bluuebunny/crossref_metadata_2025 huggingface dataset:
Cysteine protease inhibitor is specifically expressed in pre‐ and early‐vitellogenic oocytes from the brook trout periovulatory ovary*
Authors: Bobe Julien , Goetz Frederick William
Published: August 2002

A cDNA fragment hybridizing with a transcript abundant in the periovulatory ovary was obtained while performing subtractive cloning on brook trout ovulatory and postovulatory ovarian tissue. Using this fragment as a probe, a 478 bp full‐length cDNA was obtained by screening an ovulatory ovarian cDNA library. This cDNA presumably codes for an 88 amino acid protein that is structurally related to a new family of cysteine protease inhibitors characterized by the presence of a type I thyroglobulin motif in the amino acid sequence. Therefore, the protein was tentatively named an oocyte cysteine protease inhibitor (OCPI). On Northern blots, the OCPI cDNA hybridizes with a 0.5 kb transcript present in the ovary during the periovulatory period. The OCPI transcript and protein were localized to the cytoplasm of pre‐ and early‐vitellogenic oocytes. On Northern blots of RNA from other tissues, the OCPI transcript was detected only in the ovary. On Western blots, OCPI was detected in the ovarian tissue at all periovulatory stages tested. The specific localization of both OCPI transcript and protein to pre‐ and early‐vitellogenic oocytes and the structural similarity to protease inhibitors, suggest that OCPI might be involved in the protection of oocytes during the periovulatory period or in the regulation of yolk formation and degradation. Mol. Reprod. Dev. 60: 312–318, 2001. © 2001 Wiley‐Liss, Inc.
On the parameters affecting the sensitivity of MR measures of pressure with microbubbles
Authors: Dharmakumar Rohan , Plewes Donald B. , Wright Graham A.
Published: August 2002

Recently, it has been suggested that gas encapsulated distensible microbubbles may serve as pressure probes in the MR field through the relationship between bubble size and 1/T2 or 1/T. Currently, in vivo application of this technique is hindered by the ability of T2 or T to detect pressure changes that are clinically relevant. This work identifies and characterizes, through numerical simulations, the set of parameters which optimize the ability of this technique to detect small pressure changes. Results show that when the bubbles do not interact magnetically, the T2‐ and T‐based measurements of pressure are strongly influenced by the bubble size at atmospheric pressure, static magnetic field strength, magnitude of the susceptibility difference between the encapsulated gas and plasma, bubble volume fraction, and the refocusing interval. In particular, to detect clinically relevant pressure changes, microbubbles need to be approximately 2–3 μm in radius, distributed at a volume fraction of 0.15%, and have a volumetric magnetic susceptibility difference of at least 34 ppm. Magn Reson Med 47:264–273, 2002. © 2002 Wiley‐Liss, Inc.
Monitoring blood oxygen state in muscle microcirculation with transverse relaxation
Authors: Stainsby J.A. , Wright G.A.
Published: August 2002

Oxygen uptake from the microcirculation is a direct measure of tissue function. Magnetic resonance is capable of detecting differences between oxygenated and deoxygenated blood due to the paramagnetic properties of deoxyhemoglobin. At the level of the microcirculation, however, imaging methods cannot directly visualize the vessels. Instead, bulk MR parameters are investigated for their ability to monitor blood oxygen saturation (%O2) changes in the microcirculation of tissue, specifically skeletal muscle. Experiments in an in vitro model verified the feasibility of detecting changes in exponential decay signals, and also verified the prediction of only two distinct decay components. Experiments in a rabbit model demonstrate that T2′ and monoexponential T2 decay are not sensitive to blood oxygen changes, but that the long‐T2 component in a biexponential fit is correlated to the blood oxygen state. Assuming a two‐pool model for water protons in muscle, and with knowledge of the T2‐%O2 relation, estimates of the microcirculation blood oxygen state can be made with some reasonable assumptions. Magn Reson Med 45:662–672, 2001. © 2001 Wiley‐Liss, Inc.
Utilizing the diffusion‐to‐noise ratio to optimize magnetic resonance diffusion tensor acquisition strategies for improving measurements of diffusion anisotropy
Authors: Armitage P.A. , Bastin M.E.
Published: August 2002

It is well known that quantitative anisotropy measurements derived from the diffusion tensor are extremely sensitive to noise contamination. The level of noise in the diffusion tensor imaging (DTI) experiment is usually measured from some estimate of the signal‐to‐noise ratio (SNR) in the component diffusion‐weighted (DW) images. This measure is, however, highly dependent on experimental parameters, such as the diffusion attenuation b‐value and the diffusion coefficient of the subject. Conversely, the diffusion‐to‐noise ratio (DNR), defined as the SNR of the calculated diffusion tensor trace map, provides a reliable estimate of noise contamination, which is largely independent of such parameters. In this work it is demonstrated how reliable anisotropy measurements can be obtained using an image acquisition strategy that optimizes the DNR of the DTI experiment. This acquisition scheme is shown to provide noise‐independent measurements of typical diffusion anisotropy values found in the human brain. Magn Reson Med 45:1056–1065, 2001. © 2001 Wiley‐Liss, Inc.
Dependence of venous enhancement on the field of view in 3D contrast‐enhanced MRA using the elliptical centric view order
Authors: Fain Sean B. , Riederer Stephen J.
Published: August 2002

