bluuebunny/crossref_metadata_2025_split huggingface dataset:
Targeted gene expression in Drosophila dopaminergic cells using regulatory sequences from tyrosine hydroxylase
Authors: Friggi‐Grelin Florence , Coulom Hélène , Meller Margaret , Gomez Delphine , Hirsh Jay , Birman Serge 
Published: January 2003

AbstractDopamine (DA) is the only catecholaminergic neurotransmitter in the fruit fly Drosophila melanogaster. Dopaminergic neurons have been identified in the larval and adult central nervous system (CNS) in Drosophila and other insects, but no specific genetic tool was available to study their development, function, and degeneration in vivo. In Drosophila as in vertebrates, the rate‐limiting step in DA biosynthesis is catalyzed by the enzyme tyrosine hydroxylase (TH). The Drosophila TH gene (DTH) is specifically expressed in all dopaminergic cells and the corresponding mutant, pale (ple), is embryonic lethal. We have performed ple rescue experiments with modified DTH transgenes. Our results indicate that partially redundant regulatory elements located in DTH introns are required for proper expression of this gene in the CNS. Based on this study, we generated a GAL4 driver transgene, TH‐GAL4, containing regulatory sequences from the DTH 5′ flanking and downstream coding regions. TH‐GAL4 specifically expresses in dopaminergic cells in embryos, larval CNS, and adult brain when introduced into the Drosophila genome. As a first application of this driver, we observed that in vivo inhibition of DA release induces a striking hyperexcitability behavior in adult flies. We propose that TH‐GAL4 will be useful for studies of the role of DA in behavior and disease models in Drosophila. © 2003 Wiley Periodicals, Inc. J Neurobiol 54: 618–627, 2003
Activity alters muscle reinnervation and terminal sprouting by reducing the number of schwann cell pathways that grow to link synaptic sites
Authors: Love Flora M. , Son Young‐Jin , Thompson Wesley J. 
Published: January 2003

AbstractIn partially denervated rodent muscle, terminal Schwann cells (TSCs) located at denervated end plates grow processes, some of which contact neighboring innervated end plates. Those processes that contact neighboring synapses (termed “bridges”) appear to initiate nerve terminal sprouting and to guide the growth of the sprouts so that they reach and reinnervate denervated end plates. Studies conducted prior to knowledge of this potential involvement of Schwann cells showed that direct muscle stimulation inhibits terminal sprouting following partial denervation (Brown and Holland, 1979). We have investigated the possibility this inhibition results from an alteration in the growth of TSC processes. We find that stimulation of partially denervated rat soleus muscle does not alter the length or number of TSC processes but does reduce the number of TSC bridges. Stimulation also reduces the number of TSC bridges that form between end plates during reinnervation of a completely denervated muscle. The nerve processes (“escaped fibers”) that normally grow onto TSC processes during reinnervation are also reduced in length. Therefore, stimulation alters at least two responses to denervation in muscles: (1) the ability of TSC processes to form or maintain bridges with innervated synaptic sites, and (2) the growth of axons along processes extended by TSCs. © 2003 Wiley Periodicals, Inc. J Neurobiol 54: 566–576, 2003
Vitamin A deficiency leads to increased cell proliferation in olfactory epithelium of mature rats
Authors: Asson‐Batres M. A. , Zeng M.‐S. , Savchenko V. , Aderoju A. , McKanna J. 
Published: January 2003

