bluuebunny/crossref_metadata_2025 huggingface dataset:
TGFβ1 induces Jagged1 expression in astrocytes via ALK5 and Smad3 and regulates the balance between oligodendrocyte progenitor proliferation and differentiation
Authors: Zhang Yueting , Zhang Jingya , Navrazhina Kristina , Argaw Azeb Tadesse , Zameer Andleeb , Gurfein Blake T. , Brosnan Celia F. , John Gareth R.
Published: February 2010

Notch1 receptor signaling regulates oligodendrocyte progenitor differentiation and myelin formation in development, and during remyelination in the adult CNS. In active multiple sclerosis lesions, Notch1 localizes to oligodendrocyte lineage cells, and its ligand Jagged1 is expressed by reactive astrocytes. Here, we examined induction of Jagged1 in human astrocytes, and its impact on oligodendrocyte differentiation. In human astrocyte cultures, the cytokine TGFβ1 induced Jagged1 expression and blockade of the TGFβ1 receptor kinase ALK5 abrogated Jagged1 induction. TGFβ2 and β3 had similar effects, but induction was not observed in response to the TGFβ family member activin A or other cytokines. Downstream, TGFβ1 activated Smad‐dependent signaling, and Smad‐independent pathways that included PI3 kinase, p38, and JNK MAP kinase, but only inhibition of the Smad‐dependent pathway blocked Jagged1 expression. SiRNA inhibition of Smad3 downregulated induction of Jagged1, and this was potentiated by Smad2 siRNA. Purified oligodendrocyte progenitor cells (OPCs) nucleofected with Notch1 intracellular signaling domain displayed a shift towards proliferation at the expense of differentiation, demonstrating functional relevance of Notch1 signaling in OPCs. Furthermore, human OPCs plated onto Jagged1‐expressing astrocytes exhibited restricted differentiation. Collectively, these data illustrate the mechanisms underlying Jagged1 induction in human astrocytes, and suggest that TGFβ1‐induced activation of Jagged1‐Notch1 signaling may impact the size and differentiation of the OPC pool in the human CNS. © 2010 Wiley‐Liss, Inc.
A method for recording evoked local field potentials in the primate dentate gyrus in vivo
Authors: Tamura Ryoi , Eifuku Satoshi , Uwano Teruko , Sugimori Michiya , Uchiyama Kumiko , Ono Taketoshi
Published: February 2010

Recording evoked local field potentials (LFPs) in the hippocampus in vivo has yielded us useful information about the neural mechanisms of learning and memory. Although this technique has been used in studies of the hippocampus of rodents, lagomorphs, and felines, it has not yet been applied to the primate hippocampus. Here, we report a method for recording evoked LFPs in the hippocampus of monkeys. A stimulation electrode and a recording electrode were implanted in the perforant pathway and dentate gyrus, respectively, under the guidance of electrophysiological recording. With a low stimulus intensity just above the threshold, the potential appeared as a slow positive‐wave component, which was regarded as field excitatory postsynaptic potential (putative fEPSP); as stimulation intensity increased, the fEPSP amplitude increased, followed by a sharp negative component which was regarded as putative population spike. When the coordinates of the recording or stimulation electrode were moved stepwise, we observed a systematic change in the waveforms of evoked LFPs; this change corresponded to the structural arrangement through which the electrode passed. In a test for short‐term synaptic plasticity by paired‐pulse stimulation, potentials evoked by the second pulse were influenced by the first one in a manner dependent on interpulse intervals. In a test for long‐term synaptic plasticity by high‐frequency stimulation, the slopes of the fEPSPs and the area of population spikes were increased for more than 1 h. These results indicate that the method developed in the present study is useful for testing theories of hippocampal functions in primates. © 2010 Wiley‐Liss, Inc.
In vivo modulation of nitric oxide concentration dynamics upon glutamatergic neuronal activation in the hippocampus
Authors: Lourenço Cátia F. , Santos Ricardo , Barbosa Rui M. , Gerhardt Greg , Cadenas Enrique , Laranjinha João
Published: February 2010

Nitric oxide (•NO) is a labile endogenous free radical produced upon glutamatergic neuronal activity in hippocampus by neuronal nitric oxide synthase (nNOS), where it acts as a modulator of both synaptic plasticity and cell death associated with neurodegeneration. The low CNS levels and fast time dynamics of this molecule require the use of rapid analytical methods that can more accurately describe its signaling in vivo. This is critical for understanding how the kinetics of•NO‐dependent signaling pathways is translated into physiological or pathological functions. In these studies, we used•NO selective microelectrodes coupled with rapid electrochemical recording techniques to characterize for the first time the concentration dynamics of•NO endogenously produced in hippocampus in vivo following activation of ionotropic glutamate receptors. BothL‐glutamate (1–100 mM) andN‐methyl‐D‐aspartate (NMDA; 0.01–5 mM) produced transient, dose‐dependent increases in extracellular•NO concentration. The production of•NO in the hippocampus by glutamate was decreased by the nNOS inhibitor 7‐NI. Intraperitoneal administration of the NMDA receptor blocker, MK‐801, and the inhibitor of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoazolepropionic acid (AMPA) receptor, NBQX, applied locally greatly attenuated glutamate‐evoked overflow of•NO. Thus,•NO overflow elicited by activation of glutamate receptors appeared to result from an integrated activation of ionotropic glutamate receptors, both of the NMDA and AMPA receptors subtypes. Additionally, distinct concentration dynamics was observed in the trisynaptic loop with stronger and longer lasting effects of glutamate activation on•NO overflow seen in the CA1 region as compared with thedentate gyrus. Overall, the results provide a quantitative and temporal basis for a better understanding of•NO activity in the rat hippocampus. © 2010 Wiley‐Liss, Inc.
Assessing the effects of post‐pine beetle forest litter on snow albedo
Authors: Winkler Rita , Boon Sarah , Zimonick Barbara , Baleshta Karen
Published: February 2010

