frequently been reported by prior researchers. As much as 90% of the spar cap carbon fibers can be rotated to 7.5° off-axis before in-plane shear strength is exceeded.
Sustainable Vacuum-Infused Thermoplastic Composites for MW-Size Wind Turbine Blades—Preliminary Design and Manufacturing Issues
Authors: van Rijswijk K. , Joncas S. , Bersee H. E. N. , Bergsma O. K. , Beukers A.
Published: October 2005

This paper addresses the feasibility of using innovative vacuum infused anionic polyamide-6 (PA-6) thermoplastic composites for MW-size wind turbine blades structures. To compare the performance of this fully recyclable material against commonly used less sustainable thermoset blade materials in a baseline structural MW-size blade configuration (box-spar/skins), four different blade composite material options were investigated: Glass/epoxy, carbon/epoxy, glass/PA-6, and carbon/PA-6. Blade characteristics such as weight, costs, and natural frequencies were compared for rotor blades ranging between 32.5 and 75m in length, designed according to both stress and tip deflection criteria. Results showed that the PA-6 blades have similar weights and natural frequencies when compared to their epoxy counterpart. For glass fiber blades, a 10% reduction in material cost can be expected when using PA-6 rather than epoxy while carbon fiber blades costs were found to be similar. Considering manufacturing, processing temperatures of PA-6 are significantly higher than for epoxy systems; however, the associated cost increase is expected to be compensated for by a reduction in infusion and curing time.
Optimized Constant-Life Diagram for the Analysis of Fiberglass Composites Used in Wind Turbine Blades
Authors: Sutherland Herbert J. , Mandell John F.
Published: October 2005

Mandell et al. have recently presented an updated constant-life diagram (CLD) for a fiberglass composite that is a typical wind turbine blade material. Their formulation uses the MSU/DOE fatigue data base to develop a CLD with detailed S-N information at 13 R-values. This diagram is the most detailed to date, and it includes several loading conditions that have been poorly represented in earlier studies. Sutherland and Mandell have used this formulation to analyze typical loads data from operating wind farms and the failure of coupons subjected to spectral loading. The detailed CLD used in these analyses requires a significant investment in materials testing that is usually outside the bounds of typical design standards for wind turbine blades. Thus, the question has become: How many S-N curves are required for the construction of a CLD that is sufficient for an “accurate” prediction of equivalent fatigue loads and service lifetimes? To answer this question, the load data from two operating wind turbines and the failure of coupons tested using the WISPERX spectra are analyzed using a nonlinear damage model. For the analysis, the predicted service lifetimes that are based on the CLD constructed from 13 R-values are compared to the predictions for CLDs constructed with fewer R-values. The results illustrate the optimum number of R-values is 5 with them concentrated between R-values of −2 and 0.5, or −2 and 0.7.
Bulk modulus thermoviscoelasticity theory for rubbery elastomers
Authors: Burns J. , Dubbelday P. S.
Published: October 2005

Earlier attempts to develop a free-volume theory of the dynamic bulk modulus of rubbery elastomers [J. Burns et al., J. Acoust. Soc. Am. Suppl. 1 79, S62 (1986)] led to separate expressions for the frequency dependence of the modulus at constant temperature and for the temperature dependence at constant frequency. These have now been combined to give a free-volume-based theory for the bulk modulus as a function of both frequency and temperature. For certain ranges of parameters that may occur in practice, the theory does not permit master curves to be constructed by the usual WLF frequency shift method. Implications of this fact for dealing with experimental bulk modulus data are discussed.
An algorithm for applying the Williams, Landel, and Ferry method of reduced variables
Authors: Dlubac James J. , Deigan Richard J. , Reader Wayne T.
Published: October 2005

The measurement of the dynamic complex modulus of viscoelastic materials on any apparatus is confined to a limited frequency and temperature range. Williams, Landel, and Ferry (WLF) [J. D. Ferry, Viscoelastic Properties of Polymers (Wiley, New York, 1980), 3rd ed. Chap. 11] reasoned that an increase in temperature produces an identical effect in a viscoelastic material as a decrease in frequency and vice versa. Empirically, then, there is a correspondence between temperature and frequency. The WLF method of reduced variables was proposed as a method of extending the effective frequency range of the dynamic modulus and loss factor. This technique involves measuring the complex modulus over a limited frequency range and a variety of temperatures. The data at different temperatures are then plotted versus frequency and shifted along the frequency axis until a smooth curve results. The effects are shifted modulus curves describing the complex modulus over a broad frequency range at some fixed temperature. Typically, the WLF shift requires several runs at temperatures close enough so that the modulus of one run overlaps the next. In this paper, the WLF method of reduced variables is reviewed and an algorithm for accomplishing the WLF shift is investigated. This algorithm shifts dynamic modulus data at various temperatures, the consecutive runs of which may not contain overlapping moduli.
An automated system for characterizing the vibration damping properties of materials
Authors: Drake M. L. , Smiley R. G. , Hopkins D. M.
Published: October 2005

