bluuebunny/crossref_metadata_2025 huggingface dataset:
The Efficacy of a Home‐Based Nursing Program in Diabetic Control of Elderly People with Diabetes Mellitus Living Alone
Authors: Huang Chun‐Lien , Wu Shiao‐Chi , Jeng Chii‐Yuan , Lin Li‐Chan
Published: January 2004

Abstract  The purpose of this study was to evaluate the efficacy of a home‐based nursing program in the diabetic control of elderly people with diabetes mellitus living alone. Patients meeting the sampling criteria were recruited from a medical center and 10 health centers in Taipei for this quasi‐experimental study. By matching the effects of age, sex, education, and history of diabetes, subjects were assigned semirandomly to two groups based on the intensity of home‐based nursing care visitations. Group I was defined as daily visits to supervise diet, exercise, medication, and self‐monitoring blood sugar (n = 15) and Group II as weekly visits to supervise diet, exercise, medication education, and self‐monitoring blood sugar (n = 15). Patients who agreed only to receive blood examination were assigned to the control group (n = 14). The results of the study showed that reductions in fasting blood sugar, postmeal blood sugar, and hemoglobin A1c (HbA1c) in Groups I and II were significantly greater than those in the control group. The reduction in the total cholesterol and low‐density lipoprotein in Groups I and II was significantly greater than that in the control group. There were no significant differences among the three groups in the improvement of high‐density lipoprotein (HDL) and triglycerides (TGs). Group I revealed a significantly greater weight reduction compared to Group II. There was no significant difference between Groups I and II in the improvements of diabetes knowledge, depression level, or quality of life. From the research findings, based on cost‐effectiveness, it is recommend that Program II be implemented.
Public Health Education and Practice Using Geographic Information System Technology
Authors: Riner Mary E. , Cunningham Cynthia , Johnson Ann
Published: January 2004

Abstract  The use of geographic information system (GIS) technology allows public health practitioners to explore disparities in health, analyze disease outbreaks, and prioritize the use of limited resources for improving population health. Nursing students benefit from use of World Wide Web GIS resources as they develop knowledge and skill in assessing population health and planning interventions. This article identifies the benefits of GIS for public health practitioners, presents a communicable disease control application of GIS, and discusses a GIS module used in an undergraduate nursing education course. Uniform standards for making health data available for public use with GIS are discussed.
Analysis of Asymmetric Nonviscously Damped Linear Dynamic Systems
Authors: Adhikari S. , Wagner N.
Published: January 2004

Multiple-degree-of-freedom linear asymmetric nonviscously damped systems are considered. It is assumed that the nonviscous damping forces depend on the past history of velocities via convolution integrals over exponentially decaying kernel functions. An extended state-space approach involving a single asymmetric matrix is proposed. The nature of the eigensolutions in the extended state space has been explored. Some useful results relating the modal matrix in the extended state space and the modal matrix in the original space has been derived. Numerical examples are provided to illustrate the results.
The Interaction of Two Spherical Gas Bubbles in an Infinite Elastic Solid
Authors: Chalon F. , Montheillet F.
Published: January 2004

The elastic strain and stress fields between two bubbles of different sizes and different pressures were estimated by using the fundamental result of Eshelby. The equivalent inclusion method was extended to the case of two inclusions in an infinite elastic solid. This approach, which remains totally analytical, was compared successfully to finite element calculations. The mean stress provides information about gas diffusion between the bubbles: according to the results, the bubbles are likely to progressively equalize their sizes. Moreover, the derivation of the von Mises equivalent stress showed that its value, in the vicinity of the bubbles, is larger than the elasticity limit. Therefore, for a complete mechanical description of the problem, plasticity should be taken into account. In spite of its simplicity, this method nevertheless leads to results, which are very close to the prediction of numerical calculations.
Modeling Air Entrainment and Temperature Effects in Winding
Authors: Lei H. , Cole K. A. , Weinstein S. J.
Published: January 2004

Rolls of films and paper are routinely stored under varying conditions before being unwound into downstream operations. During storage, interlayer pressures can change relative to the pressures generated during winding. These changes can lead to problems such as film/paper blocking (increased interlayer pressure) and roll shifting/cinching (decreased interlayer pressure). To study the storage effect, a nonlinear wound roll stress model including air entrainment is first developed and applied to predict the in-roll stresses during film/paper winding. Thereafter, a thermal stress model is used to study the temperature effect on wound roll stresses. Key inputs to the models are the stack modulus, contact clearance, and air film reference clearance. A method is developed to measure these key model inputs. Results of a parametric study show that among the processing conditions, storage temperature and thermal expansion coefficients of the core and the film/paper are key factors that affect in-roll stresses during storage. Limitations of the models will also be discussed along with recommendations for future modeling development.
Novel Boundary Integral Equations for Two-Dimensional Isotropic Elasticity: An Application to Evaluation of the In-Boundary Stress
Authors: Manticˇ V. , Calzado F. J. , Pari´s F.
Published: January 2004

