bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new look at an old visual system: structure and development of the compound eyes and optic ganglia of the brine shrimp artemia salina linnaeus, 1758 (branchiopoda, anostraca)
Authors: Wildt Miriam , Harzsch Steffen 
Published: September 2002

AbstractCompared to research carried out on decapod crustaceans, the development of the visual system in representatives of the entomostracan crustaceans is poorly understood. However, the structural evolution of the arthropod visual system is an important topic in the new debate on arthropod relationships, and entomostracan crustaceans play a key role in this discussion. Hence, data on structure and ontogeny of the entomostracan visual system are likely to contribute new aspects to our understanding of arthropod phylogeny. Therefore, we explored the proliferation of neuronal stem cells (in vivo incorporation of bromodeoxyuridine) and the developmental expression of synaptic proteins (immunohistochemistry against synapsins) in the developing optic neuropils of the brine shrimp Artemia salina Linnaeus, 1758 (Crustacea, Entomostraca, Branchiopoda, Anostraca) from hatching to adulthood. The morphology of the adult visual system was examined in serial sections of plastic embedded specimens. Our results indicate that the cellular material that gives rise to the visual system (compound eyes and two optic ganglia) is contributed by the mitotic activity of neuronal stem cells that are arranged in three band‐shaped proliferation zones. Synapsin‐like immunoreactivity in the lamina ganglionaris and the medulla externa initiated only after the anlagen of the compound eyes had already formed, suggesting that the emergence of the two optic neuropils lags behind the proliferative action of these stem cells. Neurogenesis in A. salina is compared to similar processes in malacostracan crustaceans and possible phylogenetic implications are discussed. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 117–132, 2002
Development of depolarization‐induced calcium transients in insect glial cells is dependent on the presence of afferent axons
Authors: Lohr Christian , Tucker Eric , Oland Lynne A. , Tolbert Leslie P. 
Published: September 2002

AbstractChanges in the intracellular Ca2+ concentration ([Ca2+]i) induced by depolarization have been measured in glial cells acutely isolated from antennal lobes of the moth Manduca sexta at different postembryonic developmental stages. Depolarization of the glial cell membrane was elicited by increasing the external K+ concentration from 4 to 25 mM. At midstage 5 and earlier stages, less than 20% of the cells responded to 25 mM K+ (1 min) with a transient increase in [Ca2+]i of approximately 40 nM. One day later, at late stage 5, 68% of the cells responded to 25 mM K+, the amplitude of the [Ca2+]i transients averaging 592 nM. At later stages, all cells responded to 25 mM K+ with [Ca2+]i transients with amplitudes not significantly different from those at late stage 5. In stage 6 glial cells isolated from deafferented antennal lobes, i.e., from antennal lobes chronically deprived of olfactory receptor axons, only 30% of the cells responded with [Ca2+]i transients. The amplitudes of these [Ca2+]i transients averaged 93 nM and were significantly smaller than those in normal stage 6 glial cells. [Ca2+]i transients were greatly reduced in Ca2+‐free, EGTA‐buffered saline, and in the presence of the Ca2+ channel blockers cadmium and verapamil. The results suggest that depolarization of the cell membrane induces Ca2+ influx through voltage‐activated Ca2+ channels into antennal lobe glial cells. The development of the depolarization‐induced Ca2+ transients is rapid between midstage 5 and stage 6, and depends on the presence of afferent axons from the olfactory receptor cells in the antenna. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 85–98, 2002
Laser ablation reveals regulation of ciliary activity by serotonergic neurons in molluscan embryos
Authors: Kuang Shihuan , Goldberg Jeffrey I. 
Published: September 2002