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood‐dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south‐central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007–2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd.
Two different pathways for the transport of primitive and definitive blood cells from the yolk sac to the embryo in humans
Authors: Pereda Jaime , Monge Juan I. , Niimi Gen
Published: February 2010

During the early human embryonic period nutrients and blood cells are temporarily provided by the extraembryonic yolk sac (YS). The YS before week six is involved not only in primitive but also in definitive erythropoiesis. While the destiny of primitive erythroid cells that fill the blood vessels of the YS is well known, the final destination of erythrocytes present in the endodermal vesicular system is unknown. In the present study we have investigated, step by step, the destiny of the erythrocytes present in the endodermal vesicles during the embryonic period.

Twelve human YSs and their corresponding yolk stalks were analyzed between weeks 4 and 7 of embryonic age by light and scanning electron microscopy. It is shown that erythrocytes (according to their size and morphological features) located within the endodermal vesicles of the YS wall are pulled out through endodermal pits into the YS cavity, from where they reach the lumen of the primitive gut of the embryo through the vitelline duct, a temporary pathway communicating both compartments. During the study period no erythrocytes were seen within the embryo's vascular network where only primitive erythroblasts were identified. Our results indicate that the vitelline duct plays an important transient role as a pathway for the transport of nutrients and blood cells between the YS and the embryo before week five of embryonic development that ends just at the time when YS‐embryo circulation becomes established. Microsc. Res. Tech. 73:803–809, 2010. © 2010 Wiley‐Liss, Inc.
Impact of hepatitis B virus infection on outcome following resection for intrahepatic cholangiocarcinoma
Authors: Zhang Lei , Cai Jian‐Qiang , Zhao Jian‐Jun , Bi Xin‐Yu , Tan Xiao‐Gang , Yan Tao , Li Cong , Zhao Ping
Published: February 2010

Background

Little is known about the prognosis of intrahepatic cholangiocarcinoma (ICC) patients with hepatitis B virus (HBV) infection following surgical resection.

Methods

The clinico‐pathological data of 40 consecutive ICC patients including 29 patients with HBV infection were analyzed after surgical resection.

Results

Of all 40 ICC patients, the overall 1‐, 3‐, 5‐year survival rates and a median survival for 29 (74.4%) patients with current or previous HBV infection were 78.9%, 42.8%, 35.7%, and 32.0 months, respectively. Twenty‐nine (74.4%) patients with HBV infection, represented by HBsAg+ or anti‐HBc+, had a better prognosis than 10(25%) patients without HBV infection represented by all markers‐negative. Compared with 10 (25%) patients without HBV infection, 11 (27.5%) ICC patients with HBsAg+ had a better prognosis as well. Additionally, lymph node metastasis were identified as an independent predictors of poor overall survival on multivariate analysis in the study of all the 40 patients and 29 patients with HBV infection.

Conclusions

Patients with current or previous HBV infection, represented by HBsAg+ or anti‐HBc+, had significantly better prognosis than patients without HBV infection. Patients with HBV infection should be distinguished from other ICC patients, because of their favorable outcome after surgery. J. Surg. Oncol. 2010; 101:233–238. © 2010 Wiley‐Liss, Inc.
Test compounds for detecting the silanol effect on the elution of ionized amines in reversed‐phase LC
Authors: Okusa Kensuke , Suita Yuki , Otsuka Yukio , Tahara Mineo , Ikegami Tohru , Tanaka Nobuo , Ohira Masayoshi , Takahashi Masakazu
Published: February 2010

The effectiveness of several basic compounds for testing silica‐based stationary phases was reviewed by applying them to recent columns for reversed‐phase HPLC. Most octadecylsilylated (C18) stationary phases, prepared as a base‐deactivated material from high‐purity silica gel with endcapping, provided excellent peak shape and column efficiency for the bases including benzylamine and amitriptyline that once caused problems and were subsequently employed for testing silanol activities. However, a cyclic tertiary amine, dextrometorphan, was eluted as an acceptable peak from only a few columns at neutral pH. Such a more sensitive probe is expected to contribute to further improvement of the stationary phase for reversed‐phase HPLC.
Phonation threshold pressure predictions using viscoelastic properties up to 1,400 Hz of injectables intended for Reinke's space
Authors: Klemuk Sarah A. , Lu Xiaoying , Hoffman Henry T. , Titze Ingo R.
Published: February 2010

Objectives/Hypothesis:

Viscoelastic properties of numerous vocal fold injectables have been reported but not at speaking frequencies. For materials intended for Reinke's space, ramifications of property values are of great concern because of their impact on ease of voice onset. Our objectives were: 1) to measure viscoelastic properties of a new nonresorbing carbomer and well‐known vocal fold injectables at vocalization frequencies using established and new instrumentation, and 2) to predict phonation threshold pressures using a computer model with intended placement in Reinke's space.