The dependence of venous suppression on the acquisition field of view (FOV) in elliptical centric 3D contrast‐enhanced magnetic resonance angiography (CE‐MRA) is studied theoretically and experimentally. It is hypothesized that a reduced FOV in an arterial phase acquisition results in improved venous suppression. An expression is derived linking the k‐space representation of a vein to venous return time and acquisition parameters. For a y × z FOV reduction from 24 cm × 7.2 cm to 18 cm × 3.6 cm, equivalent voxel size, and venous return times ranging from 0–7 s, the mean improvement in venous suppression ranged from 7.0% for the 19‐mm‐diameter vein to 32.1% in the 6‐mm‐diameter vein, assuming a step function‐shaped venous enhancement profile. Decreased venous enhancement with reduced FOV is also observed for scans with equivalent acquisition times, although the degree of suppression is dependent on the shape of the venous enhancement curve. Magn Reson Med 45:1134–1141, 2001. © 2001 Wiley‐Liss, Inc.
Alternative 1‐13C glucose infusion protocols for clinical 13C MRS examinations of the brain
Authors: Moreno Angel , Blüml Stefan , Hwang Jong‐Hee , Ross Brian D.
Published: August 2002

Clinical utility of 13C MRS is limited by cost and long examination times. Three 1‐13C glucose infusion protocols—a high‐dose i.v., low‐dose i.v., and oral administration of 1‐13C glucose—were compared on a GE 1.5T MR scanner. Resolution and sensitivity were sufficient to identify 13C glucose (1α and 1β), glutamate (C1–C4), glutamine (C1–C4), aspartate (C2 and C3), lactate, alanine, and bicarbonate in brain spectra. The three protocols were efficacious, as measured by cerebral enrichment of 1‐13C glucose (62%, 42%, and 38%) and its principal metabolite, 4‐13C glutamate (13%, 11%, and 16%), respectively. Intravenous infusion of 1‐13C glucose 0.23 g/kg body weight (low dose) provides equivalent information at one third the cost of previous regimes. Magn Reson Med 46:39–48, 2001. © 2001 Wiley‐Liss, Inc.
Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties
Authors: Alecci Marcello , Collins Christopher M. , Smith Michael B. , Jezzard Peter
Published: August 2002

The RF B1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B1 distortion at high field can be explained with 3D full‐Maxwell calculations. It was found that the B1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z‐axis the B1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B1 uniformity was 9 cm with phantoms and 7 cm in the head. Magn Reson Med 46:379–385, 2001. © 2001 Wiley‐Liss, Inc.
Gd‐DTPA bolus tracking in the myocardium using T1 fast acquisition relaxation mapping (T1 FARM)
Authors: Bellamy Deanna D. , Pereira Raoul S. , McKenzie Charles A. , Prato Frank S. , Drost Dick J. , Sykes Jane , Wisenberg Gerald
Published: August 2002

MRI methods currently used for bolus tracking in the myocardium, such as saturation recovery turbo‐fast low‐angle shot (FLASH) (srTFL), are limited by signal intensity (SI) saturation at high contrast agent (CA) concentrations. By using T1 fast acquisition relaxation mapping (T1 FARM), a Gd‐DTPA bolus (0.075 vs. 0.025 mmol/kg) may be injected without causing saturation. This study tested the feasibility of in vivo T1 FARM bolus tracking under rest/stress conditions in seven beagles with multiple permanently occluded branches of the left anterior descending (LAD) coronary artery. Although it underestimated the myocardial perfusion reserve (MPR) measured ex vivo using radioactive microspheres (mean ± SEM; 3.60 ± 0.26), the MPR determined upon application of the modified Kety model (1.86 ± 0.10) enabled distinction between normal and infarcted tissue. The partition coefficient (λ) estimated at rest and stress using the modified Kety model underestimated ex vivo radioactive measurements in infarcted tissue (0.25 ± 0.01 vs. 0.26 ± 0.01 vs. 0.79 ± 0.08 ml/g, P < 0.0001) yet was accurate in normal tissue (0.28 ± 0.01 vs. 0.30 ± 0.01 vs. 0.33 ± 0.01 ml/g, P = NS). Thus, although unsuitable for myocardial viability assessment, T1 FARM bolus tracking shows potential for assessment of myocardial perfusion. Magn Reson Med 46:555–564, 2001. © 2001 Wiley‐Liss, Inc.
Comparison of aerosolized gadoteridol and gadopentetate dimeglumine for magnetic resonance ventilation imaging of the lung
Authors: Haage Patrick , Karaagac Suleyman , Adam Gerhard , Glowinski Arndt , Günther Rolf W.
Published: August 2002

