bluuebunny/crossref_metadata_2025 huggingface dataset:
Caveolin and GLT‐1 gene expression is reciprocally regulated in primary astrocytes: Association of GLT‐1 with non‐caveolar lipid rafts
Authors: Zschocke Jürgen , Bayatti Nadhim , Behl Christian
Published: October 2004

Caveolae represent membrane microdomains acting as integrators of cellular signaling and functional processes. Caveolins are involved in the biogenesis of caveolae and regulate the activity of caveolae‐associated proteins. Although caveolin proteins are found in the CNS, the regulation of caveolins in neural cells is poorly described. In the present study, we investigated different modes and mechanisms of caveolin gene regulation in primary rat astrocytes. We demonstrated that activation of cAMP‐dependent signaling pathways led to a marked reduction in protein levels of caveolin‐1/‐2 in cortical astrocytes. Application of transforming growth factor‐α (TGF‐α) also resulted in a decrease of caveolin‐1/‐2 expression. Decreased caveolin protein levels were mirrored by diminished caveolin gene transcription. The repressive effect of TGF‐α on caveolin‐1 expression was MAP kinase‐independent and partly mediated through the PI3‐kinase pathway. Further downstream, inhibition of histone deacetylases abrogated TGF‐α effects, suggesting that chromatin remodeling processes could contribute to caveolin‐1 repression. Intriguingly, alterations of caveolin gene expression in response to cAMP or TGF‐α coincided with reciprocal and brain‐region specific changes in glial glutamate transporter GLT‐1 expression. The reciprocal regulation of caveolin‐1 and GLT‐1 expression might be gated through a common PI3‐kinase dependent pathway triggered by TGF‐α. Finally, we showed that GLT‐1 is located in non‐caveolar lipid rafts of cortical astrocytes. In conclusion, this study highlights the occurrence of the reciprocal regulation of caveolin and GLT‐1 expression during processes such as astrocyte differentiation via common signaling pathways. We also provide strong evidence that GLT‐1 itself is concentrated in lipid rafts, inferring an important role for glial glutamate transporter function. © 2004 Wiley‐Liss, Inc.
Increased expression of the astrocytic glutamate transporter GLT‐1 in the prefrontal cortex of schizophrenics
Authors: Matute Carlos , Melone Marcello , Vallejo‐Illarramendi Ainara , Conti Fiorenzo
Published: October 2004

To verify whether altered glial glutamate uptake contributes to the reduced efficacy of glutamatergic transmission reported in the prefrontal cortex of schizophrenics, we studied the expression of GLT‐1, the transporter responsible for most glutamate transport, in autoptic samples of prefrontal cortex using real time quantitative RT‐PCR, immunocytochemistry, and functional assays. GLT‐1 mRNA levels in medication‐free patients were 2.5‐fold higher than in controls, whereas they were normal or reduced in patients treated with antipsychotics. We also observed a 4‐fold increase in L‐[3H]‐Glu uptake in Xenopus oocytes injected with mRNA from the prefrontal cortex of a medication‐free schizophrenic and a 2‐fold increase in GLT‐1 protein in the same cortical area of another medication‐free patient. Results suggest that GLT‐1 mRNA, protein and function are increased in prefrontal cortex of schizophrenics. © 2004 Wiley‐Liss, Inc.
5‐Hydroxytryptamine activates a barium‐sensitive, cAMP‐mediated potassium conductance in the leech giant glial cell
Authors: Britz Frank C. , Hirth Ingolf C. , Schneider Hans‐Peter , Deitmer Joachim W.
Published: October 2004

5‐Hydroxytryptamine (5‐HT), a neurotransmitter and neuromodulator in the central nervous system of the leech Hirudo medicinalis hyperpolarizes the giant glial cell in the neuropil of segmental ganglia at micromolar concentrations. The 5‐HT‐evoked glial response (EC50 ≈2.5 μM) is mediated by a non–desensitizing, G‐protein‐coupled receptor and due to activation of a Ca2+‐independent K+ conductance. The adenylyl cyclase inhibitor SQ22,536 blocks the response to 5‐HT; in the presence of 1 mM db‐cAMP, but not of 1 mM db‐cGMP, the glial response is suppressed. The 5‐HT‐evoked response is reduced by Ba2+ with half‐maximal inhibition at 50 μM Ba2+. The results suggest that release of 5‐HT from serotonergic neurons, or the maintenance of micromolar levels of extracellular 5‐HT in the ganglion, may help to set the glial membrane potential close to the K+ equilibrium potential. © 2004 Wiley‐Liss, Inc.
Involvement of adenylate cyclase and tyrosine kinase signaling pathways in response of crayfish stretch receptor neuron and satellite glia cell to photodynamic treatment
Authors: Uzdensky Anatoly , Kolosov Mikhail , Bragin Denis , Dergacheva Olga , Vanzha Olga , Oparina Lidiya
Published: October 2004