A new nonsingular system of boundary integral equations (BIEs) of the second kind for two-dimensional isotropic elasticity is deduced following a recently introduced procedure by Wu (J. Appl. Mech., 67, pp. 618–621, 2000) originally applied for anisotropic elasticity. The physical interpretation of the new integral kernels appearing in these BIEs is studied. An advantageous application of one of these BIEs as a boundary integral representation (BIR) of tangential derivative of boundary displacements on smooth parts of the boundary, and subsequently as a BIR of the in-boundary stress, is presented and analyzed in numerical examples. An equivalent BIR obtained by an integration by parts of the integral including tangential derivative of displacements in the former BIR is presented and analyzed as well. The resulting integral is only apparently hypersingular, being in fact a regular integral on smooth parts of the boundary.
Crushing of an Elastic-Plastic Ring Between Rigid Plates With and Without Unloading
Authors: McDevitt T. J. , Simmonds J. G.
Published: January 2004

Load-deflection curves are computed for an elastic-plastic ring that is slowly crushed between frictionless, rigid plates (platens). The ring is assumed to be inextensional with plane sections remaining plane and to obey a bi-linear stress-strain law with isotropic hardening. These assumptions lead to a local nonlinear moment-curvature relation identical to that developed by Liu et al. When inserted into the exact equation for moment equilibrium, this constitutive relation yields a second-order, nonlinear ordinary differential equation for the angle α between the deformed centerline of the ring and the horizontal. The numerical solution of this equation, which uses a combined penalty-continuation method, along with an auxiliary equation relating the vertical deflection to α, leads to overall load-deflection curves that depend on two dimensionless parameters, λ and μ. The first is the ratio of the plastic modulus to the elastic modulus; the second measures the ratio of plastic to elastic effects. As μ→0, the overall load-deflection curve of Frish-Fay for the elastica is recovered; as μ→∞, that of DeRuntz and Hodge for a rigid-perfectly plastic ring is recovered. Three scenarios are considered: I0, in which an initially straight, stress-free beam is bent elastically into a ring and then crushed; II0, in which an initially stress-free ring is crushed; and III0, in which an initially straight beam is bent first elastically and then elastically-plastically into a ring and then crushed. Results for scenario II0 are shown to agree well with experiments of Reddy and Reid if λ=0.01 and μ=10 and 20 and with experiments of Avalle and Goglio if λ=0.02 and μ=11. In scenarios I0 and II0, the effects of unloading prove to be small, reinforcing a similar conclusion of Liu et al., who considered the large-deflection of an elastic-plastic cantilever under a tip load. If no unloading is assumed, a more analytical treatment is possible, as shown in the second part of the present paper. The model predicts that the ring always remains in full contact with the platens, in agreement with recent experiments by Avalle and Goglio on annealed aluminum tubes. Pull-away from the platens also observed in experiments is ascribed to end effects which cannot be modeled by a one-dimensional beam theory. However, it is argued that, even if there is pull-away, the effect on the overall force-deflection relation must be small because in both cases the forces exerted by the platens are concentrated at the ends of the contact region. Moving pictures of successive stages of deformation of the ring showing the formation of plastic loading and unloading zones in all three scenarios may be found on the web site www.people.virginia.edu/∼jgs/ring.html.
Fatigue of Bovine Trabecular Bone
Authors: Moore Tara L. A. , Gibson Lorna J.
Published: January 2004

Fatigue loading of bone, from the activities of daily living in the elderly, or from prolonged exercise in the young, can lead to increased risk of fracture. Elderly patients with osteoporosis are particularly prone to fragility fractures of the vertebrae, where load is carried primarily by trabecular bone. In this study, specimens of bovine trabecular bone were loaded in compressive fatigue at four different normalized stresses to one of six maximum strains. The resulting change in modulus and residual strain accumulation were measured over the life of the fatigue test. The number of cycles to reach a given maximum compressive strain increased with decreasing normalized stress. Modulus reduction and specimen residual strain increased with increasing maximum compressive strain, but few differences were observed between specimens loaded to the same maximum strain at different normalized stresses.
Fatigue Microdamage in Bovine Trabecular Bone
Authors: Moore Tara L. A. , Gibson Lorna J.
Published: January 2004

Microdamage, in the form of small cracks, may accumulate in trabecular bone loaded in fatigue. Specimens of bovine trabecular bone were loaded in compressive fatigue at one of four normalized stresses and loading was stopped after the specimens reached one of six maximum strains. Microdamage was identified using a fluorochrome staining technique, and microdamage parameters, including the number of damaged trabeculae and the damaged area fraction, were measured. No microdamage was observed during loading to strains below the yield strain; at higher strains, all microdamage parameters increased with increasing maximum compressive strain. Few significant differences were observed in the type or amount of microdamage accumulation between specimens loaded to the same maximum strain at different normalized stresses; however, more trabecular fractures were observed at high numbers of cycles, which corresponded to low normalized stresses.
3-D Model of a Total Hip Replacement In Vivo Providing Hydrodynamic Pressure and Film Thickness for Walking and Bicycling
Authors: Meyer, Donna M. , Tichy, John A.
Published: January 2004

