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881.
Rainer Koch Justin J. Finnerty Torsten Bruhn 《Journal of Physical Organic Chemistry》2008,21(11):954-962
A systematic investigation of the hyperpolarisabilities of substituted p‐poly‐phenylenes is presented using different quantum mechanical approaches, including density functional theory and Møller–Plesset (MP2) methods. A medium‐sized basis set Hartree–Fock (HF) hyperpolarisability calculation based on either a density functional theory (DFT) or MP2 geometry gives reliable results at moderate computational costs when comparing with experimental data. A longer phenylene chain leads to a maximum in the per‐unit increase of the investigated property between 3 and 4 repeat units. Changing the underlying geometry from the minimum helix to a planar orientation leads to a significant increase in β, again dependent on the chain length. Terminal para‐substituents and their influence are studied and categorised. For push–pull groups, the substituent effects are mainly additive, allowing the design of functionalised phenylenes as molecular building blocks for nanofibres with tailored nonlinear optical (NLO) properties. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
882.
883.
A. Siber J. Marien Th. Koch P. Ziemann 《Applied Physics A: Materials Science & Processing》1993,57(3):267-270
Al/Au multilayers (average composition Al2Au, individual layer thicknesses 1 nm Al and 0.71 nm Au) are prepared at 90 K by ion beam sputtering. The electrical resistance of the growing films is monitored in situ. From the results obtained in this way it can be concluded that interface reactions occur transforming the ultrathin layers into an amorphous phase, which is stable up to 255 K.For larger individual layer thicknesses (2.1 nm Au and 3 nm Al), the interface reaction into the amorphous state is incomplete. Based on a simple parallel-resistor model, one finds that the interface reaction into the amorphous phase is restricted to a thickness of less than 3.5 nm. The temperature dependence of the resistance of such thicker multilayers indicates the onset of interdiffusion of the yet unreacted material at T=200 K resulting in the crystalline Al2Au-phase. 相似文献
884.
885.
886.
M. Koch K. Maier J. Major A. Seeger W. Sigle W. Staiger W. Templ E. Widmann R. Abela V. Claus M. Hampele D. Herlach 《Hyperfine Interactions》1991,65(1-4):1039-1045
μ− SR experiments have been performed on Si between room temperature and 6 K. The amplitude of the muon spin precession signal
in an applied magnetic field of 0.04 T decreased below 30 K. A zero-field measurement at 6 K revealed a μ− spin precession frequency of 650 MHz. The muonic atom represents an aluminium acceptor in the silicon matrix, its electronic
state is responsible for the μSR signal. A possible influence of the γ recoil produced by the X-ray cascade is discussed. 相似文献
887.
PHOTOCHEMICAL COUPLING OF 5-BROMOURACIL TO TRYPTOPHAN, TYROSINE AND HISTIDINE, PEPTIDE-LIKE DERIVATIVES IN AQUEOUS FLUID SOLUTION 总被引:4,自引:0,他引:4
Direct irradiation of 5-bromouracil (BU) in aqueous fluid solution in the presence of tryptophan (trp), tyrosine (tyr) or histidine (his) derivatives using a XeCl excimer laser at 308 nm yielded photocoupling of BU to the aromatic ring of each amino acid. Irradiation of BU at 308 nm most likely results in excitation of the n-φ* transition, intersystem crossing to the triplet manifold, and coupling via electron transfer from the aromatic amino acid. The coupling observed was regiospecific between the 5-position of uracil (U) and the 2-position of the indole and phenol rings and the 5-position of the imidazole ring of the respective amino acids. Quantum yields of photocoupling to BU ranged from 1 × 10-3 to 7 × 10-3 and paralleled known rates of electron transfer and ionization potentials of the aromatic rings. The photocoupling between BU and some of the aromatic amino acid peptide-like derivatives possibly mimics photocrosslinking of BU-DNA to associated proteins, a potentially useful photoreaction for studying nucleic acid-protein interactions. Formation of crosslinks of the type proposed here might be detected by the characteristic fluorescence emission of the uracil amino acid adducts. 相似文献
888.
Summary The complexing of Fe(II) with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine in the presence of Fe(III) represents a rapid alternative to the usual methods and provides good sensitivity. The results show that this method can also be used with very different Fe(II) or Fe(III) contents. The application described for the automatic determination of Fe(II) in ores and sinter with the continuous flow technique shows that this method can also be used in connection with automated systems. However, particular attention must be paid here to the fact that the working conditions have to be optimised for each matrix.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
889.
A. Wrońska V. Hejny C. Wilkin S. Dymov C. Hanhart V. Komarov H. R. Koch A. Kulikov A. Magiera T. Mersmann S. Mikirtytchiants H. Ohm D. Prasuhn R. Schleichert H. J. Stein H. Ströher 《The European Physical Journal A - Hadrons and Nuclei》2005,26(3):421-428
The dd↦4Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections
have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution
reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition
into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed. 相似文献
890.