bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient RCS computation for incident angle sweep with the use of the FMM and MNM techniques
Authors: Ma J. F. , Mittra R. , Prakash V. V. S.
Published: October 2002

This Letter presents an extension of a recently developed technique for speeding up the iterative solution of MOM linear equations—referred to in the literature [4,5] as the MNM method—when sweeping the frequency in the content of RCS computation. It is shown that extended MNM is useful for efficient iterative solution of the multiple right‐hand‐side situations arising in the angular sweep problem. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 273–276, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10436
Efficient multiwavelength linear cavity erbium‐doped fiber laser over 1570–1600 nm
Authors: Zhao Chun‐Liu , Yang Shiquan , Meng Hongyun , Li Zhaohui , Yuan Shuzhong , Dong Xiaoyi
Published: October 2002

A simple and efficient L‐band multiwavelength linear cavity fiber laser was obtained at room temperature by recycling detrimental 1550‐nm band amplified spontaneous emission as a secondary pump source for the unpumped EDF section of fiber laser. The cavity was formed by two linear fiber loops. By changing the states of PCs inserted to fiber loops, stable dual‐ and tri‐wavelength lasers with about 1‐mW/channel were generated at room temperature. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 296–299, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10441
Time‐domain 2D modeling of slab‐waveguide based photonic‐crystal devices in the presence of radiation losses
Authors: Qiu Min , Jaskorzynska Bozena , Swillo Marcin , Benisty Henri
Published: October 2002

Devices based on two‐dimensional (2D) photonic crystals (PCs) are typically realized as 3D structures consisting of an array of holes (or rods) vertically etched through a slab waveguide. The existence of holes in a slab waveguide may induce strong radiation losses to the slab claddings. Exact modeling of devices affected by such losses requires 3D calculations. In the present Letter, with the use of the effective‐index method to account for the vertical confinement and the effective losses method by the nonvanishing conductivity, the 3D modeling is reduced into 2D. It is then shown that good agreement with experiments can be obtained for slab‐waveguide–based photonic crystal devices. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 387–393, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10471
Clinical utility of bronchoalveolar lavage in pediatric cancer patients
Authors: Park Julie R. , Fogarty Shana , Brogan Thomas V.
Published: October 2002

Background

Pulmonary disease in the pediatric cancer patient continues to pose a difficult clinical dilemma. Bronchoalveolar lavage (BAL) is commonly utilized for the diagnosis of pulmonary complications in the immunocompromised child.

Procedure

We retrospectively reviewed 53 BAL procedures performed in pediatric cancer patients with pulmonary disease between 1988 and 1998 to determine the diagnostic and clinical utility of BAL. Patients who had undergone prior myeloablative therapy were excluded from analysis.

Results

The majority of patients (83%) had an underlying diagnosis of acute leukemia or lymphoma. BAL yielded a specific diagnosis in 16 patients (30%), including 15 infections and 1 malignant infiltration. Medical management was altered in an additional 14 patients (26%) as a consequence of a negative BAL result. Severe but transient complications associated with the BAL procedure occurred in four patients (8%). Minor complications following the BAL occurred in 21 patients (40%) and included transiently increased oxygen requirement and anesthesia‐related gastrointestinal complaints. The mortality from lung disease in this patient population was 7.5%.

Conclusions

Both positive and negative BAL results contribute to the management of pediatric cancer patients with pulmonary disease. The low incidence of significant complications associated with BAL and the high mortality rate in this patient population support the choice of BAL as an initial diagnostic test in pediatric cancer patients with pulmonary disease. Med Pediatr Oncol 2002;39:175–180. © 2002 Wiley‐Liss, Inc.
Novel double promoter approach for identification of transgenic animals: A tool for in vivo analysis of gene function and development of gene‐based therapies
Authors: Fu Liezhen , Buchholz Daniel , Shi Yun‐Bo
Published: October 2002

Advances in vertebrate genetics have allowed studies of gene function in developing animals through gene knockout and transgenic analyses. These advances have encouraged the development of gene‐based therapies through introduction of exogenous genes to enhance and/or replace dysfunctional or missing genes. However, in vertebrates, such analyses often involve tedious screening for transgenic animals, such as PCR‐based genotype determinations. Here, we report the use of double‐promoter plasmids carrying the transgene of interest and the crystallin‐promotor‐driven Green fluorescent protein (GFP) in transgenic Xenopus laevis tadpoles. This strategy allows a simple examination for the presence of GFP in the eyes to identify transgenic animals. PCR‐based genotyping and functional characterization confirms that all animals expressing GFP in the eyes indeed carry the desired promoter/transgene units. Thus, the use of this and other similar vectors should dramatically improve current transgenesis protocols and reduce the time and cost for identifying transgenic animals. Mol. Reprod. Dev. 62:470–476, 2002. © 2002 Wiley‐Liss, Inc.
Molecular cloning and expression during spermatogenesis of a cDNA encoding testicular 11β‐hydroxylase (P45011β) in rainbow trout (Oncorhynchus mykiss)
Authors: Kusakabe Makoto , Kobayashi Tohru , Todo Takashi , Mark Lokman P. , Nagahama Yoshitaka , Young Graham
Published: October 2002