Neuroglial interactions are most profound during development or damage of nerve tissue. We studied the responses of crayfish stretch receptor neurons (SRN) and satellite glial cells to photosensitization with sulfonated aluminum phthalocyanine Photosens. Although Photosens was localized mainly in the glial envelope, neurons were very sensitive to photodynamic treatment. Photosensitization gradually inhibited and then abolished neuron activity. Neuronal and glial nuclei shrank. Some neurons and glial cells lost the integrity of the plasma membrane and died through necrosis after the treatment. The nuclei of other glial cells but not neurons become fragmented, indicating apoptosis. The number of glial nuclei around neuron soma increased, probably indicating proliferation for enhanced neuron protection. Adenylate cyclase (AC) inhibition by MDL‐12330A, or tyrosine kinase (TK) inhibition by genistein, shortened neuron lifetime, whereas AC activation by forskolin or protein tyrosine phosphatases (PTP) inhibition by sodium orthovanadate prolonged neuronal activity. Therefore, cAMP and phosphotyrosines produced by AC and TK, respectively, protected SRN against photoinactivation. AC inhibition reduced photodamage of the plasma membrane and subsequent necrosis in neuronal and glial cells. AC activation prevented apoptosis in photosensitized glial cells and stimulated glial proliferation. TK inhibition protected neurons but not glia against photoinduced membrane permeabilization and subsequent necrosis whereas PTP inhibition more strongly protected glial cells. Therefore, both signaling pathways involving cAMP and phosphotyrosines might contribute to the maintenance of neuronal activity and the integrity of the neuronal and glial plasma membranes. Adenylate cyclase but not phosphotyrosine signaling pathways modulated glial apoptosis and proliferation under photooxidative stress. © 2004 Wiley‐Liss, Inc.
Complexation of retroviruses with charged polymers enhances gene transfer by increasing the rate that viruses are delivered to cells
Authors: Landázuri Natalia , Le Doux Joseph M.
Published: October 2004

Background

We have previously found that retrovirus transduction is enhanced when an anionic polymer (chondroitin sulfate C) is added to virus stocks that contain an equal weight concentration of a cationic polymer (Polybrene). This observation was unexpected given that previous work has shown that cationic polymers enhance transduction while anionic polymers have the opposite effect.

Methods

Using model recombinant retroviruses and lentiviruses that encode for the Escherichia coli lacZ gene and quantitative assays of virus adsorption and transduction, we examined the mechanism of enhancement.

Results

We found that addition of oppositely charged polymers (Polybrene and chondroitin sulfate C) to virus stocks enhanced gene transfer by increasing the flux of active viruses to the cells. Virus–polymer complexes formed that did not reduce the stability of the viruses, yet were large enough to sediment, delivering the viruses to the cells more rapidly than by simple diffusion. The size of the complexes, the rate of sedimentation, and the levels of gene transfer increased with increasing concentrations of polymers. The degree to which transduction was enhanced ranged from 2‐ to nearly 40‐fold, and varied depending on the type of cells and viruses used. Interestingly, we found that association of the viruses with the polymer complexes did not significantly hinder their ability to complete post‐binding steps of transduction.

Conclusions

Complexation of retroviruses with charged polymers significantly improves the efficiency of ex vivo gene transfer by increasing the number of active viruses that reach the cells. Copyright © 2004 John Wiley & Sons, Ltd.
Each sensory nerve arising from the geniculate ganglion expresses a unique fingerprint of neurotrophin and neurotrophin receptor genes
Authors: Farbman Albert I. , Guagliardo Nick , Sollars Suzanne I. , Hill David L.
Published: October 2004

Neurons in the geniculate ganglion, like those in other sensory ganglia, are dependent on neurotrophins for survival. Most geniculate ganglion neurons innervate taste buds in two regions of the tongue and two regions of the palate; the rest are cutaneous nerves to the skin of the ear. We investigated the expression of four neurotrophins, nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin 3 (NT‐3), and NT‐4, and five neurotrophin receptors, trkA, trkB, trkC, p75, and truncated trkB (Trn‐B) in single sensory neurons of the adult rat geniculate ganglion associated with the five innervation fields. For fungiform papillae, a glass pipette containing biotinylated dextran was placed over the target papilla and the tracer was iontophoresed into the target papilla. For the other target fields, Fluoro‐Gold was microinjected. After 3 days, geniculate ganglia were harvested, sectioned, and treated histochemically (for biotinylated dextran) or immunohistochemically (for Fluoro‐Gold) to reveal the neurons containing the tracer. Single labeled neurons were harvested from the slides and subjected to RNA amplification and RT‐PCR to reveal the neurotrophin or neurotrophin receptor genes that were expressed. Neurons projecting from the geniculate ganglion to each of the five target fields had a unique expression profile of neurotrophin and neurotrophic receptor genes. Several individual neurons expressed more than one neurotrophin receptor or more than one neurotrophin gene. Although BDNF is significantly expressed in taste buds, its primary high affinity receptor, trkB, was not prominently expressed in the neurons. The results are consistent with the interpretation that at least some, perhaps most, of the trophic influence on the sensory neurons is derived from the neuronal somata, and the trophic effect is paracrine or autocrine, rather than target derived. The BDNF in the taste bud may also act in a paracrine or autocrine manner on the trkB expressed in taste buds, as shown by others. © 2004 Wiley‐Liss, Inc.
Noradrenaline up‐regulates the neuronal and the inducible nitric oxide synthase isoforms in magnocellular neurons of rat brain slices
Authors: Grange‐Messent Valérie , Raison Danièle , Dugas Bernard , Calas André
Published: October 2004