Formulation of a 3-D lubrication simulation of a total hip replacement in vivo is presented using a finite difference approach. The goal is to determine if hydrodynamic lubrication is taking place, how thick the joint fluid film is and over what percentage of two gait cycles, (walking and bicycling), the hydrodynamic lubricating action is occurring, if at all. The assumption of rigid surfaces is made, which is conservative in the sense that pure hydrodynamic lubrication is well known to predict thinner films than elastohydrodynamic lubrication (EHL) for the same loading. The simulation method includes addressing the angular velocity direction changes and accurate geometry configuration for the acetabular cup and femoral head components and provides a range of results for material combinations of CoCrMo-on-UHMWPE, CoCrMo-on-CoCrMo, and alumina-on-alumina components. Results are in the form of the joint fluid film pressure distributions, load components and film thicknesses of the joint fluid, for the gait cycles of walking and bicycling. Results show hydrodynamic action occurs in only about 10% of a walking gait cycle and throughout nearly 90% of a bicycling gait. During the 10% of the walking cycle that develops hydrodynamic lubrication, the minimum fluid film thicknesses are determined to be between 0.05 μm and 1.1 μm, while the range of film thicknesses for bicycling is between 0.1 μm and 1.4 μm, and occurs over 90% of the bicycling gait. Pressure distributions for these same periods are in the range of 2 MPa to 870 MPa for walking and 1 MPa to 24 MPa for bicycling.
Kinetics Study of Endogenous Heat Shock Protein 70 Expression
Authors: Wang Sihong , Diller Kenneth R. , Aggarwal Shanti J.
Published: January 2004

The purpose of this study was to determine the kinetics of HSP70 expression in response to mild thermal stress. The rationale is to produce a basis for design of optimal heating methods to induce HSP70 expression for preconditioning in cardiac surgery. Bovine aortic endothelial cells were heated at 42°C for 0.5 to 5 hours followed by 37°C recovery for 1 to 48 hours. Quantitative analysis of western blot results showed HSP70 expression kinetics is a coupled function of heating temperature and time and of post-heating duration. Bimodal HSP70 expression kinetics were identified which may be an important cause of the “second window of protection” observed by other researchers.
Computational Fluid Dynamics Simulations in Realistic 3-D Geometries of the Total Cavopulmonary Anastomosis: The Influence of the Inferior Caval Anastomosis
Authors: Migliavacca Francesco , Dubini Gabriele , Bove Edward L. , de Leval Marc R.
Published: January 2004

Fluid dynamics of Total Cavo-Pulmonary Connection (TCPC) were studied in 3-D models based on real dimensions obtained by Magnetic Resonance (MR) images. Models differ in terms of shape (intra- or extra-cardiac conduit) and cross section (with or without patch enlargement) of the inferior caval (IVC) anastomosis connection. Realistic pulsatile flows were submitted to both the venae cavae, while porous portions were added at the end of the pulmonary arteries to reproduce the pulmonary afterload. The dissipated power and the flow distribution into the lungs were calculated at different values of pulmonary arteriolar resistances (PAR). The most important results are: i) power dissipation in different TCPC designs is influenced by the actual cross sectional area of the IVC anastomosis and ii) the inclusion of a patch minimizes the dissipated power (range 4–13 mW vs. 14–56 mW). Results also show that the perfusion of the right lung is between 15% and 30% of the whole IVC blood flow when the PAR are evenly distributed between the right and the left lung.
Harmonic Analysis of Perfusion Pumps
Authors: Dougherty F. Carroll , Donovan, F. M. , Townsley Mary I.
Published: January 2004

The controversy over the use of nonpulsatile versus pulsatile pumps for maintenance of normal organ function during ex vivo perfusion has continued for many years, but resolution has been limited by lack of a congruent mathematical definition of pulsatility. We hypothesized that the waveform frequency and amplitude, as well as the underlying mean distending pressure are all key parameters controlling vascular function. Using discrete Fourier Analysis, our data demonstrate the complexity of the pulmonary arterial pressure waveform in vivo and the failure of commonly available perfusion pumps to mimic in vivo dynamics. In addition, our data show that the key harmonic signatures are intrinsic to the perfusion pumps, are similar for flow and pressure waveforms, and are unchanged by characteristics of the downstream perfusion circuit or perfusate viscosity.
An Asymptotic Model of Unsteady Airway Reopening
Authors: Naire S. , Jensen O. E.
Published: January 2004