Cytochrome P450 1β‐hydroxylase (P45011β) is an important steroidogenic enzyme for glucocorticoid and mineralocorticoid production in vertebrates. In teleosts, P45011β also plays a role in the production of 11‐ketotestosterone (11‐KT), the predominant androgen in male fish. In this study, we cloned a cDNA encoding rainbow trout (Oncorhynchus mykiss) testicular P45011β. The cDNA contains 1,740 nucleotides that encode a protein of 551 amino acids which shares 65.2% homology with testicular P45011β from Japanese eel, and 33–45% homology with adrenal P45011β from rat, human, and frog. HEK293 cells transfected with an expression vector containing the rainbow trout P45011β cDNA open reading frame showed 11β‐hydroxylating activity in the presence of exogenous testosterone. Analysis of tissue distribution by RT‐PCR showed great abundance of P45011β mRNA in testis and head kidney. In order to clarify the sites of P45011β gene expression, cRNA in situ hybridization analysis was performed. Hybridization signals were detected in Leydig cells and head kidney inter‐renal cells. The results of Northern blot analysis indicated a single 1.8‐kb transcript encoding P45011β in testis and in head kidney, suggesting that the testicular form of P45011β may also be involved in cortisol production by inter‐renal cells. Seasonal changes in total P45011β mRNA levels in testes during spermatogenesis showed a pattern similar to that of plasma androgens. These results suggest that androgen production in male rainbow trout is partially regulated by changes in abundance of P45011β mRNA. Mol. Reprod. Dev. 62:456–469, 2002. © 2002 Wiley‐Liss, Inc.
Characterization of anisotropy in high angular resolution diffusion‐weighted MRI
Authors: Frank Lawrence R.
Published: October 2002

The methods of group theory are applied to the problem of characterizing the diffusion measured in high angular resolution MR experiments. This leads to a natural representation of the local diffusion in terms of spherical harmonics. In this representation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotropic diffusion from multiple fiber directions fall into distinct and separable channels. This decomposition can be determined for any voxel without any prior information by a spherical harmonic transform, and for special cases the magnitude and orientation of the local diffusion may be determined. Moreover, non‐diffusion–related asymmetries produced by experimental artifacts fall into channels distinct from the fiber channels, thereby allowing their separation and a subsequent reduction in noise from the reconstructed fibers. In the case of a single fiber, the method reduces identically to the standard diffusion tensor method. The method is applied to normal volunteer brain data collected with a stimulated echo spiral high angular resolution diffusion‐weighted (HARD) acquisition. Magn Reson Med 47:1083–1099, 2002. Published 2002 Wiley‐Liss, Inc.
Single‐point (constant‐time) imaging in radiofrequency Fourier transform electron paramagnetic resonance†
Authors: Subramanian Sankaran , Devasahayam Nallathamby , Murugesan Ramachandran , Yamada Kenichi , Cook John , Taube Andrew , Mitchell James B. , Lohman Joost A.B. , Krishna Murali C.
Published: October 2002

This study describes the use of the single‐point imaging (SPI) modality, also known as constant‐time imaging (CTI), in radiofrequency (RF) Fourier transform (FT) electron paramagnetic resonance (EPR). The SPI technique, commonly used for high‐resolution solid‐state nuclear magnetic resonance (NMR) imaging, has been successfully applied to 2D and 3D RF‐FT‐EPR imaging of phantoms containing narrow‐line EPR spin probes. The SPI scheme is essentially a phase‐encoding technique that operates by acquiring a single data point in the free induction decay (FID) after a fixed delay (phase‐encoding time), following the pulsed RF excitation, in the presence of static magnetic field gradients. Since the phase‐encoding time remains constant for a given image data set, the spectral information is automatically deconvolved, providing well‐resolved pure spatial images. Therefore, images obtained using SPI are artifact‐free and the resolution is not significantly limited by the line width, compared to the images obtained using the conventional filtered back‐projection (FBP) scheme, suggesting that the SPI modality may have advantages for EPR imaging of large objects. In this work the advantages and limitations of SPI as compared to FBP are investigated by imaging suitable phantom objects. Although SPI takes longer to perform than the FBP method, optimization of the data collection scheme may increase the temporal resolution, rendering this technique suitable for in vivo studies. Spectral information can also be extracted from a series of SPI images that are generated as a function of the delay from the excitation pulse. Magn Reson Med 48:370–379, 2002. Published 2002 Wiley‐Liss, Inc.
Time‐resolved contrast‐enhanced imaging with isotropic resolution and broad coverage using an undersampled 3D projection trajectory
Authors: Barger Andrew V. , Block Walter F. , Toropov Yuriy , Grist Thomas M. , Mistretta Charles A.
Published: October 2002