Nitric oxide (NO) and noradrenaline (NA) are suggested to be implicated in the regulation of neuropeptide secretion in the supraoptic nuclei (SON) and the paraventricular nuclei (PVN) of the hypothalamus. Our study demonstrates short‐term interactions between NA and the activity and expression of NO synthase (NOS) in magnocellular neurons, by using an ex vivo model of hypothalamic slices. In the SON as well as in the PVN, total NOS activity exhibited a time‐dependant increase after an incubation with NA. In the SON, this increase of total NOS activity was in part the consequence of stimulation of the iNOS activity. Coimmunodetections showed that cells expressing the inducible form of NOS were not astrocytes but magnocellular neurons. Steady‐state levels of iNOS and nNOS mRNA were dramatically enhanced by NA, particularly in the SON. Consequently, we provide new evidence that iNOS could play an important role in multiple physiological functions, including extracellular fluid balance, lactation, and parturition. © 2004 Wiley‐Liss, Inc.
Total suppression of the timing jitter in dispersion-managed soliton
systems
Authors: Sousa M H , Ferreira M F S
Published: October 2004

An exact analytical solution is derived for the
variance of the timing jitter of a dispersion-managed soliton in
the presence of synchronous amplitude modulators and filters. We
show that, for a given position of these control elements, a total
suppression of the timing jitter is possible, which will permit
unlimited error free transmission distances of DM solitons.
Optical switching characteristics of nonlinear periodic
multilayer structure
Authors: Rostami A , Tahmasebpour M
Published: October 2004

Optical switching is one of the basic functions in the
optical communication systems. In this paper, we will investigate
the switching properties of the nonlinear periodic multilayer
stacks. For this optical switch, the phase mismatching effect on
the switching characteristics (switching threshold and rise time)
is investigated. Also, in this analysis we study the effect of the
relative phase displacement between the linear and the nonlinear
index of refractions on switching parameters. Finally the optical
3-dB couplers for coupling the control and the signal fields in
the input and for extracting in the output ports are used.
Accurate physical modelling of multi quantum well ring lasers
Authors: DeLeonardis F , Passaro V M N
Published: October 2004

The aim of this paper is to present a model including
the fundamental physical effects of the multi quantum well (MQW)
ring laser for the understanding of the optical mode behaviour and
the control of the oscillating mode in semiconductor injection
ring laser. The fully physical model is derived from a quantum
mechanical approach and don't depend on any semi-empirical
approximation. The ring laser behaviour is related to its physical
and technological constraints, as the backscattering effect and
ring radius.
High power laser transmission through photonic band gap fibres
Authors: Al-Janabi A H , Wintner E
Published: October 2004

This present work reports preliminary results on
experimental measurements of laser energy coupled through a PBG
fibre. The PBG fibre has been evacuated to increase the laser
intensity damage threshold. Below 0.1 mbar pressure and with a
good beam input quality, 600 μJ of out coupled nanosecond
pulse width laser energy was obtained. The average coupling
efficiency was about 14%, where the biggest contribution to the
overall losses was the input coupling efficiency. The outcoupled
single mode showed no change in its shape.
Variation of the mean kinetic temperature of magnetically trapped
atoms by external shaking perturbation
Authors: Henn E A L , Magalhães K M F , Muniz S R , Silva R R , Marcassa L G , Bagnato V S
Published: October 2004

Using a shaking field overlaped to the static field of
a quadrupole trap we have performed experiments with cold Na atoms
held in a magnetic trap. As a function of the shaking frequency
the temperature of the atomic cloud is measured by time-of-flight.
We observe results similar to Kumakura et al. [Phys. Rev. A 68,
021401(R)] and the variations of the kinetic temperature in our
results are explained based on a model where we selectively affect
different velocity classes.
Multispectral confocal fluorescence imaging: monitoring of intracellular distribution of PKC influenced by photoactive drug hypericin
Authors: Kocanova S , Mateasik A , Chorvat Jr D , Miskovsky P
Published: October 2004

The spectral imaging with confocal microscopy was applied for evaluation of changes in sub-cellular distribution of protein kinase C (PKC) in glioblastoma cells after application of photosensitizer hypericin (Hyp). The distribution of PKC stained by fim-1-AM probe in presence of Hyp was determined by linear un-mixing algorithm from recorded spectral images. Comparison of the distribution of PKC in cells with and without Hyp indicates that presence of Hyp induces re-localization of PKC to the perinuclear area of cells. Moreover, linear co-localization pattern between distribution of Hyp and fim-1 indicates strong spatial overlapping of fim-1 and Hyp localization. This means that the re-localization of PKC in presence of Hyp could be the result of direct interaction between PKC and Hyp. It is shown, that spectral imaging and linear un-mixing is an approach that can enhance our ability to observe cellular structure and function by fluorescent probes even in the case of strong overlapping of their emission spectra with the spectra of photosensitizers.
The proof of a conjecture of Bouabdallah and Sotteau
Authors: Xu Min , Hou Xinmin , Xu Jun‐Ming
Published: October 2004

