bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite deformation analysis of geomaterials
Authors: Jeremić Boris , Runesson Kenneth , Sture Stein 
Published: August 2002

AbstractThe mathematical structure and numerical analysis of classical small deformation elasto–plasticity is generally well established. However, development of large deformation elastic–plastic numerical formulation for dilatant, pressure sensitive material models is still a research area.In this paper we present development of the finite element formulation and implementation for large deformation, elastic–plastic analysis of geomaterials. Our developments are based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A consistent linearization of the right deformation tensor together with the Newton method at the constitutive and global levels leads toward an efficient and robust numerical algorithm. The presented numerical formulation is capable of accurately modelling dilatant, pressure sensitive isotropic and anisotropic geomaterials subjected to large deformations. In particular, the formulation is capable of simulating the behaviour of geomaterials in which eigentriads of stress and strain do not coincide during the loading process.The algorithm is tested in conjunction with the novel hyperelasto–plastic model termed the B material model, which is a single surface (single yield surface, affine single ultimate surface and affine single potential surface) model for dilatant, pressure sensitive, hardening and softening geomaterials. It is specifically developed to model large deformation hyperelasto–plastic problems in geomechanics.We present an application of this formulation to numerical analysis of low confinement tests on cohesionless granular soil specimens recently performed in a SPACEHAB module aboard the Space Shuttle during the STS‐89 mission. We compare numerical modelling with test results and show the significance of added confinement by the thin hyperelastic latex membrane undergoing large stretching. Copyright © 2001 John Wiley & Sons, Ltd.
A shear‐dilation‐based model for evaluation of hydraulically stimulated naturally fractured reservoirs
Authors: Rahman M. K. , Hossain M. M. , Rahman S. S. 
Published: August 2002

AbstractThe role of shear dilation as a mechanism of enhancing fluid flow permeability in naturally fractured reservoirs was mainly recognized in the context of hot dry rock (HDR) geothermal reservoir stimulation. Simplified models based on shear slippage only were developed and their applications to evaluate HDR geothermal reservoir stimulation were reported. Research attention is recently focused to adjust this stimulation mechanism for naturally fractured oil and gas reservoirs which reserve vast resources worldwide. This paper develops the overall framework and basic formulations of this stimulation model for oil and gas reservoirs. Major computational modules include: natural fracture simulation, response analysis of stimulated fractures, average permeability estimation for the stimulated reservoir and prediction of an average flow direction. Natural fractures are simulated stochastically by implementing ‘fractal dimension’ concept. Natural fracture propagation and shear displacements are formulated by following computationally efficient approximate approaches interrelatingin situstresses, natural fracture parameters and stimulation pressure developed by fluid injection inside fractures. The average permeability of the stimulated reservoir is formulated as a function of discretized gridblock permeabilities by applying cubic law of fluid flow. The average reservoir elongation, or the flow direction, is expressed as a function of reservoir aspect ratio induced by directional permeability contributions. The natural fracture simulation module is verified by comparing its results with observed microseismic clouds in actual naturally fractured reservoirs. Permeability enhancement and reservoir growth are characterized with respect to stimulation pressure,in situstresses and natural fracture density applying the model to two example reservoirs. Copyright © 2002 John Wiley & Sons, Ltd.
BPH with coexisting overactive bladder dysfunction—an everyday urological dilemma
Authors: Knutson Tomas , Edlund Christer , Fall Magnus , Dahlstrand Christer 
Published: August 2002

