bluuebunny/crossref_metadata_2025_split huggingface dataset:
A time‐marching finite element method for an electromagnetic scattering problem
Authors: Van Tri , Wood Aihua 
Published: July 2003

AbstractIn this paper, Newmark time‐stepping scheme and edge elements are used to numerically solve the time‐dependent scattering problem in a three‐dimensional polyhedral cavity. Finite element methods based on the variational formulation derived in Van and Wood (Adv. Comput. Math., to appear) are considered. Existence and uniqueness of the discrete problem is proved by using Babuska–Brezzi theory. Finite element error estimate and stability of the Newmark scheme are also established. Copyright © 2003 John Wiley & Sons, Ltd.
Initial boundary value problem for a class of non‐linear strongly damped wave equations
Authors: Zhijian Yang 
Published: July 2003

AbstractThe paper studies the existence, asymptotic behaviour and stability of global solutions to the initial boundary value problem for a class of strongly damped non‐linear wave equations. By a H00.5ptk‐Galerkin approximation scheme, it proves that the above‐mentioned problem admits a unique classical solution depending continuously on initial data and decaying to zero as t→+∞as long as the non‐linear terms are sufficiently smooth; they, as well as their derivatives or partial derivatives, are of polynomial growth order and the initial energy is properly small. Copyright © 2003 John Wiley & Sons, Ltd.
Higher order non‐resonance for differential equations with singularities
Authors: Yan Ping , Zhang Meirong 
Published: July 2003

AbstractIn this paper we prove an existence result of positive periodic solutions to second order differential equations with certain strong repulsive singularities near the origin and with some semilinear growth near infinity. Different from the nonsingular case, the result in this paper shows that both of the periodic and the antiperiodic eigenvalues play the same role in such an existence result. Copyright © 2003 John Wiley & Sons, Ltd.
Abnormal spermatogenesis at low temperatures in the Japanese red‐bellied newt, Cynops pyrrhogaster: Possible biological significance of the cessation of spermatocytogenesis
Authors: Yazawa Takashi , Nakayama Yuki , Fujimoto Kenta , Matsuda Yoshiko , Abe Keisuke , Kitano Takeshi , Abé Shin‐Ichi , Yamamoto Takashi 
Published: July 2003

AbstractIn newt testis, spermatocytes never appear during winter, because secondary spermatogonia die by apoptosis just before meiosis. In the current study, we examined the effect of low temperatures on spermatogenesis. Incubation of newts at low temperatures (8, 12, 15°C) induced defects in spermatogenesis in a temperature‐dependent manner. At 8°C, multinucleated giant cells (MGCs) were observed in spermatocytes and spermatogenesis never proceeded beyond meiosis. Although spermatocytes completed meiotic divisions at 12°C, severe cell death was observed in the spermatids. At 15°C both normal and abnormal spermiogenesis were observed. Under these conditions, impaired meiotic synapsis/recombination and down‐regulation of the expression of the DMC1 protein, which play pivotal roles in meiotic pairing in eukaryotes, were also observed. Furthermore, to examine the quality of the sperm produced at low temperature for supporting development, artificial insemination was performed. The eggs inseminated with spermatozoa derived from newts kept at 15°C demonstrated a restricted developmental capacity, even though these spermatozoa had an equal capacity for carrying out fertilization to those kept at 22°C. These results suggest that meiosis at low temperatures cause the production of abnormal spermatozoa. Conservation and the significance of this phenomenon in poikilothermic vertebrates living in the temperate zones are also discussed. Mol. Reprod. Dev. 66: 60–66, 2003. © 2003 Wiley‐Liss, Inc.
Bioactive aldehydes from diatoms block the fertilization current in ascidian oocytes
Authors: Tosti Elisabetta , Romano Giovanna , Buttino Isabella , Cuomo Annunziata , Ianora Adrianna , Miralto Antonio 
Published: July 2003