We consider a simple physical model for the reopening of a collapsed lung airway involving the unsteady propagation of a long bubble of air, driven at a prescribed flow-rate, into a liquid-filled channel formed by two flexible membranes that are held under large longitudinal tension and are confined between two parallel rigid plates. This system is described theoretically using an asymptotic approximation, valid for uniformly small membrane slopes, which reduces to a fourth-order nonlinear evolution equation for the channel width ahead of the bubble tip, from which the time-evolution of the bubble pressure pb* and bubble speed may be determined. The model shows that there can be a substantial delay between the time at which the bubble starts to grow in volume and the time at which its tip starts to move. Under certain conditions, the start of the bubble’s motion is accompanied by a transient overshoot in pb*, as seen previously in experiment; the model predicts that the overshoot is greatest in narrow channels when the bubble is driven with a large volume flux. It is also shown how the threshold pressure for steady bubble propagation in wide channels has distinct contributions from the capillary pressure drop across the bubble tip and viscous dissipation in the channel ahead of the bubble.
Modeling of Microstructural Kinematics During Simple Elongation of Central Nervous System Tissue
Authors: Bain Allison C. , Shreiber David I. , Meaney David F.
Published: January 2004

Damage to axons and glial cells in the central nervous system (CNS) white matter is a nearly universal feature of traumatic brain injury, yet it is not clear how the tissue mechanical deformations are transferred to the cellular components of the CNS. Defining how cellular deformations relate to the applied tissue deformation field can both highlight cellular populations at risk for mechanical injury, and define the fraction of cells in a specific population that will exhibit damage. In this investigation, microstructurally based models of CNS white matter were developed and tested against measured transformations of the CNS tissue microstructure under simple elongation. Results show that axons in the unstretched optic nerves were significantly wavy or undulated, where the measured axonal path length was greater than the end-to-end distance of the axon. The average undulation parameter—defined as the true axonal length divided by the end-to-end length—was 1.13. In stretched nerves, mean axonal undulations decreased with increasing applied stretch ratio (λ)—the mean undulation values decreased to 1.06 at λ=1.06, 1.04 at λ=1.12, and 1.02 at λ=1.25. A model describing the gradual coupling, or tethering, of the axons to the surrounding glial cells best fit the experimental data. These modeling efforts indicate the fraction of the axonal and glial populations experiencing deformation increases with applied elongation, consistent with the observation that both axonal and glial cell injury increases at higher levels of white matter injury. Ultimately, these results can be used in conjunction with computational simulations of traumatic brain injury to aid in establishing the relative risk of cellular structures in the CNS white matter to mechanical injury.
Development and Validation of a 3-D Model to Predict Knee Joint Loading During Dynamic Movement
Authors: McLean S. G. , Su A. , van den Bogert A. J.
Published: January 2004

The purpose of this study was to develop a subject-specific 3-D model of the lower extremity to predict neuromuscular control effects on 3-D knee joint loading during movements that can potentially cause injury to the anterior cruciate ligament (ACL) in the knee. The simulation consisted of a forward dynamic 3-D musculoskeletal model of the lower extremity, scaled to represent a specific subject. Inputs of the model were the initial position and velocity of the skeletal elements, and the muscle stimulation patterns. Outputs of the model were movement and ground reaction forces, as well as resultant 3-D forces and moments acting across the knee joint. An optimization method was established to find muscle stimulation patterns that best reproduced the subject’s movement and ground reaction forces during a sidestepping task. The optimized model produced movements and forces that were generally within one standard deviation of the measured subject data. Resultant knee joint loading variables extracted from the optimized model were comparable to those reported in the literature. The ability of the model to successfully predict the subject’s response to altered initial conditions was quantified and found acceptable for use of the model to investigate the effect of altered neuromuscular control on knee joint loading during sidestepping. Monte Carlo simulations (N=100,000) using randomly perturbed initial kinematic conditions, based on the subject’s variability, resulted in peak anterior force, valgus torque and internal torque values of 378 N, 94 Nm and 71 Nm, respectively, large enough to cause ACL rupture. We conclude that the procedures described in this paper were successful in creating valid simulations of normal movement, and in simulating injuries that are caused by perturbed neuromuscular control.
Improving Elbow Torque Output of Stroke Patients with Assistive Torque Controlled by EMG Signals
Authors: Cheng Hang-Shing , Ju Ming-Shaung , Lin Chou-Ching K.
Published: January 2004

This paper develops an assistive torque system which uses homogenic surface electromyogram (EMG) signals to improve the elbow torque capability of stroke patients by applying an external time-varying assistive torque. In determining the magnitude of the torque to apply, the incorporated assistive torque algorithm considers the difference between the weighted biceps and triceps EMG signals such that the applied torque is proportional to the effort supplied voluntarily by the user. The overall stability of the assistive system is enhanced by the incorporation of a nonlinear damping element within the control algorithm which mimics the physiological damping of the elbow joint and the co-contraction between the biceps and triceps. Adaptive filtering of the control signal is employed to achieve a balance between the bandwidth and the system adaptability so as to ensure a smooth assistive torque output. The innovative control algorithm enables the provision of an assistive system whose operation is both natural to use and simple to learn. The effectiveness of the proposed assistive system in assisting elbow movement performance is investigated in a series of tests involving five stroke patients and five able-bodied individuals. The results confirm the ability of the system to assist all of the subjects in performing a number of reaching and tracking tasks with reduced effort and with no sacrifice in elbow movement performance.
Effects of Cyclic Stress on the Mechanical Properties of Cultured Collagen Fascicles from the Rabbit Patellar Tendon
Authors: Yamamoto Ei , Tokura Susumu , Hayashi Kozaburo
Published: January 2004