AbstractEarly in embryonic development, the pond snail Helisoma trivolvis exhibits a rotational behavior that is generated by beating of cilia in the dorsolateral and pedal bands. Although previous anatomical and pharmacological studies provided indirect evidence that a pair of serotonergic neurons, Embryonic Neurons C1 (ENC1s), is involved in regulating embryonic rotation, direct evidence linking ENC1 to ciliary function is still lacking. In the present study, we used laser microbeams to perturb ENC1 in vivo while monitoring ciliary activity in identified ciliary bands. A laser treatment protocol to specifically ablate ENC1 without damaging the surrounding cells was established. Unilateral laser treatment of ENC1 caused transient increases in the activity of the pedal and ipsidorsolateral cilia, lasting 30–50 min. In contrast, activity of cilia that were not anatomically associated with ENC1 was unaffected by laser treatment. Mianserin, an effective serotonin antagonist in Helisoma ciliated cells, decreased the overall CBF of pedal and dorsolateral cilia by reducing the occurrence of spontaneous CBF surges in these cilia. Finally, the cilioexcitatory action of ENC1 laser treatment was mimicked by serotonin and reduced in the presence of mianserin. These results suggest that laser treatment provokes a release of serotonin from ENC1, resulting in a prolonged elevation of activity in the target ciliary cells. We conclude that, in addition to their previously established role in regulating neurodevelopment, ENC1s also function as serotonergic motor neurons to regulate ciliary activity, and therefore the rotational behavior of early embryos. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 1–15, 2001
Drosophila neuropeptide F mediates integration of chemosensory stimulation and conditioning of the nervous system by food
Authors: Shen Ping , Cai Haini N. 
Published: September 2002

AbstractThe conserved neuropeptide Y (NPY) signaling pathway has been strongly implicated in the stimulation of food uptake in vertebrates as well as in the regulation of food conditioned foraging behaviors of Caenorhabditis elegans. Using in situ RNA hybridization and immunocytochemistry, we report the neuronal network of Drosophila neuropeptide F (dNPF), a human NPY homologue, in the larval central nervous system and its food‐dependent modifications. We provide indications that gustatory stimulation by sugar, but not its ingestion or metabolism, is sufficient to trigger long‐term, dose‐dependent alterations of the dNPF neuronal circuit through both dnpf activation and increased synaptic transmission. Our results strongly suggest that the dNPF neuronal circuit is an integral part of the sensory system that mediates food signaling, providing the neural basis for understanding how invertebrate NPY regulates food response. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 16–25, 2001
Calmodulin and profilin coregulate axon outgrowth in Drosophila
Authors: Kim You‐Seung , Furman Senta , Sink Helen , VanBerkum Mark F.A. 
Published: September 2002

AbstractCoordinated regulation of actin cytoskeletal dynamics is critical to growth cone movement. The intracellular molecules calmodulin and profilin actively regulate actin‐based motility and participate in the signaling pathways used to steer growth cones. Here we show that in the developing Drosophila embryo, calmodulin and profilin convey complimentary information that is necessary for appropriate growth cone advance. Reducing calmodulin activity by expression of a dominant inhibitor (KA) stalls axon extension of pioneer neurons within the CNS, while a partial loss of profilin function decreases extension of motor axons in the periphery. Yet, surprisingly, when calmodulin and profilin are simultaneously reduced, the ability of both CNS pioneer axons and motor axons to extend beyond the choice points is restored. In the CNS, at the time when growth cones must decide whether to cross or not to cross the midline, a reduction in calmodulin and/or roundabout signaling causes axons to cross the midline inappropriately. These inappropriate crossings are suppressed when profilin activity is simultaneously reduced. Interestingly, the mutual suppression of calmodulin and profilin activity requires a minimal level of profilin. In KA combinations with profilin null alleles, defects in axon extension and midline guidance are synergistically enhanced rather than suppressed. Together, our data indicate that the growth cone must coordinate the activity of both calmodulin and profilin in order to advance past selected choice points, including those dictating midline crossovers. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 26–38, 2001
Primal and polar approach for computing the symmetric diagonally dominant projection
Authors: Raydan Marcos , Tarazaga Pablo 
Published: September 2002