Let G be a connected graph of order n. A routing in G is a set of n(n − 1) fixed paths for all ordered pairs of vertices of G. The edge‐forwarding index of G, π(G), is the minimum of the maximum number of paths specified by a routing passing through any edge of G taken over all routings in G, and πΔ,n is the minimum of π(G) taken over all graphs of order n with maximum degree at most Δ. To determine πn−2p−1,n for 4p + 2⌈p/3⌉ + 1 ≤ n ≤ 6p, A. Bouabdallah and D. Sotteau proposed the following conjecture in [On the edge forwarding index problem for small graphs, Networks 23 (1993), 249–255]. The set 3 × {1, 2, … , ⌈(4p)/3⌉} can be partitioned into 2p pairs plus singletons such that the set of differences of the pairs is the set 2 × {1, 2, … , p}. This article gives a proof of this conjecture and determines that πn−2p−1,n is equal to 5 if 4p + 2⌈p/3⌉ + 1 ≤ n ≤ 6p and to 8 if 3p + ⌈p/3⌉ + 1 ≤ n ≤ 3p + ⌈(3p)/5⌉ for any p ≥ 2. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(4), 292–296 2004
Desminopathies in muscle disease
Authors: Paulin Denise , Huet Alexis , Khanamyrian Luiza , Xue Zhigang
Published: October 2004

A recently identified class of myopathies is produced by abnormal desmin, and is characterized by a disorganization of the desmin filament network, the accumulation of insoluble desmin‐containing aggregates, and destructive changes in the sarcomeric organization of striated muscles. The desmin filaments interact with various other cytoskeletal proteins. The distinct clinical phenotypes are heterogeneous, with progressive skeletal myopathy, cardiomyopathy, and respiratory insufficiency as the most prominent features. Most of the desmin mutations are autosomal dominant. Identification of the causal genetic mutations shows that the desmin gene is not the only gene implicated in desminopathies; other genes encoding desmin‐associated proteins, such as alpha‐B‐crystallin, and synemin may also be involved. Patients with mutations in their alpha‐B‐crystallin gene, which produce similar skeletal and cardiac myopathies, also have opaque lenses. Knockout mice have helped to reveal the fundamental role of desmin filaments in cell architecture, sarcomere alignment, myofibril organization, and the distribution of mitochondria. Transgenic mice, which accumulate aggregates of desmin and associated proteins in their muscles, show that the loss of desmin intermediate function as a result of mutations in desmin itself, or in the desmin‐associated constituents, is important for disease progression. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
The keratin cytoskeleton in liver diseases
Authors: Zatloukal Kurt , Stumptner Conny , Fuchsbichler Andrea , Fickert Peter , Lackner Carolin , Trauner Michael , Denk Helmut
Published: October 2004

The keratin intermediate filament (IF) cytoskeleton of hepatocytes has continuously gained medical relevance over the last two decades. Originally it was mainly recognized as a differentiation marker for diagnostic purposes in pathology. However, keratin IFs were soon identified as major cellular structures to be affected in a variety of chronic liver diseases, such as alcoholic and non‐alcoholic steatohepatitis (ASH, NASH), copper toxicosis, and cholestasis. Based on observations in keratin gene knock‐out mice, the insight into the functional role of keratins was extended from a mere structural role providing mechanical stability to hepatocytes, to an additional role as target and modulator of toxic stress and apoptosis. The functional relevance of keratins in human diseases has recently been underlined by the identification of mutations in keratin genes in patients with liver cirrhosis. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
The cytoskeleton and disease
Authors: Ramaekers Frans CS , Bosman Fred T
Published: October 2004

Cytoskeletal research in recent years has revolutionized cell biology and biomedicine. The cytoskeleton spans the cytoplasm and interconnects the cell nucleus with the extracellular matrix, thereby forming a structural link between molecules involved in cell communication on the one hand, and gene expression on the other. Since the cytoskeleton is involved in virtually all cellular processes, abnormalities in this essential cellular component frequently result in disease. In this introduction, the basic structure of the cytoskeleton is briefly outlined. Furthermore, the disease processes in which the cytoskeleton plays a decisive role, and which are reviewed in detail in the papers in this issue, are briefly introduced. The advances in our understanding of the cytoskeleton and its function in disease will lead to new diagnostic and therapeutic applications in the foreseeable future. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Effect of the core‐shell impact modifier shell thickness on toughening PVC
Authors: Lee Juh‐Shyong , Chang Feng‐Chih
Published: October 2004

The shell thickness of a core/shell impact modifier is found to be the single most important factor in the toughening of rigid polyvinyl chloride (PVC). When the shell thickness is greater than a critical value of 15.8 nm, these core‐shell elastomeric particles are able to remain structurally intact and well dispersed within the PVC matrix after melt blending. However, too thick a shell thickness results in a hard core (high modulus) of these core/shell particles and loss of the rubbery nature required of an efficient impact modifier. Therefore, these over‐thick particles can act only as rigid fillers, not as efficient rubbery modifiers. On the other hand, when the shell thickness is less than the critical value of 4.9 nm, too thin a shell layer is simply unable to fully protect and cover the inner rubbery core during vigorous processing conditions, and these core‐shell particles tend to connect with one another through the partially exposed core to form a cellular‐like structure, thus resulting in poor toughening efficiency. Regardless of the particle size, as long as the shell thickness of these core/shell elastomers is between these two critical values (15.8 nm and 4.9 nm), they all display high efficiency in toughening rigid PVC. Polym. Eng. Sci. 44:1885–1889, 2004. © 2004 Society of Plastics Engineers.
Dynamics of foam growth: Bubble growth in a limited amount of liquid
Authors: Favelukis Moshe
Published: October 2004