AbstractThe effects of bioactive aldehydes from diatoms, unicellular algae at the base of the marine food web, were studied on fertilization and early development processes of the ascidian Ciona intestinalis. Using whole‐cell voltage clamp techniques, we show that 2‐trans‐4‐trans‐decadienal (DD) and 2‐trans‐4‐cis‐7‐cis‐decatrienal (DT) inhibited the fertilization current which is generated in oocytes upon interaction with the spermatozoon. This inhibition was dose‐dependent and was accompanied by inhibition of the voltage‐gated calcium current activity of the plasma membrane. DD and DT did not inhibit the subsequent contraction of the cortex. Moreover, DD specifically acted as a fertilization channel inhibitor since it did not affect the steady state conductance of the plasma membrane or gap junctional (GJ) communication within blastomeres of the embryo. On the other hand, DD did affect actin reorganization even though the mechanism of action on actin filaments differed from that of other actin blockers. Possibly this effect on actin reorganization was responsible for the subsequent teratogenic action on larval development. The effect of DD was reversible if oocytes were washed soon after fertilization indicating that DD may specifically target certain fertilization mechanisms. Thus, diatom reactive aldehydes such as DD may have a dual effect on reproductive processes, influencing primary fertilization events such as gating of fertilization channels and secondary processes such as actin reorganization which is responsible for the segregation of cell lineages. These findings add to a growing body of evidence on the antiproliferative effects of diatom‐derived aldehydes. Our results also report, for the first time, on the action of a fertilization channel blocker in marine invertebrates. Mol. Reprod. Dev. 66: 72–80, 2003. © 2003 Wiley‐Liss, Inc.
Comparison of developmental capacity for intra‐ and interspecies cloned cat (Felis catus) embryos
Authors: Wen Duan‐Cheng , Yang Cai‐Xia , Cheng Yong , Li Jin‐Song , Liu Zhong‐Hua , Sun Qing‐Yuan , Zhang Jia‐Xin , Lei Lei , Wu Yu‐Qi , Kou Zhao‐Hui , Chen Da‐Yuan 
Published: July 2003

AbstractInterspecies nuclear transfer is an invaluable tool for studying nucleus–cytoplasm interactions; and at the same time, it provides a possible alternative to clone animals whose oocytes are difficult to obtain. In the present study, we investigated the possibility of cloning cat embryos using rabbit oocytes, and compared the developmental capacity; the timing of embryogenesis of the cat–rabbit cloned embryos with that of the cat–cat or the rabbit–rabbit cloned embryos. When cultured in M199, the rate of blastocyst formation of the cat–rabbit embryos was 6.9%, which was not significantly different than that of the cat–cat embryos (10.5%). However, the rate of blastocyst formation of rabbit–rabbit embryos (22.9%) was significantly greater than that of both the cat–rabbit and the cat–cat embryos (P < 0.05). The timing of the first three cleavages for the cat–rabbit embryos was similar to that of the rabbit–rabbit embryos, but significantly faster than that of the cat–cat embryos (P < 0.05), while the time to form blastocysts was similar to that of cat–cat embryos, but significantly slower than that of the rabbit–rabbit embryos (P < 0.05). Both M199 and SOF medium were evaluated for culturing cat–rabbit embryos; the rate of blastocyst formation in SOF (14.5%) was significantly greater than that in M199 (6.9%) (P < 0.05). These results demonstrate that: (1) the cat–rabbit embryos possess equal developmental capacity as cat–cat embryos; (2) the timing of the first three cleavages for the cat–rabbit embryos is recipient‐specific, while the time to form blastocysts is donor nucleus‐specific; and (3) SOF medium may be beneficial to overcome the morula‐to‐blastocyst block for cat–rabbit cloned embryos. Mol. Reprod. Dev. 66: 38–45, 2003. © 2003 Wiley‐Liss, Inc.
Rainbow trout follicular maturational competence acquisition is associated with an increased expression of follicle stimulating hormone receptor and insulin‐like growth factor 2 messenger RNAs
Authors: Bobe Julien , Maugars Gersende , Nguyen Thaovi , Rime Hélène , Jalabert Bernard 
Published: July 2003

AbstractPost‐vitellogenic female rainbow trout (Oncorhynchus mykiss) were assayed in vitro for follicular maturational competence (FMC). Ovarian follicles were stimulated with a range of concentrations of partially purified gonadotropin. The efficient concentration for 50% germinal vesicle breakdown (GVBD) was calculated and used as an indicator of FMC. Before in vitro assay, ovarian tissue was sampled in order to quantify mRNA abundance of specific genes in the ovarian follicle by real‐time PCR. In addition, maturation‐inducing steroid (MIS, 17, 20beta‐dihydroxy‐4‐pregnen‐3‐one) and estradiol (E2) plasma levels were measured by radioimmunoassay. The mRNA expression of several genes such as luteinizing hormone receptor (LH‐r), follicular stimulating hormone receptor (FSH‐r), insulin‐like growth factor 1 (IGF1), insulin‐like growth factor 2 (IGF2), insulin‐like growth factor receptor 1a (IGF‐r1a), and 20beta‐hydroxysteroid dehydrogenase (20beta‐HSD) that are putatively expressed in the preovulatory ovary, was studied in females of varying FMC using real‐time PCR. FMC acquisition is characterized by an increase of MIS circulating levels and a concomitant drop of E2 levels. At the ovarian level, no significant variation of LH‐r, 20beta‐HSD, IGF1, and IGF‐r1a mRNA abundance was observed among females of varying FMC. In contrast, FSH‐r and IGF2 mRNA levels were significantly higher in females exhibiting high FMC. In addition, correlation analyses showed that IGF2 and FSH‐r, mRNA levels were positively correlated with FMC. These results indicate that FMC acquisition is associated with an increased expression of these gene products that may be useful markers of FMC. Mol. Reprod. Dev. 66: 46–53, 2003. © 2003 Wiley‐Liss, Inc.
Real‐time accelerated interactive MRI with adaptive TSENSE and UNFOLD
Authors: Guttman Michael A. , Kellman Peter , Dick Alexander J. , Lederman Robert J. , McVeigh Elliot R. 
Published: July 2003