The purpose of this study was to compare aerosolized gadoteridol and gadopentetate dimeglumine in regard to homogeneity of aerosol distribution and relative pulmonary signal intensity (SI) changes after a 10‐min mechanical ventilation period. Twenty experimental procedures were performed in 10 intubated domestic pigs that were mechanically aerosolized with the nebulized contrast medium. Images were obtained by using a respiratory‐gated T1‐weighted TSE sequence. Pulmonary SI increase for the right and left lung was 26% ± 25% and 25% ± 12%, respectively, for gadopentetate dimeglumine, and 45% ± 12% and 43% ± 10%, respectively, for gadoteridol. Aerosol distribution was rated homogeneous in all cases by two readers. It is concluded that both contrast agents in aerosolized form are capable of depicting pulmonary ventilation in healthy animals with lung capacities comparable to those of humans. SI differences between gadoteridol and gadopentetate dimeglumine are explained by their considerable difference in viscosity. Magn Reson Med 46:803–806, 2001. © 2001 Wiley‐Liss, Inc.
NKT‐associated markers and perforin in hyperplastic thymuses from patients with Myasthenia gravis
Authors: Nagane Yuriko , Utsugisawa Kimiaki , Obara Daiji , Tohgi Hideo
Published: August 2002

Immunohistochemical expression of natural killer T (NKT) cell–associated markers (Vα24 and CD56) and perforin in relation to CD44–highly positive (CD44high) cells was studied in hyperplastic thymuses from patients with myasthenia gravis (MG) whose symptoms dramatically improved after thymectomy and compared with non‐MG control thymuses. In the control thymuses, Vα24‐positive (Vα24+) and CD56‐positive (CD56+) cells were sparsely distributed in the medullary area only. In contrast, in hyperplastic MG thymus, Vα24+ and CD56+ cells were more frequent in connective tissue, appeared to have penetrated the thymic parenchyma, and most coexpressed CD44high. Perforin‐positive cells were not present in the control thymus, but were in the connective tissue and perilobular cortical areas in the hyperplastic MG thymus. Most of these perforin‐positive cells were CD44high and were located near blood vessels. They appeared to have migrated directly from the vascular system and penetrated the thymic parenchyma. Some perforin‐positive cells coexpressed Vα24, CD56, or both. These findings suggest that in this particular type of MG thymus, NKT‐like cells may have increased via a CD44‐ and perforin‐mediated mechanism, leading to an imbalance in the immune system that favored an antibody‐mediated autoimmunity against the acetylcholine receptor. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1359–1364, 2001
Differences in responses of cutaneous afferents in the human median and sural nerves to ischemia
Authors: Lin Cindy S.‐Y. , Mogyoros Ilona , Kuwabara Satoshi , Cappelen‐Smith Cecilia , Burke David
Published: August 2002

Recent evidence suggests that two conductances responsible for accommodation to changes in membrane potential (a slow K+ conductance and inward rectification [IH]) are less active on cutaneous afferents in the sural nerve than on those in the median nerve, and it has been suggested that these axons would therefore respond differently to stress, whether natural or due to disease. The present study was undertaken in eight healthy volunteers to determine whether these afferents respond differently to the depolarizing and hyperpolarizing stresses that accompany ischemia for 13 min and subsequent recovery. During ischemia, the decrease in threshold was quantitatively less for the sural afferents, as were the changes in the other indices of axonal excitability, presumably because the ischemic depolarization was less for sural afferents. Following release of ischemia, there was, as predicted, a divergence in the pattern of threshold change. With median afferents there was evidence of a transient depolarization, believed to be due to inward rectification, superimposed on a long‐lasting hyperpolarization. The response of sural afferents lacked this transient depolarizing threshold change. Cutaneous afferents in the median and sural nerves behave differently in response to ischemic and postischemic stresses, and it is likely that they will also respond differently to disease processes. In a number of respects the differences between sural and median afferents are analogous to differences between diabetic and normal nerves. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1503–1509, 2001
Frictional contact of laminated elastic half‐spaces allowing interface cavities. Part 2: Numerical results
Authors: Kryshtafovych A. A. , Matysiak S. J.
Published: August 2002

The paper presents some numerical results of the problem on contact of stratified elastic half‐spaces possessing unevenness of their surface layers. The approach of the Jacobi polynomials is used to reduce the singular integral equation of the problem to a system of linear algebraic equations. On the basis of the system's solution the dependence of gaps' geometric characteristics on external load and friction is investigated for two types of initial boundary disturbances, namely a local symmetric recess and a periodic set of recesses at a flat boundary. Numerical results are presented in figures for a few elastic and geometric parameters of joint components. The analysis shows that elastic properties and geometric structure of a laminated half‐space have a significant influence on the shape of interface gaps and their location. Copyright © 2001 John Wiley & Sons, Ltd.
Efficient conditional modeling for geotechnical uncertainty evaluation
Authors: Graettinger A. J. , Lee J. , Reeves H. W.
Published: August 2002