AbstractThe aim of this study was to use a systematic schedule, including urodynamics, to describe the rate of coexisting overactive bladder (OB) in patients with bladder outlet obstruction (BOO) caused by benign prostatic hyperplasia (BPH). We also identified differences between the patients with pure BOO compared with those with BOO combined with OB (BOO + OB). One hundred and sixty‐two men referred to our clinic due to LUTS were included. Patients with a history that might affect their bladder function were excluded. After cystometry and pressure–flow studies, the patients were divided into pure BOO and BOO + OB. Of the 162 men, 55% had pure BOO. BOO + OB was found in 45%. Age, s‐PSA, voided volume, and obstruction grade differed significantly between the groups. The patients with BOO + OB were older, had a higher s‐PSA, voided smaller volumes, and were more obstructed. We found no differences in TRUS‐volume, Q‐max, IPS score, or PVR. There was a strong association between OB and BOO, the percentage of OB increasing with increased obstruction. TRUS‐volume, Q‐max, IPS score, and PVR did not predict whether the patients had a combined BOO + OB or not. These findings indicate that BOO is a progressive disease, which in time causes pronounced obstruction and perhaps in itself contributes to the development of OB. Neurourol. Urodynam. 20:237–247, 2001. © 2001 Wiley‐Liss, Inc.
1‐13C glucose magnetic resonance spectroscopy of pediatric and adult brain disorders
Authors: Blüml Stefan , Moreno Angel , Hwang Jong‐Hee , Ross Brian D. 
Published: August 2002

AbstractWith protocols designed for use in a clinical environment we investigated the feasibility and diagnostic potential of 13C MRS after 1‐13C labeled glucose infusion. 13C MRS brain examinations were performed in 27 subjects (17 children and pediatric patients, six adult patients, and four adult controls), using a standard 1.5 T clinical MR scanner. 1‐13C glucose, 99% enriched (20% w/v) was administered intravenously (690 or 210 mg/kg body weight) or orally (730 mg/kg). Cerebral 13C‐enrichment patterns and time courses were compared. 1‐13C glucose appeared in brain spectra within 2.5–15 min, with ensuing enrichment of its metabolites. No complications were encountered. When data obtained in patients were compared with controls, striking abnormalities in hepatic encephalopathy and in premature brain were observed, consistent with reduced cerebral glucose metabolism. Abnormalities in the 13C enrichment pattern were also observed in pediatric patients with leukodystrophies and mitochondrial disorders. In this preliminary survey, we conclude that 13C MRS in combination with glucose infusion is safe and efficient and provides new insights into the pathophysiology of brain disorders. Copyright © 2001 John Wiley & Sons, Ltd.
Abbreviations used:

Ala

alanine

ALD

adrenoleukodystrophy

Asp

aspartate

CACH

childhood ataxia with diffuse central nervous system hypomyelination

Glc

glucose

Gln

glutamine

Glu

glutamate, HE, hepatic encephalopathy

HCO3−

bicarbonate

i.v.

intravenous

Lac

lactate

mI

myo‐inositol

NAA

N‐acetylaspartate

TCA

tricarboxylic acid.
Combined diffusion weighting and CSF suppression in functional MRI
Authors: Andersson Linda , Bolling Max , Wirestam Ronnie , Holtås Stig , Ståhlberg Freddy 
Published: August 2002

AbstractIn this study, EPI pulse sequences with diffusion weighting for reduction of contributions from large vessels and inversion pulses in order to minimize the effects of CSF pulsations and CSF partial volume effects were developed for BOLD contrast investigations in functional MR imaging. One inversion recovery echo‐planar imaging (IR‐EPI) pulse sequence and one IR‐EPI with additional diffusion weighting (DW‐IR‐EPI) were developed and compared to a standard gradient‐echo EPI sequence in a cortical stimulation experiment in nine healthy volunteers. Stimulation of motor cortex was performed using a semi‐complex finger‐tapping paradigm in seven periods of alternating rest and stimulation. Comparison between the three pulse sequences was made by measuring the activated volume in each subject, as well as by calculating the relative signal increase during stimulation. Due to different baseline signal‐to‐noise levels in the images generated by the three pulse sequences, artificial noise was added so that the comparative investigation could be performed independently of the noise level. The activated volume was 128 ± 73 pixels (mean ± SD) using the standard EPI pulse sequence, 31 ± 12 pixels using IR‐EPI and 15 ± 13 pixels when DW‐IR‐EPI was employed. The relative signal increase was 5.7 ± 1.1% using standard EPI, 11.5 ± 3.1% using IR‐EPI and 9.9 ± 2.4% using DW‐IR‐EPI. The activated volume obtained with the addition of extra noise, i.e. at equal S/N, was 70 ± 50 pixels using the standard EPI, and when using IR‐EPI, the activated volume was 28 ± 13 pixels. At equal S/N, the signal increase was 7.3 ± 1.4% using standard EPI and 12.0 ± 3.6% using IR‐EPI. In BOLD contrast imaging, a combination of diffusion weighting and inversion recovery appeared to reduce false activation caused by CSF pulsation and blood flow in large vessels. Copyright © 2002 John Wiley & Sons, Ltd.
An adaptive load balancing scheme for web servers
Authors: Aweya James , Ouellette Michel , Montuno Delfin Y. , Doray Bernard , Felske Kent 
Published: August 2002