AbstractReduced field‐of‐view (FOV) acceleration using time‐adaptive sensitivity encoding (TSENSE) or unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD) can improve the depiction of motion in real‐time MRI. However, increased computational resources are required to maintain a high frame rate and low latency in image reconstruction and display. A high‐performance software system has been implemented to perform TSENSE and UNFOLD reconstructions for real‐time MRI with interactive, on‐line display. Images were displayed in the scanner room to investigate image‐guided procedures. Examples are shown for normal volunteers and cardiac interventional experiments in animals using a steady‐state free precession (SSFP) sequence. In order to maintain adequate image quality for interventional procedures, the imaging rate was limited to seven frames per second after an acceleration factor of 2 with a voxel size of 1.8 × 3.5 × 8 mm. Initial experiences suggest that TSENSE and UNFOLD can each improve the compromise between spatial and temporal resolution in real‐time imaging, and can function well in interactive imaging. UNFOLD places no additional constraints on receiver coils, and is therefore more flexible than SENSE methods; however, the temporal image filtering can blur motion and reduce the effective acceleration. Methods are proposed to overcome the challenges presented by the use of TSENSE in interactive imaging. TSENSE may be temporarily disabled after changing the imaging plane to avoid transient artifacts as the sensitivity coefficients adapt. For imaging with a combination of surface and interventional coils, a hybrid reconstruction approach is proposed whereby UNFOLD is used for the interventional coils, and TSENSE with or without UNFOLD is used for the surface coils. Magn Reson Med 50:315–321, 2003. Published 2003 Wiley‐Liss, Inc.
On the artifact of a subvoxel susceptibility deviation in spoiled gradient‐echo imaging
Authors: Bos Clemens , Viergever Max A. , Bakker Chris J.G. 
Published: July 2003

AbstractIn MRI, susceptibility‐based negative contrast amplifies the effect of objects that are too small to be detected by water displacement or intrinsic contrast properties. In this work, a simplified description of the susceptibility artifact of a subvoxel object in spoiled gradient‐echo imaging is presented that focuses on the elimination of signal in its vicinity: the dephased‐volume. The size and position of the dephased‐volume are investigated using 3D time‐domain simulations and in vitro experiments in which scan parameters and object magnetic moment are systematically varied. Overall signal loss is found to be linearly related to a dephasing parameter that contains the susceptibility difference with tissue, object volume, and echo time (TE), and thus allows the magnetic moment of the object to be assessed. Gradient strength, in‐plane resolution, fractional echo, and slice orientation have limited influence. For the settings used, the center of mass of the artifact was always within 0.5 mm of the object's in‐plane position. Magn Reson Med 50:400–404, 2003. © 2003 Wiley‐Liss, Inc.
Intravascular extended sensitivity (IVES) MRI antennas
Authors: Susil Robert C. , Yeung Christopher J. , Atalar Ergin 
Published: July 2003

AbstractThe design and application of an intravascular extended sensitivity (IVES) MRI antenna is described. The device is a loopless antenna design that incorporates both an insulating, dielectric coating and a winding of the antenna whip into a helical shape. Because this antenna produces a broad region of high SNR and also allows for imaging near the tip of the device, it is useful for imaging long, luminal structures. To elucidate the design and function of this device, the effects of both insulation and antenna winding were characterized by theoretical and experimental studies. Insulation broadens the longitudinal region over which images can be collected (i.e., along the lumen of a vessel) by increasing the resonant pole length. Antenna winding, conversely, allows for imaging closer to the tip of the antenna by decreasing the resonant pole length. Over a longitudinal region of 20 cm, the IVES imaging antenna described here produces a system SNR of approximately 40,000/r (mL–1Hz1/2), where r is the radial distance from the antenna axis in centimeters. As opposed to microcoil antenna designs, these antennas do not require exact positioning and allow for imaging over broad tissue regions. While focusing on the design of the IVES antenna, this work also serves to enhance our overall understanding of the properties and behavior of the loopless antenna design. Magn Reson Med 50:383–390, 2003. © 2003 Wiley‐Liss, Inc.
Novel interleaved spiral imaging motion correction technique using orbital navigators
Authors: Moriguchi Hisamoto , Lewin Jonathan S. , Duerk Jeffrey L. 
Published: July 2003