AbstractWe solve the problem of minimizing the distance from a given matrix to the cone of symmetric and diagonally dominant matrices with positive diagonal (SDD+). Using the extreme rays of the polar cone we project onto the supporting hyperplanes of the faces of SDD+ and then, applying the cyclic Dykstra's algorithm, we solve the problem. Similarly, using the extreme rays of SDD+ we characterize the projection onto the polar cone, which also allows us to obtain the projection onto SDD+ by means of the orthogonal decomposition theorem for convex cones. In both cases the symmetry and the sparsity pattern of the given matrix are preserved. Preliminary numerical experiments indicate that the polar approach is a promising one. Copyright © 2002 John Wiley & Sons, Ltd.
Modular solvers for image restoration problems using the discrepancy principle
Authors: Blomgren Peter , Chan Tony F. 
Published: September 2002

AbstractMany problems in image restoration can be formulated as either an unconstrained non‐linear minimization problem, usually with aTikhonov‐like regularization, where the regularization parameter has to be determined; or as a fully constrained problem, where an estimate of the noise level, either the variance or the signal‐to‐noise ratio, is available.The formulations are mathematically equivalent. However, in practice, it is much easier to develop algorithms for the unconstrained problem, and not always obvious how to adapt such methods to solve the corresponding constrained problem.In this paper, we present a new method which can make use ofanyexisting convergent method for the unconstrained problem to solve the constrained one. The new method is based on a Newton iteration applied to an extended system of non‐linear equations, which couples the constraint and the regularized problem, but it does not require knowledge of the Jacobian of the irregularity functional. The existing solver is only used as a black box solver, which for a fixed regularization parameter returns an improved solution to the unconstrained minimization problem given an initial guess.The new modular solver enables us to easily solve the constrained image restoration problem; the solver automatically identifies the regularization parameter, during the iterative solution process.We present some numerical results. The results indicate that even in the worst case the constrained solver requires only about twice as much work as the unconstrained one, and in some instances the constrained solver can be even faster. Copyright © 2002 John Wiley & Sons, Ltd.
ARMS: an algebraic recursive multilevel solver for general sparse linear systems
Authors: Saad Y. , Suchomel B. 
Published: September 2002

AbstractThis paper presents a general preconditioning method based on a multilevel partial elimination approach. The basic step in constructing the preconditioner is to separate the initial points into two parts. The first part consists of ‘block’ independent sets, or ‘aggregates’. Unknowns of two different aggregates have no coupling between them, but those in the same aggregate may be coupled. The nodes not in the first part constitute what might be called the ‘coarse’ set. It is natural to call the nodes in the first part ‘fine’ nodes. The idea of the methods is to form the Schur complement related to the coarse set. This leads to a natural block LU factorization which can be used as a preconditioner for the system. This system is then solved recursively using as preconditioner the factorization that could be obtained from the next level. Iterations between levels are allowed. One interesting aspect of the method is that it provides a common framework for many other techniques. Numerical experiments are reported which indicate that the method can be fairly robust. Copyright © 2002 John Wiley & Sons, Ltd.
A method for representing boundaries in discrete element modelling—part II: Kinematics
Authors: Kremmer M. , Favier J. F. 
Published: September 2002

AbstractThe application of the DEM to engineering problems involving the dynamic behaviour of discontinuous media has necessitated the introduction of moving boundary surfaces. In this paper a method is presented for modelling three‐dimensional moving boundary surfaces within the discrete element framework. The surfaces of boundary objects are discretized into triangular planar surfaces using the finite wall method. Wall elements are grouped and each group is associated with a single discrete boundary object which may move independently. Movement comprises any combination of translation and rotation of wall element groups, subject to a given acceleration and velocity during a calculation cycle. The scheme is explicit due to rigidity of the wall elements which are stationary fixed in position and orientation over a time step. Any in‐plane velocity is handled as a contact point velocity within a calculation cycle. The kinematic conditions at each calculation cycle may be pre‐defined or returned from a separate calculation of rigid body motion of the boundary object. The method provides a means for coupling sphere‐based particle dynamics with rigid body dynamics and structural analysis of boundary components. Copyright © 2001 John Wiley & Sons, Ltd.
Three‐dimensional cohesive modeling of dynamic mixed‐mode fracture
Authors: Ruiz Gonzalo , Pandolfi Anna , Ortiz Michael 
Published: September 2002