Time‐resolved contrast‐enhanced 3D MR angiography (MRA) methods have gained in popularity but are still limited by the tradeoff between spatial and temporal resolution. A method is presented that greatly reduces this tradeoff by employing undersampled 3D projection reconstruction trajectories. The variable density k‐space sampling intrinsic to this sequence is combined with temporal k‐space interpolation to provide time frames as short as 4 s. This time resolution reduces the need for exact contrast timing while also providing dynamic information. Spatial resolution is determined primarily by the projection readout resolution and is thus isotropic across the FOV, which is also isotropic. Although undersampling the outer regions of k‐space introduces aliased energy into the image, which may compromise resolution, this is not a limiting factor in high‐contrast applications such as MRA. Results from phantom and volunteer studies are presented demonstrating isotropic resolution, broad coverage with an isotropic field of view (FOV), minimal projection reconstruction artifacts, and temporal information. In one application, a single breath‐hold exam covering the entire pulmonary vasculature generates high‐resolution, isotropic imaging volumes depicting the bolus passage. Magn Reson Med 48:297–305, 2002. © 2002 Wiley‐Liss, Inc.
Multiecho segmented EPI with z‐shimmed background gradient compensation (MESBAC) pulse sequence for fMRI
Authors: Li Zhu , Wu Gaohong , Zhao Xiaoli , Luo Feng , Li Shi‐Jiang
Published: October 2002

A MultiEcho Segmented EPI with z‐shimmed BAckground gradient Compensation (MESBAC) pulse sequence is proposed and validated for functional MRI (fMRI) study in regions suffering from severe susceptibility artifacts. This sequence provides an effective tradeoff between spatial and temporal resolution and reduces image distortion and signal dropout. The blood oxygenation level‐dependent (BOLD)‐weighted fMRI signal can be reliably obtained in the region of the orbitofrontal cortex (OFC). To overcome physiological motion artifacts during prolonged multisegment EPI acquisition, two sets of navigator echoes were acquired in both the readout and phase‐encoding directions. Ghost artifacts generally produced by single‐shot EPI acquisition were eliminated by separately placing the even and odd echoes in different k‐space trajectories. Unlike most z‐shim methods that focus on increasing temporal resolution for event‐related functional brain mapping, the MESBAC sequence simultaneously addresses problems of image distortion and signal dropout while maintaining sufficient temporal resolution. The MESBAC sequence will be particularly useful for pharmacological and affective fMRI studies in brain regions such as the OFC, nucleus accumbens, amygdala, parahippocampus, etc. Magn Reson Med 48:312–321, 2002. © 2002 Wiley‐Liss, Inc.
Brainstem reflexes: Electrodiagnostic techniques, physiology, normative data, and clinical applications
Authors: Aramideh M. , Ongerboer De Visser B.W.
Published: October 2002

An overview is provided on the physiological aspects of the brainstem reflexes as they can be examined by use of clinically applicable neurophysiological tests. Brainstem reflex studies provide important information about the afferent and efferent pathways and are excellent physiological tools for the assessment of cranial nerve nuclei and the functional integrity of suprasegmental structures. In this review, the blink reflex after trigeminal and nontrigeminal inputs, corneal reflex, levator palpebrae inhibitory reflex, jaw jerk, masseter inhibitory reflex, and corneomandibular reflex are discussed. Following description of the recording technique, physiology, central pathways, and normative data of these reflexes, including an account of the recording of recovery curves, the application of these reflexes is reviewed in patients with various neurological abnormalities, including trigeminal pain and neuralgia, facial neuropathy, and brainstem and hemispherical lesions. Finally, simultaneous electromyographic recording from the orbicularis oculi and the levator palpebrae muscles is discussed briefly in different eyelid movement disorders. © 2002 Wiley Periodicals Inc. Muscle Nerve 26: 14–30, 2002
Central fatigue and motor cortical excitability during repeated shortening and lengthening actions
Authors: Löscher Wolfgang N. , Nordlund Maria M.
Published: October 2002

A decline in voluntary muscle activation and adaptations in motor cortical excitability contribute to the progressive decline in voluntary force during sustained isometric contractions. However, the neuronal control of muscle activation differs between isometric and dynamic contractions. This study was designed to investigate voluntary activation, motor cortex excitability, and intracortical inhibition during fatiguing concentric and eccentric actions. Eight subjects performed 143 torque motor–controlled, repeated shortening and lengthening actions of the elbow flexor muscles. Transcranial magnetic stimulation (TMS) was applied three times every 20 cycles. Magnetic evoked motor potentials (MEP), duration of the silent period (SP), and the torque increase due to TMS were analyzed. TMS resulted in a small torque increase in unfatigued actions. With repeated actions, voluntary torque dropped rapidly and the amplitude of the TMS‐induced twitches increased, especially during repeated lengthening actions. MEP area of biceps brachii and brachioradialis muscles increased during repeated actions to a similar extent during lengthening and shortening fatigue. The duration of biceps and brachioradialis SP did not change with fatigue. Thus, voluntary activation became suboptimal during fatiguing dynamic actions and motor cortex excitability increased without any changes in intracortical inhibition. The apparent dissociation of voluntary activation and motor cortex excitability suggests that the central fatigue observed, especially during lengthening actions, did not result from changes in motor cortex excitability. © 2002 Wiley Periodicals, Inc. Muscle Nerve 25: 000–000, 2002
Mechanisms of force failure during repetitive maximal efforts in a human upper airway muscle
Authors: DelloRusso Christiana , Khurana Nilam , Rankin Lucinda , Sullivan Jenna , Fregosi Ralph F.
Published: October 2002

