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  • 11
    ISSN: 1573-4846
    Keywords: hybrid materials ; ORMOLYTES ; ionic conductivity ; nuclear magnetic resonance (NMR) ; polymers ; SiO2-PEG, SiO2-PPG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two families of hybrid organic-inorganic composites exhibiting Li+ ionic conduction (ORMOLYTES) have been prepared by the sol-gel process. The first family, prepared from a mixture of 3-isocyanatopropyltriethoxysilane, O,O′ Bis (2-aminopropyl)-polyethyleneglycol (or O,O′ Bis (2-aminopropyl)-polypropyleneglycol) and lithium salt, presents chemical bonds between the organic and the inorganic phase and an ionic conductivity σ higher than 10−4 S m−1 at room temperature. Their properties have been related to their structure using liquid state NMR measurements of7Li between −100°C and +100°C and the DMTA technique. In the second family, prepared by ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol (PEG) and lithium salt, the organic and inorganic phases are not chemically bonded. Ionic conductivity σ has been studied as a function of the polymer chain length and concentration. Values of σ up to 10−2S m−1 at room temperature have been obtained (with a silica-PEG300 system, PEG/TEOS=40% in weight). Again, structure was investigated by liquid state7Li NMR measurements.
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  • 12
    ISSN: 1573-4846
    Keywords: ormocer ; coatings ; chemical protection ; stainless steel ; PMMA-ZrO2 ; corrosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The chemical protection of 316 L stainless steel coated with ORMOCER coatings of polymethylmethacrylate (PMMA) and ZrO2 has been verified. The coatings were dip-coated on the substrates from sols prepared by mixing zirconium propoxide (ZrOC3H7)4, isopropanol (C3H7OH), glacial acetic acid (CH3COOH), polymethylmethacrylate and water under application of ultrasounds. The films were heat treated between 40 and 300°C in air up to 20 h. Their morphology was studied by electron scanning microscopy (SEM). Their anticorrosion behavior was analysed in 0.5M-H2SO4 solutions through potentiodynamic polarization curves at room temperature.The influence of the sol preparation, coating composition as well as of the duration and temperature of heat treatments on the corrosion parameters is reported. The films act as geometric blocking layers against the corrosive media and increase the lifetime of the substrate up to a factor 30.
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  • 13
    ISSN: 1573-4846
    Keywords: sol-gel ; Nb2O5 ; film ; photoconductivity ; photoelectrochemistry ; semiconductor ; solar cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb2O5 coatings have been determined. The coatings aren-type semiconductor with indirect allowed transition and present an overall low quantum efficiency (ϕ〈4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb2O5 coatings can be made of 10–20 nm size nanoparticles.
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  • 14
    ISSN: 1573-4846
    Keywords: hybrid materials ; ORMOLYTES ; ionic conductivity ; nuclear magnetic resonance (NMR) ; polymers ; SiO2-PEG ; SiO2-PPG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two families of hybrid organic-inorganic composites exhibiting Li+ ionic conduction (ORMOLYTES) have been prepared by the sol-gel process. The first family, prepared from a mixture of 3-isocyanatopropyltriethoxysilane, O,O′ Bis (2-aminopropyl)-polyethyleneglycol (or O,O′ Bis (2-aminopropyl)-polypropyleneglycol) and lithium salt, presents chemical bonds between the organic and the inorganic phase and an ionic conductivity σ higher than 10-4 S m-1 at room temperature. Their properties have been related to their structure using liquid state NMR measurements of 7Li between -100°C and +100°C and the DMTA technique. In the second family, prepared by ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol (PEG) and lithium salt, the organic and inorganic phases are not chemically bonded. Ionic conductivity σ has been studied as a function of the polymer chain length and concentration. Values of σ up to 10-2 S m-1 at room temperature have been obtained (with a silica-PEG300 system, PEG/TEOS = 40% in weight). Again, structure was investigated by liquid state 7Li NMR measurements.