AbstractA cohesive formulation of fracture is taken as a basis for the simulation of processes of combined tension‐shear damage and mixed‐mode fracture in specimens subjected to dynamic loading. Our three‐dimensional finite‐element calculations account explicitly for crack nucleation, microcracking, the development of macroscopic cracks and inertia. In particular, a tension‐shear damage coupling arises as a direct consequence of slanted microcrack formation in the process zone. We validate the model against the three‐point‐bend concrete beam experiments of Guo et al. (International Journal of Solids and Structures 1995; 32(17/18):2951–2607), John (PhD Thesis, Northwestern University, 1988), and John and Shah (Journal of Structural Engineering 1990; 116(3):585–602) in which a pre‐crack is shifted from the central cross‐section, leading to asymmetric loading conditions and the development of a mixed‐mode process zone. The model accurately captures the experimentally observed fracture patterns and displacement fields, as well as crack paths and crack‐tip velocities, as a function of pre‐crack geometry and loading conditions. In particular, it correctly accounts for the competition between crack‐growth and nucleation mechanisms. Copyright © 2001 John Wiley & Sons, Ltd.
Selective serotonin reuptake inhibitors alter NPY immunostaining in the rat hypothalamus
Authors: Acebes I. , Saracíbar G. , Echevarría E. , Casado A. , Valiente F.J. , Pascual J. , Casis L. 
Published: September 2002

AbstractChronic fluoxetine administration in rats generates a significant decrease in NPY immunostaining in the paraventricular and supraoptic nuclei, with respect to controls. However, a significant increase was found in arcuate nucleus. A lack of changes was observed in periventricular and suprachiasmatic nuclei, lateral hypothalamic area and medial preoptic area. Similar results were observed after chronic administration of sertraline. NPY expression is altered in appetite regulatory regions after in vivo chronic treatment with selective serotonin reuptake inhibitors, suggesting that arcuate‐paraventricular NPY projection impairment is involved in the anorectic effects of these drugs.
Cortical activation patterns in functional magnetic resonance images following monaural pure tone stimulation
Authors: Suzuki M. , Kouzaki H. , Ito R. , Shiino A. , Nishida Y. , Kitano H. 
Published: September 2002

AbstractTo investigate cross‐projection of pure tone stimulation, optimal stimulation level and cross‐talk effect, we examined the auditory processing of monaural pure‐tone stimuli using functional magnetic resonance imaging (fMRI). We examined fMRI responses to monaural pure tones (1 kHz, 95 or 115 dB SPL) in 11 subjects with normal hearing and 4 patients with with profound unilateral deafness. Group analysis showed bilateral cortical activation in primary auditory and auditory association regions at 115 dB SPL. The activation was strong and mostly contralateral. At 95 dB SPl, only 2 of 11 subjects showed weak cortical activation. No activated area in the auditory cortex was observed in subjects with profound unilateral deafness in response to monaural stimulation of the deaf ear. The results supported the cross‐projection of pure tone stimulation. Pure tone with 115 dB SPL was needed to obtain intense and stable activation without cross‐talk using conventional boxcar model.
On the relationship between finite volume and finite element methods applied to the Stokes equations
Authors: Ye Xiu 
Published: September 2002

AbstractWe investigate the relationship between finite volume and finite element approximations for the lower‐order elements, both conforming and nonconforming for the Stokes equations. These elements include conforming, linear velocity‐constant pressure on triangles, conforming bilinear velocity‐constant pressure on rectangles and their macro‐element versions, and nonconforming linear velocity‐constant pressure on triangles and nonconforming rotated bilinear velocity‐constant pressure on rectangles. By applying the relationship between the two methods, we obtain the convergence finite volume solutions for the Stokes equations. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 440–453, 2001.
Measuring the hospital practice environment: A Canadian context
Authors: Estabrooks Carole A. , Tourangeau Ann E. , Humphrey Charles K. , Hesketh Kathryn L. , Giovannetti Phyllis , Thomson Donna , Wong Jennifer , Acorn Sonia , Clarke Heather , Shamian Judith 
Published: September 2002