The upper airway respiratory muscles play an important role in the regulation of airway resistance, but surprisingly little is known about their contractile properties and endurance performance. We developed a technique that allows measurement of force and the electromyogram (EMG) of human nasal dilator muscles (NDMs). Endurance performance was quantified by measuring NDM “flaring” force and EMG activity as healthy human subjects performed 10 s maximal voluntary contractions (MVCs), separated by 10 s rest, until the area under the force curve fell to 50% MVC (the time limit of the fatigue task, Tlim), which was reached in 34.2 ± 3.1 contractions (685.0 ± 62.3 s). EMG activity was unchanged except at Tlim, where it averaged 78.7 ± 3.6% of pretest activity (P < 0.01). M‐wave amplitude did not change, suggesting that neuromuscular propagation was not impaired. MVC force increased to 80% of the pretest level within 10 min of recovery but twitch force failed to recover, suggesting low‐frequency fatigue. The data suggest that a failure of the nervous system to excite muscle could explain at most only a small fraction of the NDM force loss during an intermittent fatigue task, and then only at Tlim. Thus, the majority of the force failure during this task is due to impairment of mechanisms that reside within the muscle fibers. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 94–100, 2002
Small‐fiber neuropathy
Authors: Lacomis David
Published: October 2002

Small‐fiber neuropathy is a common disorder. It is often “idiopathic” and typically presents with painful feet in patients over the age of 60. Autoimmune mechanisms are often suspected, but rarely identified. Known causes of small‐fiber neuropathy include diabetes mellitus, amyloidosis, toxins, and inherited sensory and autonomic neuropathies. Occasionally, small‐fiber neuropathy is diffuse or multifocal. Depending on the type of small‐fiber neuropathy, autonomic dysfunction can be significant or subclinical. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies, and abnormal specialized tests of small‐fiber function. These specialized studies include assessment of epidermal nerve fiber density as well as sudomotor, quantitative sensory, and cardiovagal testing. The sensitivities of these tests range from 59–88%. Each has certain advantages and disadvantages, and the tests may be complementary. Unless an underlying disease is identified, treatment is usually directed toward alleviation of neuropathic pain. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 173–188, 2002
Conduction slowing in diabetic distal polyneuropathy
Authors: Herrmann David N. , Ferguson Michele L. , Logigian Eric L.
Published: October 2002

The pathophysiologic significance of motor conduction slowing observed in diabetic distal symmetrical polyneuropathy (DSP) remains controversial. We have used multiple linear regression analysis of compound muscle action potential (CMAP) amplitude vs. motor conduction velocity (CV) and distal latency (DL) in 57 patients with diabetic DSP and 34 patients with amyotrophic lateral sclerosis (ALS) to determine whether motor conduction slowing in diabetic DSP is due mainly to loss of large axons as in ALS or whether there is an additional demyelinative component. We found amplitude‐dependent slowing of CV and DL in both diabetic DSP and ALS in the upper and lower extremities, consistent with a loss of large myelinated fibers. However, in diabetic DSP, there was also significant amplitude‐independent slowing in intermediate but not distal nerve segments, supportive of an additional demyelinative component. CMAP amplitude vs. CV and DL regression analyses using ALS as a control group for relatively pure axon loss may provide pathophysiologic information about motor nerves in other neuropathic disorders. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 232–237, 2002
Tensor visualizations in computational geomechanics
Authors: Jeremić Boris , Scheuermann Gerik , Frey Jan , Yang Zhaohui , Hamann Bernd , Joy Kenneth I. , Hagen Hans
Published: October 2002

We present a novel technique for visualizing tensors in three dimensional (3D) space. Of particular interest is the visualization of stress tensors resulting from 3D numerical simulations in computational geomechanics. To this end we present three different approaches to visualizing tensors in 3D space, namely hedgehogs, hyperstreamlines and hyperstreamsurfaces. We also present a number of examples related to stress distributions in 3D solids subjected to single and load couples. In addition, we present stress visualizations resulting from single‐pile and pile‐group computations. The main objective of this work is to investigate various techniques for visualizing general Cartesian tensors of rank 2 and it's application to geomechanics problems. Copyright © 2002 John Wiley & Sons, Ltd.
New job selection and location policies for load‐distributing algorithms
Authors: Al‐Amri Marei S. , Ahmed Rana Ejaz
Published: October 2002

This paper presents a new distributing algorithm that uses new job selection and location policies. The algorithm is shown to outperform the best‐reported load distributing algorithms. Copyright © 2002 John Wiley & Sons, Ltd.
The least‐squares finite element method in elasticity—Part I: Plane stress or strain with drilling degrees of freedom
Authors: Jiang Bo‐nan , Wu Jie
Published: October 2002

A new least‐squares finite element method (LSFEM) for plane elasticity problems is developed based on the first‐order displacement–stress–rotation formulation which includes two new first‐order compatibility constraints among the stresses and the drilling rotation. This LSFEM can accommodate all kinds of equal‐order interpolations. Numerical experiments on various examples including incompressible materials show that the method achieves an optimal rate of convergence for all variables. Copyright © 2001 John Wiley & Sons, Ltd.
An efficient multi‐layer planar 3D fracture growth algorithm using a fixed mesh approach
Authors: Siebrits Eduard , Peirce Anthony P.
Published: October 2002