A first‐order Taylor series method including direct derivative coding (DDC) is presented as a computationally efficient method for producing the probability distribution associated with calculated geotechnical performance. The probability distribution is employed in reliability analyses to calculate the probability of failure, valuable information that is not typically associated with deterministic analyses. The probability distribution also is used to identify important input parameters and to direct sampling efforts. Another approach to generate the probability distribution is the Monte Carlo (MC) method, however, Taylor series results generally are calculated in less time than the MC approach. One key to the implementation of the Taylor series approach is efficient approximation of the sensitivities required by the Taylor series calculation. DDC provides the technique to produce an efficient Taylor series algorithm. Directly coding the sensitivity analysis into the engineering model is accomplished by automatic and hand programming of derivatives. ADIFOR 2.0 was employed to automatically add derivatives to an existing engineering analysis model. For this paper a meshing program and 3D FEM for soil deformation is used to demonstrate the DDC approach. Although DDC requires a large up‐front programming effort, it is not site or data specific. Therefore, once the derivative programming has been performed, the numerical model can be applied to a wide variety of problems without additional user intervention. Copyright © 2001 John Wiley & Sons, Ltd.
Instability of wave propagation in saturated poroelastoplastic media
Authors: Li Xikui , Zhang Junbo , Zhang Hongwu
Published: August 2002

In the present work, stationary discontinuities and fluttery instabilities of wave propagation in saturated poro‐elastoplastic media are analysed in the frame of Biot theory. The generalized Biot formulations are particularly employed for simulating non‐linear coupled hydro‐mechanical behaviour of the media. Inertial coupling effect between the solid and the fluid phases of the media is also taken into account. The non‐associated Drucker–Prager criterion to describe non‐linear constitutive behaviour of pressure dependent elasto‐plasticity for the solid skeleton of the media is particularly considered. With omission of compressibility of solid grains and the pore fluid, the critical conditions of stationary discontinuities and flutter instabilities occurring in wave propagation are given in explicit forms. It is shown that when the stationary discontinuity is triggered at the surface of discontinuity there still may exist real wave speeds. The wave speeds across the stationary discontinuity surface entirely cease to be real only in non‐associated plasticity, certain ranges of value of Poisson's ratio and when compression stress normal to the surface of discontinuity dominates the stress state at the surface. It is also indicated that the fluttery instabilities, under which some wave speeds cease to be real even in strain hardening stage, may occur prior to stationary discontinuities only for non‐associated plasticity under certain conditions. These conditions are: (1) both the porosity and the Poisson's ratio possess relatively low values and (2) the deviatoric part of the effective stress normal to the surface of discontinuity is compressive. A region in the porosity–Poisson's ratio plot, in which fluttery instabilities are possible to occur, is given. Copyright © 2002 John Wiley & Sons, Ltd.
Duality in constrained multi‐facility location models
Authors: Üster Halit , Love Robert F.
Published: August 2002

We consider the 𝓁p‐norm multi‐facility minisum location problem with linear and distance constraints, and develop the Lagrangian dual formulation for this problem. The model that we consider represents the most general location model in which the dual formulation is not found in the literature. We find that, because of its linear objective function and less number of variables, the Lagrangian dual is more useful. Additionally, the dual formulation eliminates the differentiability problem in the primal formulation. We also provide the Lagrangian dual formulation of the multi‐facility minisum location problem with the 𝓁pb‐norm. Finally, we provide a numerical example for solving the Lagrangian dual formulation and obtaining the optimum facility locations from the solution of the dual formulation. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 410–421, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10010
Magnetic coupling between water and creatine protons in human brain and skeletal muscle, as measured using inversion transfer 1H‐MRS
Authors: Kruiskamp M. J. , de Graaf R. A. , van der Grond J. , Lamerichs R. , Nicolay K.
Published: August 2002

Using the inversion transfer technique, the possible magnetic coupling between water protons and the protons of low‐molecular weight metabolites was investigated in human brain and skeletal muscle at 1.5 T. The localized 1H‐MR spectra were recorded at different times after selective inversion of the water resonance. Water inversion led to a significant transient reduction in the signal intensity of the methyl protons of creatine/phosphocreatine, in both tissues. This is indicative of magnetic coupling between the protons of water and those of creatine/phosphocreatine. Neither the choline and N‐acetylaspartate protons in brain nor the protons of the trimethylammonium pool in skeletal muscle showed a significant magnetic coupling to mobile water. Copyright © 2001 John Wiley & Sons, Ltd.

Abbreviations used:

tCr

total creatine

NAA

N‐acetylaspartate

Cho

choline‐containing compounds

TMA

trimethylammonium‐containing compounds.
Comparison of the experimental BOLD signal change in event‐related fMRI with the balloon model
Authors: Feng Ching‐Mei , Liu Ho‐Ling , Fox Peter T. , Gao Jia‐Hong
Published: August 2002

Event‐related functional MRI (ER‐fMRI) based on both blood oxygenation level‐dependent (BOLD) contrast and cerebral blood flow (CBF) contrast has been developed to study the human brain response to transient stimulation. A balloon model has been developed and used in understanding the relationship between changes in CBF and in the BOLD signal in block‐designed fMRI. In this report, the balloon model was used to interpret experimental event‐related fMRI. Using experimental data acquired from CBF‐based ER‐fMRI as an input function in the balloon model, simulated BOLD signal changes were obtained. The simulated time course of the BOLD signal changes was directly compared with the experimentally acquired data. A chi‐square (χ2) test showed excellent correlation between the simulated and experimental data (α ≤ 0.05). Our results have demonstrated that the balloon model is useful in interpreting the transient features of the experimental data from the ER‐fMRI studies. Copyright © 2001 John Wiley & Sons, Ltd.
Monitoring acute inflammatory processes in mouse muscle by MR imaging and spectroscopy: a comparison with pathological results
Authors: Ruiz‐Cabello Jesús , Regadera Javier , Santisteban Carmen , Graña Manuel , Alejo Rigoberto Pérez de , Echave Imanol , Avilés Pablo , Rodriguez Ignacio , Santos Inmaculada , Gargallo Domingo , Cortijo Manuel
Published: August 2002

