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31.
Skarpos H Osipov SN Vorob'eva DV Odinets IL Lork E Röschenthaler GV 《Organic & biomolecular chemistry》2007,5(15):2361-2367
An efficient general synthetic approach giving the possibility for facile, rapid and cheap access to a wide range of novel nitrogen-bisphosphonates (N-BPs) as potent drug candidates, based on the reaction of mono- and bis-propargyl-substituted bisphosphonates with a variety of azides under Cu(i) catalysis ("click" methodology), has been developed. The method allows the incorporation of two functionalities into the N-BP molecule simultaneously, as well as to ligate in situ two N-BPs to one another via the one-pot reaction of organic dibromides with propargyl-substituted bisphosphonates, generating both the diazide and Cu(I) moieties. 相似文献
32.
Dommergue A Bahlmann E Ebinghaus R Ferrari C Boutron C 《Analytical and bioanalytical chemistry》2007,388(2):319-327
Snow surfaces play an important role in the biogeochemical cycle of mercury in high-latitude regions. Snowpacks act both as
sources and sinks for gaseous compounds. Surprisingly, the roles of each environmental parameter that can govern the air–surface
exchange over snow are not well understood owing to the lack of systematic studies. A laboratory system called the laboratory
flux measurement system was used to study the emission of gaseous elemental mercury from a natural snowpack under controlled
conditions. The first results from three snowpacks originating from alpine, urban and polar areas are presented. Consistent
with observations in the field, we were able to reproduce gaseous mercury emissions and showed that they are mainly driven
by solar radiation and especially UV-B radiation. From these laboratory experiments, we derived kinetic constants which show
that divalent mercury can have a short natural lifetime of about 4–6 h in snow. 相似文献
33.
34.
DmitriV. Sevenard OlegG. Khomutov KazimirI. Pashkevich Enno Lork Gerd‐Volker Rschenthaler 《Helvetica chimica acta》2002,85(7):1960-1972
The 2‐acylcycloalkanones 1a – g and 3a – c , possessing a polyfluoroalkyl group, react with hydroxylamine regio‐ and stereoselectively to yield 4,5‐dihydroisoxazol‐5‐ols 2a – g and 4a – c , respectively, i.e., products of N‐addition to the oxo group at the cycloalkane ring (Schemes 1 and 2). The products 2 and 4 can be dehydrated under drastic conditions only (Schemes 3 and 4). The structure of one of the 4,5‐dihydroisoxazol‐5‐ols was confirmed by X‐ray crystal‐structure analysis. 相似文献
35.
Joachim Krieger Enno Lenzmann Pierre Raphaël 《Archive for Rational Mechanics and Analysis》2013,209(1):61-129
We consider the focusing L 2-critical half-wave equation in one space dimension, $$i \partial_t u = D u - |u|^2 u$$ , where D denotes the first-order fractional derivative. Standard arguments show that there is a critical threshold ${M_{*} > 0}$ such that all H 1/2 solutions with ${\|u\|_{L^2} < M_*}$ extend globally in time, while solutions with ${\|u\|_{L^2} \geq M_*}$ may develop singularities in finite time. In this paper, we first prove the existence of a family of traveling waves with subcritical arbitrarily small mass. We then give a second example of nondispersive dynamics and show the existence of finite-time blowup solutions with minimal mass ${\|u_0\|_{L^2} = M_*}$ . More precisely, we construct a family of minimal mass blowup solutions that are parametrized by the energy E 0 > 0 and the linear momentum ${P_0 \in \mathbb{R}}$ . In particular, our main result (and its proof) can be seen as a model scenario of minimal mass blowup for L 2-critical nonlinear PDEs with nonlocal dispersion. 相似文献
36.
Raivo Stern Ivo Heinmaa Enno Joon Alexander A. Tsirlin Hiroyuki Nakamura Tsuyoshi Kimura 《Applied magnetic resonance》2014,45(11):1253-1260
We present low-temperature (low-T, sub-liquid-N2) high-speed high-resolution 29Si solid-state (cryoMAS) nuclear magnetic resonance studies on a model 2D-BEC quantum magnet BaCuSi2O6, known also as Han Purple. We observe broadened 29Si lines below the well-established 100 K structural phase transition confirming the existence of inhomogeneities at low temperatures. Interestingly, the low-T spectra of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) closely resemble those of the novel compound Ba2CoSi2O6Cl2 taken at room temperature. This suggests that the Co compound features structural modulations or inhomogeneities already at room temperature. The low-T crystal structure and magnetism of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) are more complex than previously believed, and deserve further investigation. 相似文献
37.
W Schweinberger A Sommer E Bothschafter J Li F Krausz R Kienberger M Schultze 《Optics letters》2012,37(17):3573-3575
We demonstrate the generation of waveform-controlled laser pulses with 1?mJ pulse energy and a full-width-half-maximum duration of ~4 fs, therefore lasting less than two cycles of the electric field oscillating at their carrier frequency. The laser source is carrier-envelope-phase stabilized and used as the backbone of a kHz repetition rate source of high-harmonic continua with unprecedented flux at photon energies between 100 and 200?eV (corresponding to a wavelength range between 12-6?nm respectively). In combination we use these tools for the complete temporal characterization of the laser pulses via attosecond streaking spectroscopy. 相似文献
38.
Maurizio Roczen Enno Malguth Martin Schade Andreas Schöpke Abdelazize Laades Michael Blech Orman Gref Thomas Barthel Jan Amaru Töfflinger Manfred Schmidt Hartmut S. Leipner Lars Korte Bernd Rech 《Journal of Non》2012,358(17):2253-2256
Two different growth mechanisms are compared for the fabrication of Si/SiO2 nanostructures on crystalline silicon (c-Si) to be used as hetero-emitter in high-efficiency solar cells: (1) The decomposition of substoichiometric amorphous SiOx (a-SiOx) films with 0 < x < 1.3 and (2) the dewetting of thin amorphous silicon (a-Si) layers.The grown layers are investigated with regard to their structural properties, their passivation quality for c-Si wafer substrates and their electrical properties in order to evaluate their suitability as a nanodot hetero-emitter. While by layer decomposition, no passivating nanodots could be formed, the dewetting process allows fabricating nanodot passivation layers at temperatures as low as 600 °C. The series resistance through Ag/[Si-nanodots in SiO2]/c-Si/Al structures for dewetting is similar to nanostructured silicon rich SiOx films. Still, a nanodot hetero-emitter which exhibits both a satisfying passivation of the substrate and induces a high band bending by doping at the same time could not be fabricated yet. 相似文献
39.
Dmitri V. Sevenard Peer Kirsch Enno LorkGerd-Volker Röschenthaler 《Tetrahedron letters》2003,44(32):5995-5998
With 2-trifluoromethyl-1,3-dithianylium triflate for the first time the synthesis, isolation and full structural characterization of an α-perfluoroalkylcarbenium salt was achieved. The title compound can be easily obtained on a preparative scale. The thermally stable dithianylium salt in combination with fluorodesulfurization chemistry is a promising novel reagent for the electrophilic polyfluoroalkylation of organic substrates, demonstrated by the pentafluoroethylation of O-nucleophiles. 相似文献
40.