We present a planar three‐dimensional (3D) fracture growth simulator, based on a displacement discontinuity (DD) method for multi‐layer elasticity problems. The method uses a fixed mesh approach, with rectangular panel elements to represent the planar fracture surface. Special fracture tip logic is included that allows a tip element to be partially fractured in the tip region. The fracture perimeter is modelled in a piece‐wise linear manner. The algorithm can model any number of interacting fractures that are restricted to lie on a single planar surface, located orthogonal to any number of parallel layers. The multiple layers are treated using a Fourier transform (FT) approach that provides a numerical Green's function for the DD scheme. The layers are assumed to be fully bonded together. Any fracture growth rule can be postulated for the algorithm. We demonstrate this approach on a number of test problems to verify its accuracy and efficiency, before showing some more general results. Copyright © 2001 John Wiley & Sons, Ltd.
Detection of bifurcation points along a curve traced by a continuation method
Authors: Lopez S.
Published: October 2002

The methods for computing the singular points based on approximations of the equilibrium curve by asymptotic extrapolation usually have a limited range of validity. This is because the power series are only built on the local properties of the primary solution branch. This paper suggests ways to improve such a situation: the asymptotic extrapolation is used in the predictor phase of a continuation method and an effective parametrization equation is adopted. In this way the description of the equilibrium curve between two consecutive solution points is improved while the local nature of the extrapolation is retained. The bifurcation points computed on the extrapolation are then used to initialize a classical method for the detection of the bifurcation points on the exact equilibrium curve. Moreover the accurate location of the limit points is an immediate consequence of the precision obtained in the description of the solution curve in the predictor–corrector step. Overall the computational cost of the analysis is appreciably reduced. In effect a low number of predictor–corrector steps are required to complete the description of the solution curve and most of the computations performed in the detection of bifurcation points are carried out on the extrapolation. The good initialization obtained also makes Newton's classical method for calculating the bifurcation points on the exact equilibrium curve more reliable with regard to the convergence. Generalization to cases of more bifurcation points within two consecutive solution points is then obtained by a non‐linear subspace procedure defined on the asymptotic extrapolation. Applications to frame structures and cylindrical shells analysis are presented. Copyright © 2001 John Wiley & Sons, Ltd.
Higher‐order accurate time‐step‐integration algorithms by post‐integration techniques
Authors: Fung T. C.
Published: October 2002

In this paper, a framework to construct higher‐order‐accurate time‐step‐integration algorithms based on the post‐integration techniques is presented. The prescribed initial conditions are naturally incorporated in the formulations and can be strongly or weakly enforced. The algorithmic parameters are chosen such that unconditionally A‐stable higher‐order‐accurate time‐step‐integration algorithms with controllable numerical dissipation can be constructed for linear problems. Besides, it is shown that the order of accuracy for non‐linear problems is maintained through the relationship between the present formulation and the Runge–Kutta method. The second‐order differential equations are also considered. Numerical examples are given to illustrate the validity of the present formulation. Copyright © 2001 John Wiley & Sons, Ltd.
Three‐dimensional finite element calculations in acoustic scattering using arbitrarily shaped convex artificial boundaries
Authors: Tezaur Radek , Macedo Antonini , Farhat Charbel , Djellouli Rabia
Published: October 2002

We report on a generalization of the Bayliss–Gunzburger–Turkel non‐reflecting boundary conditions to arbitrarily shaped convex artificial boundaries. For elongated scatterers such as submarines, we show that this generalization can improve significantly the computational efficiency of finite element methods applied to the solution of three‐dimensional acoustic scattering problems. Copyright © 2001 John Wiley & Sons, Ltd.
On non‐linear behaviour of spherical shallow shells bonded with piezoelectric actuators by the differential quadrature element method (DQEM)
Authors: Wang Xinwei , Wang Yongliang
Published: October 2002

The static behaviour of spherical shallow shells bonded with piezoelectric actuators and subjected to electrical loading are studied in this paper by using the differential quadrature element method (DQEM). Geometrical non‐linear effects are considered. Detailed formulations for the DQ circular spherical shallow shell element and the DQ annular spherical shallow shell element are given for the first time. Numerical studies are performed to evaluate the effects of actuator size, thickness and boundary conditions. Very accurate results are obtained by the DQEM. Based on the results reported in this paper, one may conclude that the DQEM is a useful tool for obtaining solutions for smart materials and structures exhibiting geometric non‐linear behaviours. Thickness effects cannot be neglected when the actuator thickness is comparable to that of the base material. Snap‐through may occur when the applied voltage reaches a critical value even without mechanical loading for certain geometric configurations. Copyright © 2001 John Wiley & Sons, Ltd.
Stress analysis of gear teeth using displacement potential function and finite differences
Authors: Akanda M. A. Salam , Ahmed S. Reaz , Uddin M. Wahhaj
Published: October 2002

