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41.
Li J Tammer M Kremer F Komp A Finkelmann H 《The European physical journal. E, Soft matter》2005,17(4):423-428
Polarized Fourier transform infrared (FTIR) spectroscopy is employed to study the segmental orientation and mobility of liquid-crystalline elastomers (LCEs) with a monodomain structure in response to external mechanical fields parallel and perpendicular to the initial nematic director. The mean orientation and the molecular order parameter of the different molecular moieties referring to the mesogen, the spacer and the network are analyzed in detail. Parallel stretch leaves the mean orientation of the different molecular moieties and its molecular order parameter nearly uninfluenced. Perpendicular stretch results in a threshold-like dependence: for elongation ratios λ ⩽ λc = 1.3 (10 mol% crosslinker density), respectively λ ⩽ λc = 1.6 (5 mol% crosslinker density) no change of the mean orientation and the molecular order parameters is observed, while for λ ≥ λc all molecular units reorient and their molecular order parameters are strongly decreased. The present studies give no indications that the reorientational dynamics of the network and the mesogens differ as long as the elongation ratio is smaller than λc. 相似文献
42.
Casanova F Perlo J Blümich B Kremer K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,166(1):76-81
A new pulsed field gradient multi-echo imaging technique to encode position in the phase of every echo generated by a CPMG sequence in the presence of a strongly inhomogeneous static magnetic field is presented. It was applied to improve the sensitivity in an imaging experiment by adding the echo train acquired during the CPMG sequence and to spatially resolve relaxation times of inhomogeneous specimens using single-sided probes. The sequence was implemented in a new bar-magnet MOUSE equipped with a gradient coil system to apply a pulsed magnetic field with a constant gradient along one spatial coordinate. An important reduction by a factor larger than two orders of magnitude in the acquisition time was obtained compared to the previously published single-point imaging technique. 相似文献
43.
We report a mechanism which can lead to long-range attractions between like-charged spherical macroions, stemming from the existence of metastable ionized states. We show that the ground state of a single highly charged colloid plus a few excess counterions is overcharged. For the case of two highly charged macroions in their neutralizing divalent counterion solution we demonstrate that, in the regime of strong Coulomb coupling, the counterion clouds are very likely to be unevenly distributed, leading to one overcharged and one undercharged macroion. This long-living metastable configuration in turn leads to a long-range Coulomb attraction. 相似文献
44.
B. Vincent R. Kremer A. Boudrioua P. Moretti Y.-C. Zhang C.-C. Hsu L.-H. Peng 《Applied physics. B, Lasers and optics》2007,89(2-3):235-239
An optical planar waveguide is investigated in ZnO-doped periodically poled lithium niobate formed by He+ implantation. Optical losses were found to be 2 dB/cm. Second-harmonic generation is used to produce a green laser beam by
quasi-phase matching in the obtained waveguide. The conversion efficiency was found to be 10-2%/W. Photorefractive resistance properties are reported and discussed relating to un-doped periodically poled lithium niobate.
PACS 42.65.-k; 42.65.Wi; 42.82.-m 相似文献
45.
Received March 12, 2001 / Published online: June 1, 2001 相似文献
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49.
Julia Torres Patricia Santos Carolina Ferrari Carlos Kremer Eduardo Kremer 《Journal of solution chemistry》2017,46(12):2231-2247
The interaction of arsenic(V) and arsenic(III) oxyanions with metal cations was investigated by potentiometry under temperature and ionic strength conditions approaching those prevailing in natural waters. The selection includes the major metal cations and some other ions of high environmental relevance. Ionic pairs [M(AsVO4)]?, [M(HAsVO4)] and [M(H2AsIIIO3)]+ formation is suggested for all +2 metal cations, based on the potentiometric results. These ion-pairs between arsenic anions and other metal cations are hardly ever mentioned or taken into account when arsenic speciation in natural waters is considered. These results provide the basis for studying arsenic speciation in natural aquatic systems, on which environmental fate, bioavailability and toxicity of the element depend. Some extrapolations to the conditions of the natural waters are presented as well as some insights into the adsorption process onto hydrous oxides. 相似文献
50.
A kinetic theory is developed for rarefied polyatomic gases of spherical and rough molecules with rotational energy in the
presence of an external constant magnetic field. A method of solution of Boltzmann equation that combines features of the
methods of Chapman-Enskog and Grad is used to determine transport coefficients that depend on the external magnetic field
(Senftleben-Beenakker effect).
Received August 4, 1997 相似文献