AbstractAlthough spiral imaging seldom produces apparent artifacts related to flow, it remains sensitive to rapid object motion. In this article, a new correction method is presented for rapid rigid body motion in interleaved spiral imaging. With this technique, an identical circular navigator k‐space trajectory is linked to each spiral trajectory. Data inconsistency due to both rotation and translation among spiral interleaves can be corrected by evaluating the magnitudes and phases of the data contained in the navigator “ring.” Further, it is difficult to create a frequency field map for off‐resonance correction when an object moves during a scan, because there is motion‐dependent misregistration between the two images acquired with different TEs. However, this difficulty can be overcome by combining the motion‐correction method with a recently proposed technique (off‐resonance correction using variable‐density spirals (ORC‐VDS)), thereby enabling both motion compensation and off‐resonance correction with no additional scanning. Magn Reson Med 50:423–428, 2003. © 2003 Wiley‐Liss, Inc.
Determinants of intramyocellular lipid concentrations in rat hindleg muscle
Authors: Neumann‐Haefelin Claudia , Kuhlmann Johanna , Belz Ulrich , Kalisch Juergen , Quint Manfred , Gerl Martin , Juretschke Hans‐Paul , Herling Andreas W. 
Published: July 2003

AbstractThe investigation of intramyocellular lipids (IMCLs) with proton MR spectroscopy (1H‐MRS) in humans has recently received increasing attention. IMCL levels correlate with insulin resistance and are affected by diet and exercise, making IMCL an interesting marker for metabolic investigations. In the present in vivo study, the feasibility of using 1H MRS for the detection of IMCL in rats is demonstrated, and the influence of various factors, such as age, gender, muscle type, and rat strain, on IMCL levels is systematically analyzed. In healthy Wistar and Sprague Dawley (SD) rats, the highest ratios of IMCL/tCr were found in young rats, and IMCL/tCr decreased with increasing age. In addition, IMCL concentration was clearly influenced by gender and muscle type. Insulin‐resistant, male, obese, Zucker diabetic fatty (ZDF) rats showed significantly higher IMCL levels than Wistar or SD rats. In conclusion, although IMCL levels are clearly influenced by insulin resistance, several other factors influence IMCL levels, such as age, gender, muscle type, and rat strain. Therefore, when using IMCL as a surrogate marker for insulin resistance, it is necessary to carefully compare results with age‐ and gender‐matched controls, and to use identical conditions. Magn Reson Med 50:242–248, 2003. © 2003 Wiley‐Liss, Inc.
Functional magnetic resonance imaging based on changes in vascular space occupancy
Authors: Lu Hanzhang , Golay Xavier , Pekar James J. , van Zijl Peter C.M. 
Published: July 2003

AbstractDuring brain activation, local control of oxygen delivery is facilitated through microvascular dilatation and constriction. A new functional MRI (fMRI) methodology is reported that is sensitive to these microvascular adjustments. This contrast is accomplished by eliminating the blood signal in a manner that is independent of blood oxygenation and flow. As a consequence, changes in cerebral blood volume (CBV) can be assessed through changes in the remaining extravascular water signal (i.e., that of parenchymal tissue) without need for exogenous contrast agents or any other invasive procedures. The feasibility of this vascular space occupancy (VASO)‐dependent functional MRI (fMRI) approach is demonstrated for visual stimulation, breath‐hold (hypercapnia), and hyperventilation (hypocapnia). During visual stimulation and breath‐hold, the VASO signal shows an inverse correlation with the stimulus paradigm, consistent with local vasodilatation. This effect is reversed during hyperventilation. Comparison of the hemodynamic responses of VASO‐fMRI, cerebral blood flow (CBF)‐based fMRI, and blood oxygenation level‐dependent (BOLD) fMRI indicates both arteriolar and venular temporal characteristics in VASO. The effect of changes in water exchange rate and partial volume contamination with CSF were calculated to be negligible. At the commonly‐used fMRI resolution of 3.75 × 3.75 × 5 mm3, the contrast‐to‐noise‐ratio (CNR) of VASO‐fMRI was comparable to that of CBF‐based fMRI, but a factor of 3 lower than for BOLD‐fMRI. Arguments supporting a better gray matter localization for the VASO‐fMRI approach compared to BOLD are provided. Magn Reson Med 50:263–274, 2003. © 2003 Wiley‐Liss, Inc.
Using the vector potential in evaluating the likelihood of peripheral nerve stimulation due to switched magnetic field gradients
Authors: Bencsik Martin , Bowtell Richard , Bowley Roger M. 
Published: July 2003