We have studied an animal model of acute local inflammation in muscle induced by Aspergillus fumigatus by using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We have compared our data to those found using histopathology and segmentation maps obtained by the mathematical processing of three‐dimensional T2‐weighted MRI data via a neural network. The MRI patterns agreed satisfactorily with the clinical and biological evidence of the phases of acute local infection and its evolution towards chronicity. The MRS results show a statistically significant increase in inorganic phosphate and a significant decrease in phosphocreatine levels in the inflamed region. Image segmentation made with a self‐organizing, neural‐network map yielded a set of ordered representatives that remained constant for all animals during the inflammatory process, allowing a non‐invasive, three‐dimensional identification and quantification of the inflamed infected regions by MRI. Copyright © 2002 John Wiley & Sons, Ltd.
A new—old algorithm for minimum‐cut and maximum‐flow in closure graphs
Authors: Hochbaum Dorit S.
Published: August 2002

We present an algorithm for solving the minimum‐cut problem on closure graphs without maintaining flow values. The algorithm is based on an optimization algorithm for the open‐pit mining problem that was presented in 1964 (and published in 1965) by Lerchs and Grossmann. The Lerchs—Grossmann algorithm (LG algorithm) solves the maximum closure which is equivalent to the minimum‐cut problem. Yet, it appears substantially different from other algorithms known for solving the minimum‐cut problem and does not employ any concept of flow. Instead, it works with sets of nodes that have a natural interpretation in the context of maximum closure in that they have positive total weight and are closed with respect to some subgraph. We describe the LG algorithm and study its features and the new insights it reveals for the maximum‐closure problem and the maximum‐ flow problem. Specifically, we devise a linear time procedure that evaluates a feasible flow corresponding to any iteration of the algorithm. We show that while the LG algorithm is pseudopolynomial, our variant algorithms have complexity of O(mn log n), where n is the number of nodes and m is the number of arcs in the graph. Modifications of the algorithm allow for efficient sensitivity and parametric analysis also running in time O(mn log n). © 2001 John Wiley & Sons, Inc.
Characterization results of all shortest paths interval routing schemes
Authors: Flammini M. , Gambosi G. , Nanni U. , Tan R.B.
Published: August 2002

We give complete characterizations for the classes of graphs with uniform cost links that admit optimum all shortest paths 1‐SLIRS (strict linear interval routing schemes) and 1‐LIRS (linear interval routing schemes). The characterization of all the interval routing schemes with uniform cost links that represent only a single shortest path is known to be NP‐complete. For any integer k > 0, we also show that the class of graphs with dynamic cost links that admit optimum all shortest paths k‐IRS (SIRS, LIRS, SLIRS) is equivalent to the class of graphs with dynamic cost links that admit an optimum single shortest path k‐IRS (SIRS, LIRS, SLIRS) and also equivalent to the class of graphs with dynamic cost links that admit single paths up to any constant stretch factor k‐IRS (SIRS, LIRS, SLIRS). © 2001 John Wiley & Sons, Inc.
Effects of excess thyroid hormone on cell death, cell proliferation, and new neuron incorporation in the adult zebra finch telencephalon
Authors: Tekumalla P. K. , Tontonoz M. , Hesla M. A. , Kirn J. R.
Published: August 2002

Widespread telencephalic neuronal replacement occurs throughout life in birds. We explored the potential relationship between thyroxine (T4) and cell turnover in the adult male zebra finch. We found that many cells in the zebra finch brain, including long‐projection neurons in the high vocal center (HVC), stained positively with an antibody to thyroid hormone receptors (TR). Labeling was generally weak in the ventricular zone (VZ) that gives rise to new neurons but some proliferative VZ cells and/or their progeny, identified by [3H]‐thymidine labeling, co‐labeled with anti‐TR antibody. Acute T4 treatment dramatically increased the number of pyknotic and TUNEL‐positive cells in HVC and other telencephalic regions. In contrast, degenerating cells were never observed in the archistriatum or sub‐telencephalic regions, suggesting that excess T4 augments cell death selectively in regions that show naturally occurring neuronal turnover. VZ mitotic activity was not altered shortly after acute T4 treatment at a dosage that stimulated cell death, although [3H]‐labeling intensity per cell was slightly reduced. Moreover, the incorporation rates for neurons formed shortly before or after acute hormone treatment were no different from control values. Chronic T4 treatment resulted in a reduction in the total number of HVC neurons. Thus, hyperthyroidism augmented neuronal death, which was not compensated for by neuronal replacement. Collectively, these results indicate that excess T4 affects adult neuronal turnover in birds, and raises the possibility that thyroxine plays an important role in the postnatal development of the avian brain and vocal behavior. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 323–341, 2002
Conditional ablation of neurones in transgenic mice
Authors: Isles Anthony R. , Ma Dan , Milsom Chloe , Skynner Michael J. , Cui Wei , Clark John , Keverne Eric B. , Allen Nicholas D.
Published: August 2002