Effects of cyclic stress on the mechanical properties of collagen fascicles were studied by in vitro tissue culture experiments. Collagen fascicles (approximately 300 μm in diameter) obtained from the rabbit patellar tendon were applied cyclic load at 4 Hz for one hour per day during culture period for one or two weeks, and then their mechanical properties were determined using a micro-tensile tester. There was a statistically significant correlation between tensile strength and applied peak stress in the range of 0 to 5 MPa, and the relation was expressed by a quadratic function. The maximum strength (19.4 MPa) was obtained at the applied peak stress of 1.8 MPa. The tensile strength of fascicles were within a range of control values, if they were cultured under peak stresses between 1.1 and 2.6 MPa. Similar results were also observed in the tangent modulus, which was maintained at control level under applied peak stresses between 0.9 and 2.8 MPa. The stress of 0.9 to 1.1 MPa is equivalent to approximately 40% of the in vivo peak stress which is developed in the intact rabbit patellar tendon by running, whereas that of 2.6 to 2.8 MPa corresponds to approximately 120% of the in vivo peak stress. Therefore, the fascicles cultured under applied peak stresses of lower than 40% and higher than 120% of the in vivo peak stress do not keep the original strength and modulus. These results indicate that the mechanical properties of cultured collagen fascicles strongly depend upon the magnitude of the stress applied during culture, which are similar to our previous results observed in stress-shielded and overstressed patellar tendons in vivo.
Finite-Element Simulation of Cooling of Realistic 3-D Human Head and Neck
Authors: Dennis Brian H. , Eberhart Robert C. , Dulikravich George S. , Radons Steve W.
Published: January 2004

Rapid cooling of the brain in the first minutes following the onset of cerebral ischemia is a potentially attractive preservation method. This computer modeling study was undertaken to examine brain-cooling profiles in response to various external cooling methods and protocols, in order to guide the development of cooling devices suitable for deployment on emergency medical vehicles. The criterion of successful cooling is taken to be the attainment of a 33°C average brain temperature within 30 min of treatment. The transient cooling of an anatomically correct realistic 3-D head and neck with realistically varying local tissue properties was numerically simulated using the finite-element method (FEM). The simulations performed in this study consider ice packs applied to head and neck as well as using a head-cooling helmet. However, it was found that neither of these cooling approaches satisfies the 33°C temperature within 30 min. This central conclusion of insubstantial cooling is supported by the modest enhancements reported in experimental investigations of externally applied cooling. The key problem is overcoming the protective effect of warm blood perfusion, which reaches the brain via the uncooled carotid arterial supply and effectively blocks the external cooling wave from advancing to the core of the brain. The results show that substantial cooling could be achieved in conjunction with neck cooling if the blood speed in the carotid artery is reduced from normal by a factor of 10. The results suggest that additional cooling means should be explored, such as cooling of other pertinent parts of the human anatomy.
Blood Flow in Small Curved Tubes
Authors: Wang C. Y. , Bassingthwaighte J. B.
Published: January 2004

Blood flow in small curved tubes is modeled by the two-fluid model where a relatively cell-free fluid layer envelops a fluid core of higher viscosity. The parameters in the model are successfully curve fitted to experimental data for straight tubes. The curved tube equations are then solved by perturbation theory. It was found that curvature in general lowers the tube resistance, but increases the shear stress near the inside wall.
A Novel Device to Evaluate the Stiffness of Ankle-Foot Orthosis Devices
Authors: Cappa, P. , Patane`, F. , Pierro M. M.
Published: January 2004

The evaluation of mechanical behavior of plastic Ankle-Foot Orthosis (AFO) is important since AFO can provide an efficient support to patients with disabilities in locomotion. This paper reports on a novel testing apparatus that allows: (a) the evaluation of AFO stiffness in sagittal and frontal planes; (b) the conduction of semi-automatic trials; and, finally, (c) a global accuracy associated to the AFO stiffness values always less than 4%. The stiffness values are determined by the measurements of the imposed relative displacements between the foot and the shank of the orthosis and the induced reaction forces. The data collected together in an exact 2-D approach, together with those provided by gait analysis systems, allows to better understand gait alteration induced by ankle orthosis, and to improve clinical management of patients.
The Influence of Inflow Boundary Conditions on Intra Left Ventricle Flow Predictions
Authors: Long, Q. , Merrifield, R. , Yang, and G. Z. , Xu X. Y. , Kilner and P. J. , Firmin D. N.
Published: January 2004

The combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) offers a promising tool that enables the prediction of blood flow patterns in subject-specific cardiovascular models. The influence of the model geometry on the accuracy of the simulation is well recognized. This paper addresses the impact of different boundary conditions on subject-specific simulations of left ventricular (LV) flow. A novel hybrid method for prescribing effective inflow boundary conditions in the mitral valve plane has been developed. The detailed quantitative results highlight the strengths as well as the potential pitfalls of the approach.
Nonlinear synthesis of input signals in ultrasonic experimental setups
Authors: Conil Frédéric , Gibert Dominique , Nicollin Florence
Published: January 2004

A method is proposed to find the digital input signals to enter in nonlinear acoustical systems (power amplifiers, transducers, etc.) in order to obtain desired arbitrary response signals. The searched input signals are found by performing a Monte Carlo search guided by a simulated annealing process applied to a hidden model with a small number of parameters. The physical system is actually used in the optimization procedure, in a real-time manner, so that no theoretical model of the system response is required. The main aspects of the algorithm are described and illustrated with several examples.
Inversion of guided-wave dispersion data with application to borehole acoustics
Authors: Braunisch Henning , Habashy Tarek M. , Sinha Bikash K. , Pabon Jahir , Kong Jin A.
Published: January 2004

The problem of inferring unknown geometry and material parameters of a waveguide model from noisy samples of the associated modal dispersion curves is considered. In a significant reduction of the complexity of a common inversion methodology, the inner of two nested iterations is eliminated: The approach described does not employ explicit fitting of the data to computed dispersion curves. Instead, the unknown parameters are adjusted to minimize a cost function derived directly from the determinant of the boundary condition system matrix. This results in an efficient inversion scheme that, in the case of noise-free data, yields exact results. Multimode data can be simultaneously processed without extra complications. Furthermore, the inversion scheme can accommodate an arbitrary number of unknown parameters, provided that the data have sufficient sensitivity to these parameters. As an important application, we consider the sonic guidance condition for a fluid-filled borehole in an elastic, homogeneous, and isotropic rock formation for numerical forward and inverse dispersion analysis. We investigate numerically the parametric inversion with errors in the model parameters and the influence of bandwidth and noise, and examine the cases of multifrequency and multimode data, using simulated flexural and Stoneley dispersion data.
The diffraction of sound by an impedance sphere in the vicinity of a ground surface
Authors: Li Kai Ming , Lui Wai Keung , Frommer Glenn H
Published: January 2004

The problem of sound diffraction by an absorbing sphere due to a monopole point source was investigated. The theoretical models were extended to consider the case of sound diffraction by an absorbing sphere with a locally reacting boundary or an extended reaction boundary placed above an outdoor ground surface of finite impedance. The separation of variables techniques and appropriate wave field expansions were used to derive the analytical solutions. By adopting an image method, the solutions could be formulated to account for the multiple scattering of sound between the sphere and its image near a flat acoustically hard or an impedance ground. The effect of ground on the reflected sound fields was incorporated in the theoretical model by employing an approximate analytical solution known as the Weyl–van der Pol formula. An approximation solution was suggested to determine the scattering coefficients from a set of linearly coupled complex equations for an absorbing sphere not too close to the ground. The approximate method substantially reduced the computational time for calculating the sound field. Preliminary measurements were conducted to characterize the acoustical properties of an absorbing sphere made of open cell polyurethane foam. Subsequent experiments were carried out to demonstrate the validity of the proposed theoretical models for various source/receiver configurations around the sphere above an acoustically hard ground and an impedance ground. Satisfactory comparative results were obtained between the theoretical predictions and experimental data. It was found that the theoretical predictions derived from the approximate solution agreed well with the results obtained by using the exact solutions.
Within-ear and across-ear interference in a dichotic cocktail party listening task: Effects of masker uncertainty
Authors: Brungart Douglas S. , Simpson Brian D.
Published: January 2004

Increases in masker variability have been shown to increase the effects of informational masking in non-speech listening tasks, but relatively little is known about the influence that masker uncertainty has on the informational components of speech-on-speech masking. In this experiment, listeners were asked to extract information from a target phrase that was presented in their right ear while ignoring masking phrases that were presented in the same ear as the target phrase and in the ear opposite the target phrase. The level of masker uncertainty was varied by holding constant or “freezing” the talkers speaking the masking phrases, the semantic content used in the masking phrases, or both the talkers and the semantic content in the masking phrases within each block of 120 trials. The results showed that freezing the semantic content of the masking phrase in the target ear was the only reduction in masker uncertainty that ever resulted in a significant improvement in performance. Providing feedback after each trial improved performance overall, but did not prevent the listeners from making incorrect responses that matched the content of the frozen target-ear masking phrase. However, removing the target-ear contents corresponding to the masking phrase from the response set resulted in a dramatic improvement in performance. This suggests that the listeners were generally able to understand both of the phrases presented to the target ear, and that their incorrect responses in the task were almost entirely a result of their inability to determine which words were spoken by the target talker.
Acoustic cavity modes in lens-shaped structures
Authors: Willatzen M. , Lew Yan Voon L. C.
Published: January 2004