Study Design:

Rheology and phonation threshold pressure calculations.

Methods:

Injectables were evaluated with a traditional rotational rheometer and a new piezo‐rotary vibrator. Using these data at vocalization frequencies, phonation threshold pressures (PTP) were calculated for each biomaterial, assuming a low dimensional model with supraglottic coupling and adjusted vocal fold length and thickness at each frequency. Results were normalized to a nominal PTP value.

Results:

Viscoelastic data were acquired at vocalization frequencies as high as 363 to 1,400 Hz for six new carbomer hydrogels, Hylan B, and Extracel intended for vocal fold Reinke's space injection and for Cymetra (lateral injection). Reliability was confirmed with good data overlap when measuring with either rheometer. PTP predictions ranged from 0.001 to 16 times the nominal PTP value of 0.283 kPa.

Conclusions:

Accurate viscoelastic measurements of vocal fold injectables are now possible at physiologic frequencies. Hylan B, Extracel, and the new carbomer hydrogels should generate easy vocal onset and sustainable vocalization based on their rheologic properties if injected into Reinke's space. Applications may vary depending on desired longevity of implant. Laryngoscope, 2010
Thermosensitive Nanoparticles Self‐Assembled from PCL‐b‐PEO‐b‐PNIPAAm Triblock Copolymers and their Potential for Controlled Drug Release
Authors: Sun Peijian , Zhang Yu , Shi Linqi , Gan Zhihua
Published: February 2010

Thermosensitive nanoparticles with a core‐shell structure were prepared by self‐assembly of PCL‐b‐PEO‐b‐PNIPAAm triblock copolymers, which were synthesized by anionic ring‐opening polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization. At temperatures above the lower critical solution temperature (LCST), the collapse of PNIPAAm chains in the outer shell and in the core of nanoparticle caused a decrease in size, while the constantly hydrophilic PEO chains in the shell endowed nanoparticles with excellent stability in water. The release of doxorubicin from these nanoparticles showed that both the length of PNIPAAm chains and temperature have great influence on drug release, which indicates the great potential of thermosensitive nanoparticles as drug carriers.

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An Investigation of Free Radical Copolymerization Kinetics of the Bio‐renewable Monomer γ‐Methyl‐α‐methylene‐γ‐butyrolactone with Methyl methacrylate and Styrene
Authors: Cockburn Robert A. , McKenna Timothy F.L. , Hutchinson Robin A.
Published: February 2010

The free‐radical copolymerization propagation kinetics of the bio‐renewable monomer γ‐methyl‐α‐methylene‐γ‐butyrolactone (MeMBL) with styrene (ST) and with methyl methacrylate (MMA) have been investigated by the pulsed laser polymerization (PLP)—size exclusion chromatography (SEC) technique, in addition to DSC and proton NMR measurements. Monomer reactivity ratios for bulk MeMBL/ST and MeMBL/MMA copolymerizations are rMeMBL = 0.80 ± 0.04 and rST = 0.34 ± 0.04 and rMeMBL = 3.0 ± 0.3 and rMMA = 0.33 ± 0.01, respectively, with no significant variation with temperature found between 22 and 90 °C. The implicit penultimate unit effect (IPUE) model best represents the composition‐averaged copolymerization propagation rate coefficient, kp,cop for the MeMBL/ST system. Arrhenius parameters were estimated for MeMBL homopolymerization and found to be quite similar to those of MMA. DSC results show that copolymers of well controlled composition can be produced to suit specific Tg requirements over a much higher temperature range than possible with current acrylic glasses.

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From Fundamental Polymerization Kinetics to Process Application—A Realistic Vision?
Authors: Bauer Christian , Becker Katrin , Herrmann Thomas , Lilge Dieter , Roth Marion , Busch Markus
Published: February 2010

This contribution presents a ramble through the past, inspecting the developments of fundamental scientific investigations into the elementary reaction steps of polymerizations. Often the question arises whether benefits from fundamental scientific investigation find their way into industrial practice and how these pay off in better understanding large‐scale processes. The high‐pressure ethene polymerization is the system of interest here because 1) it is a complex process with a world production of several million tons per year and 2) although dealing with system pressures up to 3000 bar is not an easy task, a long history—if not tradition—exists between the scientific efforts to improve the process and the research groups of Franck and Buback in Karlsruhe, Schönemann and Luft in Darmstadt, and later Buback in Göttingen. The scope of this discussion will range from non‐invasive on‐ and in‐line monitoring by spectroscopic methods up to process modeling by advanced kinetic models and their potential for explorative work.