AbstractThe time‐varying magnetic field gradients used in MRI can cause peripheral nerve stimulation (PNS) in human subjects, as a result of the electric fields induced in tissue. The local electric field, E, is given by E = −∂A/∂t − ∇ϕ where A, is the vector potential and ϕ is the scalar electric potential generated by charges accumulated at boundaries between regions of different conductivity. Difficulties in calculating ϕ have led some investigators to use −∂A/∂t alone as a predictor of the induced field. Here the spatial variation of −∂A/∂t and E is investigated for the case of a simple spherical conductor exposed to time‐varying gradients produced by two different gradient coils that generate identical internal magnetic fields, but very different vector potentials. The results indicate that the temporal derivative of A bears little relation to the induced electric field, and that consequently neglecting the effect of the scalar potential introduces significant errors in estimating the likelihood of PNS. Magn Reson Med 50:405–410, 2003. © 2003 Wiley‐Liss, Inc.
Real‐time MR temperature mapping of rabbit liver in vivo during thermal ablation
Authors: Weidensteiner Claudia , Quesson Bruno , Caire‐Gana Bénédicte , Kerioui Noureddine , Rullier Anne , Trillaud Hervé , Moonen Chrit T.W. 
Published: July 2003

AbstractIt has been shown that quantitative MRI thermometry using the proton resonance frequency (PRF) method can be used to noninvasively monitor the evolution of tissue temperature, and to guide minimally‐invasive tumor ablation based on local hyperthermia. Although hepatic tumors are among the main targets for thermal ablation, PRF‐based temperature MRI of the liver is difficult to perform because of motion artifacts, fat content, and low T. In this study the stability of real‐time thermometry was tested on a clinical 1.5 T scanner for rabbit liver in vivo. The fast segmented EPI principle was used together with respiratory gating to limit respiratory motion artifacts. Lipid signal suppression was achieved with a binomial excitation pulse. Saturation slabs were applied to suppress artifacts due to flowing blood. The respiratory‐gated MR thermometry in the rabbit liver in vivo showed a standard deviation (SD) of 1–3°C with a temporal resolution of 3 s per slice and 1.4 mm × 1.9 mm spatial resolution in plane (slice thickness = 5 mm). The method was used to guide thermal ablation experiments with a clinical infrared laser. The estimated size of the necrotic area, based on the thermal dose calculated from MR temperature maps, corresponded well with the actual lesion size determined by histology and conventional MR images obtained 5 days posttreatment. These results show that quantitative MR temperature mapping can be obtained in the liver in vivo, and can be used for real‐time control of thermal ablation and for lesion size prediction. Magn Reson Med 50:322–330, 2003. © 2003 Wiley‐Liss, Inc.
Magnitude image CSPAMM reconstruction (MICSR)
Authors: NessAiver Moriel , Prince Jerry L. 
Published: July 2003

AbstractImage reconstruction of tagged cardiac MR images using complementary spatial modulation of magnetization (CSPAMM) requires the subtraction of two complex datasets to remove the untagged signal. Although the resultant images typically have sharper and more persistent tags than images formed without complementary tagging pulses, handling the complex data is problematic and tag contrast still degrades significantly during diastole. This article presents a magnitude image CSPAMM reconstruction (MICSR) method that is simple to implement and produces images with improved contrast and tag persistence. The MICSR method uses only magnitude images — i.e., no complex data — but yields tags with zero mean, sinusoidal profiles. A trinary display of MICSR images emphasizes their long tag persistence and demonstrates a novel way to visualize myocardial deformation. MICSR contrast and contrast‐to‐noise ratios (CNR) were evaluated using simulations, a phantom, and two normal volunteers. Tag contrast 1000 msec after the R wave trigger was 3.0 times better with MICSR than with traditional CSPAMM reconstruction techniques, while CNRs were 2.0 times better. Magn Reson Med 50:331–342, 2003. © 2003 Wiley‐Liss, Inc.