A new numerical approach has been developed for the analysis of displacements and stresses in arbitrary‐shaped elastic bodies subjected to mixed boundary conditions. An ideal mathematical model, based on the displacement‐potential function, has been used in the finite‐difference solution to investigate the state of stresses at the critical sections of spur gear teeth. Two different types of gear tooth and two different regions of loading are included in the present analysis. The solutions found by the present approach are compared and discussed in the light of available finite‐element results in the literature. Copyright © 2001 John Wiley & Sons, Ltd.
Moving particle finite element method
Authors: Hao Su , Park Harold S. , Liu Wing Kam
Published: October 2002

This paper presents the fundamental concepts behind the moving particle finite element method, which combines salient features of finite element and meshfree methods. The proposed method alleviates certain problems that plague meshfree techniques, such as essential boundary condition enforcement and the use of a separate background mesh to integrate the weak form. The method is illustrated via two‐dimensional linear elastic problems. Numerical examples are provided to show the capability of the method in benchmark problems. Copyright © 2001 John Wiley & Sons, Ltd.
A stream function implicit finite difference scheme for 2D incompressible flows of Newtonian fluids
Authors: Bubnovich Valeri I. , Rosas César E. , Moraga Nelson O.
Published: October 2002

The development of a new algorithm to solve the Navier–Stokes equations by an implicit formulation for the finite difference method is presented, that can be used to solve two‐dimensional incompressible flows by formulating the problem in terms of only one variable, the stream function. Two algebraic equations with 11 unknowns are obtained from the discretized mathematical model through the ADI method. An original algorithm is developed which allows a reduction from the original 11 unknowns to five and the use of the Pentadiagonal Matrix Algorithm (PDMA) in each one of the equations. An iterative cycle of calculations is implemented to assess the accuracy and speed of convergence of the algorithm. The relaxation parameter required is analytically obtained in terms of the size of the grid and the value of the Reynolds number by imposing the diagonal dominancy condition in the resulting pentadiagonal matrixes. The algorithm developed is tested by solving two classical steady fluid mechanics problems: cavity‐driven flow with Re=100, 400 and 1000 and flow in a sudden expansion with expansion ratio H/h=2 and Re=50, 100 and 200. The results obtained for the stream function are compared with values obtained by different available numerical methods, to evaluate the accuracy and the CPU time required by the proposed algorithm. Copyright © 2002 John Wiley & Sons, Ltd.
Chebyshev rational spectral and pseudospectral methods on a semi‐infinite interval
Authors: Guo Ben‐yu , Shen Jie , Wang Zhong‐qing
Published: October 2002

A weighted orthogonal system on the half‐line based on the Chebyshev rational functions is introduced. Basic results on Chebyshev rational approximations of several orthogonal projections and interpolations are established. To illustrate the potential of the Chebyshev rational spectral method, a model problem is considered both theoretically and numerically: error estimates for the Chebyshev rational spectral and pseudospectral methods are established; preliminary numerical results agree well with the theoretical estimates and demonstrate the effectiveness of this approach. Copyright © 2001 John Wiley & Sons, Ltd.
A p‐adaptive algorithm for the BEM with the hypersingular operator on the plane screen
Authors: Heuer Norbert , Mellado Mario E. , Stephan Ernst P.
Published: October 2002

We propose a p‐adaptive algorithm for the Galerkin method solving the hypersingular integral operator of the Laplacian on the plane screen. The error indicators/estimators are based on projections of the actual error onto local subspaces. These subspaces are defined by decompositions of specially designed enriched ansatz spaces. Our algorithm uses different strategies for the refinement and the stopping criterion. The error estimator that stops the algorithm is based on an overlapping decomposition of an ansatz space that is defined by mesh refinement. The error indicators that steer the p‐refinement are computed via an almost direct decomposition of an enriched ansatz space that uses the same mesh but higher polynomial degrees. Numerical results support the efficiency of our algorithm. Copyright © 2001 John Wiley & Sons, Ltd.
Hybrid‐stress solid elements for shell structures based upon a modified variational functional
Authors: Sze K. Y. , Lo S. H. , Yao L.‐Q.
Published: October 2002

In this paper, we start with a modified generalized laminate stiffness matrix that serves as a remedy to resolve the thickness locking and some abnormalities encountered by solid‐shell elements in laminate analyses. A modified Hellinger–Reissner functional having displacement and a set of generalized stresses as independent fields is devised. Based upon the functional, eight‐node and 18‐node hybrid‐stress solid‐shell elements are proposed. A number of benchmark tests on homogenous and laminated plates/shells are conducted. The accuracy of the elements is promising. Copyright © 2002 John Wiley & Sons, Ltd.
Remeshing for metal forming simulations—Part I: Two‐dimensional quadrilateral remeshing
Authors: Kwak Dae‐Young , Cheon Jae‐Seung , Im Yong‐Taek
Published: October 2002