A method for solving exactly the Helmholtz equation in parabolic rotational coordinates is presented using separability of the eigenfunctions and the Frobenius power series expansion technique. Two examples of interest in acoustics are considered and analyzed quasianalytically: The acoustic pressure in a cavity defined by two paraboloids (forming a lens-shaped structure) with (I) rigid wall boundary conditions and (II) pressure-release boundaries. The rigid-wall (pressure-release) acoustic enclosure problem is a Neumann (Dirichlet) boundary condition problem. In both cases, eigenfunctions and eigenmodes are calculated and the shape dependence of the eigenvalue for the ground state is examined.
Interaction of a scanning laser-generated ultrasonic line source with a surface-breaking flaw
Authors: Sohn Younghoon , Krishnaswamy Sridhar
Published: January 2004

The scanning laser source (SLS) technique has been proposed recently as an effective way to investigate small surface-breaking cracks. By monitoring the amplitude and frequency changes of the ultrasound generated as the SLS scans over a defect, the SLS technique has provided enhanced signal-to-noise performance compared to the traditional pitch–catch or pulse–echo ultrasonic methods. In previous work, either a point source or a short line source was used for generation of ultrasound. The resulting Rayleigh wave was typically bipolar in nature. In this paper, a scanning laser line source (SLLS) technique using a true thermoelastic line source (which leads to generation of monopolar surface waves) is demonstrated experimentally and through numerical simulation. Experiments are performed using a line-focused Nd:YAG laser and interferometric detection. For the numerical simulation, a hybrid model combining a mass-spring lattice method (MSLM) and a finite difference method (FDM) is used. As the SLLS is scanned over a surface-breaking flaw, it is shown both experimentally and numerically that the monopolar Rayleigh wave becomes bipolar, dramatically indicating the presence of the flaw.
Propagation of ultrasonic guided waves in lap-shear adhesive joints: Case of incident a0 Lamb wave
Authors: Lanza di Scalea Francesco , Rizzo Piervincenzo , Marzani Alessandro
Published: January 2004

This paper deals with the propagation of ultrasonic guided waves in adhesively bonded lap–shear joints. The topic is relevant to bond inspection by ultrasonic testing. Specifically, the propagation of the lowest-order, antisymmetric a0 mode through the joint is examined. An important aspect is the mode conversion at the boundaries between the single-plate adherents and the multilayer overlap. The a0 strength of transmission is studied for three different bond states in aluminum joints, namely a fully cured adhesive bond, a poorly cured adhesive bond, and a slip bond. Theoretical predictions indicate that the dispersive behavior of the guided waves in the multilayer overlap is highly dependent on bond state. Experimental tests are conducted in lap–shear joints by a hybrid, broadband laser/air-coupled ultrasonic setup in a through-transmission configuration. The Gabor wavelet transform is employed to extract energy transmission coefficients in the 100 kHz 1.4 MHz range for the three different bond states examined. The cross-sectional mode shapes of the guided waves are shown to have a substantial role in the energy transfer through the joint.
Hybrid near-field acoustic holography
Authors: Wu Sean F.
Published: January 2004

Hybrid near-field acoustical holography (NAH) is developed for reconstructing acoustic radiation from an arbitrary object in a cost-effective manner. This hybrid NAH is derived from a modified Helmholtz equation least squares (HELS) formula that expands the acoustic pressure in terms of outgoing and incoming waves. The expansion coefficients are determined by solving an overdetermined linear system of equations obtained by matching the assumed-form solution to measured acoustic pressures through the least squares. Measurements are taken over a conformal surface around a source at close range so that the evanescent waves can be captured. Next, the modified HELS is utilized to regenerate as much acoustic pressures on the conformal surface as necessary and take them as input to the Helmholtz integral formulation implemented numerically by boundary element method (BEM). The acoustic pressures and normal velocities on the source surface are reconstructed by using a modified Tikhnov regularization (TR) with its regularization parameter determined by generalized cross validation (GCV) method. Results demonstrate that this hybrid NAH combines the advantages of HELS and inverse BEM. This is because a majority of the input data are regenerated but not measured, thus the efficiency of reconstruction is greatly enhanced. Meanwhile, the accuracy of reconstruction is ensured by the Helmholtz integral theory and modified TR together with GCV method, provided that HELS converges fast enough on the measurement surface. Numerical examples of reconstructing acoustic quantities on the surface of a simplified engine block are demonstrated. [Work supported by NSF.]
Application of theoretical modeling to multichannel active control of cooling fan noise
Authors: Gee Kent L. , Sommerfeldt Scott D.
Published: January 2004