In 1980 ASTM finalized the damping characterization standard E-756-80 around the resonant beam test method (M. L. Drake and G. E. Terborg, Technical Report AFWAL-TR-80-4093, 15 January 1976-31 December 1979). The University of Dayton, in conjunction with Entek Scientific, developed a computer-aided test system that automated the test procedures and data reduction equation prescribed in E-756. This software package, combined with the appropriate hardware system, results in an efficient workstation for conducting damping characterization studies of materials and designing effective damping systems utilizing the damping properties determined. The presentation will outline the philosophy and operation of the system, including discussions on the system autonomy and the function of each system component; a typical test setup, data reduction, and nomogram generation; and an example of a damping design development.
Dynamic material property measurements using the Polymer Laboratories' dynamic mechanical thermal analyzer
Authors: Deigan Richard J. , Reader Wayne T. , Dlubac James J.
Published: October 2005

The basic principle of measurement of any dynamic mechanical property apparatus is to infer the elastic and loss moduli from the measured response of a sample and a known theoretical solution. The extent to which the measured response is modeled by the theoretical solution determines the validity of the inferred material properties. The purpose of this paper is to investigate the measurement of the dynamic moduli of viscoelastic materials using the dynamic mechanical thermal analyzer manufactured by Polymer Laboratories, Inc. The complex Young's modulus [E* = E′(1 + iηE)] or shear modulus [G* = G′(1 + iηG)] is determined at frequencies ranging from 0.01 to 200 Hz at temperatures ranging from − 150 °C to 300 °C. The Young's modulus is found through the bending of either a double or single cantilever beam. The WLF shift is employed on data at several different temperatures to generate shifted modulus curves of E′ and ηE and/or G′ and ηG versus extended frequency for fixed temperature. Computer-generated shifted modulus curves of viscoelastic materials are discussed.
Measurement of complex electromechanical properties of highly damped piezoelectric materials
Authors: Shields F. Douglass , Rittenmyer Kurt M.
Published: October 2005

The mechanical resonance technique for determining the dielectric, elastic, and electromechanical properties of piezoelectric materials has been developed and refined for over 40 years, as described in the different versions of the IRE-IEEE standard on piezoelectricity. The conventional method assumes the piezoelectric resonator is nearly mechanically loss-less. This assumption is valid for some piezoelectric ceramic compositions, but is inaccurate for more highly damped materials used in hydrophone applications. New methods based on the measurement of the real and imaginary parts of the complex admittance have been devised by Smits [IEEE Trans. Sonics Ultrason. SU-23, 393–402 (1976)] and Saitah et al. [IEEE Ultrason. Symp. Proc. 620–623 (1985)]. One of these methods has been accepted and the parameter fitting routines improved upon to determine the electromechanical properties of several important piezoelectric materials that have a high degree of damping. The importance, applications, and limitations of this method will be described for these piezoelectric materials.
Transverse cusp caustics produced by reflection and transmission: The caustic surface and optical simulations
Authors: Marston Philip L. , Frederickson Carl K.
Published: October 2005

High-frequency sound reflected from curved surfaces or refracted by inhomogeneities may produce cusped caustics that open up roughly transverse to the direction of propagation. Though the better-known longitudinal cusp or arête is produced by a concave cylindrical wave front, transverse cusps are produced by distinctly noncylindrical wave fronts of the form W(x,y) = − (a1x2 + a2y2x + a3y2), where a2≠0 and the distance z to the observation plane ≠ (−2a1)−1 [Marston, J. Acoust. Soc. Am. 81, 226–232 (1987)]. The wave front propagates in the z direction and in the orthogonal (u,v) observation plane the caustic has the form D(u − uc)3 = v2. The present research is concerned with the caustic surface generated by considering the z dependence of the caustic parameters D and uc. Reflection and transmission problems that lead to this W(x,y) in the paraxial approximation are discussed as well as a novel property of merging rays. Sound radiated by a point source so as to reflect from a surface whose height relative to the xy plane is of the form h1x2 + h2 y2x + h3 y2 produces a transverse cusp. The reflected wavefield is described by the Pearcey function. Transverse cusps were simulated by reflecting light from a surface of this form. [Work supported by ONR.]
An efficient enhancement of finite-difference implementations for solving parabolic equations
Authors: Robertson J. S. , Arney D. C. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

