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Acta Mathematica Hungarica - Minkowski’s classical existence theorem provides necessary and sufficient conditions for a Borel measure on the unit sphere of Euclidean space to be the surface... 相似文献
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Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
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We consider front solutions of the Swift–Hohenberg equation ∂
t
u= -(1+ ∂
x
2)2
u + ɛ2
u -u
3. These are traveling waves which leave in their wake a periodic pattern in the laboratory frame. Using renormalization techniques
and a decomposition into Bloch waves, we show the non-linear stability of these solutions. It turns out that this problem
is closely related to the question of stability of the trivial solution for the model problem ∂
t
u(x,t) = ∂
x
2
u (x,t)+(1+tanh(x-ct))u(x,t)+u(x,t)
p
with p>3. In particular, we show that the instability of the perturbation ahead of the front is entirely compensated by a diffusive
stabilization which sets in once the perturbation has hit the bulk behind the front.
Received: 23 February 2001 / Accepted: 27 August 2001 相似文献
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Biosorption of Chromium(III) by Biomass of Seaweed Sargassum sp. in a Fixed-Bed Column 总被引:2,自引:0,他引:2
Eneida Sala Cossich Edson Antonio da Silva Célia Regina Granhen Tavares Lúcio Cardozo Filho Teresa Massako Kakuta Ravagnani 《Adsorption》2004,10(2):129-138
This work aimed at modeling chromium biosorption using the biomass of seaweed Sargassum sp. in a fixed-bed column. The mathematical model used was obtained from the mass balance of the component in the liquid phase and in the biosorbent material. The effects of both axial dispersion in the column and the resistance to mass transfer in the solid were considered for the solution of the partial differential equations of the model, using the Galerkin method on finite elements. To represent the equilibrium data of the batch system the Langmuir isotherm were used. The chromium ion adsorption capacity of the seaweed Sargassum sp., at a temperature of 30°C and pH 3.5, was 2.61 mmol/g. The model performance was evaluated from experimental data obtained at 30°C for flow rates of 2, 6 and 8 mL/min. The parameters of the model, mass transfer and axial dispersion coefficients, were adjusted from these experimental data. The model proved adequate to describe chromium biosorption dynamics in fixed-bed columns. 相似文献
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Yu. V. Belovitskaya I. V. Pekov E. R. Gobechiya N. A. Yamnova Yu. K. Kabalov N. V. Chukanov J. Schneider 《Crystallography Reports》2002,47(2):223-228
The crystal structures of two ancylite specimens from Khibiny massif (the Kola Peninsula, Russia)—ancylite-(Ce) from alkali hydrothermalites (Sr1.01Ca0.02Ba0.01)Σ1.04(Ce0.52La0.28Nd0.11Pr0.04 Sm0.01)Σ0.96(CO3)2(OH0.83F0.13)Σ0.96 · 0.9H2O and ancylite-(Ce) from carbonatites—have (Sr0.80Ca0.05Ba0.01)Σ0.86(Ce0.62La0.40Nd0.09Pr0.03) Σ1.14(CO3)2(OH0.99F0.15)Σ1.14 · 1.0H2O been refined by the Rietveld method. A focusing STOE-STADIP diffractometer with a bent Ge(111) primary monochromator was used (λ MoK α 1 radiation, 2.16° < 2θ < 54.98°; reflection number 237–437). All the computations for ancylite from alkali hydrothermalites were performed within the sp. gr. Pmc21, a = 5.0634(1) Å, b = 8.5898(1) Å, c = 7.2781(1) Å, V = 316.55(1) Å3, R wp = 1.90; the computations for ancylite from carbonatites were performed within the sp. gr. Pmcn, a = 5.0577(1) Å, b = 8.5665(2) Å, c = 7.3151(2) Å, V = 316.94(1) Å3, R wp = 2.38 in the anisotropic approximation of thermal vibrations of cations and oxygen atoms. 相似文献
10.
B. MacMillan M. Halse M. Schneider L. Fardy Y. H. Chui B. J. Balcom 《Applied magnetic resonance》2002,22(2):247-256
Magnetic resonance imaging has rarely been applied to rigid polymeric materials, due primarily to the strong dipolar coupling and short signal lifetimes inherent in these materials. SPRITE (single point ramped imaging withT 1 enhancement) (B. J. Balcom, R. P. MacGregor, S. D. Beyea, D. P. Green, R. L. Armstrong, T. W. Bremner: J. Magn. Reson. A123, 131–134, 1996) is particularly well suited to imaging solid materials. With SPRITE, the only requirement is thatT 2* be long enough so that the signal can be phase-encoded. The minimum phase encoding time is limited by the maximum gradient strength available and by the instrument deadtime. At present this is usually tens of microseconds and will only improve with refinements in technology. We have used the SPRITE sequence in conjunction with raising the sample temperature to obtain images of rigid polymers that have largely frustrated conventional imaging methods. This approach provides a straightforward and reliable method for imaging a class of samples that, up until now, have been very difficult to image. 相似文献