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41.
Time-resolved emission measurements in subpicosecond time domain have been carried out for 1-nitropyrene in different solvents to understand the mechanism for the observed ultrafast decay of its first excited singlet state. Excited-state dynamics of 1-nitropyrene is found to be independent of the solvent viscosity. This result contradicts the proposition in the literature (J. Phys. Chem. A 2007, 111, 552) that the ultrafast decay in 1-nitropyrene is due to the large amplitude torsional motion of the nitro group around the pyrene moiety. Excited-state dynamics of 1-nitropyrene in solvents with different dielectric constants shows that excited-state lifetime suddenly increases after a certain value of the dielectric constant. Detailed quantum chemical calculations have been carried out to understand the process that is responsible for the observed effect of the dielectric constant on the excited-state dynamics of 1-nitropyrene. It is seen that the excited-state lifetime and the singlet-triplet energy gap follow similar variation with the dielectric constant of the medium. Such a correlation between the excited-state lifetime and the singlet-triplet energy gap supports the fact that the observed ultrafast decay for 1-nitropyrene is due to an efficient intersystem crossing rather than to the torsional motion of the nitro group as proposed in the literature. 相似文献
42.
Steven van Zutphen Vicente J. Margarit Guilhem Mora Pascal Le Floch 《Tetrahedron letters》2007,48(16):2857-2859
Nucleophilic substitution of a phospholide anion onto protected 3-iodoalanine leads to the formation of an amino acid with an appended phosphole in excellent yield. Manipulation of the protecting groups, leads to building blocks suitable for the synthesis of phosphole-containing polypeptides. 相似文献
43.
M. A. Mora Laura Galicia M. A. Mora‐Ramirez 《International journal of quantum chemistry》2004,97(6):983-991
The molecular and electronic structures of 5‐amino‐1,10‐phenanthroline and its monoprotonated and diprotonated species were obtained from ab initio quantum mechanical calculations with unrestricted Hartree–Fock (HF) and Møller–Plesset perturbation theories. The analysis of the net atomic charges and the total spin densities show three possible sites for the monomeric coupling in the polymerization process. The minimal energy conformation for the different kinds of coupling in the formation of the dimers was obtained. The studies were extended to the HF/6‐311 + G(2d,p)//B3LYP (Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar)/6‐31G(d) level of theory to obtain theoretical nuclear magnetic resonance spectra to study the number and kinds of species involved in the protonation mechanism. Theoretical and experimental nuclear magnetic resonance spectra are in excellent agreement. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
44.
The combination of gas chromatography and atomic absorption spectrophotometry offers high sensitivity and specificity in the analysis of volatile organometallic species, and has been applied to alkyl derivatives of As, Pb, Se and Sn in environmental samples of air, water, sediment and biological tissues. Techniques of sample introduction and detector design are discussed with regard to the sensitivity attainable. 相似文献
45.
Yu-Hui Huang Zhuo-Mei Li Herbert Mora Wetz 《Journal of polymer science. Part A, Polymer chemistry》1985,23(3):795-799
Poly(vinyl benzyl chloride) latex was reacted with ethanolamine and with amine terminated chain molecules containing up to 33 ethylene oxide residues. The kinetics of these reactions were essentially independent of the length of the chain carrying the amine group. An increasing length of the chains bound to the surface of the latex particles produced an increasing latex stabilization. 相似文献
46.
Balint Farkas Mate Matolcsi Peter Mora 《Journal of Fourier Analysis and Applications》2006,12(5):483-494
Recent methods developed by Tao [18], Kolountzakis and Matolcsi [7] have led to counterexamples to Fugelde’s Spectral Set
Conjecture in both directions. Namely, in
Tao produced a spectral set which is not a tile, while Kolountzakis and Matolcsi showed an example of a nonspectral tile.
In search of lower dimensional nonspectral tiles we were led to investigate the Universal Spectrum Conjecture (USC) of Lagarias
and Wang [14]. In particular, we prove here that the USC and the "tile → spectral" direction of Fuglede’s conjecture are equivalent
in any dimensions. Also, we show by an example that the sufficient condition of Lagarias and Szabó [13] for the existence
of universal spectra is not necessary. This fact causes considerable difficulties in producing lower dimensional examples
of tiles which have no spectra. We overcome these difficulties by invoking some ideas of Révész and Farkas [2], and obtain
nonspectral tiles in
. Fuglede’s conjecture and the Universal Spectrum Conjecture remains open in 1 and 2 dimensions. The one-dimensional case
is closely related to a number theoretical conjecture on tilings by Coven and Meyerowitz [1]. 相似文献
47.
We study three same-spin-state fermions of mass M interacting with a distinguishable particle of mass m in the unitary limit where the interaction has a zero range and an infinite s-wave scattering length. We predict an interval of mass ratio 13.384相似文献
48.
This paper shows, by means of Kronecker’s theorem, the existence of infinitely many privileged regions called $r$ -rectangles (rectangles with two semicircles of small radius $r$ ) in the critical strip of each function $L_{n}(z)\!:=\!$ $1-\sum _{k=2}^{n}k^{z}$ , $n\!\ge \!2$ , containing exactly $\left[ \dfrac{T\log n}{2\pi }\right] +1$ zeros of $L_{n}(z)$ , where $T$ is the height of the $r$ -rectangle and $\left[\cdot \right]$ represents the integer part. 相似文献
49.
Fernando Barrera Mora 《代数通讯》2013,41(10):4641-4649
A Jordan pair is constructed from a pair of cubic forms satisfying the adjoint identities. Given some parameters and an incidence structure S having three points on each line and no more than one line through two points, a pair of cubic forms are constructed. These forms satisfy the adjoint identities if and only if S is either a star or a generalized quadrangle and the parameters are precisely determined. 相似文献
50.
G. E. Delgado A. J. Mora P. Grima‐Gallardo S. Durn M. Muoz M. Quintero 《Crystal Research and Technology》2008,43(7):783-785
The crystal structure of the quaternary compound CuTaInSe3 belonging to the system (CuInSe2)1‐x(TaSe)x with x= 0.5, was analyzed using X‐ray powder diffraction data. This material is isostructural with the CuFeInSe3 compound, and crystallize in the tetragonal space group P42c (Nº 112), Z = 1, with unit cell parameters a = 5.7831(1) Å, c = 11.6227(4) Å, V = 388.71(2) Å3. The Rietveld refinement of 18 instrumental and structural variables led to Rp = 8.0%, Rwp = 9.5%, Rexp = 6.3% and χ2 = 1.5 for 4501 step intensities and 144 independent reflections. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献