The parabolic approximation method is widely recognized as useful for accurately analyzing sound transmissions in diverse ocean environments. One reason for its attractiveness is because solutions are marched in range, thereby avoiding the massive internal storage required when using the full wave equation. Present implementations employ a range step size that is prescribed either by the user or by the code and remains fixed for the duration of the computation. An algorithm is presented in which the range step is adaptively selected by a procedure within the implicit finite-difference (IFD) implementation of the parabolic approximation. An error indicator is computed at each range step, and its value is compared to a user-specified error tolerance window. If the error indicator falls outside this window, a new range step size is computed and used until the error indicator again leaves the tolerance window. For a given tolerance, the algorithm generates a range step size that is optimal in a specified sense and which often leads to large decreases in run time. Additional related modifications to the IFD implementation will also be discussed. Several examples are presented that illustrate the efficacy of the enhanced algorithm. [Work supported by ONR.]
Multiple array processors for three-dimensional acoustic problems
Authors: Teng Yu-chiung
Published: October 2005

Presently available analytic techniques for solving wave propagation problems are only useful for simple cases. In realistic cases, the presence of inhomogeneities and irregular boundary conditions defies analytical solutions. One of the best numerical techniques suitable for solving wave propagation problems in a complex geological medium is the finite element method. In principle, the finite element method is capable of dealing with any two- or three-dimensional acoustic and elastodynamic problems. However, the computer incore storage and computing time for solutions increase greatly with each dimension and are beyond the capabilities of the conventional computers. It is, therefore, always desirable to search for alternatives that may reduce the computational labor. In taking advantage of the current advances in hardware technology, the goal is to develop the finite element algorithm for an extraordinarily fast and inexpensive computer system. In particular, the implementation of the finite element method on multi-array processor system was considered. The algorithm, based on the nodal-podal-point-oriented approach, for implementing the finite element method on the parallel computation system has been developed. As a demonstrative example, the three-dimensional problem for the acoustic case has been successfully tested on the IBM loosely Coupled Array Processors (ICAP) by using one to eight processors. By using the 31 × 31 × 31-element model on PRIME 750, the computing time for 200 time steps is about 8.8 h and I/O time is 1.7 h. If using the ICAPI to calculate the same model, the elapse time is about 16.7 min with two processors, 8.8 min with four processors, and 4.9 min with eight processors.
Average intensity of an acoustic beam after propagating through a turbulent ocean
Authors: Tarng J. H. , Yang C. C.
Published: October 2005

The average intensity of an acoustic beam propagating in a turbulent ocean is evaluated using the path integral technique. Because of the existence of the vertical sound-speed profile in the ocean, there is more than one stationary path for the path integral formulation. Also, these stationary paths are curved rays which are derived by the method of ray tracing. The effects of random fluctuations in sound speed are studied by introducing both internal waves and temperature fine structure. The results show that the acoustic beam becomes broader and asymmetric along the vertical axis. The effects of the broadening, asymmetry, and multiple stationary paths are examined in detail. Interference among multiple stationary paths is expected. In addition, these results are compared with those of others obtained by using different approaches. [Work supported by ARL, The Pennsylvania State University.]
Acoustic pulse propagation in a turbulent ocean
Authors: Tarng J. H. , Yang C. C.
Published: October 2005

Temporal behavior of acoustic pulse propagation in a turbulent ocean is investigated by using the method of temporal moments. In this method, the zeroth, first, and second temporal moments are related to the total energy of the pulse, arrival time, and pulse width, respectively. To compute these moments, instead of the two-frequency mutual coherence function, only the coefficients in a power series expansion of this function are required. In particular, only the coefficients up to the second-order terms are needed. The path integral technique, incorporated with the method of ray tracing, is used for evaluating those coefficients. The vertical sound-speed profile is taken into account. The turbulences in the ocean include the internal waves and temperature fine structure. For mathematical simplicity, a bilinear sound-speed profile is considered, and it is assumed that the propagation range along a horizontal axis is short, such that the rays always stay either above or below the depth of minimum sound speed. More general results can be extended easily. [Research supported by ONR.]
Modeling of acoustic transmission in the Straits of Florida
Authors: Monjo Charles L. , DeFerrari H. A.
Published: October 2005