In this paper, a general framework of practical two‐dimensional quadrilateral remeshing, which includes the determination of remeshing time, automatic quadrilateral mesh generation, and data transfer process, will be formulated. In particular, the current work contains new algorithms of mesh density specification according to the distribution of effective strain‐rate gradients, mesh density smoothing by fast Fourier transform (FFT) and low‐pass filtering techniques, coarsening it by node placement scheme, and a modified Laplacian mesh smoothing technique. The efficiency of the developed remeshing scheme was tested through three practical two‐dimensional metal forming simulations. The results clearly indicate that the algorithms proposed in this study make it possible to simulate two‐dimensional metal forming problems efficiently and automatically. Copyright © 2002 John Wiley & Sons, Ltd.
An optimal high‐order non‐reflecting finite element scheme for wave scattering problems
Authors: Givoli Dan , Patlashenko Igor
Published: October 2002

A new finite element scheme is proposed for the numerical solution of time‐harmonic wave scattering problems in unbounded domains. The infinite domain in truncated via an artificial boundary ℬ︁ which encloses a finite computational domain Ω. On ℬ︁ a local high‐order non‐reflecting boundary condition (NRBC) is applied which is constructed to be optimal in a certain sense. This NRBC is implemented in a special way, by using auxiliary variables along the boundary ℬ︁, so that it involves no high‐order derivatives regardless of its order. The order of the scheme is simply an input parameter, and it may be arbitrarily high. This leads to a symmetric finite element formulation where standard C0 finite elements are used in Ω. The performance of the method is demonstrated via numerical examples, and it is compared to other NRBC‐based schemes. The method is shown to be highly accurate and stable, and to lead to a well‐conditioned matrix problem. Copyright © 2002 John Wiley & Sons, Ltd.
Automatic generation of anisotropic quadrilateral meshes on three‐dimensional surfaces using metric specifications
Authors: Lee Y. K. , Lee C. K.
Published: October 2002

A new algorithm for constructing full quadrilateral anisotropic meshes on 3D surfaces is proposed in this paper. The proposed method is based on the advancing front and the systemic merging techniques. Full quadrilateral meshes are constructed by systemically converting triangular elements in the background meshes into quadrilateral elements.By using the metric specifications to describe the element characteristics, the proposed algorithm is applicable to convert both isotropic and anisotropic triangular meshes into full quadrilateral meshes. Special techniques for generating anisotropic quadrilaterals such as new selection criteria of base segment for merging, new approaches for the modifications of the background mesh and construction of quadrilateral elements, are investigated and proposed in this study. Since the final quadrilateral mesh is constructed from a background triangular mesh and the merging procedure is carried out in the parametric space, the mesh generator is robust and no expensive geometrical computation that is commonly associated with direct quadrilateral mesh generation schemes is needed. Copyright © 2002 John Wiley & Sons, Ltd.
Extended preconditioners for the FETI method applied to constrained problems
Authors: Rixen Daniel J.
Published: October 2002

An efficient and simple approach for handling linear multipoint constraints in a class of substructure‐based solvers, namely the finite element tearing and interconnecting (FETI) method, is proposed. Previously, it was argued that multipoint constraints should be handled in FETI by adding a second level iteration on a coarse grid such that the FETI iterates satisfy the multipoint constraints exactly. The procedure presented here does not require an additional coarse grid but instead takes account of the multipoint constraints in the preconditioning step. The preconditioning strategy is shown to be mechanically consistent and to incur only a small additional computational cost. This strategy is simpler and computationally less expensive than the two‐level FETI procedure. Its numerical scalability even for highly heterogeneous problems is demonstrated in several test examples. Copyright © 2002 John Wiley & Sons, Ltd.
Large strain finite element analysis of a local second gradient model: application to localization
Authors: Matsushima Takashi , Chambon René , Caillerie Denis
Published: October 2002

A large strain finite element formulation based on a local second gradient plasticity model is presented. The corresponding constitutive equations were developed as a direct extension of microstructured (SIAM J. Appl. Math. 1973; 25(3):556–575; Arch. Rational Mech. Anal. 1964; 16:51–78) or micromorphic (In Mechanics of Generalized Continua, IUTAM Symposium, Kröner (ed.), Springer: Berlin, 1968; 18–35; J. Math. Mech. 1966; 15(6):909–924.) continua in which a mathematical constraint between the micro kinematics description and the usual macrodeformation gradient field has been introduced. This constraint is enforced in a weak sense by the use of Lagrange multipliers in order to avoid difficulties with the C1 continuity, for the finite element method. Corresponding finite elements are then constructed involving the Lagrange multipliers field. A geometrically non‐linear 2‐D finite element code is developed within a framework of an incremental method. For every step, a full Newton–Raphson involving a numerical consistent tangent stiffness operator for the complete model (i.e., the second gradient terms as well as the classical ones) is done and some numerical tests allow to validate the method and to discuss the influence of the geometrical non‐linearity. Copyright © 2002 John Wiley & Sons, Ltd.
Testing the asymptotic behaviour of shell elements—Part I: the classical benchmark tests
Authors: Briassoulis D.
Published: October 2002