Conditional targeted ablation of specific cell populations in living transgenic animals is a very powerful strategy to determine cell functions in vivo. This approach would be of particular value to study the functions of distinct neuronal populations; however, the transgene of choice for conditional cell ablation studies in mice, the herpes simplex virus thymidine kinase gene, cannot be used to ablate neurones as its principal mode of action relies on cell proliferation. Here we report that expression of the E.coli nitroreductase gene (Ntr) and metabolism of the prodrug CB1954 (5‐aziridin‐1‐yl‐2‐4‐dinitrobenzamide) to its cytotoxic derivative can be used to conditionally and acutely ablate specific neuronal populations in vivo. As proof of principal, we have ablated olfactory and vomeronasal receptor neurones by expressing Ntr under the control of the olfactory marker protein (OMP) gene promoter. We demonstrate that following CB1954 administration, olfactory and vomeronasal receptor neurones expressing the transgene were selectively eliminated from the olfactory epithelium (OE), and projections to the olfactory bulb (OB) were lost. The functional efficacy of cell ablation was demonstrated using a highly sensitive behavioural test to show that ablated mice had lost the olfactory ability to discriminate distinct odors and were consequently rendered anosmic. Targeted expression of Ntr to specific neuronal populations using conventional transgenes, as described here, or by “knock‐in” gene targeting using embryonic stem cells may be of significant value to address the functions of distinct neuronal populations in vivo. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 183–193, 2001
Combination of Jacobi–Davidson and conjugate gradients for the partial symmetric eigenproblem
Authors: Notay Y.
Published: August 2002

To compute the smallest eigenvalues and associated eigenvectors of a real symmetric matrix, we consider the Jacobi–Davidson method with inner preconditioned conjugate gradient iterations for the arising linear systems. We show that the coefficient matrix of these systems is indeed positive definite with the smallest eigenvalue bounded away from zero. We also establish a relation between the residual norm reduction in these inner linear systems and the convergence of the outer process towards the desired eigenpair. From a theoretical point of view, this allows to prove the optimality of the method, in the sense that solving the eigenproblem implies only a moderate overhead compared with solving a linear system. From a practical point of view, this allows to set up a stopping strategy for the inner iterations that minimizes this overhead by exiting precisely at the moment where further progress would be useless with respect to the convergence of the outer process. These results are numerically illustrated on some model example. Direct comparison with some other eigensolvers is also provided. Copyright © 2001 John Wiley & Sons, Ltd.
Inverse optimal design of cooling conditions for continuous quenching processes
Authors: Ruan Yimin
Published: August 2002

This paper presents an inverse design methodology to obtain a required yield strength with an optimal cooling condition for the continuous quenching of precipitation hardenable sheet alloys. The yield strength of a precipitation hardenable alloy can be obtained by allowing solute to enter into solid solution at a proper temperature and rapidly cooling the alloy to hold the solute in the solid solution. An aging process may be needed for the alloy to develop the final mechanical property. The objective of the design is to optimize the quenching process so that the required yield strength can be achieved. With the inverse design method, the required yield strength is specified and the sheet thermal profile at the exit of the quenching chamber can also be specified. The conjugate gradient method is used to optimize the cooling boundary condition during quenching. The adjoint system is developed to compute the gradient of the objective functional. An aluminium sheet quenching problem is presented to demonstrate the inverse design method. Copyright © 2001 John Wiley & Sons, Ltd.
A semi‐analytical locally transversal linearization method for non‐linear dynamical systems
Authors: Roy D. , Ramachandra L. S.
Published: August 2002

An numeric‐analytical, implicit and local linearization methodology, called the locally transversal linearization (LTL), is developed in the present paper for analyses and simulations of non‐linear oscillators. The LTL principle is based on deriving the locally linearized equations in such a way that the tangent space of the linearized equations transversally intersects that of the given non‐linear dynamical system at that particular point in the state space where the solution vector is sought. For purposes of numerical implementation, two different numerical schemes, namely LTL‐1 and LTL‐2 schemes, based on the LTL methodology are presented. Both LTL‐1 and LTL‐2 procedures finally reduce the given set of non‐linear ordinary differential equations (ODEs) to a set of transcendental algebraic equations valid over a short interval of time or over a short segment of the evolving trajectories as projected on the phase space. While in the LTL‐1 scheme the desired solution vector at a forward time point enters the linearized differential equations as an unknown parameter, in the LTL‐2 scheme a set of unknown residues enters the linearized system as parameters. A limited set of examples involving a few well‐known single‐degree‐of‐freedom (SDOF) non‐linear oscillators indicate that the LTL methodology is capable of accurately predicting many complicated non‐linear response patterns, including limit cycles, quasi‐periodic orbits and even strange attractors. Copyright © 2001 John Wiley & Sons, Ltd.
Genetic optimization of stiffened plates and shells
Authors: Marcelin J. L.
Published: August 2002