AbstractWe have shown previously that vitamin A deficiency (VAD) leads to the decreased expression of gene products that are specifically synthesized by mature neurons in the olfactory epithelium (OE) of adult rats. These results support the hypothesis that retinoic acid, a derivative of vitamin A, is required for neurogenesis and neuron replacement in vivo. VAD does not cause gross degeneration of the OE, raising the question: what types of cells continue to populate VAD OE? In this study, we compared the cell densities of VAD and VA‐sufficient (VAS) OE and investigated whether cell proliferation is upregulated in VAD OE. The results show that (1) total cell number in VAD and VAS OE are comparable; (2) localized areas of hyperplasia are present in the basal regions of VAD, but not VAS, OE; (3) there is a substantial increase in the number of PCNA (proliferating cell nuclear antigen) positive cells in the basal region of VAD OE relative to VAS OE; and (4) there is a relative increase in the levels of mRNA encoding the transcription factor, MASH I, in VAD OE. We conclude that reduced availability of vitamin A derivatives, such as retinoic acid, leads to a loss of control over proliferation, hyperplasia, and increased numbers of pro‐neural cells in vivo. © 2003 Wiley Periodicals, Inc. J Neurobiol 54: 539–554, 2003
Estrogen regulates tyrosine hydroxylase expression in the neonate mouse midbrain
Authors: Ivanova Tatiana , Beyer Cordian 
Published: January 2003

AbstractEstrogen plays an important role during differentiation of midbrain dopaminergic neurons. This is indicated by the presence of estrogen receptors and the transient expression of the estrogen‐forming enzyme aromatase within the dopaminergic cell groups. We have previously shown that estrogen regulates the plasticity of dopamine cells through the stimulation of neurite growth/arborization. In this study, we have analyzed the capability of estrogen to influence the activity of developing mouse dopamine neurons. The expression of tyrosine hydroxylase (TH) was assessed by competitive RT‐PCR and Western blotting. The developmental expression of TH in the ventral midbrain was studied from embryonic day 15 until postnatal day 15 and revealed highest TH levels early postnatally. This profile coincides with the transient aromatase expression in this brain area. Using cultured midbrain cells, we found that estrogen increased TH mRNA/protein levels. The application of the estrogen receptor antagonist ICI 182,780 resulted in a complete inhibition of estrogen effects. To verify these data in vivo, fetuses were exposed in utero from E15 until birth to the aromatase inhibitor CGS 16949A or to CGS supplemented with estrogen. CGS caused a robust reduction in TH mRNA/protein levels in the midbrain, which could be restored by estrogen substitution. Taken together, our data strongly suggest that estrogen controls dopamine synthesis in the developing nigrostriatal dopaminergic system and support the concept that estrogen is implicated in the regulation of ontogenetic steps but also in the function of midbrain dopamine neurons. © 2003 Wiley Periodicals, Inc. J Neurobiol 54: 638–647, 2003
Wasp venom blocks central cholinergic synapses to induce transient paralysis in cockroach prey
Authors: Haspel G. , Libersat F. 
Published: January 2003

AbstractThe parasitoid wasp Ampulex compressa induces a set of unique behavioral effects upon stinging its prey, the cockroach. It stings into the first thoracic segment inducing 2 to 3 min of transient flaccid paralysis of the front legs. This facilitates a second sting in the cockroach's head that induces 30 min of excessive grooming followed by a 2 to 5‐week long lethargic state. In the present study, we examine the immediate effect of the first sting, which is a transient paralysis of the front legs. Using radiolabeled wasps, we demonstrate that the wasp injects its venom directly into the cockroach's first thoracic ganglion. The artificial injection of milked venom into a thoracic ganglion abolishes spontaneous and evoked responses of the motoneurons associated with leg movements. To investigate the physiological mechanism of action of the venom, we injected venom into the last abdominal ganglion of the cockroach, which houses a well‐characterized cholinergic synapse. Injected venom abolishes both sensory‐evoked and agonist‐evoked postsynaptic potentials recorded in the postsynaptic neuron for 2 to 3 min without affecting action potential propagation. Thus, the venom blocking effect has a postsynaptic component that follows the same time course as the transient paralysis induced by the thoracic sting. Finally, injection of a nicotinic antagonist in the front thoracic ganglion induces paralysis of the front legs. We conclude that the transient paralytic effect of the thoracic sting can be mainly accounted for by the presence of a venom active component that induces a postsynaptic block of central cholinergic synaptic transmission. © 2003 Wiley Periodicals, Inc. J Neurobiol 54: 628–637, 2003
Time accurate consistently stabilized mesh‐free methods for convection dominated problems
Authors: Huerta Antonio , Fernández‐Méndez Sonia 
Published: January 2003