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Tocopheryl quinones and mitochondria
Authors: Gille Lars , Staniek Katrin , Rosenau Thomas , Duvigneau J. Catharina , Kozlov Andrey V.
Published: February 2010

In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR‐α‐congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E‐related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of α‐/γ‐tocopheryl quinones and their parent α‐/γ‐tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities.
α‐Tocopheryl phosphate – An active lipid mediator?
Authors: Zingg Jean‐Marc , Meydani Mohsen , Azzi Angelo
Published: February 2010

The vitamin E (α‐tocopherol, αT) derivative, α‐tocopheryl phosphate (αTP), is detectable in small amounts in plasma, tissues, and cultured cells. Studies done in vitro and in vivo suggest that αT can become phosphorylated and αTP dephosphorylated, suggesting the existence of enzyme(s) with αT kinase or αTP phosphatase activity, respectively. As a supplement in animal studies, αTP can reach plasma concentrations similar to αT and only a part is dephosphorylated; thus, αTP may act both as pro‐vitamin E, but also as phosphorylated form of vitamin E with possibly novel regulatory activities. Many effects of αTP have been described: in the test tube αTP modulates the activity of several enzymes; in cell culture αTP affects proliferation, apoptosis, signal transduction, and gene expression; in animal studies αTP prevents atherosclerosis, ischemia/reperfusion injury, and induces hippocampal long‐term potentiation. At the molecular level, αTP may act as a cofactor for enzymes, as an active lipid mediator similar to other phosphorylated lipids, or indirectly by altering membrane characteristics such as lipid rafts, fluidity, and curvature. In this review, the molecular and cellular activities of αTP are examined and the possible functions of αTP as a natural compound, cofactor and active lipid mediator involved in signal transduction and gene expression discussed.
Tautomerism and isotopic multiplets in the 13C NMR spectra of partially deuterated 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones and their sulfur analogs—evidence for elucidation of the structure backbone and tautomeric forms
Authors: Rimaz Mehdi , Noroozi Pesyan Nader , Khalafy Jabbar
Published: February 2010

The tautomerism of the synthesized 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones (1a–d) and 3‐aryl‐7‐thioxo‐7,8‐dihydro‐6H‐pyrimido[4,5‐c]pyridazine‐5‐ones (2a–d) was studied in dimethyl sulfoxide (DMSO)‐d6. 1H NMR spectra of 1a–d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (χ) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a–d was also studied. All of 1a–d and also 2d compounds existed in lactam (I) form, whereas 2a–c compounds have two distinguished tautomers in DMSO‐d6 [lactam (I) and lactim (II) forms]. The solvent‐substrate proton exchange was examined in compounds 1a–d and 2a–d by adding one drop of D2O. All compounds (except 1d) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D2O. Some compounds (but not all of them) that are easily soluble in DMSO‐d6 containing D2O showed isotopic splitting (β‐isotope effect) in their 13C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon‐13 splitting (β‐isotope effect). Copyright © 2010 John Wiley & Sons, Ltd.
Validation of an incremental motor unit number estimation technique in rabbits
Authors: David William S. , Goyal Namita , Henry Francis P. , Baldassari Laura E. , Redmond Robert W.
Published: February 2010

Motor unit number estimation (MUNE) allows for quantitative assessment of functional motor units in a nerve. Several techniques have been applied to human studies. Although MUNE has been performed in animals to study neurological disorders, reproducibility has not been addressed. We analyzed the test–retest reproducibility of an incremental MUNE technique in rabbits and performed histological correlation. A peroneal MUNE was performed in 9 rabbits on two occasions separated by 30 days. MUNE was then performed on 18 rabbits prior to euthanize. A count of total fibers and a second count of large myelinated fibers were performed on nerve cross‐sections. Test–retest reproducibility revealed an intraclass correlation coefficient (ICC) of 0.75. The average test–retest relative difference was 26.6%. Comparison of MUNE and histomorphometrical counts revealed a correlation coefficient (r) of 0.21 (total fiber counts) and 0.27 (large fibers). Although incremental MUNE has a high degree of reproducibility in rabbits, there is poor correlation with histological fiber counts. Muscle Nerve, 2010
Effects of prolonged repetitive stimulation of median, ulnar and peroneal nerves
Authors: Baumann Fusun , Henderson Robert D. , Tremayne Fred , Hutchinson Nicole , McCombe Pamela A.
Published: February 2010