The asymptotic behaviour is considered to be one of the most demanding levels of benchmark testing for shell elements. In the present paper, the asymptotic behaviour of classical benchmark problems is analytically and numerically investigated. The aim is to examine the possibility of using the classical benchmark tests for testing the asymptotic behaviour of shell elements. Appropriate analytical approaches are introduced to investigate the asymptotic behaviour of the classical benchmark problems. The reformulated four‐node shell element (RFNS) is employed in the numerical analyses. It is shown that the classical benchmark tests, in addition to testing the reliability and robustness of shell elements, also represent strong challenging tests for the asymptotic behaviour of shell elements. In the course of the numerical investigation of the asymptotic behaviour of the classical benchmark problems, the reliability and efficiency of the RFNS element already established by means of the classical configuration of the benchmark tests is re‐confirmed in all cases of the corresponding asymptotic test configurations. Copyright © 2002 John Wiley & Sons, Ltd.
Elastic wave propagation in a 3‐D unbounded random heterogeneous medium coupled with a bounded medium. Application to seismic soil–structure interaction (SSSI)
Authors: Savin E. , Clouteau D.
Published: October 2002

We present a sub‐structuring method for the coupling between a large elastic structure, and a stratified soil half‐space exhibiting random heterogeneities over a bounded domain and impinged by incident waves. Both media are also weakly dissipative. The concept of interfaces classically used in sub‐structuring methods is extended to ‘volume interfaces’ in the proposed approach. The random dimension of the stochastic fields modelling the heterogeneities in the soil is reduced by introducing a Karhunen–Loéve expansion of these stochastic fields. The coupled overall problem is solved by Monte‐Carlo simulation techniques. A realistic example of a large industrial structure interacting with an uncertain stratified soil medium under earthquake is finally presented. This case study and others validate the presented methodology and its ability to handle complex mechanical systems. Copyright © 2002 John Wiley & Sons, Ltd.
Numerical inclusion methods of solutions for variational inequalities
Authors: Ryoo C. S. , Agarwal R. P.
Published: October 2002

We consider a numerical method that enables us to verify the existence of solutions for variational inequalities. This method is based on the infinite dimensional fixed point theorems and explicit error estimates for finite element approximations. Using the finite element approximations and explicit a priori error estimates, we present an effective verification procedure that through numerical computation generates a set which includes the exact solution. Copyright © 2002 John Wiley & Sons, Ltd.
A new shear flexible cubic spline plate element for vibration analysis
Authors: Patel B. P. , Ganapathi M.
Published: October 2002

Here, a new cubic B‐spline plate element is developed using field consistency principle, for vibration analysis. The formulation includes anisotropy, transverse shear deformation, in‐plane and rotary inertia effects. The element is based on a laminated refined plate theory, which satisfies the interface transverse shear stress and displacement continuity, and has a vanishing shear stress on the top and bottom surfaces of the plates. The lack of consistency in the shear strain field interpolations in its constrained physical limits produces poor convergence and results in unacceptable solutions due to locking phenomenon. Hence, numerical experimentation for the evaluation of natural frequencies of plates is carried out to check this deficiency with a series of assumed shear strain functions, redistributed in a field consistent manner. Copyright © 2002 John Wiley & Sons, Ltd.
Classical and advanced multilayered plate elements based upon PVD and RMVT. Part 1: Derivation of finite element matrices
Authors: Carrera Erasmo , Demasi Luciano
Published: October 2002

This paper deals with the formulation of finite plate elements for an accurate description of stress and strain fields in multilayered, thick plates subjected to static loadings in the linear, elastic cases. The so‐called zig‐zag form and interlaminar continuity are addressed in the considered formulations. Two variational statements, the principle of virtual displacements (PVD) and the Reissner mixed variational theorem (RMVT) are employed to derive finite element matrices. Transverse stress assumptions are made in the framework of RMVT and the resulting finite elements describe a priori interlaminar continuous transverse shear and normal stresses. Both modellings which preserve the number of variables independent of the number of layers (equivalent single‐layer models, ESLM) and layer‐wise models (LWM) in which the same variables are independent in each layer, have been treated. The order N of the expansions assumed for both displacement and transverse stress fields in the plate thickness direction z as well as the number of element nodes Nn have been taken as free parameters of the considered formulations. By varying N, Nn, variable treatment (LW or ESL) as well as variational statements (PVD and RMVT), a large number of newly finite elements have been presented. Finite elements that are based on PVD and RMVT have been called classical and advanced, respectively.

In order to write the matrices related to the considered plate elements in a concise form and to implement them in a computer code (see Part 2), extensive indicial notations have been set out. As a result, all the finite element matrices have been built from only five arrays that were called fundamental nuclei (four are related to RMVT applications and one to PVD cases). These arrays have 3×3 dimensions and are therefore constituted of only nine terms each. The different formulations are then obtained by expanding the indices that were introduced for the N‐order expansion, for the number of nodes Nn and for the constitutive layers Nl. Compliances and/or stiffness are accumulated from layer to multilayered level according to the corresponding variable treatment (ESLM or LWM). The numerical evaluations and assessment for the presented plate elements have been provided in the companion paper (Part 2), where it has been concluded that it is convenient to refer to RMVT as a variational tool to formulate multilayered plate elements that are able to give a quasi‐three‐dimensional description of stress/strain fields in multilayered thick structures. Copyright © 2002 John Wiley & Sons, Ltd.