Multichannel active control has been applied to the global reduction of tonal noise from a cooling fan. In order to achieve consistent far-field attenuation of multiple harmonics of the blade passage frequency (BPF) of the fan, an analytical model has been applied to the control system in order to determine appropriate transducer configurations. The results of the modeling show that the additional global reduction possible by locating acoustically compact secondary sources coplanar with a compact primary source rapidly lessens as the number of symmetrically placed sources is increased beyond three. Furthermore, the model suggests that there are locations in the extreme near field of the sources that can be considered ideal for the minimization of far-field radiated power. Experiments carried out show that a four-channel control system is more effective than a two-channel system at achieving far-field attenuations, especially at the higher harmonics of the BPF for the fan tested. In addition, greater far-field mean-square pressure attenuations are achieved with the error microphones located along the calculated ideal regions than for nonideal placement.
Ultrasonic interferometry for the measurement of shear velocity and attenuation in viscoelastic solids
Authors: Simonetti F. , Cawley P.
Published: January 2004

A method for the measurement of the shear properties of solid viscoelastic materials is presented. The viscoelastic material is cut into a cylindrical sample which is clamped between two rods. The transmission and reflection coefficient spectra of the fundamental torsional mode through the sample are measured by means of two pairs of piezoelectric transducers placed at the free ends of the rod-sample-rod system. Such spectra exhibit maxima and minima which occur approximately at the resonance frequencies of the free viscoelastic cylinder. Therefore, the shear velocity can be obtained by measuring the frequency interval between two consecutive maxima or minima. The shear attenuation is derived by best fitting the analytical expression of the reflection and transmission coefficients to the experimental spectra. The test is very quick to set up as the sample is simply clamped between the two rods.
Separation of concurrent broadband sound sources by human listeners
Authors: Best Virginia , van Schaik André , Carlile Simon
Published: January 2004

The effect of spatial separation on the ability of human listeners to resolve a pair of concurrent broadband sounds was examined. Stimuli were presented in a virtual auditory environment using individualized outer ear filter functions. Subjects were presented with two simultaneous noise bursts that were either spatially coincident or separated (horizontally or vertically), and responded as to whether they perceived one or two source locations. Testing was carried out at five reference locations on the audiovisual horizon (0°, 22.5°, 45°, 67.5°, and 90° azimuth). Results from experiment 1 showed that at more lateral locations, a larger horizontal separation was required for the perception of two sounds. The reverse was true for vertical separation. Furthermore, it was observed that subjects were unable to separate stimulus pairs if they delivered the same interaural differences in time (ITD) and level (ILD). These findings suggested that the auditory system exploited differences in one or both of the binaural cues to resolve the sources, and could not use monaural spectral cues effectively for the task. In experiments 2 and 3, separation of concurrent noise sources was examined upon removal of low-frequency content (and ITDs), onset/offset ITDs, both of these in conjunction, and all ITD information. While onset and offset ITDs did not appear to play a major role, differences in ongoing ITDs were robust cues for separation under these conditions, including those in the envelopes of high-frequency channels.
Uncertainties associated with parameter estimation in atmospheric infrasound arrays
Authors: Szuberla Curt A. L. , Olson John V.
Published: January 2004

This study describes a method for determining the statistical confidence in estimates of direction-of-arrival and trace velocity stemming from signals present in atmospheric infrasound data. It is assumed that the signal source is far enough removed from the infrasound sensor array that a plane-wave approximation holds, and that multipath and multiple source effects are not present. Propagation path and medium inhomogeneities are assumed not to be known at the time of signal detection, but the ensemble of time delays of signal arrivals between array sensor pairs is estimable and corrupted by uncorrelated Gaussian noise. The method results in a set of practical uncertainties that lend themselves to a geometric interpretation. Although quite general, this method is intended for use by analysts interpreting data from atmospheric acoustic arrays, or those interested in designing and deploying them. The method is applied to infrasound arrays typical of those deployed as a part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization.
Tabu for matched-field source localization and geoacoustic inversion
Authors: Michalopoulou Zoi-Heleni , Ghosh-Dastidar Urmi
Published: January 2004

Tabu is a global optimization technique that has been very successful in operations research. In this paper, a Tabu-based method is developed for source localization and geoacoustic inversion with underwater sound data; the method relies on memory to guide the multiparameter search. Tabu is evaluated through a comparison to simulating annealing. Both methods are tested by inverting synthetic data for various numbers of unknown parameters. Tabu is found to be superior to the simulated annealing variant implemented here in terms both of accuracy and efficiency. Inversion results from the SWellEX-96 data set are also presented.
A simplified algorithm for second-order sound beams with arbitrary source distribution and geometry (L)
Authors: Ding Desheng
Published: January 2004

An earlier investigation [J. Acoust. Soc. Am. 108, 2759–2764 (2000)] of the simplified algorithm for the second-order sound fields with circular axial symmetry is extended to a more general case of the sound sources with an arbitrary distribution. This extension is based on the fact that the source function is expanded into the sum of a series of two-dimensional Gaussian ones. The two- and five-dimensional integral expressions for the primary and second-order fields are, respectively, reduced in terms of Gaussian functions and simple one-dimensional integrals. Numerical calculations are then greatly simplified.