A mathematical model for the growth of a spherical gas bubble in a limited amount of a viscous liquid is presented. The growth of the bubble is assumed to be controlled by both momentum and mass transfer. The simplified approach suggested, by assuming a parabolic concentration profile for the volatile component in the liquid, results in approximated analytical expressions for the final parameters of the process. The numerical results of the model can be used to predict the increase in the bubble size as well as the decrease of the solute concentration in the liquid and the decrease of the cell density with time. The model is able to deal with real processes, such as polymer melt devolatilization and the production of polymeric foams, where many bubbles grow simultaneously. Polym. Eng. Sci. 44:1900–1906, 2004. © 2004 Society of Plastics Engineers.
Viscoelastic changes and cell opening of reacting polyurethane foams from soy oil
Authors: Singh Ajay Pal , Bhattacharya Mrinal
Published: October 2004

The modulus development of reacting polyurethane foams from modified soy oil (soy polyol) was studied. The reaction and buildup of rheological properties were monitored using vane geometry in a strain‐controlled rheometer. Normal force exerted on the vanes by the expanding foam was measured as a function of time to study the phenomenon of cell opening. The effect of foam ingredients and process parameters on the modulus development was investigated. The morphology of the cured foam was studied using scanning electron microscope (SEM). Experiments were carried out to elucidate the effect of water and addition of petroleum‐based polyol on the modulus development of the reacting foam and the morphology of the cured product. The effect of frequency and thermal history on the modulus development of the reacting foam was also studied. Ozonolysis of soybean oil was carried out to study the effect of adding OH groups on the modulus development during the foaming reaction. Four stages of modulus development, similar to those observed for synthetic polyol (voranol, Aldrich Chemicals) foams, were observed. Increase in water content led to an earlier stiffening of the polymer and a higher modulus. Addition of voranol in soy polyol reduced the liquid foam plateau and significantly reduced the reaction time. Ozonolysis of soy oil led to an earlier phase separation as compared with foams from soy polyol. The temperature at which the foaming reaction takes place dominated the rate of modulus buildup. Higher texture (urea aggregates) and an increase in the cell size were observed with an increase in water content for soy polyol foams. Addition of voranol increased the number of open cells. Polym. Eng. Sci. 44:1977–1986, 2004. © 2004 Society of Plastics Engineers.
Influence of molecular weight on strain‐gradient yielding in polystyrene
Authors: Tjernlund Jessica Agde , Gamstedt E. Kristofer , Xu Zhi‐Hui
Published: October 2004

Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length‐scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano‐indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length‐scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver‐Pharr method. It was also shown that the length‐scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length‐scale parameter. The length‐scale parameter for strain‐gradient plasticity has a size of around 0.1 μm for polystyrene. Polym. Eng. Sci. 44:1987–1997, 2004. © 2004 Society of Plastics Engineers.
Tetrafunctional initiators for cationic polymerization of olefins
Authors: Taylor Stacy J. , Storey Robson F.
Published: October 2004

3,3′,5,5′‐Tetrakis(2‐chloro‐2‐propyl)biphenyl (biphenyl tetracumyl chloride, BPTCC) and 1,3‐bis[3,5‐bis(2‐chloro‐2‐propyl)phenoxy]propane (diphenoxypropane tetracumyl chloride, DPPTCC) were synthesized as initiators for quasiliving cationic polymerization of isobutylene (IB). In the synthesis of BPTCC, tetrafunctionality was achieved via the coupling of dimethyl 5‐bromoisophthalate (DMBI) using nickel dibromide bis(triphenylphosphine) and zinc in the presence of a base; in the synthesis of DPPTCC, two equivalents of dimethyl 5‐hydroxyisophthalate were linked via reaction with 1,3‐dibromopropane in the presence of potassium carbonate. Both initiators were used to initiate the polymerization of IB under quasiliving cationic polymerization conditions. PIB initiated from BPTCC revealed a chain end/molecule value (as determined by 1H‐NMR) of 3.85, verifying the nearly exclusive production of 4‐arm polyisobutylene (PIB). GPC analysis revealed a narrow peak representing the target four‐arm PIB, with a slight shoulder at high elution volumes (low molecular weights). GPC analysis of the PIB initiated by DPPTCC revealed multimodal distributions, suggesting the formation of two‐, three‐, and four‐arm star polymers during the polymerization. This behavior was attributed to Friedel–Crafts alkylation of the initiator core after the addition of one IB unit, which was activated by the electron‐donating oxytrimethyleneoxy linking moiety. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5942–5953, 2004
Stereoselective polymerization of rac‐lactide with a bulky aluminum/Schiff base complex
Authors: Tang Zhaohui , Chen Xuesi , Yang Yongkun , Pang Xuan , Sun Jingru , Zhang Xuefei , Jing Xiabin
Published: October 2004