It is important to know the effects of prolonged repetitive nerve stimulation (RNS) when it is used in neurophysiological studies. RNS with up to 100 supramaximal stimuli was given to the median, ulnar, and peroneal nerves of normal subjects and the ulnar nerves of subjects with early amyotrophic lateral sclerosis (ALS), recording evoked compound muscle action potentials (CMAPs). In all nerves, there was a decline in the CMAP area and a decrease in CMAP duration. For the peroneal nerve there was a decline in the CMAP amplitude, but a similar decline was not seen in the median or ulnar nerves. Cooling of the muscles resulted in decrement of both the amplitude and area with RNS. In ALS subjects, CMAP amplitude and area both declined after RNS of the ulnar nerve. In this study we describe the changes in CMAP with prolonged RNS among commonly tested normal nerves. Our findings have important implications with regard to RNS. Muscle Nerve, 2010
Branched‐chain amino acids protect against dexamethasone‐induced soleus muscle atrophy in rats
Authors: Yamamoto Daisuke , Maki Taiki , Herningtyas Elizabeth Henny , Ikeshita Nobuko , Shibahara Hiromi , Sugiyama Yuka , Nakanishi Shiho , Iida Keiji , Iguchi Genzo , Takahashi Yutaka , Kaji Hidesuke , Chihara Kazuo , Okimura Yasuhiko
Published: February 2010

We investigated the utility of branched‐chain amino acids (BCAA) in dexamethasone‐induced muscle atrophy. Dexamethasone (600 μg/kg, intraperitoneally) and/or BCAA (600 mg/kg, orally) were administered for 5 days in rats, and the effect of BCAA on dexamethasone‐induced muscle atrophy was evaluated. Dexamethasone decreased total protein concentration of rat soleus muscles. Concomitant administration of BCAA reversed the decrease. Dexamethasone decreased mean cross‐sectional area of soleus muscle fibers, which was reversed by BCAA. Dexamethasone increased atrogin‐1 expression, which has been reported to play a pivotal role in muscle atrophy. The increased expression of atrogin‐1 mRNA was significantly attenuated by BCAA. Furthermore, dexamethasone‐induced conversion from microtubule‐associated protein 1 light chain 3 (LC3)‐I to LC3‐II, which is an indicator of autophagy, was blocked by BCAA. These findings suggest that BCAA decreased protein breakdown to prevent muscle atrophy. BCAA administration appears to be useful for prevention of steroid myopathy. Muscle Nerve, 2010
Sinusoidal oscillations radiating from a cylindrical source in thermal conduction or groundwater flow: Closed‐form solutions
Authors: Saucier Antoine , Frappier Clément , Chapuis Robert P.
Published: February 2010

The diffusion equation governs thermal conduction and groundwater flow phenomena. In this paper, we study the two‐dimensional radial propagation of a sinusoidal perturbation radiating from a cylindrical source within an infinite slab of homogeneous material. The solution of this problem has several applications. For instance, it can be used to determine the hydraulic diffusivity of the subsurface based on measurements of the hydraulic head around a vertical well during its development. For thermal problems, it can be used to determine the thermal diffusivity based on measurements of the temperature distribution around a cylindrical heat source generating a sinusoidal power per unit length. In this paper, we present a comprehensive analytical solution of this problem and we compare these solutions with numerical solutions. Two approximate analytical solutions, which can be relevant in practice, are also presented. Finally, we give an upper bound for the survival time of the transient part of the solution and we provide an estimate of the radius of influence of the sinusoidal solicitation. Copyright © 2010 John Wiley & Sons, Ltd.
Time‐scale analysis in unsaturated porous media under external wave loads
Authors: Xiao Heng , Young Yin Lu , Prévost Jean H.
Published: February 2010

Extreme waves caused by tsunamis and storm surges can lead to soil failures in the near‐shore region, which may have severe impact on coastal environments and communities. Multiphase flows in deformable porous media involve several coupled processes and multiple time scales, which are challenging for numerical simulations. The objective of this study is to investigate the roles of the various processes and their interactions in multiphase flows in unsaturated soils under external wave loading, via theoretical time‐scale analysis and numerical simulations. A coupled geomechanics–multiphase flow model based on conservation laws is used. Theoretical analysis based on coupled and decoupled models demonstrates that transient and steady‐state responses are governed by pore pressure diffusion and saturation front propagation, respectively, and that the two processes are essentially decoupled. Numerical simulations suggest that the compressibility of the pore fluids and the deformation of the soil skeleton are important when the transient responses of the media are of concern, while the steady‐state responses are not sensitive to these factors. The responses obtained from the fully coupled numerical simulations are explained by a simplified time‐scale analysis based on coupled and decoupled models. Copyright © 2010 John Wiley & Sons, Ltd.
Constitutive modeling of unsaturated aggregated soils
Authors: Koliji A. , Laloui L. , Vulliet L.
Published: February 2010

A coupled water retention–mechanical constitutive model for unsaturated aggregated soils is presented here. Based on the multi‐scale experimental results, the model incorporates the inter‐particle bonding, fabric and partial saturation effects in a single framework. It is formulated within the framework of hardening elasto‐plasticity and is based on the critical state concept. Prior to model validation, we evaluate the model parameters and propose determination procedures for the main new parameters. Finally, the model is examined for its capability in simulating the experimental results of aggregated and bonded soils. Results of these simulations show that the model addresses the most features arising from the combined effects of soil structure and partial saturation. Copyright © 2010 John Wiley & Sons, Ltd.
Smooth particle hydrodynamics simulations of low Reynolds number flows through porous media
Authors: Holmes David W. , Williams John R. , Tilke Peter
Published: February 2010

