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291.
Vu T. Nguyen Graham C. Haug Viet D. Nguyen Ngan T. H. Vuong Guna B. Karki Hadi D. Arman Oleg V. Larionov 《Chemical science》2022,13(14):4170
The reactivity of the sulfonyl group varies dramatically from nucleophilic sulfinates through chemically robust sulfones to electrophilic sulfonyl halides—a feature that has been used extensively in medicinal chemistry, synthesis, and materials science, especially as bioisosteric replacements and structural analogs of carboxylic acids and other carbonyls. Despite the great synthetic potential of the carboxylic to sulfonyl functional group interconversions, a method that can convert carboxylic acids directly to sulfones, sulfinates and sulfonyl halides has remained out of reach. We report herein the development of a photocatalytic system that for the first time enables direct decarboxylative conversion of carboxylic acids to sulfones and sulfinates, as well as sulfonyl chlorides and fluorides in one step and in a multicomponent fashion. A mechanistic study prompted by the development of the new method revealed the key structural features of the acridine photocatalysts that facilitate the decarboxylative transformations and provided an informative and predictive multivariate linear regression model that quantitatively relates the structural features with the photocatalytic activity.Carboxylic acids can now serve as a single point of entry to several sulfonyl functional groups by a one-step organophotocatalytic sulfonylation, revealing structural effects that enable the photocatalysis. 相似文献
292.
Ferroelectrics are polycrystalline materials consisting of intragranular regions with different polarization directions, called domains. The domains can be switched into different states by the application of an electric field or mechanical stress. We study the influence of grain-to-grain interactions on the overall and local switching behavior. The behavior inside each grain is represented by the micromechanics model of Huber et al. [1999. A constitutive model for ferroelectric polycrystals. J. Mech. Phys. Solids 47 (8), 1663-1697]. The predictions of a self-consistent model of the polycrystal response are compared with those of a multi-grain model in which grains are represented individually. In one flavor of the multi-grain model, each grain is represented by a single finite element, while in the other the fields inside each grain are captured in more detail through a fine discretization. Different electrical and mechanical loading situations are investigated. It is found that the overall response is only mildly dependent on the accuracy with which grain-to-grain interactions are captured, while the distribution of grain-average stresses is quite sensitive to the resolution of the intragranular fields. 相似文献
293.
Control of the magnetic domain wall propagation in Pt/Co/Pt ultra thin films using direct mechanical AFM lithography 总被引:1,自引:0,他引:1
H. W. Schumacher D. Ravelosona F. Cayssol J. Wunderlich C. Chappert V. Mathet A. Thiaville J. -P. Jamet J. Ferr R. J. Haug 《Journal of magnetism and magnetic materials》2002,240(1-3):53-56
We create mesoscopic point and line defects by scanning probe lithography to control the magnetization reversal process in Pt/Co/Pt ultra thin film devices. The domain wall propagation near the defects is studied by the Kerr microscopy and extraordinary Hall effect measurements. The observed domain wall pinning is used to block and channel the domain expansion and to create artificial domain patterns. 相似文献
294.
Avati V. Bergholm V. Boccone V. Bozzo M. Buenerd M. Buzzo A. Cereseto R. Cuneo S. Vi C. Da Deile M. Eggert K. Ferro F. Guillaud J.P. Hasi J. Haug F. Herzog R. Jarron P. Kalliopuska J. Kiiskinen A. Kurvinen K. Kok A. Kundrat W. Lauhakangas R. Lokajichek M. Macina D. Macr M. Mki T. Minutoli S. Morelli A. Musico P. Negri M. Noschis E. Oljemark F. Orava R. Oriunno M. sterberg K. Palmieri V.G. Protasov K. Puppo R. Rebreyend D. Rudischer R. Ruggiero G. Saarikko H. Santroni A. Sanguinetti G. Sette G. Snoeys W. Tapprogge S. Toppinen A. Verdier A. Watts S. Wobst E. 《The European Physical Journal C - Particles and Fields》2004,34(1):s255-s268
The European Physical Journal C - TOTEM will measure the total pp cross-section at LHC by using a luminosity independent method based on simultaneous evaluation of the total elastic and inelastic... 相似文献
295.
Andrea Haug Sabine Schweizer Florian Latteyer Maria Benedetta Casu Dr. Heiko Peisert Dr. Christian Ochsenfeld Prof. Thomas Chassé Prof. 《Chemphyschem》2008,9(5):740-747
The structures of the DNA and RNA bases cytosine, uracil, and thymine in thin films with a nominal film thickness of about 20 nm are studied by using X‐ray photoemission spectroscopy (XPS) and Fourier‐transform infrared spectroscopy. The molecules are evaporated in situ from powder on a gold foil. The experimental results indicate that cytosine is composed of two energetically close tautomeric forms, whereas uracil and thymine exist in only one tautomeric form. Additionally, quantum chemical calculations are performed to complement the experimental results. The relative energies of the tautomeric forms of cytosine, uracil, and thymine are calculated using Hartree–Fock (HF), density functional theory (DFT), and post‐HF methods. Furthermore, the assignment of the XPS spectra is supported by using simple model considerations employing Koopmans ionization energies and Mulliken net atomic charges. 相似文献
296.
We report small angle neutron scattering of spontaneous and magnetic field aligned components of the helical spin polarization in MnSi for temperatures T down to 0.35 K, at pressures p up to 21 kbar, and magnetic field B up to 0.7 T. The parameter range of our study spans the first order transition between helical order and partial magnetic order at p{c}=14.6 kbar, which coincides with the onset of an extended regime of non-Fermi liquid resistivity. Our study suggests that MnSi above p{c} is not dominated by the remnants of the first order transition at p{c}, but that an unidentified mechanism favors stabilization of a new ground state other than helical order. 相似文献
297.
We have bridged a pair of gold electrodes with a single nanoparticle stabilized with citrate. The device exhibited a pronounced linear current-voltage characteristic that is attributed to charge transport in a one-dimensional path. Switching of the current at a fixed bias voltage was observed. We conclude that the latter results from conformational changes in the citrate molecules induced by charge transfer to the molecules. 相似文献
298.
299.
A numerical method for solving distributed parameter structural optimization problems in which repeated eigenvalues may occur is formulated. Recent results on directional differentiability of repeated eigenvalues are used to develop a generalized steepest descent method for structural optimization. The algorithm is shown to overcome technical difficulties associated with nondifferentiability of repeated eigenvalues. The method is used to optimize design of a clamped-clamped column in which a repeated eigenvalue occurs. 相似文献
300.