Acoustic transmission experiments, over a 24-km range in the Straits of Florida, have been modeled using ray theory. Three acoustic moorings and three thermister moorings were operated for a 30-day period. Pulse responses (460-Hz carrier with 100-Hz bandwidth) were recorded every 12 min, and temperature at several depths every half hour. Pulses were found to be highly variable in travel time, duration, and shape. The MEDUSA ray tracing eigenray model was used to explain the pulse formation and variation, using the thermister time series as input. Model predictions of pulse responses agree with the data. Positive temperature anomalies bring about long duration pulses, 200 ms, while negative temperature anomalies bring about short duration pulses, 50 ms. The mechanism behind the pulse duration variation was found to be a function of bottom loss, not a focusing effect of the sound-speed profile. Negative temperature anomalies tend to direct grazing eigenrays more steeply into the bottom, causing greater bottom loss to the front end of the pulse. The front end of the 200-ms pulse is “lost” below the noise level and a short duration 50-ms pulse results. [Work supported by ONR.]
The influence of bubbles on sea surface backscatter measurements
Authors: Koenigs Paul D. , Monti Joseph M. , Nuetzel Bernd , Herwig Heinz
Published: October 2005

The results from a recent sea surface acoustic scattering experiment, which was conducted in the North Sea, are presented with accompanying sea surface roughness parameters and subsurface bubble information. The acoustic data were obtained utilizing a high-resolution (narrow beamwidth) pulsed parametric sonar transmitter and conventional receiver. Scattering strength values were obtained as functions of frequency (3–18 kHz) for wind speeds from 2–45 knots. It appears that the backscattering strength at 30° grazing angle is caused by the high-frequency wavenumber spectrum at low wind speeds and by subsurface bubbles at high wind speeds. The backscattering strength shows strong fluctuations in the intermediate region caused by both scattering mechanisms.
Limitations of mechanical structures as wave vector filters
Authors: Hwang Y. F. , Maidanik G.
Published: October 2005

Although the high-wavenumber content in a highly subsonic (low Mach number) turbulent boundary layer (TBL) is known with reasonable certainty, the low-wavenumber content is not. In a wave vector filter chosen and designed to measure the low-wavenumber content of TBL, the major sensitivity region is appropriately placed in that spectral domain. Inevitably, some minor sensitivity regions lie in the high- (convective) wavenumber region. These minor sensitivity regions are then fed by the spectral pressure ridge in the TBL. This feeding may substantially contaminate the measurements. The proper choice and the novel design of a filter is judged, by and large, by its ability to subdue such contamination. In this paper wave vector filters, for measurements of the low-wavenumber content of TBL, as provided by ideal rectangular and circular panels, are compared and contrasted. In this examination, the contamination caused by the high-wavenumber content in the minor sensitivity regions is estimated by simulating it as a low-wavenumber content in the major sensitivity region. These estimated equivalent low-wavenumber contents constitute the lower bounds that the wave vector filters are capable of measuring.
Acoustic levitation in the presence of gravity
Authors: Barmatz M. , Collas P.
Published: October 2005

A theory of acoustic levitation in the presence of gravity has been developed for arbitrarily oriented chambers of rectangular, cylindrical, and spherical geometries. Simultaneous mode excitation was also included in the analysis. Examples of the total potential and force profile will be given for commonly used levitation modes as a function of chamber orientation. Additional levitation positions are obtained within the chamber for appropriately chosen modes and orientations. Levitation positions within a chamber where the acoustic forces are isotropic will be presented for the case of small kR. The effects of mode degeneracy on the total potential and force for the case of the triple axis levitator flown on the Space Shuttle will also be discussed. [Work supported by NASA.]
Theory of oscillational instabilities in acoustic levitators
Authors: Rudnick Joseph , Barmatz M.
Published: October 2005