In this paper, a three‐dimensional smooth particle hydrodynamics (SPH) simulator for modeling grain scale fluid flow in porous media is presented. The versatility of the SPH method has driven its use in increasingly complex areas of flow analysis, including the characterization of flow through permeable rock for both groundwater and petroleum reservoir research. SPH provides the means to model complex multi‐phase flows through such media; however, acceptance of the methodology has been hampered by the apparent lack of actual verification within the literature, particulary in the three‐dimensional case. In this paper, the accuracy of SPH is addressed via a comparison to the previously recognized benchmarks of authors such as Sangani and Acrivos (Int. J. Multiphase Flow1982;8(4): 343–360), Zick and Homsy (J. Fluid Mech.1982;115:13–26) and Larson and Higdon (Phys. Fluids A1989;1(1):38–46) for the well‐defined classical problems of flow through idealized two‐ and three‐dimensional porous media. The accuracy of results for such low Reynolds number flows is highly dependent on the implementation of no‐slip boundary conditions. A new, robust and numerically efficient, method for implementing such boundaries in SPH is presented. Simulation results for friction coefficient and permeability are shown to agree well with the available benchmarks. Copyright © 2010 John Wiley & Sons, Ltd.
On the impact of the scheme for solving the higher dimensional equation in coupled population balance systems
Authors: John Volker , Roland Michael
Published: February 2010

Population balance systems are models for processes in nature and industry that lead to a coupled system of equations (Navier–Stokes equations, transport equations, etc.) where the equations are defined in domains with different dimensions. This paper will study the impact of using different schemes for solving the three‐dimensional (3D) equation of a precipitation process in a two‐dimensional flow domain. The numerical schemes for the 3D equation are assessed with respect to the median of the volume fraction of the particle size distribution and the computational costs. It turns out that in the case of a structured flow field with small variations in time all schemes give qualitatively the same results. For a highly time‐ dependent flow field, the evolution of the median of the volume fraction differs considerably between first order and higher order schemes. Copyright © 2010 John Wiley & Sons, Ltd.
A geometric integral formulation for eddy‐currents
Authors: Codecasa L. , Specogna R. , Trevisan F.
Published: February 2010

In the computational electromagnetism community it is known how the differential formulation of an eddy‐current problem, can be translated into a finite dimensional system of equations involving circulations and fluxes, by means of the so‐called Discrete Geometric Approach. This is done by exploiting the geometric structure behind Maxwell's equations. In this paper, we will show how the same Discrete Geometric Approach can be profitably used also to discretize an eddy‐current problem formulated in an integral way.

We rely on a purely geometric definition of a novel set of face vector basis functions that we use to construct the discrete counterparts—matrices—of both the Ohm's constitutive relation and of the integral relation between the magnetic vector potential and the eddy‐current density vector. The symmetry and positive‐definiteness of such matrices will be demonstrated and their geometric structure will be apparent. Copyright © 2010 John Wiley & Sons, Ltd.
Polymerization of trimethylene carbonate in aqueous solutions: Reaction mechanism and characterization
Authors: Okada Takao , Imamura Yukari , Matsuda Takehisa
Published: February 2010

Polymerization of a trimethylene carbonate (TMC) in an aqueous solution was investigated by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. The polymerization reaction proceeded rapidly in the aqueous solution and high conversion was achieved in a relatively short time. 1,3‐Propanediol (PPD) formed by hydrolysis of TMC was used as the initiator. The TMC oligomer obtained by ring‐opening polymerization had a TMC unit backbone with terminal 3‐hydroxypropyl groups at both chain ends. The oligomer underwent transesterification reaction with elimination of PPD, resulting in a gradual increase in the molecular weight of the product. The molecular weight was affected by the concentration of TMC. The thermal properties of the polymers were investigated by differential scanning calorimetry. Polymers within the molecular weight (Mn) range from 6.0 × 103 to 2.3 × 104 g/mol crystallized, and endothermic peaks corresponding to the melting temperature were observed. The glass transition temperature increased with the molecular weight of the polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1485–1492, 2010
Stereospecific styrene polymerization and ethylene–styrene copolymerization with titanocenes containing a pendant amine donor
Authors: Son Kyung‐Sun , Waymouth Robert M.
Published: February 2010

A series of monocyclopentadienyl titanium complexes containing a pendant amine donor on a Cp group (A = CpTiCl3, B = CpNTiCl3, C = CpNTiCl2TEMPO, for Cp = C5H5, CpN = C5H4CH2CH2N(CH3)2, and TEMPO = 2,2,6,6‐tetramethylpiperidine‐N‐oxyl) are investigated for styrene homopolymerization and ethylene–styrene (ES) copolymerization. When activated by methylaluminoxane at 70 °C, complexes with the amine group (B and C) are active for styrene homopolymerization and afford syndiotactic polystyrene (sPS). The copolymerizations of ethylene and styrene with B and C yield high‐molecular weight ES copolymer, whereas complex A yields mixtures of sPS and polyethylene, revealing the critical role that the pendant amine has on the polymerization behavior of the complexes. Fractionation, NMR, and DSC analyses of the ES copolymers generated from B and C suggest that they contain sPS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1579–1585, 2010
A new titanium (IV) complex bearing phenoxyimine‐fluorene ligand and its use as catalyst for ethylene homo‐ and copolymerization
Authors: Zhong Liang , Cui Kun , Xie Peng , Chen Jian‐Zhuang , Ma Zhi
Published: February 2010