This work gives two examples of application of stochastic techniques for the optimization of stiffened plates or shells. The research strategy consists in substituting, for finite‐element calculations in the optimization process, an approximate response of a neural network, or an approximate response from the Ritz method. More precisely, the paper describes the use of a backpropagation neural network or the Ritz method in creating function approximations for use in computationally intensive design optimization based on genetic algorithms. Two examples of applications are presented; the first one deals with the optimization of stiffeners on a plate by varying their positions, while having well‐defined dimensions; the second example deals with the optimization of a thin shell subject to buckling. Copyright © 2001 John Wiley & Sons, Ltd.
Evolutionary thickness design with stiffness maximization and stress minimization criteria
Authors: Li Qing , Steven Grant P. , Xie Y. M.
Published: August 2002

A shape or topology design with the stiffness maximized and the maximum stress minimized is usually of practical significance in structural optimization. This paper proposes a thickness based evolutionary procedure for such multicriteria design problems. To make the multicriteria optimization suit to more realistic structural situations, multiple maximum stress locations and multiple load cases are taken into account in this paper. To balance the stiffness and stress criteria, a weighting average scheme is adopted to identify the overall effects on the two components of design objective due to varying an element's thickness. Adopting the proposed optimization procedure, a design with maximized static stiffness and minimized peak stress is achieved by gradually shifting material from the under‐utilized regions onto the over‐utilized ones. The examples show the capabilities of the proposed method for solving multicriteria size and topology designs for both single and multiple load cases. Copyright © 2001 John Wiley & Sons, Ltd.
Efficient simulation of parameter‐dependent vehicle dynamics
Authors: Stämpfle M. , Hunt K. J. , Kalkkuhl J.
Published: August 2002

The vast majority of dynamical systems depend on system parameters. In this paper, we consider dynamical systems that arise from variation of two parameters within given parameter domains. Efficient adaptive methods for simultaneous simulation of such dynamical systems with parameter sets are presented. To enhance performance two key principles are introduced. Firstly, the principle of changing activity enables different states of activity for points of the parameter domain. And secondly, the principle of changing roles enables the usage of points of the parameter domain as mesh nodes, error grid points, and additional spare points in a flexible way. Various methods are tested on a model that describes the dynamics of a passenger vehicle. The model includes longitudinal and lateral motion as well as rotation around the vertical axis. As an example, the behaviour of the side slip angle is computed as a function of the vehicle mass and the height of the centre of gravity. The side slip angle is of special interest since it is an indicator for vehicle stability and thus passenger safety. Copyright © 2001 John Wiley & Sons, Ltd.
Singular perturbations for sensitivity analysis in symmetric bifurcation buckling
Authors: Godoy Luis A. , Banchio Enrique G.
Published: August 2002

A direct procedure for the evaluation of imperfection‐sensitivity in bifurcation problems is presented. The problems arise in the context of the general theory of elastic stability (Koiter's theory) for discrete structural systems, in which the total potential energy is employed together with a stability criterion based on energy derivatives. The imperfection sensitivity of critical states, such as bifurcations and trifurcations, is usually represented as a plot of the critical load versus the amplitude ε of the imperfection considered. However, such plots have a singularity at the point with ε=0, so that a regular perturbation expansion of the solution is not possible. In this work, we describe a direct procedure to obtain the sensitivity of the critical load (eigenvalue of the bifurcation problem) and the sensitivity of the critical direction (eigenvector of the bifurcation problem) using singular perturbation analysis. The perturbation expansions are constructed as a power series in terms of the imperfection amplitude, in which the exponents and the coefficients are the unknowns of the problem. The solution of the exponents is obtained by means of trial and error using a least degenerate criterion, or by geometrical considerations. To compute the coefficients a detailed formulation is presented, which employs the conditions of equilibrium and stability at the critical state and their contracted forms. The formulation is applied to symmetric bifurcations, and the coefficients are solved up to third‐order terms in the expansion. The algorithmis illustrated by means of a simple example (a beam on an elastic foundation under axial load) for which the coefficients are computed and the imperfection‐sensitivity is plotted. Copyright © 2001 John Wiley & Sons, Ltd.
Fast exact linear and non‐linear structural reanalysis and the Sherman–Morrison–Woodbury formulas
Authors: Akgün Mehmet A. , Garcelon John H. , Haftka Raphael T.
Published: August 2002

Several exact fast static structural reanalysis techniques, introduced by researchers mostly for truss structures and some for frames and plate structures, are reviewed. Most utilize the property that the solution of a system of linear equations can be updated inexpensively when the matrix is changed by a low‐rank increment. This paper shows that these methods are variants of the well‐known Sherman–Morrison and Woodbury (SMW) formulas for the update of the inverse of a matrix. In addition, the paper extends the low‐cost linear reanalysis in the spirit of the SMW formulas to some non‐linear reanalysis problems. For a linear reanalysis, the extension reduces to the SMW formulas. Copyright © 2001 John Wiley & Sons, Ltd.
Variational Delaunay approach to the generation of tetrahedral finite element meshes
Authors: Krysl Petr , Ortiz Michael
Published: August 2002