AbstractThis paper describes an overload control scheme for web servers which integrates admission control and load balancing. The admission control mechanism adaptively determines the client request acceptance rate to meet the web servers' performance requirements while the load balancing or client request distribution mechanism determines the fraction of requests to be assigned to each web server. The scheme requires no prior knowledge of the relative speeds of the web servers, nor the work required to process each incoming request. Copyright © 2002 John Wiley & Sons, Ltd.
On the geodetic number of a graph
Authors: Chartrand Gary , Harary Frank , Zhang Ping 
Published: August 2002

AbstractFor two vertices u and v of a graph G, the set I(u, v) consists of all vertices lying on some u − v geodesic in G. If S is a set of vertices of G, then I(S) is the union of all sets I(u, v) for u, v ∈ S. The geodetic number g(G) is the minimum cardinality among the subsets S of V(G) with I(S) = V(G). It is shown that if G is a graph of order n and diameter d then g(G) ≤ n − d + 1 and this bound is sharp. For positive integers r, d, and k ≥ 2 with r ≤ d ≤ 2r, there exists a connected graph G of radius r, diameter d, and g(G) = k. Also, for integers n, d, and k with 2 ≤ d < n, 2 ≤ k < n, and n − d − k + 1 ≥ 0, there exists a graph G of order n, diameter d, and g(G) = k. It is shown, for every nontrivial connected graph G, that g(G) ≤ g(G × K2). A sufficient condition for the equality of g(G) and g(G × K2) is presented. A graph F is a minimum geodetic subgraph if there exists a graph G containing F as an induced subgraph such that V(F) is a minimum geodetic set for G. Minimum geodetic subgraphs are characterized. © 2002 John Wiley & Sons, Inc.
A comparative analysis of several formulations for the generalized minimum spanning tree problem
Authors: Feremans Corinne , Labbé Martine , Laporte Gilbert 
Published: August 2002

AbstractThis article describes eight formulations for the Generalized Minimum Spanning Tree Problem (GMSTP). Relationships between the polytopes of their linear relaxations are established. It is shown that four of these polytopes are strictly included in the remaining ones. This analysis suggests which formulations should be preferred for the construction of a branch‐and‐cut algorithm and for the evaluation of heuristics. © 2002 John Wiley & Sons, Inc.
Estradiol‐induced phosphorylation of ERK1/2 in explants of the mouse cerebral cortex: The roles of heat shock protein 90 (Hsp90) and MEK2
Authors: Sétáló György , Singh Meharvan , Guan Xiaoping , Toran‐Allerand C. Dominique 
Published: August 2002

AbstractConfocal laser scanning microscopy was used to identify the cells within organotypic slice cultures of the developing mouse cerebral cortex that respond to estradiol treatment by phosphorylation of ERK1 and ERK2. Estrogen‐responsive cells resembled neurons morphologically and expressed the neuronal marker microtubule‐associated protein 2B. The intracellular distribution of the phospho‐ERK signal was both cytoplasmic and nuclear, but inhibition of protein synthesis abolished the appearance of the nuclear signal. ERK1and ERK2 also coimmunoprecipitated with heat shock protein 90 (Hsp90) in the cerebral cortical explants. Geldanamycin effectively disrupted this association and prevented ERK phosphorylation. Surprisingly, MEK2 but not MEK1 was the principal mediator of estradiol‐induced activation of ERK. Our data demonstrate the requirement for Hsp90 in estrogen‐induced activation of ERK1 and ERK2 by MEK2 in the developing mouse cerebral cortex and also provide insight into alternative mechanisms by which estradiol may influence cytoplasmic and nuclear events in responsive neurons via the MAP kinase cascade. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 1–12, 2002
Sexual dimorphism in neuromuscular junction size on a muscle used in courtship by green anole lizards
Authors: O'Bryant Erin L. , Wade Juli 
Published: August 2002