A new titanium (IV) complex bearing phenoxyimine‐fluorene ligand was prepared and its behaviors in ethylene homo‐ and copolymerization with 1‐hexene, 1‐octene, and norbornene in the presence of modified methylaluminoxane (MMAO) were studied respectively. The effects of various polymerization conditions including polymerization temperature, ethylene pressure and the concentration of comonomer on the catalytic activities and properties of the resultant polymer were investigated. The broad molecular weight distribution of resulting polymer indicated that the multiple active species were formed during polymerization. Such complex showed good catalytic activities in ethylene homo‐ and copolymerizations and good capabilities of incorporating various comonomers into polyethylene backbone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1617–1621, 2010
Controlled synthesis and functionalization of PEGylated methacrylates bearing cyclic carbonate pendant groups
Authors: Jana Satyasankar , Yu Han , Parthiban Anbanandam , Chai Christina L.L.
Published: February 2010

Homopolymer bearing cyclic carbonate (CC) group, ABA type triblock copolymers, and (AC)B(AC) type terpolymers with statistical arrangement of A and C monomers bearing side chain CC groups are reported here. Difunctional poly(ethylene glycol) macroinitiators (PEGMIs) were prepared from PEG of three different molecular weights. PEGMIs were subsequently used for the preparation of polymers bearing CC pendant groups from cyclic carbonate methacrylate (CCMA) under atom transfer radical polymerization to yield polymers with low polydispersity index. Homopolymer and ABA type triblock copolymers were obtained by polymerizing CCMA monomer and (AC)B(AC) type statistical terpolymers were obtained when methyl methacrylate was included as a comonomer. No polymer was obtained when styrene was used as comonomer. The cyclic carbonate groups were subjected to ring‐opening reaction with monoamine to yield side chain hydroxyurethane polymers with increased solubility and diamines to yield crosslinked insoluble materials. Changes in wettability characteristics were studied by following the water contact angle of the polymers before and after ring‐opening reaction involving the cyclic carbonate pendant group. The polymers which composed of electrolyte in the form of PEG and coordinating species in the form of pendant cyclic carbonate groups showed conductivity in the range of 2–5 × 10−6 Scm−1 at 23 °C after doping with lithium bis(trifluoromethane)sulfonimide as characterized by impedance spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1622–1632, 2010
Synthesis of poly(vinyl ether) polyols with pendant oxyethylene chains and properties of hydrophilic, thermo‐responsive polyurethanes prepared therefrom
Authors: Hashimoto Tamotsu , Takahashi Ayumi , Urushisaki Michio , Sakaguchi Toshikazu
Published: February 2010

Hydroxy‐terminated telechelic poly(vinyl ether)s with pendant oxyethylene chains were synthesized by the reaction of the CH3CH(OCOCH3)O[CH2]4OCH(OCOCH3)CH3/Et1.5AlCl1.5/THF‐based bifunctional living cationic polymers of 2‐methoxyethyl vinyl ether (MOVE), 2‐ethoxyethyl vinyl ether (EOVE), and 2‐(2‐methoxyethoxy)ethyl vinyl ether (MOEOVE) with water and the subsequent reduction of the aldehyde polymer terminals with NaBH4. The obtained poly(vinyl ether) polyols were reacted with an equimolar amount of toluene diisocyanates [a mixture of 2,4‐ (80%) and 2,6‐ (20%) isomers] to give water‐soluble polyurethanes. The aqueous solutions of these polyurethanes caused thermally induced precipitation at a particular temperature depending on the sort of the thermosensitive poly(vinyl ether) segments containing oxyethylene side chains. These polyurethanes also function as polymeric surfactants, lowered the surface tension of their aqueous solutions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1641–1648, 2010
Chitosan/silver nanoparticles composite: Molecular relaxations investigation by dynamic mechanical analysis and impedance spectroscopy
Authors: González‐Campos J. Betzabe , Prokhorov Evgen , Luna‐Bárcenas Gabriel , Sanchez Isaac C. , Lara‐Romero Javier , Mendoza‐Duarte M. E. , Villaseñor Francisco , Guevara‐Olvera Lorenzo
Published: February 2010

By impedance spectroscopy, Gonzalez‐Campos et al. J Polym Sci Part B: Polym Phys 2009, 47, 932–943, reported the first evidence of a glass transition in a polysaccharide. To gain a better understanding on the molecular relaxations in polysaccharides, we study composites of chitosan (CS)/silver nanoparticles (AgnP) films by dynamic mechanical analysis (DMA) and dielectric spectroscopy in the 2–250 °C temperature range. CS/AgnP films conductivity increases in two orders of magnitude in comparison with pristine CS. Three relaxation processes ascribed to the α‐relaxation, σ‐relaxation, and degradation process have been observed for the first time. Molecular dynamics and conductivity strongly depends on moisture content; since a plasticizing effect on the glass transition temperature is observed, similarly the increase in AgnP weight percent leads to a glass transition temperature decrease and also increases CS thermal stability. Infrared spectroscopy analysis reveals the AgnPs interaction with OH, NH2, CO.NH2, and COC groups implying an evident redistribution of the vibration bands for these groups. These new bonds affects the molecular dynamics of the CS chain bearing important changes in relaxations processes when compared CS/AgnP composite with pristine CS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 739–748, 2010
Structure–tribological property relationship of nanoparticles and short carbon fibers reinforced PEEK hybrid composites
Authors: Zhang G.
Published: February 2010