An aluminum/Schiff base complex {[2,2‐dimethyl‐1,3‐propylenebis(3,5‐di‐tert‐butylsalicylideneiminato)](isopropanolato)aluminum(III) (2)} based on a bulky ligand and aluminum isopropoxide was prepared and employed for the stereoselective ring‐opening polymerization (ROP) of rac‐lactide (rac‐LA). The initiator was characterized with nuclear magnetic resonance (NMR), crystal structure measurements, and elemental analysis. It contained a five‐coordinate aluminum atom that was trigonal bipyramidal in the solid state according to the crystal structure measurements. The two conformational stereoisomers of 2 exchanged quickly on the NMR scale. Compound 2 polymerized rac‐LA into a crystalline polymer that was characterized with 1H NMR, wide‐angle X‐ray diffraction, electrospray ionization mass spectrometry, and gel permeation chromatography. The kinetics of the polymerization were first‐order in both the monomer and initiator, and there was a linear relationship between the rac‐LA conversion and the number‐average molecular weight of poly(rac‐LA) with a narrow molecular distribution (1.04–1.08). These features showed that the polymerization was well controlled. The high melting temperature (196–201 °C) and isotacticity of poly(rac‐LA) indicated that complex 2 was a highly stereoselective initiator for the ROP of rac‐LA. The stereoselectivity was as high as 90%, and the stereoblocks of poly(rac‐LA) by complex 2 contained an average of 20 units (average block length = 20) of enantiomerically pure lactic acid. The activation energy (23.6 kJ mol−1) was obtained according to an Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5974–5982, 2004
Numerical modeling of flow and bed evolution in meandering submarine channels
Authors: Das Himangshu Shekhar , Imran Jasim , Pirmez Carlos , Mohrig David
Published: October 2004

We present a numerical model of flow and bed morphology in meandering submarine channels. The conservation equations of fluid mass and momentum, suspended sediment concentration, and turbulent kinetic energy are expressed in depth‐averaged form and an intrinsic coordinate system. These equations, along with the Exner equation of bed sediment continuity, are solved using a predictor‐corrector explicit finite difference scheme. The numerical model is validated against laboratory experiments conducted in a straight flume. The model is generalized to any sinuous planform geometry, but this study focuses on sine‐generated sinuous channels. A series of numerical experiments have been performed with various inflow conditions and channel shapes to characterize the nature of in‐channel flow, deposition, and erosion, as well to investigate the tendency for meander migration. The model predicts an overall decrease in depth‐averaged current velocity and suspended sediment concentration in the down‐channel direction. Variations of current thickness, streamwise velocity, concentration, and bed level across the channel have been found to increase with an increase in channel curvature. Model runs made with erosional currents display significant change in bed level in the lateral direction because of erosion near the out side and deposition near the inside of a bend. The lateral bed slope generated by the flow of a depositional current is found to be relatively small. Model results are compared with the sedimentation pattern of a seismically interpreted buried submarine channel.
Numerical modeling of an impact‐induced hydrothermal system at the Sudbury crater
Authors: Abramov Oleg , Kring David A.
Published: October 2004

Large impact events, like the one that formed the Sudbury crater in Ontario, Canada, at 1.85 Ga, significantly increase the temperature of target rocks. The heat sources generated by such an impact event can drive the circulation of groundwater, establishing a hydrothermal system. We report on the results of numerical modeling of postimpact cooling with and without the presence of water at the Sudbury crater. A hydrothermal system is initiated in the annular trough between the peak ring and final crater rim, perhaps venting through faults that bound blocks of the crust in the modification zone of the crater. Although circulation through the overlying breccias may occur in the center of the crater, the central melt sheet is initially impermeable to circulating fluids. By ∼105 years the central melt sheet crystallizes and partially cools, allowing fluids to flow through it. Host rock permeability is the main factor affecting fluid circulation and lifetimes of hydrothermal systems. High permeabilities lead to a rapid system cooling, while lower permeabilities allow a steady transport of hot fluids to the surface, resulting in high surface temperatures for longer periods of time than cooling by conduction alone. The simulations presented in this paper show that a hydrothermal system at a Sudbury‐sized impact crater can remain active for several hundred thousand to several million years, depending on assumed permeability. These results suggest that a hydrothermal system induced by an impact event can remain active for sufficiently long periods of time to be biologically significant, supporting the idea that impact events may have played an important biological role, especially early in Earth's history.
Ice floe distribution in the Sea of Okhotsk in the period when sea‐ice extent is advancing
Authors: Inoue Jun , Wakatsuchi Masaaki , Fujiyoshi Yasushi
Published: October 2004

Ice floe distribution in the Sea of Okhotsk during a cold‐air outbreak was investigated by analyzing several thousand of sea‐ice images obtained by the aircraft observation on 18 February in 2000. The effective floe size became small (from 10 m to 2 m) within the marginal ice zone (MIZ). The scaling properties of floe distribution are demonstrated by a cumulative number frequency which follows a power law scaling with an exponent α. The value of α increased from 1.5 within the internal ice zone to 2.1 within the MIZ, which means that relatively small ice floes dominate in the MIZ. The effective width of the MIZ estimated by a wave attenuation theory agreed with the observed width, suggesting that the flexural stress of waves penetrating into the ice is one of the possible mechanisms which cause the difference in the scaling property.
Magnetospheric electron densities inferred from upper‐hybrid band emissions
Authors: Benson R. F. , Webb P. A. , Green J. L. , Garcia L. , Reinisch B. W.
Published: October 2004

The magnetospheric electron density Ne can often be obtained to within a few percent from passive radio‐wave dynamic spectra when the electron plasma frequency fpe (∝ Ne1/2) is greater than the electron cyclotron frequency fce. This conclusion is based on interleaved active and passive observations from the Radio Plasma Imager (RPI) on the IMAGE satellite in the vicinity of the plasmapause. The Ne determinations are based on the frequency limits of an intense narrowband emission identified as the upper‐hybrid band. The lower limit is identified with fpe and the upper limit with the upper‐hybrid frequency fuh = (fpe2 + fce2)1/2. These frequency limits and the large amplitude of the emission, typically 20 dB or more above background, suggest strong Z‐mode waves, rather than quasi‐thermal fluctuations, as the emission source.
Diagnosing long‐term trends of the water mass properties in the East Sea (Sea of Japan)
Authors: Kwon Young‐Oh , Kim Kuh , Kim Young‐Gyu , Kim Kyung‐Ryul
Published: October 2004