AbstractThe green anole lizard exhibits seasonal courtship behavior that is sexually dimorphic. This courtship consists of the extension of a bright red throat fan (dewlap) associated with head‐bobbing display behavior. While males extend their dewlaps in aggressive encounters as well as in courtship, females use their considerably smaller dewlaps much less frequently and mainly in agonistic encounters. In parallel, a number of components of the neuromuscular system controlling dewlap extension are greater in males than in females during the breeding season, including dewlap motoneuron soma size and muscle fiber size and number. These features do not seem to change substantially in adulthood, despite a dramatic decline in dewlap use during the nonbreeding season. We explored the morphology of this neuromuscular system in more detail in the present experiment in males and females during both the breeding and nonbreeding seasons. Fiber and whole muscle length (approximately perpendicular to the fibers) were measured. Acetylcholinesterase histochemistry was used to visualize neuromuscular junctions (NMJs), and the surface area and density of NMJs were assessed for each animal. During the breeding season, NMJ size was larger in males than in females, but NMJ density along each fiber was equivalent between the sexes. In addition, whole muscle length and that of individual muscle fibers, was larger in males than in females. However, when corrected for body size, the sex difference in muscle fiber length disappeared. In the nonbreeding season, the sexual dimorphisms were maintained, suggesting that these features do not change substantially due to differences in circulating testosterone or a difference in use across seasons. Overall, these results are consistent with the idea that enhanced NMJ size is a relatively stable feature of the dewlap muscle in adulthood that either facilitates or is a consequence of using a larger muscle to extend a bigger dewlap in males compared to females. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 24–30, 2002
GABA and development of the Xenopus optic projection
Authors: Ferguson Shane C. D. , McFarlane Sarah 
Published: August 2002

AbstractIn the developing visual system of Xenopus laevis retinal ganglion cell (RGC) axons extend through the brain towards their major target in the midbrain, the optic tectum. Enroute, the axons are guided along their pathway by cues in the environment. In vitro, neurotransmitters have been shown to act chemotropically to influence the trajectory of extending axons and regulate the outgrowth of developing neurites, suggesting that they may act to guide or modulate the growth of axons in vivo. Previous work by Roberts and colleagues (1987) showed that populations of cells within the developing Xenopus diencephalon and midbrain express the neurotransmitter gamma amino butyric acid (GABA). Here we show that Xenopus RGC axons in the midoptic tract grow alongside the GABAergic cells and cross their GABA immunopositive nerve processes. Moreover, RGC axons and growth cones express GABA‐A and GABA‐B receptors, and GABA and the GABA‐B receptor agonist baclofen both stimulate RGC neurite outgrowth in culture. Finally, the GABA‐B receptor antagonist CGP54626 applied to the developing optic projection in vivo causes a dose‐dependent shortening of the optic projection. These data indicate that GABA may act in vivo to stimulate the outgrowth of Xenopus RGC axons along the optic tract. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 272–284, 2002
Telomerase and oligodendrocyte differentiation
Authors: Caporaso Gregg L. , Chao Moses V. 
Published: August 2002

AbstractMyelin in the mammalian central nervous system (CNS) is produced by oligodendrocytes, most of which arise from oligodendrocyte precursor cells (OPCs) during late embryonic and early postnatal development. Both external and internal cues have been implicated in regulating OPC exit from the cell cycle and differentiation into oligodendrocytes. In this study, we demonstrate that differentiation of cultured OPCs into mature oligodendrocytes is associated with lower levels of activity of telomerase, the ribonucleoprotein that synthesizes telomeric DNA at the ends of chromosomes. Differentiation is also associated with lower levels of mRNA encoding the catalytic subunit of telomerase (TERT), whereas no difference is seen in the expression of its telomeric template RNA component (TR). These data suggest a possible role for telomerase during normal growth and differentiation of oligodendrocytes that may be relevant to the mechanism of myelination in the CNS. © 2001 John Wiley & Sons, Inc. J Neurobiol 49: 224–234, 2001
A parallel balance scheme for banded linear systems
Authors: Golub Gene H. , Sameh Ahmed H. , Sarin Vivek 
Published: August 2002