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  • 15
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The linear viscoelastic behavior of commercial broad-distribution polypropylenes is studied. The samples underwent different controlled peroxide degradation rates, so they exhibit different molecular distributions. The relaxation spectrum is obtained by assuming that it takes the shape of a Log-Normal distribution. It is in agreement with the linear viscoelasticity theory by providing limiting values, contrary to other models. Moreover, the ratio τw/τn which takes place in this law is very useful to distinguish the synthesis differences of the samples when the Melt Flow Index alone cannot.
    Additional Material: 4 Ill.
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  • 16
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Using an integral nonlinear constitutive equation including the Log-Normal relaxation spectrum, the fiber-spinning behavior of commercial polypropylenes is studied. The relaxation spectrum is strongly related to the molecular weight distribution. Moreover, by means of a finite element analysis, simulated stress and velocity profiles are obtained either in isothermal or nonisothermal cases. In the isothermal case, broadening the relaxation spectrum leads to more pronounced curvature of the velocity profile. In the nonisothermal case, the critical draw ratio is sensitive to the mean relaxation time which depends on both average molecular weight and distribution breadth. It is shown that increasing the average relaxation time leads to a less rapid growth of the velocity. Furthermore, this effect is less pronounced when the relaxation spectrum is wider.
    Additional Material: 11 Ill.
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  • 17
    ISSN: 0887-6266
    Keywords: polyethylene ; poly(butylene terephthalate) ; blend ; rheology ; Palierne's model ; morphology ; differential scanning calorimetry ; crystallization ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crystallization at high supercooling of polybutylene terephthalate (PBT) droplets dispersed in a molten polyethylene (PE) matrix was investigated through rheological and DSC experiments. The Palierne's emulsion model was used as a theoretical framework for studying the viscoelastic behavior of the blends in different ranges of temperature: on the one hand, when the two polymers are molten (T 〉 225°C) and on the other hand, when PBT droplets are at high supercooling in the molten PE matrix (130°C 〈 T 〈 205°C). From rheological experimental evidences it was shown that molten and solidified droplets coexist at high supercooling. The Palierne's model was then successfully adapted to take into account the three phases (molten PE, molten PBT droplets, and solidified PBT droplets). The evolution of the behavior with the temperature is consistent with the growing amount of crystallized droplets. Moreover, a calculation taking into account the droplets size distribution and the number of nuclei is introduced to explain the crystallization behavior of three different blend ratios.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2573-2585, 1998
    Additional Material: 9 Ill.
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  • 18
    ISSN: 0029-5981
    Keywords: variational elements method ; multipole expansion ; acoustic radiation ; variational formulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The acoustic radiation of general structures with Neumann's boundary condition using Variational Boundary Element Method (VBEM) is considered. The classical numerical implementation of the VBEM suffers from the computation cost associated with double surface integration. To alleviate this limitation, a novel acceleration method is proposed. The method is based on the expansion of the cross influence matrices in terms of multipoles using the expansion of the Green's function in terms of spherical Bessel functions. Since the resulting multipoles are not dependent on the elements locations, large computation time savings are achieved. Moreover, it is shown that by accounting for the monopole, dipole and quadrupole terms in the multipole expansion, the classical convergence criteria usually used in boundary element guarantee convergence of the proposed method. Several numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 19
    ISSN: 1432-1912
