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51.
Moritz Balkenhohl Harish Jangra Ilya S. Makarov Shu‐Mei Yang Hendrik Zipse Paul Knochel 《Angewandte Chemie (International ed. in English)》2020,59(35):14992-14999
The development of a predictive model towards site‐selective deprotometalation reactions using TMPZnCl?LiCl is reported (TMP=2,2,6,6‐tetramethylpiperidinyl). The pKa values of functionalized N‐, S‐, and O‐heterocycles, arenes, alkenes, or alkanes were calculated and compared to the experimental deprotonation sites. Large overlap (>80 %) between the calculated and empirical deprotonation sites was observed, showing that thermodynamic factors strongly govern the metalation regioselectivity. In the case of olefins, calculated frozen state energies of the deprotonated substrates allowed a more accurate prediction. Additionally, various new N‐heterocycles were analyzed and the metalation regioselectivities rationalized using the predictive model. 相似文献
52.
Hirnet A Schroeder K Blügel S Torrelles X Albrecht M Jenichen B Gierer M Moritz W 《Physical review letters》2002,88(22):226102
Sb induces on Ge(113) a c(2 x 2) reconstruction in which Sb breaks one Ge-Ge bond and occupies an interstitial site, in contrast to Sb adsorption on other Si or Ge surfaces. Sb saturates the three dangling bonds per unit cell of the (113) surface inducing a large strain which is released by occupation of the interstitial site. Two neighboring Sb at interstitial sites form a dimer. The structure has been determined by x-ray diffraction, applying direct methods, and ab initio density-functional-theory calculations. The adsorption geometry and the high binding energy lead one to expect that Sb cannot be used as a surfactant for the growth of Si/Ge layers on the (113) surface. 相似文献
53.
Diode-pumped passively mode-locked Nd:YAG laser with 10-W average power in a diffraction-limited beam 总被引:2,自引:0,他引:2
Spühler GJ Paschotta R Keller U Moser M Dymott MJ Kopf D Meyer J Weingarten KJ Kmetec JD Alexander J Truong G 《Optics letters》1999,24(8):528-530
We present a passively mode-locked Nd:YAG laser with 10.7-W average output power in a diffraction-limited beam. Stable self-starting mode locking with a pulse duration of 16 ps and a pulse energy of 120 nJ is obtained with a semiconductor saturable-absorber mirror. The laser is directly side pumped with two 20-W diode bars. Single-pass frequency doubling in an external 5-mm-thick KTP crystal yields 3.2-W average power at 532 nm. 相似文献
54.
Zusammenfassung Die an der Cellulose schon vielfach erprobte Pfropfung mit polymerisierbaren olefinischen Monomeren, wie Styrol, Acrylnitril, Methylacrylat, Vinylchlorid u. a., wurde hier mit polykondensierbaren Siliciumverbindungen versucht. Die gewonnenen Pfropfprodukte, die technisch als Siliconcellulosen bezeichnet werden könnten, sind einer kurzen Prüfung in bezug auf ihre Hydrophobie und ihren Siloxangehalt unterzogen worden.Mit 6 AbbildungenHerrn Prof. Dr.Fritz Wessely zu seinem 70. Geburtstag mit den herzlichsten Glückwünschen gewidmet. 相似文献
55.
56.
Ionization constants of chloro, iodo and nitro substituted 4-methyl-thioanilines were determined over the range 30° to 50° using a spectro-photometric method. The results were analyzed in terms of the Harned-Robinson equation and values of heat, free energy and entropy of ionization were calculated. The free energies are additive, except in the case of 3, 5-diiodo-4-methylthioaniline, while the heats and the entropies are not. 相似文献
57.
Spötl C 《Isotopes in environmental and health studies》2005,41(3):217-221
The stable carbon isotopic composition of dissolved inorganic carbon (delta13C(DIC)) is traditionally determined using either direct precipitation or gas evolution methods in conjunction with offline gas preparation and measurement in a dual-inlet isotope ratio mass spectrometer. A gas evolution method based on continuous-flow technology is described here, which is easy to use and robust. Water samples (100-1500 microl depending on the carbonate alkalinity) are injected into He-filled autosampler vials in the field and analysed on an automated continuous-flow gas preparation system interfaced to an isotope ratio mass spectrometer. Sample analysis time including online preparation is 10 min and overall precision is 0.1 per thousand. This method is thus fast and can easily be automated for handling large sample batches. 相似文献
58.
We have studied interacting and noninteracting quantum degenerate Fermi gases in a three-dimensional optical lattice. We directly image the Fermi surface of the atoms in the lattice by turning off the optical lattice adiabatically. Because of the confining potential, gradual filling of the lattice transforms the system from a normal state into a band insulator. The dynamics of the transition from a band insulator to a normal state is studied, and the time scale is measured to be an order of magnitude larger than the tunneling time in the lattice. Using a Feshbach resonance, we increase the interaction between atoms in two different spin states and dynamically induce a coupling between the lowest energy bands. We observe a shift of this coupling with respect to the Feshbach resonance in free space which is anticipated for strongly confined atoms. 相似文献
59.
Spühler GJ Krainer L Innerhofer E Paschotta R Weingarten KJ Keller U 《Optics letters》2005,30(3):263-265
We report on a simple diode-pumped passively mode-locked Er:Yb:glass laser generating transform-limited 1536-nm solitons of 255-fs duration with a repetition rate of 50 MHz and average power of 58 mW. We also discuss timing jitter and the trade-off between short pulses and high output power in these lasers. 相似文献
60.
Krainer L Nodop D Spühler GJ Lecomte S Golling M Paschotta R Ebling D Ohgoh T Hayakawa T Weingarten KJ Keller U 《Optics letters》2004,29(22):2629-2631
We demonstrate a compact, diode-pumped Nd:GdVO4 laser with a repetition rate of 9.66 GHz and 0.5-W average output power. The laser is passively mode locked with a semiconductor saturable absorber mirror (SESAM), yielding 12-ps-long sech2-shaped pulses. For synchronization of the pulse train to an external reference clock, the SESAM is mounted on a piezoelectric transducer. With an electronic feedback loop of only a few kilohertz loop bandwidth we achieved a rms timing jitter of 146 fs (integrated from 10 Hz to 10 MHz). This is an upper limit because it is mostly limited by the measurement system. The laser setup with a simple linear cavity has a footprint of only 130 mm x 30 mm. 相似文献