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1.
Syntheses, Single-Crystal X-Ray Analyses and Solid-State 29Si NMR Studies of a Zwitterionic λ5-Spirosilicate and a Cage-like Octa(silasesquioxane) The zwitterionic λ5-spirosilicate bis[2,3-naphthalenediolato(2 ?)][2-(dimethylammonio)phenyl]silicate ( 1 ; isolated as 1 · 1/2 CH3CN) was synthesized by reaction of the [2-(dimethylamino)phenyl]dimethoxyorganosilanes 5, 6 and 7 [2-(Me2N)C6H4Si(OMe)2R: R = Ph ( 5 ), cyclo? C6H11 ( 6 ), Me ( 7 )] with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 1 · 1/2 CH3CN or [2-(dimethylamino)phenyl]trimethoxysilane ( 3 ) with water in acetonitrile yielded the cage-like octa{[2-(dimethylamino)phenyl]silasesquioxane} ( 2 ). The crystal structures of 1 · 1/2 CH3CN and 2 were studied by X-ray diffraction. In addition, 1 · 1/2 CH3CN and 2 were characterized by solid-state (29Si CP/MAS) and solution NMR studies (1H, 13C, 29Si). 相似文献
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The continuous miniaturization in microelectronics requires advanced materials and processes. Novel specifically functionalized anhydride-containing filmforming polymers which spontaneously react with bisaminoalkylsiloxanes were synthesized for use in photolithographic processes. This allows the modelling of photoresist patterns and thus enhancement of practical resolution. In addition, efficient polymeric dielectrics with improved solubility in environmentally safe solvents were developed. The latter can be patterned using the above mentioned photolithographic process. 相似文献
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Double-quantum filtered MAS NMR spectra of an isolated homonuclear spin-1/2 pair are considered, at and away from rotational resonance conditions. The pulse sequence used is the solid-state NMR equivalent of double-quantum filtered COSY, known from solution-state NMR. The 119Sn spin pair in [(chex3Sn)2S] is characterized by a difference in isotropic chemical shielding smaller than the two chemical shielding anisotropies and by direct dipolar and isotropic J-coupling constants of similar magnitudes. At rotational resonance, one-dimensional double-quantum filtered 119Sn lineshapes yield the relative orientation of the two 119Sn chemical shielding tensors. Good double-quantum filtration efficiencies are found at and away from rotational resonance conditions, despite the presence of large chemical shielding anisotropies. Numerical simulations illustrate the interplay of the direct dipolar and J-coupling pathways and identify the latter as the main pathway even at rotational resonance conditions. 相似文献
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The design and simulation of power transducers are difficult since piezoelectric, dielectric and elastic properties of ferroelectric materials differ from linear behavior when driven at large levels. This paper is devoted to modeling of a resonant power transducer at a high level of dynamic mechanical stress. The power transducer is subjected to a sine electrical field E of varying frequency which was considered as the excitation of the transducer.The mechanical equation of the piezoelectric element is written using electrostriction. The dielectric part is written as a nonlinear function of an equivalent electric field including stress influence (scaling relationship between electric field and mechanical stress). Using various simulations, we show then that typical resonance nonlinearities are obtained, such as jump phenomenon of transducer speed amplitude and phase, resonance peak that become asymmetric, and diminution of mechanical quality factor. As a consequence, we state that those typical nonlinearities are only due to dielectric nonlinearities, in good correlation with typical ferroelectric behavior. Moreover, this demonstrates the usefulness of scaling relationships in ferroelectrics, which explain static depoling under stress and butterfly strain hysteresis loop. The same scaling law gives here several nonlinearities for resonant transducers as well. 相似文献
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N. Sebald 《Applied Physics A: Materials Science & Processing》1980,21(3):221-236
A straight, steady-state cross-flow arc is burning in an N2 wind tunnel. The arc is held in position by the balance of the Lorentz forces produced by an external magnetic field perpendicular
to the arc axis and by the viscous forces of the gas flow acting on the arc column. The temperature field in the discharge
is determined spectroscopically using the radiation of N I lines. Because of the lack of rotational symmetry an inversion
method developed by Maldonado was used to determine the local emission coefficient from the measured integrated spectral intensity
distributions across the arc in various directions. For known local temperature the mass flow field inside the arc may be
evaluated from the convective term of the energy equation and the continuity equation. This is done by expanding the terms
of these two equations around the point of the temperature maximum into Fourier-Taylor series and determining coefficients
of the same order and power. The solution of the resulting set of algebraic equations yields the unknown coefficients of the
mass flow. The flow field obtained by these calculations shows a relatively strong counterflow through the arc core. In the
region for which the series expansion holds a partial structure pertaining to a closed double vortex can be recognized.
The terms of the momentum equation are calculated on the basis of these results. In order to obtain a better understanding
of the importance attributed to the individual local forces acting on the plasma, a simple model was devised which separates
the momentum equation into gradient and curl terms. The discussion shows that the gradient part of the Lorentz force causes
mainly the pressure gradient, while the much smaller rotational part of thej×B forces is responsible for propelling the mass flow. The momentum transport inside the arc as well as in its neighbourhood
is due to the viscous forces and to the pressure gradient. By contrast, at larger distances from the arc it is essentially
the inertial force that determines the momentum transport. It is shown that viscosity as a damping mechanism is necessary
for the existence of stationary flow fields as investigated in this work. 相似文献
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J. Sebald S. Krohns P. Lunkenheimer S.G. Ebbinghaus S. Riegg A. Reller A. Loidl 《Solid State Communications》2010,150(17-18):857-860
In the present work we demonstrate that in addition to the well-known colossal-dielectric-constant material CaCu3Ti4O12 various members of the series Ln2/3Cu3Ti4O12 with Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm also exhibit giant values of the dielectric constant. Just as CaCu3Ti4O12, all these materials show a Maxwell–Wagner type relaxation process. For the best material, Pr2/3Cu3Ti4O12, we provide a detailed investigation of its dielectric properties in a broad frequency range up to 1 GHz. Polarization at internal barriers, most likely grain boundaries, seems to be the reason for the observed very high values of the dielectric constant. Taking into account the present results and those reported in the literature, we conclude that CaCu3Ti4O12 is not exceptional at all and there seem to be various isostructural materials with similar dielectric properties. 相似文献
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Ostwald Cohen Kohlrausch Heydweiller van't Hoff A. Naumann A. Rücker Arrhenius Walker Shields J. Walker E. Aston C. Kullgren Bredig Fraenkel W. E. Pawloff D. G. Gerassimoff Seth E. Moody R. W. Wood Will Koelichen M. Le Blanc K. Novotny Gernez H. Goldschmidt O. Girard Hantzsch Sebald G. Wiedemann B. E. Moore Dibbits W. Müller A. Birnbaum 《Analytical and bioanalytical chemistry》1907,46(2-3):159-165