A general theory describes the oscillational instabilities of an acoustically levitated sample in a resonant cavity. The theory, based on a Green's function method, predicts the onset of instabilities and their saturation. Important factors controlling these instabilities inculde drive frequency, spatial structure of the levitation mode, and the size of the sample. The instability in a zero gravity environment has fundamentally different onset characteristics than in finite gravity. Calculations reveal hysteresis and saturation effects. Many of the present results are consistent with a previously developed empirical model of the instabilities [S. L. Garrett and M. Barmatz, J. Acoust. Soc. Am. Suppl. 1 77, S21 (1985)]. Typical examples of the above effects will be discussed. [Work supported by NASA.]
Eigenfrequencies of a cylindrical cavity with an internal off-axis spherical obstacle
Authors: Barmatz M. , Aveni G. , Mehl James B.
Published: October 2005

A hard spherical obstacle is mounted inside a cylindrical cavity at a variable position. The resonance frequencies of the cavity were determined as a function of the position of the sphere for obstacle positions on and off the axis of the cylinder. The dependence of the resonance frequency on the sphere position is important in analyzing the stability of acoustically levitated samples. The results are in good agreement with theoretical calculations based on the singular perturbation theory of Mehl and Hill. The measurements will also be compared to a new theory that utilizes the Boltzmann-Ehrenfest adiabatic principle to predict the spatial dependence of the acoustic potential from the resonance frequencies. [Work supported by NASA.]
A new acoustic levitation device using the interference sound field generated from two opposed radiators
Authors: Rey Charles A. , Danley Thomas J. , Merkley Dennis R. , Hammarlund Gregory R.
Published: October 2005

A new technique for acoustically levitating a specimen is described. The technique deviates from a previous single-axis acoustic levitation method that utilizes a single-acoustic radiator and a passive reflector to generate the interference produced sound field. The new method involves the use of two opposing focusing acoustic radiators that produce an interference field that has capabilities for the levitation and positioning of small objects or liquid drops. The theoretical predictions regarding this technique are examined and those results are compared with laboratory measurements. The nature of the apparatus and its capabilities is also addressed. [Work supported by NASA.]
Enhancements of acoustic levitation in the presence of increased gas pressure
Authors: Hammarlund Gregory R. , Merkley Dennis R. , Rey Charles A. , Danley Thomas J.
Published: October 2005

Acoustic levitation for containerless materials processing has been investigated for use in the 1-g environment. Enhancements have been obtained by increasing the gas pressure of the acoustic levitation system. Interdependence of gas pressure, sound pressure level, acoustic positioning force, and gas temperature has been measured. Also, nonlinear acoustic effects and harmonic content within the acoustic field are examined as a function of pressure. Finally, results of 1-g acoustic levitation experiments utilizing increased gas pressures are presented. [Work supported by NASA.]
Ear advantages for monaural periodicity detection
Authors: Bashford James A. , Warren Richard M.
Published: October 2005

Monaural asymmetries were found for periodicity detection in experiments using repeated 200-ms segments of Gaussian noise (repetition frequency 5 Hz). In experiment 1, an overall left ear advantage was found for repeated noise delivered monaurally and opposed by contralateral silence. In experiment 2, lateralization of the monaural signal was abolished by simultaneous presentation of on-line noise to the opposite ear (contralateral induction caused the monaural signal to be perceived as centered on the medial plane). Although this manipulation eliminated the possible influence of attentional biases favoring one of the sides, ear advantages were still obtained. Alternative mechanisms will be discussed, including possible asymmetries in active subcortical processing of periodicity information. [Work supported by AFOSR.]
Binaural envelope correlation detection as a function of frequency separation
Authors: Richards Virginia M.
Published: October 2005

Recent comodulation masking release (CMR) experiments suggest that listeners are able to determine whether the envelopes of dichotically presented bands of noise are temporally similar (no signal) or different (signal added to one of the two bands, of noise). In an effort to determine the sensitivity to changes in envelope synchrony as a function of the frequency separation of the two bands of noise, listeners discriminated between noise bands whose envelopes were either identical or statistically independent. The noise bands were 100 Hz wide. The band presented to the left ear was centered at 2625 Hz; the band presented to the fight ear was centered at values between 2625 and 5250 Hz. Although there were considerable individual differences, discriminations tended to be best when both noise bands were centered at 2625 Hz. Increasing the frequency separation between the two bands of noise led to poorer performance, but the percentage of correct responses remained above 60. Subsequent experiments indicate that the discrimination is based on envelope similarity rather than the similarity of the power spectrum. [Research supported by NIH.]
Effects of forward masker fringe on binaural detection
Authors: Simpson B. D. , Gilkey R. H.
Published: October 2005