AbstractThe behaviour of high‐order time stepping methods combined with mesh‐free methods is studied for the transient convection–diffusion equation. Particle methods, such as the element‐free Galerkin (EFG) method, allow to easily increase the order of consistency and, thus, to formulate high‐order schemes in space and time. Moreover, second derivatives of the EFG shape functions can be constructed with a low extra cost and are well defined, even for linear interpolation. Thus, consistent stabilization schemes can be considered without loss in the convergence rates. Copyright © 2003 John Wiley & Sons, Ltd.
Particulate flow simulations using lubrication theory solution enrichment
Authors: Wagner G. J. , Ghosal S. , Liu W. K. 
Published: January 2003

AbstractA technique for the numerical simulation of suspensions of particles in fluid based on the extended finite element method (X‐FEM) is developed. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The finite element basis is enriched with the Stokes flow solution for flow past a single particle and the lubrication theory solution for flow between particles. The latter enrichment allows the simulation of particles that come arbitrarily close together without refining the mesh in the gap between them. Example problems illustrating both types of enrichment are shown, along with a study of a 50% solution in channel flow. Copyright © 2003 John Wiley & Sons, Ltd.
An improved crack analysis technique by element‐free Galerkin method with auxiliary supports
Authors: Lee Sang‐Ho , Yoon Young‐Cheol 
Published: January 2003

AbstractIn this study, an improved crack analysis technique by element‐free Galerkin method (EFGM) with auxiliary supports is proposed. To efficiently model the singularity and the discontinuity of the crack, a singular basis function which varies only on the auxiliary supports is added to enrich the standard EFG approximation and the discontinuous shape function is used in the vicinity of the crack surface. The proposed technique improves the accuracy in the near tip field, by using only an initial node arrangement without any modification until the completion of an analysis. A parametric study, which can guide the analyst on the reasonable choice for the formulation and modelling parameters to be used in the technique, is performed on a relative stress norm error and stress intensity factor. In addition, some numerical examples are analysed to verify the effectiveness of the proposed technique for a crack problem. Copyright © 2003 John Wiley & Sons, Ltd.
A non‐iterative finite element method for inverse heat conduction problems
Authors: Ling Xianwu , Keanini Russell G. , Cherukuri H. P. 
Published: January 2003

AbstractA non‐iterative, finite element‐based inverse method for estimating surface heat flux histories on thermally conducting bodies is developed. The technique, which accommodates both linear and non‐linear problems, and which sequentially minimizes the least squares error norm between corresponding sets of measured and computed temperatures, takes advantage of the linearity between computed temperatures and the instantaneous surface heat flux distribution. Explicit minimization of the instantaneous error norm thus leads to a linear system, i.e. a matrix normal equation, in the current set of nodal surface fluxes. The technique is first validated against a simple analytical quenching model. Simulated low‐noise measurements, generated using the analytical model, lead to heat transfer coefficient estimates that are within 1% of actual values. Simulated high‐noise measurements lead to h estimates that oscillate about the low‐noise solution. Extensions of the present method, designed to smooth oscillatory solutions, and based on future time steps or regularization, are briefly described. The method's ability to resolve highly transient, early‐time heat transfer is also examined; it is found that time resolution decreases linearly with distance to the nearest subsurface measurement site. Once validated, the technique is used to investigate surface heat transfer during experimental quenching of cylinders. Comparison with an earlier inverse analysis of a similar experiment shows that the present method provides solutions that are fully consistent with the earlier results. Although the technique is illustrated using a simple one‐dimensional example, the method can be readily extended to multidimensional problems. Copyright © 2003 John Wiley & Sons, Ltd.
A gradient‐based adaptation procedure and its implementation in the element‐free Galerkin method
Authors: Luo Yunhua , Häussler‐Combe Ulrich 
Published: January 2003