Steady changes of temperature and oxygen concentration since the 1950s have been observed in the East Sea. In addition to temperature and oxygen, this study extends the analysis to salinity observations. Salinity has increased between 300 and 1000 m and decreased below 1500 m with a trend of about 0.06 and −0.02 psu/century, respectively. A simple diagnostic inverse model indicates that the changes in the intermediate depth (300–1000 m) were primarily due to a change in salinity at the surface outcrop, and those in the deep and bottom water were due to not only a warming of the surface source water but also a circulation change in the deep and bottom water, with similar magnitudes of contributions from the two factors. Both the observations and model consistently suggest that the water mass structures have changed during the last few decades.
Two teleconnection patterns involved in the North Atlantic/Arctic Oscillation
Authors: Kodera Kunihiko , Kuroda Yuhji
Published: October 2004

The North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) are known as phenomena influencing the weather and climate of the Euro‐Atlantic region. Often, however, they are treated together. In this study, two indices representing two independent teleconnection patterns in the sea level pressure are introduced to characterize their differences. One is a seesaw between the Azores and Iceland (AI), and the other is that between the Polar and Mediterranean (PM) regions. The result of our study shows that differences in the NAO/AO indices mainly arise from the inclusion of different portions of the AI and PM, and the NAO/AO indices can be reproduced by a linear combination of the AI and PM indices.
Interdecadal variability of the thermocline along the west coast of South America
Authors: Pizarro Oscar , Montecinos Aldo
Published: October 2004

Using gridded MBT and XBT data for the period 1955–2002, we analyze the interdecadal variability of the thermocline along the western coast of South America between the equator and 32°S. Results show a relatively small, but coherent, interdecadal oscillation of the depth of different isotherms representing the thermocline along the region. This oscillation is well correlated with interdecadal SST anomalies. At the end of the 1960s the thermocline was on average 10 m shallower than during the beginning of the 1980s, while SST anomalies changed from −0.3°C to 0.5°C during the same period. The transition from shallow to deep thermocline depths during the mid‐1970s is consistent with the change from cold to warm conditions observed at the surface. Changes in the depth of the thermocline base may modify the properties of the subsurface water that feeds the coastal upwelling, with further consequences for the ecosystem of the region.
Electrical characteristics of narrow bipolar events
Authors: Eack Kenneth B.
Published: October 2004

Narrow bipolar events (NBE) are the electromagnetic signature of a distinct class of impulsive and energetic intra‐cloud discharge that occurs in some thunderstorms. NBE are characterized by strong VHF RF emissions and bipolar waveforms when observed by broadband field‐change antennas at large distances. These discharges may occur in isolation or precede and perhaps initiate conventional intra‐cloud flashes. When observed at close range, NBE waveforms exhibit electrostatic field changes in addition to the bipolar radiation field change. At extremely close range, the induction and electrostatic fields dominate in our measurements. Using close‐range observations in conjunction with the radiation‐field measurements, I calculate that on average, an NBE transfers 0.3 C of charge over a distance of 3.2 km and that the discharge wave front propagates at a speed equal to one‐half the speed of light.
Measurements of ice thickness and seabed topography under the Fimbul Ice Shelf, Dronning Maud Land, Antarctica
Authors: Nøst Ole Anders
Published: October 2004

This paper presents results from seismic measurements of the ice and water column thickness of the Fimbul Ice Shelf in the northeastern Weddell Sea. Seismic reflection measurements were conducted at 183 stations covering most of the ice shelf. Seismic velocities in the ice were derived from refraction measurements at 12 stations, distributed evenly across the area, as well as from temperature and density data from the Fimbul Ice Shelf. Velocities in the water were derived from temperature and salinity data from beneath the Fimbul Ice Shelf. Ice thicknesses were found to vary between 160 m and 550 m with uncertainties up to ±10 m. Water column thicknesses up to 900 m were found within the central ice shelf cavity, and values exceed 2000 m where the ice shelf overhangs the continental slope. Uncertainties in water column thickness are estimated to be ±60 m, and are dominated by the uncertainties in the shape of the seabed. Ice draft and seabed elevation was derived from ice and water column thickness assuming hydrostatic pressure. The resulting map of seabed elevation and water column thickness suggests that the strong westward flowing coastal current will be steered under the ice shelf and thus drive a sub‐ice‐shelf flow. Warm Deep Water does not have direct access to the ice shelf cavity, while relatively cold coastal waters shallower than 500 m will interact closely with the Fimbul Ice Shelf.
Estimates of net CO2 flux by application of equilibrium boundary layer concepts to CO2 and water vapor measurements from a tall tower
Authors: Helliker Brent R. , Berry Joseph A. , Betts Alan K. , Bakwin Peter S. , Davis Kenneth J. , Denning A. Scott , Ehleringer James R. , Miller John B. , Butler Martha P. , Ricciuto Daniel M.
Published: October 2004