We describe an algorithm which generates tetrahedral decomposition of a general solid body, whose surface is given as a collection of triangular facets. The principal idea is to modify the constraints in such a way as to make them appear in an unconstrained triangulation of the vertex set à priori. The vertex set positions are randomized to guarantee existence of a unique triangulation which satisfies the Delaunay empty‐sphere property. (Algorithms for robust, parallelized construction of such triangulations are available.) In order to make the boundary of the solid appear as a collection of tetrahedral faces, we iterate two operations, edge flip and edge split with the insertion of additional vertex, until all of the boundary facets are present in the tetrahedral mesh. The outcome of the vertex insertion is another triangulation of the input surfaces, but one which is represented as a subset of the tetrahedral faces. To determine if a constraining facet is present in the unconstrained Delaunay triangulation of the current vertex set, we use the results of Rajan which re‐formulate Delaunay triangulation as a linear programming problem. Copyright © 2001 John Wiley & Sons, Ltd.
NMDA receptor mediates the response of trigeminovascular neurons of rats
Authors: Ahn Dong K. , Ju Jin S. , Park Jae S.
Published: August 2002

The present study was performed to evaluate the characteristics of excitory amino acid receptors in the synaptic transmission of trigeminovascular neurons in trigeminal subnucleus caudalis. Extracellular single‐unit recording of trigeminovascular neurons driven from dura or the superior sagittal sinus was made with a central barrel of seven‐barrel micropipette. DL‐2 amino‐5 phosphonovaleric acid, N‐methyl‐D‐aspartic acid (NMDA) receptor antagonist, produced a reversible inhibition of mechanical‐evoked responses in 10 of 12 examined trigeminovascular neurons. The maximal inhibition was 59 ± 5 % of the control. However, CNQX did not affect trigeminovascular neuronal responses. Substance P also facilitated NMDA‐evoked responses in 8 of 10 examined trigeminovascular neurons. The maximal facilitation was 153 ± 13 % of the control. These results imply that the NMDA receptor has a major role in the transmission of vascular headache (migraine) in trigeminovascular neurons and substance P also seems to be involved in maintenance migraine symptom.
Effect of brain‐derived neurotrophic factor in neural differentiation of mouse embryonic stem cells and neural precursor cells
Authors: Kang S.K. , Lee R.H. , Jung J.S.
Published: August 2002

Embryonic stem (ES) cells, which have pluripotency in differentiation, have been considered as an excellent source for cell replacement therapy of damaged tissues. Although neurotrophic factors induce neural differentiation in neural precursor cells, their actions in ES cells are not clear. This study was designated to examine the effect of brain‐derived neurotrophic factor (BDNF) on neural differentiation in mouse ES cells. Undifferentiated mouse ES cells were maintained at suspension culture in the presence of leukemia inhibitory factor (LIF), and neural precursor cells were isolated from the subventricular zone (SVZ) of the 2–3 day old mice brain. Oct‐4 was expressed in undifferentiated ES cells and neural precursor cells, of which expression was markedly decreased by induction of differentiation. RT‐PCR analysis showed that neural differentiation of ES cells induced expression of various neural markers, and that BDNF increased their expression. Western blot analysis demonstrated that BDNF induced expression of synaptophysin, a neuronal marker, and inhibited expression of glial fibrillary acidic protein, a glial marker. Undifferentiated ES cells expressed TrkA, TrkB and TrkC, of which expressions were increased during differentiation. Neural differentiation increased their expression, and BDNF further increased them. The treatment of BDNF during differentiation decreased expression of Notch1. These results indicated that BDNF induces neural differentiation and inhibits glial differentiation in ES cells as well as neuronal precursor cells.
Small dense‐cored vesicles are depleted of the classical synaptic vesicle membrane proteins synaptobrevin, synaptotagmin and Rab3
Authors: Strecker S. , Partoens P. , Slembrouck D. , Wang J‐M. , Courtoy P.J. , Nouwen E. , De Potter W.P.
Published: August 2002

To verify the association of vesicular docking/fusion proteins to small dense‐cored vesicles, we further purified a small dense‐cored vesicle population from rat vas deferens and searched for three components of the vesicular docking/fusion machinery known to act on target receptors at the plasma membrane: synaptobrevin (p18), synaptotagmin (p65) and the small GTPase Rab3. Further purification of small dense‐cored vesicles actually resulted in a depletion of these proteins, arguing against a direct participation of small dense‐cored vesicles in the exocytotic process. This finding points to a functional difference between small dense‐cored vesicles and either large dense‐cored or small clear synaptic vesicles.
Strategies associated with altered segment parameters during voluntary gait modifications
Authors: Reid M.J. , Prentice S.D.
Published: August 2002

The coordination of movement results from complex interactions between neural and mechanical systems. To investigate the influence of limb mechanics on the control strategies used during gait modifications, participants were instructed to walk and step over various obstacles (2,10, & 30cm) with and without an external mass (4.5kg) attached around the centre of mass of each leg segment. Overall, with the attached mass there was an increase in the amount of pull‐off energy applied at the hip, while the contribution of the knee to limb flexion decreased particularly for the higher obstacles. It was further found that knee action during weighted conditions served more to slow the backward motion of the leg following toe off than to flex the knee. The modifications employed to accomodate the change in limb dynamics illustrate both the flexibility of the locomotor control system and its sensitivity to the mechanical properties of the limb.