AbstractA gradient‐based adaptation procedure is proposed in this paper. The relative error in the total strain energy from two adjacent adaptation stages is used as a stop‐criterion. The refinement–coarsening process is guided by the gradient of strain energy density, based on the assumption: a larger gradient needs a richer mesh and vice versa. The procedure is then implemented in the element‐free Galerkin method for linear elasto‐static problems. Numerical examples are presented to show the performance of the proposed procedure. Copyright © 2003 John Wiley & Sons, Ltd.
Tetrahedral mesh generation and optimization based on centroidal Voronoi tessellations
Authors: Du Qiang , Wang Desheng 
Published: January 2003

AbstractThe centroidal Voronoi tessellation based Delaunay triangulation (CVDT) provides an optimal distribution of generating points with respect to a given density function and accordingly generates a high‐quality mesh. In this paper, we discuss algorithms for the construction of the constrained CVDT from an initial Delaunay tetrahedral mesh of a three‐dimensional domain. By establishing an appropriate relationship between the density function and the specified sizing field and applying the Lloyd's iteration, the constrained CVDT mesh is obtained as a natural global optimization of the initial mesh. Simple local operations such as edges/faces flippings are also used to further improve the CVDT mesh. Several complex meshing examples and their element quality statistics are presented to demonstrate the effectiveness and efficiency of the proposed mesh generation and optimization method. Copyright © 2003 John Wiley & Sons, Ltd.
Digital redesign of analog controllers based on minimizing integral of squared errors
Authors: Hwang Chyi , Chang Fang‐Pi , Hwang Jyh‐Haur 
Published: January 2003

AbstractDigital redesign is to replace an existing well‐designed analog feedback controller by a digital one along with a sampler and a hold. In this paper, we present a digital redesign technique which takes into account both closed‐loop and intersample behaviour. More precisely, we give a numerical procedure to optimally discretize an analog controller such that the integral of the squared error between the closed‐loop step responses of the analog and digital controlled systems is minimized. A parametric expression is derived for evaluating the integral performance index. With this expression, the optimal digital redesign problem becomes an optimal parameter selection problem which can be solved using existing optimal parameter search algorithms. Moreover, it allows one to obtain optimal reduced‐order digital controllers for sampled‐data control systems over a range of sampling periods. Copyright © 2003 John Wiley & Sons, Ltd.
Optimality of greedy and sustainable policies in the management of renewable resources
Authors: Rapaport A. , Sraidi S. , Terreaux J.P. 
Published: January 2003

AbstractWe consider a discrete‐time modelling of renewable resources, which regenerate after a delay once harvested. We study the qualitative behaviour of harvesting policies, which are optimal with respect to a discounted utility function over infinite horizon. Using Bellman's equation, we derive analytically conditions under which two types of policies (greedy and sustainable) are optimal, depending on the discount rate and the marginal utility. For this particular class of problems, we show also that the greedy policy is attractive in a certain sense. The techniques of proof lie on concavity, comparison of value functions and Lyapunov‐like functions. Copyright © 2003 John Wiley & Sons, Ltd.
Optimal control for non‐linear integrodifferential functional equations
Authors: Jeong Jin‐Mun , Park Jong‐Yeoul 
Published: January 2003

AbstractAn optimal control problem for a non‐linear control system with a hemicontinuous and coercive operator is studied. The existence, uniqueness, and a variation of solutions of the system are also given. An example is presented to illustrate the theory. Copyright © 2003 John Wiley & Sons, Ltd.
Miscibility of poly(vinyl alcohol)/polyacrylamide blends before and after gamma irradiation
Authors: El‐din Horia M Nizam , El‐Naggar Abdel Wahab M , Ali Faten I 
Published: January 2003