Convective turbulence within the atmospheric boundary layer (ABL) and movement of the ABL over the surface results in a large spatial (104–105 km2) integration of surface fluxes that affects the CO2 and water vapor mixing ratios. We apply quasi‐equilibrium concepts for the terrestrial ABL to measurements of CO2 and water vapor made within the ABL from a tall tower (396 m) in Wisconsin. We suppose that CO2 and water vapor mixing ratios in the ABL approach an equilibrium on timescales longer than a day: a balance between the surface fluxes and the exchange with the free troposphere above. By using monthly averaged ABL‐to‐free‐tropospheric water vapor differences and surface water vapor flux, realistic estimates of vertical velocity exchange with the free troposphere can be obtained. We then estimated the net surface flux of CO2 on a monthly basis for the year of 2000, using ABL‐to‐free‐tropospheric CO2 differences, and our flux difference estimate of the vertical exchange. These ABL‐scale estimates of net CO2 flux gave close agreement with eddy covariance measurements. Considering the large surface area which affects scalars in the ABL over synoptic timescales, the flux difference approach presented here could potentially provide regional‐scale estimates of net CO2 flux.
Determination of the features of the low‐level temperature inversions above a suburban site in Oman using radiosonde temperature measurements: Long‐term analysis
Authors: Abdul‐Wahab Sabah A. , Al‐Saifi Sultan Y. , Alrumhi Badar A. , Abdulraheem Mahmood Y. , Al‐Uraimi Mohammed
Published: October 2004

The objective of this investigation is to examine the characteristics of the low‐level tropospheric temperature inversions to a height of 4 km above a suburban site in Oman by using 10‐year records of daily upper‐air meteorological data. The temperature profile data included in this study were derived from the radiosonde data collected by the Meteorology Department at Seeb International Airport station. The study addresses the statistical analysis of inversion parameters and investigates whether changes in these parameters (i.e., depth and strength) have occurred during the last decade. Both surface‐based and elevated inversions are investigated. The study indicated a monthly change in inversion frequency, depth, and strength. Overall, most of the inversions tended to be surface based. The surface‐based inversion was more common in winter compared with summer. An opposite trend in elevated inversion was seen where a maximum in their frequencies was found in summer. The elevated inversions were generally shallower and weaker than the surface‐based inversions. The data for the past 10 years also indicated a reduction in surface‐based inversion depths, accompanied by a rise in both the strength of the surface‐based inversions and surface temperatures. It was found that the surface temperature increased by about 0.33°C per year, and the inversion depths declined by about 16.3 m yr−1.
New modeling of the Vostok ice flow line and implication for the glaciological chronology of the Vostok ice core
Authors: Parrenin F. , Rémy F. , Ritz C. , Siegert M. J. , Jouzel J.
Published: October 2004

We have used new spaceborne (elevation) and airborne (ice thickness) data to constrain a 2D1/2 model of snow accumulation and ice flow along the Ridge B‐Vostok station ice flow line (East Antarctica). We show that new evaluations of the ice flow line geometry (from the surface elevation), ice thickness (from low‐frequency radar data), and basal melting and sliding change significantly the chronology of the Vostok ice core. This new Vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the Dome Fuji glaciological timescale. At the same time, the new model shows significantly older ages than the previous GT4 timescale for the last glacial part, being thus in better agreement with the GRIP and GISP2 chronologies.
An ozone episode in the Philadelphia metropolitan area
Authors: Kleinman Lawrence I. , Ryan William F. , Daum Peter H. , Springston Stephen R. , Lee Yin‐Nan , Nunnermacker Linda J. , Weinstein‐Lloyd Judith
Published: October 2004

In July and August 1999 a Northeast Oxidant and Particle Study field campaign was conducted in the Philadelphia metropolitan area to determine causes for episodically high levels of O3 and particulate matter ≤2.5 μm in aerodynamic diameter. We report emission estimates, weather information, surface O3 monitoring data, and aircraft observations, with a focus on 31 July, the last day of an O3 episode in which concentrations in Philadelphia reached 165 ppb, the highest level observed there in the past 11 years. As is common in the northeastern states, this O3 episode started with the development of a broad ridge over the central United States and ended with the northeast corridor under the influence of an Appalachian lee trough with airflow from the SW in an along‐corridor direction. For a portion of the morning of 31 July, winds were nearly stagnant, allowing local emissions to accumulate. In contrast to typical O3 episodes in the northeast, transport on 31 July was limited, and O3 hot spots occurred close to NOx and volatile organic compound (VOC) emission sources. High O3 was observed downwind of Baltimore and Philadelphia, both major urban areas. High O3 was also observed in a less likely region near the Delaware‐Pennsylvania border, downwind of Wilmington, Delaware, but near utility and industrial emission sources. Surface O3 monitoring data and morning aircraft observations show that the residual layer aloft contained 80–100 ppb of O3 but almost no O3 precursors. Same‐day photochemistry on 31 July caused surface O3 concentrations to increase by 60–80 ppb. Photochemical model calculations indicate O3 production rates in excess of 20 ppb h−1 in regions with NOx > 5 ppb. High NOx concentrations are a consequence of poor ventilation. Peroxide observations and calculations indicate that O3 production is VOC limited in the high‐NOx portions of the Philadelphia urban plume. Our results are contrasted against a severe O3 episode that occurred in 1995. While the 1999 episode had stagnation conditions leading to local O3 hot spots, there were mesoscale meteorological features in 1995 that favored interregional transport.