Yost [J. Acoust. Soc. Am. 78, 901–907 (1985)] found that detectability of a 20-ms dichotic signal (Sπ) in a 20-ms diotic noise (No) was not affected by the presence of a 500-ms dichotic forward fringe (Nπ). However, Kollmeier and Gilkey [J. Acoust. Soc. Am. Suppl. 1 74, S39 (1982)] varied the onset time of a 20-ms Sπ signal in a 750-ms noise that switched, after 375 ms, from Nπ to No, and found that the Nπ noise reduced detectability even when the signal was well into the No noise. They concluded that the Nπ noise acted as a forward masker. The present study investigates detectability of a 500-Hz, 20-ms Sπ signal in a 20-ms No masker as a function of the signal onset time. The masker is preceded by quiet or an Nπ forward fringe and followed by quiet, an No, or Nπ backward fringe. Overall, the results are compatible with a forward masking interpretation. Further, when the signal onset is simultaneous with the onset of the 20-ms masker, the Nπ forward fringe reduces detectability. [Work supported by NSF and AFOSR.]
Further research on free-field masking
Authors: Gatehouse R. Wayne
Published: October 2005

Gatehouse (Proc. 12th Int. Congr. Acoust., B2-7, 1986) compared free-field masked and unmasked thresholds (two-alternative forced-choice procedure) with a WN masker fixed at 0° while 5 tonal probes were delivered from 11 frontal plane positions. Masking was not necessarily greatest for masker-signal coincidence but varied with frequency and signal position. For 1.0- and 2.5- kHz signals, detectability was best and approximately equal at 0° and + 90°, while for the others (0.25, 0.5, and 4.0 kHz) there were generally lower thresholds as signal and masker separated. The task was repeated now with 0.5-, 1.0-, and 2.0-kHz probes and the masker set at 0° and + 45°. Again, free-field masking varied with both signal position and frequency, and best and least detection was not solely determined by azimuthal separation of the masker and signal. On average, masking level differences were approximately 24.0 dB for 0.5-, 11.5 dB for 1.0-, and 13.5 dB for 2.0-kHz signals. The apparent differences between earphone-derived and free-field masked thresholds, which seem more subject to frequency and positional variations, will be discussed.
Resolution of pairs of simple and complex sounds in simulated auditory space
Authors: Divenyi Pierre L. , Oliver Susan K.
Published: October 2005

A simulated acoustic replica of a sound source moving along a circle with a 4-m radius in the frontal horizontal half-plane was generated by obtaining, in 5-deg azimuthal steps, external ear transfer functions for both ears of an artificial head placed in an anechoic room. When an arbitrary sound is passed through the digital filter defined by the left and right transfer functions corresponding to a given angle, the sound will acquire a subjective azimuth comparable to which the transfer function was measured [J. Blauert and P. Laws, Acustica 29, 273–277 (1973)]. This technique was used to measure resolution thresholds for pairs of amplitude-modulated as well as pure sinusoids. With the listener required to identify the relative location of the two sounds in a two-alternative forced-choice paradigm, in one set of experiments the two sounds were fixed and the minimum audible angular separation was obtained, whereas, in another set, the angular separation was fixed and the minimum modulation- or carrier-frequency separation was measured. Generally, both kinds of resolution are better around 0 azimuth than at the sides: In the “auditory fovea,” simultaneous resolution for pure tones and AM sounds (a 3- or 6-kHz carrier sinusoidally modulated in the 150- to 400-Hz range) is almost as good as the jnd obtained in the usual sequential presentation. The poorest spatial resolution was obtained for a pair of 6-kHz carriers modulated by a 100- and a 400-Hz sinusoid and the best for pairs of AM tones with different carriers. [Work supported by the Veterans Administration and by a NATO Travel Fellowship.]
The enhancement of binaural source location by scuba divers
Authors: Glegg Stewart A. L. , Kloske John , Hansen Chris , Johnson Terry R.
Published: October 2005

This paper will describe the development of a passive source localization device to enhance the ability of scuba divers to locate acoustic sources. The device consists of a hat that is worn by the scuba divers and provides a distinct null in the observed acoustic field when the diver is facing the acoustic source. Tests were carried out in a 25-ft-deep, 198-ft-diam tank at the EPCOT Center in Orlando, FL on 25 subjects. The results of these tests show that there is a clear improvement using this device, which is comfortable to wear and suitable for most applications.