AbstractA parallel algorithm is proposed for the solution of narrow banded non‐symmetric linear systems. The linear system is partitioned into blocks of rows with a small number of unknowns common to multiple blocks. Our technique yields a reduced system defined only on these common unknowns which can then be solved by a direct or iterative method. A projection based extension to this approach is also proposed for computing the reduced system implicitly, which gives rise to an inner–outer iteration method. In addition, the product of a vector with the reduced system matrix can be computed efficiently on a multiprocessor by concurrent projections onto subspaces of block rows. Scalable implementations of the algorithm can be devized for hierarchical parallel architectures by exploiting the two‐level parallelism inherent in the method. Our experiments indicate that the proposed algorithm is a robust and competitive alternative to existing methods, particularly for difficult problems with strong indefinite symmetric part. Copyright © 2001 John Wiley & Sons, Ltd.
Woven fabric composites—part II: Characterization of macro‐crack initiation loads for global damage analysis
Authors: Choi Jaehyon , Tamma Kumar K. 
Published: August 2002

AbstractIn Part 2, finite element techniques are developed to additionally investigate the global damage of woven fabric composites, focusing on plain weaves. The homogenized elastic properties of the original undamaged and the damaged woven fabric composites from the micromechanical homogenization and the micromechanical progressive damage analysis investigated earlier in Part 1 are subsequently employed in the present global damage analysis. The theory of continuum damage mechanics is utilized in the global damage analysis. The damage variables, the most important material properties of the continuum damage mechanics, are measures of average material degradation at a macro‐mechanics scale. In the present study, these damage variables are calculated numerically using the results from the micromechanical damage analysis in Part 1, instead of being obtained experimentally. Subsequently, a finite element formulation for the global damage analysis of woven fabric composites is developed to predict the initiation loads of macro‐cracks. Copyright © 2001 John Wiley & Sons, Ltd.
Three‐dimensional stochastic finite element method for elasto‐plastic bodies
Authors: Anders Maciej , Hori Muneo 
Published: August 2002

AbstractA new stochastic finite element method (SFEM) is formulated for three‐dimensional softening elasto‐plastic bodies with random material properties. The method is based on the Karhunen–Loeve and polynomial chaos expansions, and able to efficiently estimate complete probabilistic characteristics of the response, such as moments or PDFs. To reduce the computational complexity in the three‐dimensional setting, two alterations are made with respect to the two‐dimensional SFEM proposed earlier by the authors. First, a variability preserving modification of the Karhunen–Loeve expansion is rigorously derived and applied in the stochastic discretization of random fields representing material properties. Second, an efficient algorithm for parallel processing is developed, with time consumption being the same order as for an ordinary FEM, rendering the proposed SFEM an effective alternative to Monte‐Carlo simulation. The applicability of the proposed method to stochastic analysis of strain localization is examined using Monte‐Carlo simulation. Then, it is applied to a fault formation problem which is a recent concern of earthquake engineering. Ground surface layers are modelled by a softening elasto‐plastic body, and the evolution of probabilistic characteristics of the rupture process is analysed in detail. Some practical observations are made regarding the nature of the fault formation from the stochastic viewpoint. Copyright © 2001 John Wiley & Sons, Ltd.
Random walk method for the two‐ and three‐dimensional Laplace, Poisson and Helmholtz's equations
Authors: Chati Mandar K. , Grigoriu Mircea D. , Kulkarni Salil S. , Mukherjee Subrata 
Published: August 2002

AbstractThe random walk method (RWM) is developed here for solving the Laplace, Poisson, and Helmholtz equations in two and three dimensions. The RWM is a local method, i.e. the solution at an arbitrary point can be determined without having to obtain the complete field solution. The method is based on the properties of diffusion processes, the Itô formula, the Dynkin formula, the Feynman–Kac functional, and Monte Carlo simulation. Simplicity, stability, accuracy, and generality are the main features of the proposed method. The RWK is inherently parallel and this fact has been fully exploited in this paper. Extensive numerical results have been presented in order to understand the various parameters involved in the method. Copyright © 2001 John Wiley & Sons, Ltd.