AbstractThe primary purpose of this study is to document the psychometric properties of the revised Nursing Work Index (NWI‐R) in the context of a large Canadian sample of registered nurses. A self‐administered survey containing the NWI‐R was completed by 17,965 registered nurses working in 415 hospitals in three Canadian provinces. Using exploratory principal components analysis, with a forced one‐factor solution, the practice environment index was obtained. In addition, key assumptions were tested from previous work about the rationale for the aggregation of NWI‐R responses. In the Canadian context the one‐factor solution provides a parsimonious index of the practice environment of registered nurses working in acute care hospitals. Further work is needed to determine the predictive capability of this index and its relevance to cross‐national organizational contexts. © 2002 Wiley Periodicals, Inc. Res Nurs Health 25:256–268, 2002
Understanding the kinetics and network formation of dimethacrylate dental resins
Authors: Lovell Lale G. , Berchtold Kathryn A. , Elliott Jeannine E. , Lu Hui , Bowman Christopher N. 
Published: September 2002

AbstractDimethacrylate monomers are commonly used as the organic phase of dental restorative materials but many questions remain about the underlying kinetics and network formation in these highly crosslinked photopolymer systems. Several novel experimental and modeling techniques that have been developed for other multifunctional (meth)acrylates were utilized to gain further insight into these resin systems. Specifically, this work investigates the copolymerization behavior of­bis‐GMA (2,2‐bis[p‐(2‐hydroxy‐3‐methacryloxyprop‐1‐oxy)‐phenyl]propane) and TEGDMA (triethylene glycol dimethacrylate), two monomers typically used for dental resin formulations. Near‐infrared spectroscopy, electron paramagnetic resonance spectroscopy, as well as dynamic mechanical and dielectric analysis were used to characterize the kinetics, radical populations, and structural properties of this copolymer system. In addition, a kinetic model is described that provides valuable information about the network evolution during the formation of this crosslinked polymer. The results of these numerous studies illustrate that all of the aforementioned techniques can be readily applied to dental resin systems and consequently can be used to obtain a wealth of information about these systems. The application of these techniques provides insight into the complex polymerization kinetics and corresponding network formation, and as a result, a more complete understanding of the anomolous behaviors exhibited by these systems, such as diffusion controlled kinetics and conversion dependent network formation, is attained. Copyright © 2001 John Wiley & Sons, Ltd.
Hyperbranched polyesters and their application in dental composites: monomers for low shrinking composites
Authors: Klee J. E. , Schneider C. , Hölter D. , Burgath A. , Frey H. , Mülhaupt R. 
Published: September 2002

AbstractUsing trimethylolpropane (TMP) and 2,2‐bishydroxymethylpropionic acid (Bis‐MPA), aliphatic hyperbranched polyesters (HBP) were synthesized, with a degree of branching of DB = 0.47 and a degree of polymerization of Pn = 16.5. Aromatic HBPs with repetitive units of 2,2‐bis(4‐hydroxyphenyl)pivalonic acid (Bis‐PVA) lead to a higher DB = 0.48 and Pn = 30.5 compared to the aliphatic HBP. Reactive functionalization of the hyperbranched polymers was achieved via esterification of mixtures of methacrylic acid and carboxylic acids. In this manner, i‐butyric acid and methacryloyl terminated HBPs were obtained. They have a low viscosity ranging from 200 to 364 Pa*s and exhibit relatively low volume shrinkage (1.9 to 3.6%) during photoinitiated cure. Dental composites with volume shrinkage of 0.5 to 1.5% have been prepared using these methacryloyl terminated HBPs in combination with a Ba/alumosilicate glass filler. Copyright © 2001 John Wiley & Sons, Ltd.