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151.
Lukas J. Goossen Hong Liu K. Ruprecht Dress K. Barry Sharpless 《Angewandte Chemie (International ed. in English)》1999,38(8):1080-1083
The suprafacial, vicinal addition of a heterocyclic moiety and a hydroxyl group is achieved by the osmium-catalyzed asymmetric aminohydroxylation (AA) of olefins with amino-substituted heterocycles as the nitrogen sources. Amino alcohols are obtained in up to 97 % yield and with up to 99 % ee when a ligand derived from dihydroquinidine (DHQD-L) is used [Eq. (1); Ri indicates the remaining portion of the heterocycle (Het); H2O is the O source]. The AA can now be considered as a means to directly introduce complex, biologically relevant substructures to hydrocarbon backbones. 相似文献
152.
Peter Barthazy Lukas Hintermann RobertM. Stoop Michael Wrle Antonio Mezzetti Antonio Togni 《Helvetica chimica acta》1999,82(12):2448-2453
The 16-electron, five-coordinate fluoro complex [RuF(dppp)2]PF6 ( 1a ; dppp=propane-1,3-diylbis[diphenylphosphine] smoothly reacts with 1,3-diphenylallyl bromide (=1,1′-(3-bromoprop-1-ene-1,3-diyl)bis[benzene]) in dry CDCl3 to give 1,3-diphenylallyl fluoride and [RuBr(dppp)2]+ in nearly quantitative yield. Under similar conditions, bromide (or chloride)/fluoride exchange also occurs with chlorotriphenylmethane, bromodiphenylmethane, and tert-butyl bromide. The crystal structure of 1a is reported. 相似文献
153.
154.
Romain Fardel Lukas Urech Thomas Lippert Claude Phipps James M. Fitz-Gerald Alexander Wokaun 《Applied Physics A: Materials Science & Processing》2009,94(3):657-665
Laser plasma thrusters are a new kind of propulsion system for small satellites, and work with the thrust created by the laser
ablation of a target. Liquid polymer solutions are very promising fuels for such systems, provided that no splashing of the
target occurs, because ejection of droplets strongly decreases the performances of the system. We have investigated the nanosecond
infrared laser ablation of glycidyl azide polymer solutions containing carbon nanoparticles as absorber. Shadowgraphy imaging
revealed two cases, namely splashing regime and solid-like behavior. The transition between both regimes depends on the viscosity
of the solution and on the laser fluence, and is explained by the recoil force acting on the target. Appropriate conditions
to avoid splashing were identified, showing that this liquid polymer solution is a suitable fuel for laser plasma thrusters. 相似文献
155.
156.
Karla M. Robotti Hongfeng Yin Reid Brennen Lukas Trojer Kevin Killeen 《Journal of separation science》2009,32(20):3379-3387
Polyimide HPLC‐Chip devices containing poly(methylstyrene‐bis‐p‐vinylphenyl)ethane (MS/BVPE) stationary phase within the device channels and with wall attachment were prepared by thermally initiated free radical polymerization. The microfluidic devices were coupled to both UV and MS detectors. The potential of the MS/BVPE monolith as an alternative separation media within chip devices was investigated by side‐by‐side comparisons to particulate media within commercial devices. The chromatographic behavior of this stationary phase was comparable to particulate media for separations of proteins as the average peak width at half‐height was equal (6.2 s) for a separation within 8 min under gradient elution conditions. The ability to control the porosity characteristics of the MS/BVPE monolith with changes in polymerization time also extended its utility into small analyte (< 500 Da) applications, although more optimization is needed to match conventional RP media for these applications. The good mechanical stability of the MS/BVPE monolith within the microdevices enabled excellent run‐to‐run repeatability (%RSD retention time (? 0.16) and chip‐to‐chip reproducibility (%RSD retention time (1.4). The use of this material within enrichment channels also shows its potential value in more complex work flows. 相似文献
157.
The state estimation problem is considered for a diffusion-reaction system with spatially varying parameters defined on a 3-dimensional rectangular domain with the measured output being restricted to a single surface. For this, a backstepping-based observer design is applied, which enables to obtain the observer gains such that the observer error dynamics decays exponentially in the L2-norm. At first, an idealized system output restricted to a single surface is assumed as an available measurement. Secondly, in view of a practical realization of the proposed observer, the idealized system output is reconstructed from a set of finite-dimensional measurements. The observer error convergence and the applicability of the proposed approach are evaluated by means of numerical simulations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
158.
Kroeze JE Hirata N Koops S Nazeeruddin MK Schmidt-Mende L Grätzel M Durrant JR 《Journal of the American Chemical Society》2006,128(50):16376-16383
The optimization of interfacial charge transfer is crucial to the design of dye-sensitized solar cells. In this paper we address the dynamics of the charge separation and recombination in liquid-electrolyte and solid-state cells employing a series of amphiphilic ruthenium dyes with varying hydrocarbon chain lengths, acting as an insulating barrier for electron-hole recombination. Dynamics of electron injection, monitored by time-resolved emission spectroscopy, and of charge recombination and regeneration, monitored by transient optical absorption spectroscopy, are correlated with device performance. We find that increasing dye alkyl chain length results in slower charge recombination dynamics to both the dye cation and the redox electrolyte or solid-state hole conductor (spiro-OMeTAD). These slower recombination dynamics are however paralleled by reduced rates for both electron injection into the TiO2 electrode and dye regeneration by the I-/I3- redox couple or spiro-OMeTAD. Kinetic competition between electron recombination with dye cations and dye ground state regeneration by the iodide electrolyte is found to be a key factor for liquid electrolyte cells, with optimum device performance being obtained when the dye regeneration is just fast enough to compete with electron-hole recombination. These results are discussed in terms of the minimization of kinetic redundancy in solid-state and liquid-electrolyte dye-sensitized photovoltaic devices. 相似文献
159.
Lara B. Anderson James Gray Dan Grayson Yang-Hui He André Lukas 《Communications in Mathematical Physics》2010,297(1):95-127
We present a practical, algebraic method for efficiently calculating the Yukawa couplings of a large class of heterotic compactifications
on Calabi-Yau three-folds with non-standard embeddings. Our methodology covers all of, though is not restricted to, the recently
classified positive monads over favourable complete intersection Calabi-Yau three-folds. Since the algorithm is based on manipulating
polynomials it can be easily implemented on a computer. This makes the automated investigation of Yukawa couplings for large
classes of smooth heterotic compactifications a viable possibility. 相似文献
160.
Lukas Pietzonka Thomas Lautenschläger Daniel Spemann Annemarie Finzel Jürgen W. Gerlach Frank Frost Carsten Bundesmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(10):252
TiO2 thin films were grown by ion beam sputter deposition (IBSD) using oxygen ions, with the ion energy and geometrical parameters (ion incidence angle, polar emission angle, and scattering angle) being varied systematically. Metallic Ti and ceramic TiO2 served as target materials. The thin films were characterized concerning thickness, growth rate, surface topography, structural properties, mass density, and optical properties. It was found that the scattering geometry has the main impact on the film properties. Target material, ion energy, and ion incidence angle have only a marginal influence. Former studies on reactive IBSD of TiO2 using Ar and Xe ions reported equivalent patterns. Nevertheless, the respective ion species distinctively affects the film properties. For instance, mass density and the refractive index of the TiO2 thin films are remarkably lower for sputtering with oxygen ions than for sputtering with Ar or Xe ions. The variations in the thin film properties are tentatively attributed to the angular and the energy distribution of the film-forming particles, especially, to those of the backscattered primary particles. 相似文献