In a previous work, the roles of low‐loading, that is, 1 vol %, nano‐SiO2 particles on the tribological behavior of short carbon fibers (SCFs)/polytetrafluoroethylene (PTFE)/graphite filled polyetheretherketone (PEEK) were studied. In the present work, the effects of nanoparticle content, varying from 1 to 4 vol %, on the structure and the tribological performance of the composite was investigated. The polished cross sections of the composites were inspected using a scanning electron microscope (SEM). The incorporated nanoparticles significantly reduce the friction coefficients of the composite. With low pressure‐sliding velocity (pv) factors, nanoparticle agglomerates seem to exert an abrasive effect on SCF, and thereby lead to high wear rates. Under such conditions, an increase in nanoparticle content decreases the wear resistance. With high pv factors, the nanoparticles remarkably improve the wear resistance of the composite and the nanoparticle contents do not play an important role on the wear resistance. The worn surfaces, transfer films and wear debris of the composites were analyzed. The tribological mechanisms were discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 801–811, 2010
Rain drop size distribution variability and impact on X‐band polarimetric radar retrieval: Results from the AMMA campaign in Benin
Authors: Gosset Marielle , Zahiri Eric‐Pascal , Moumouni Sounmaila
Published: February 2010

During the African Monsoon Multidisciplinary Analysis (AMMA) field campaign, polarimetric weather radars, a rain‐gauge network and disdrometers were available to analyse the convective systems and the rainfall in Benin. In this paper a three‐year dataset of drop size distributions is used to compute theoretical relationships between X‐band polarimetric variables and the rain rate, adjusted for the region of interest. The variability of these relationships from storm to storm and between rain types is studied. With an X‐band polarimetric radar the rain rate can be retrieved from the differential specific phase shift KDP, the specific attenuation AH, the reflectivity Z or differential reflectivity ZDR corrected for attenuation, or a combination of these variables. The set of coefficients needed to run the rain retrieval or the attenuation correction schemes under the conditions found in Benin are computed. The rain retrieval schemes are compared on the basis of simulations. The retrievals based on one single propagative variable like KDP or AH perform well. Preliminary results from direct comparisons between X‐band polarimetric radar estimates and rain‐gauges are consistent with the disdrometer‐based analysis. Copyright © 2010 Royal Meteorological Society
Fitting VAD winds to aliased Doppler radial‐velocity observations: A global minimization problem in the presence of multiple local minima
Authors: Xu Qin , Nai Kang , Wei Li
Published: February 2010

When the horizontal vector wind is estimated by the traditional velocity azimuth display (VAD) analysis from radar radial‐velocity observations on a selected range circle, the observations should be thoroughly de‐aliased first. When the effect of aliasing is formulated into the cost function, the VAD analysis can be applied to raw aliased radial‐velocity observations, but the minimization problem for the VAD fitting is complicated by the multiple local minima caused by the zigzag‐discontinuities of the aliasing operator. An efficient two‐step VAD algorithm is thus developed in this paper to find the global minimum in properly transformed subspaces of the VAD wind parameters. The algorithm is then extended into a three‐step volume velocity processing (VVP) method to estimate the vertical profile of horizontal winds from each volume of radar radial‐velocity scans. Examples are presented to illustrate the capability and robustness of the method. Copyright © 2010 Royal Meteorological Society
Influence of a low dose of amphetamine on vesicular monoamine transporter binding: A PET (+)[11C]DTBZ study in humans
Authors: Boileau Isabelle , Houle Sylvain , Rusjan Pablo M. , Furukawa Yoshiaki , Wilkins Diana , Tong Junchao , Selby Peter , Wilson Alan A. , Kish Stephen J.
Published: February 2010

We previously reported increased binding of (+)[11C]DTBZ (dihydrotetrabenazine), the vesicular monoamine transporter (VMAT2) positron emission tomography (PET) radioligand, in striatum of some methamphetamine users. This finding might be explained by stimulant‐induced vesicular DA depletion resulting in decreased DA (+)[11C]DTBZ competition at VMAT2. In a prospective PET study, we now find that administration of an acute oral dose of amphetamine (0.4 mg/kg) to humans does not cause increased striatal (+)[11C]DTBZ binding but a slight 5% decrease. Our data suggest that a low amphetamine dose is unlikely to cause sufficient DA depletion to detect increased (+)[11C]DTBZ binding and that a higher dose might be required. Synapse 64:417–420, 2010. © 2010 Wiley‐Liss, Inc.