    Keywords: Key words P2X Purinoceptor ; βγ-Methylene-L-ATP ; Rat vagus nerve ; Nodose ganglion neurones ; Rat vas deferens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The effects of the putative selective P2X purinoceptor agonist, β,γ-methylene-L-adenosine 5′-triphosphate (βγme-L-ATP), were determined at rat neuronal and smooth muscle P2X purinoceptors. βγMe-L-ATP had no effect on the extracellularly recorded membrane potential of the rat isolated vagus nerve preparation at concentrations up to 300 μM. In contrast, the archetypal P2X purinoceptor agonist, α,β-methylene ATP (αβmeATP; 1–100 μM), produced concentration-related depolarisation responses with a mean EC50 value of 10.8 μM. The depolarising effects of αβmeATP were not attenuated by βγme-L-ATP (100 μM). In voltage clamp experiments on single nodose ganglion neurones, ATP (100 μM), but not βγme-L-ATP (1–300 μM), evoked rapid (〈20 ms onset) inward currents when applied using a concentration-clamp method. In receptor binding studies to rat brain membranes, βγme-D-ATP and αβmeATP competed with high affinity for [3H]αβmeATP binding sites, with mean pIC50 values of 7.7 and 8.3, respectively. However, βγme-L-ATP possessed low affinity for these sites and competed only at concentrations in excess of 10 μM (mean pIC50 value 4.1). In prostatic segments of the rat vas deferens, βγme-L-ATP (1–100 μM) and αβmeATP (0.3–100 μM) each produced concentration-related contractile responses with mean EC50 values of 17.1 and 3.6 μM, respectively. βγMe-L-ATP (1–10 μM) evoked fast inward currents in freshly dispersed vas deferens smooth muscle cells, indicative of an action at ligand-gated ion channels. Binding sites in vas deferens membranes labelled using 1 nM [3H]αβmeATP exhibited high affinity for βγme-L-ATP, αβmeATP and βγme-D-ATP with mean pIC50 values of 7.7, 8.4 and 7.3, respectively. These results indicate that βγme-L-ATP exhibits neither agonist nor antagonist properties at P2X purinoceptors on rat vagal neurones and possesses only very low affinity for [3H]αβmeATP binding sites in rat brain. In contrast, βγme-L-ATP is a potent, high affinity agonist at smooth muscle P2X purinoceptors of the rat vas deferens. This selective agonist action of βγme-L-ATP suggests that P2X purinoceptors in smooth muscle and neurones are different and represent distinct P2X purinoceptor subtypes.
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  • 20
    ISSN: 1432-1912
    Keywords: P2X Purinoceptor ; βγ-Methylene-l-ATP ; Rat vagus nerve ; Nodose ganglion neurones ; Rat vas deferens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of the putative selective P2X purinoceptor agonist, β,γ-methylene-l-adenosine 5′-triphosphate (βγme-l-ATP), were determined at rat neuronal and smooth muscle P2X purinoceptors. βγMe-l-ATP had no effect on the extracellularly recorded membrane potential of the rat isolated vagus nerve preparation at concentrations up to 300 μM. In contrast, the archetypal P2X purinoceptor agonist, α, β methylene ATP (αβmeATP;1–100 μM), produced concentration-related depolarisation responses with a mean EC50 value of 10.8 μM. The depolarising effects of αβmeATP were not attenuated by βγme-l-ATP (100 μM). In voltage clamp experiments on single nodose ganglion neurones, ATP (100 μM), but not βγme-l.-ATP (1–300 μM), evoked rapid ( 〈 20 ms onset) inward currents when applied using a concentration-clamp method. In receptor binding studies to rat brain membranes, βγme-d-ATP and αβmeATP competed with high affinity for [3H]Lx βmeATP binding sites, with mean pIC50 values of 7.7 and 8.3, respectively. However, βγme-l-ATP possessed low affinity for these sites and competed only at concentrations in excess of 10 μM (mean pIC50 value 4.1). In prostatic segments of the rat vas deferens, βγme-l-ATP (1–100 μM) and αβmeATP (0.3–100 μM) each produced concentration-related contractile responses with mean EC50 values of 17.1 and 3.6 μM, respectively. βγMe-l-ATP (1–10 μM) evoked fast inward currents in freshly dispersed vas deferens smooth muscle cells, indicative of an action at ligand-gated ion channels. Binding sites in vas deferens membranes labelled using 1 nM [3H]αβmeATP exhibited high affinity for ββ γme-l-ATP, αβmeATP and βγme-d-ATP with mean PIC50 values of 7.7, 8.4 and 7.3, respectively. These results indicate that βγme-l-ATP exhibits neither agonist nor antagonist properties at P2X purinoceptors on rat vagal neurones and possesses only very low affinity for [3H]αβmeATP binding sites in rat brain. In contrast, βγme-l-ATP is a potent, high affinity agonist at smooth muscle P2X purinoceptors of the rat vas deferens. This selective agonist action of βγme-l-ATP suggests that P2X purinoceptors in smooth muscle and neurones are different and represent distinct P2X purinoceptor subtypes.
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