AbstractFilms of polymer blends having various contents of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) were prepared by the solution casting technique using water as a common solvent. The thermal, mechanical and morphological properties of these blends before and after exposure to various doses of gamma radiation, up to 100 kGy, have been investigated. The visual observation and reflectance measurements show that PVA/PAM blends are miscible over a wide range of composition. Moreover, the differential scanning calorimetry (DSC) thermograms show only a single glass transition temperature (Tg), but not those of PVA or PAM homopolymers, giving further support to the complete compatibility of such blends. The Tg of PVA/PAM blends decreases with increasing content of PAM but increases after exposure to gamma irradiation, indicating the occurrence of crosslinking. These findings were demonstrated by the scanning electron micrographs of the fracture surfaces and the tensile mechanical properties. The TGA thermograms and percentage mass loss at different decomposition temperatures show that unirradiated PVA homopolymer possesses higher thermal stability than PAM homopolymer and their blends within the heating temperature range investigated, up to 250 °C. An opposite trend is observed within the temperature range 300–500 °C. In general, the thermal stability of homopolymers or their blends improves slighly after exposure to an irradiation dose of 100 kGy. These findings are clearly confirmed by the calculated activation energies of the thermal decomposition reaction of the homopolymers and the blends.© 2003 Society of Chemical Industry
Synthesis of amphiphilic magnetic microspheres by dispersion copolymerization of styrene and poly(ethylene oxide) macromonomer
Authors: Liu Xue‐Yong , Ding Xiao‐Bin , Zheng Zhao‐Hui , Peng Yu‐Xing , Chan Albert S C , Yip C W , Long Xin‐Ping 
Published: January 2003

AbstractAmphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g−1.© 2003 Society of Chemical Industry
Impact modification of waste PET by polyolefinic elastomer
Authors: Chaudhari K P , Kale D D 
Published: January 2003

AbstractWaste poly(ethylene terephthalate) [PET] and a polyolefinic elastomer (POE), Engage™ 8150, were melt blended in a co‐rotating twin screw extruder having initial distributive mixing followed by high shearing/stretching. Compositions having POE up to 10% with and without poly(ethylene‐co‐acrylic acid), as a compatibilizer were studied. The blends were characterized for mechanical, thermal and rheological properties as well as for morphological characteristics. Incorporation of POE improved the impact properties of PET very significantly.© 2003 Society of Chemical Industry
New nanocomposite materials based on polymerization of [oligo(oxyethylene) methacrylates] in the presence of montmorillonite clay
Authors: Salahuddin Nehal , Rehab Ahmed 
Published: January 2003

AbstractIntercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d001 spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix.© 2003 Society of Chemical Industry
Plasma‐induced grafting of hydroxyethyl methacrylate (HEMA) onto chitosan membranes by a swelling method
Authors: Li Yeping , Liu Li , Fang Yue‐e 
Published: January 2003

AbstractHydroxyethyl methacrylate (HEMA) was grafted onto chitosan membranes by plasma‐graft polymerization. Effects of monomer concentration, plasma power and plasma time on the amount of grafting were investigated. The results showed that there were two processes: grafting polymerization and etching of the membrane. The surface of the grafted membrane was evaluated by FTIR. Scanning electron microscopy indicated that the surface morphology of the grafted membrane could be adjusted through plasma power. Water contact angles of the chitosan surface decreased from 78.2° to 45.4° while the amount of grafting increased from 0 to 12.2%, indicating improved hydrophilicity of the membrane surface. Permeation coefficients through the original membrane, the membrane treated at 55 W for 15 min, and the membrane treated at 55 W for 30 min for creatinine were 9.12 × 10−7, 10.6 × 10−7 and 8.57 × 10−7 cm2 s−1, respectively. Thermogravimetry and mechanical testing showed that there were no significant changes on the bulk property of chitosan membrane after modification.© 2003 Society of Chemical Industry