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81.
Wasylenko WA Kebede N Showalter BM Matsunaga N Miceli AP Liu Y Ryzhkov LR Hadad CM Toscano JP 《Journal of the American Chemical Society》2006,128(40):13142-13150
New sulfoximine- and phenanthrene-based photochemical precursors to oxynitrenes have been developed. These precursors have been used to examine the chemistry and spectroscopy of oxynitrenes. The first EPR spectra of oxynitrenes are reported and are consistent with their triplet ground states. Additional support for the triplet ground state of oxynitrenes is provided by trapping and reactivity studies, nanosecond time-resolved IR investigations, and computational studies. 相似文献
82.
Abdurahman Ahmed Yonis Vadim Nickolaevich Mal nev Belayneh Mesfin Ali 《中国物理 B》2016,25(2):27801-027801
The propagation of narrow packets of electromagnetic waves(EMWs) in frequency dispersive medium with the consideration of the complex refractive index is studied. It is shown that counting in the dispersion of the complex refractive index within the context of the conventional expression of the group velocity of narrow wave packets of EMWs propagating in a dispersive medium results in the appearance of additional constraints on the group velocity, which dictates that the physically acceptable group velocity can only be realized in the case of a negligible imaginary part of the group index. In this paper, the conditions that allow one to realize the physically acceptable group velocity are formulated and analyzed numerically for the relevant model of the refractive index of a system of two-level atoms in the optical frequency range. It is shown that in the frequency band where superluminal light propagation is expected, there is a strong dispersion of the refractive index that is accompanied with strong absorption, resulting in a strongly attenuated superluminal light. 相似文献
83.
Abbotto A Beverina L Bradamante S Facchetti A Klein C Pagani GA Redi-Abshiro M Wortmann R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(9):1991-2007
The strongly enhanced cooperative influence of medium polarity and organic structural design on the first hyperpolarizability beta of a novel family of highly polarizable azinium-(CH=CH-thienyl)-dicyanomethanido chromophores 1-3 is described. The dyes can be efficiently synthesized by regioselective protonation/alkylation of the corresponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine-->quinoline-->acridine) and medium polarity effects are responsible for an extraordinarily variable range of intramolecular charge transfer (ICT), leading to a large set of pi-electron distribution patterns. Accordingly, systems with remarkably different zwitterionic/quinoid character in the ground and excited states present beta values in a broad range, eventually switching from negative to positive. Our investigation is based on a combination of experimental (UV/Vis spectroscopy, multinuclear NMR spectroscopy, and electrooptical absorption measurements) and computational (ab initio) approaches. It is shown that: 1) beta and mubeta are dramatically influenced, even by orders of magnitude, by a complex, non-monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alternation (BLA), 2) the computations, validated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1-3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most efficiently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polarity of the medium. 相似文献
84.
Dimethylpyridines undergo deuterium-hydrogen exchange when heated in deuterium oxide containing potassium carbonate at ring positions 2 and 6 when these positions are unsubstituted and at methyl groups located at ring positions 2,4, and 6 exclusively. 相似文献
85.
Mesfin Asfaw 《Physica A》2008,387(14):3526-3536
We present a theory of unbinding transitions for membranes that interact via short and long receptor/ligand bonds. The detail of unbinding behaviour of the membranes is governed by the binding energies and concentrations of receptors and ligands. We investigate the unbinding behaviour of these membranes with Monte Carlo simulations and via a comparison with strings. We derive the scaling laws for strings analytically. The exact analytical results provide scaling estimate for membranes in the vicinity of the critical point. 相似文献
86.
Mesfin Asfaw 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):109-116
We discuss various properties of a homogeneous random multifractal
process, which are related to the issue of scale correlations. By
design, the process has no built-in scale correlations. However, when
it comes to observables like breakdown coefficients, which are based on
a coarse-graining of the multifractal field, scale correlations do
appear. In the log-normal limit of the model process, the conditional
distributions and moments of breakdown coefficients reproduce the
observations made in fully developed small-scale turbulence. These
findings help to understand several puzzling empirical details, which
have been extracted from turbulent data already some time ago. 相似文献
87.