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451.
Afanas'ev A.V. Antipov O.L. Benfield R.E. Bushuk B.A. Bushuk S.B. Domrachev G.A. Douglas W.E. Fominikh Zh. Jones R.G. Klapshina L.G. Kuzhelev A.S. Lopatina Tatiana I. Mustafa Alkay Rubinov A.N. Semenov V.V. Yurasova Irena V. Zinoviev A.P. 《Silicon Chemistry》2002,1(2):145-154
A variety of novel poly[ethynediyl-arylidene-ethynediyl-silylene]s (PEAES), including those containing hypercoordinate silicon atom as well as donor and acceptor groups, has been synthesized. The presence of hypercoordinate silicon favours high values of fast Kerr-type non-linearities, and the incorporation of amide groups gives rise to good optical quality nanocomposites in a silica matrix. The inorganic-organic hybrid sol-gel film incorporating 5–14 mass% of the polymer containing pentacoordinate silicon showed Re (3) = –9.5 ×10–11 esu. The predominant rôle of the electron nonlinear mechanism has been demonstrated by using test beams with linear and circular polarizations. The photorefractive properties of composites based on PEAES as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm without preliminary electric poling. The photorefractive origin of the refractive index changes was confirmed by the high two-beam gain under an externally applied electric field. Refractive index gratings affording two-beam gain can also be written under zero field conditions. To explain this unique property of the materials it is suggested that chromophore orientation asymmetry arises either during film formation or is induced by the longitudinal intensity gradient. 相似文献
452.
We use Langevin dynamics simulations of a minimalist off-lattice model to study the translocation of a beta hairpin forming peptide through a tunnel that mimics the exit tunnel in a ribosome. We have computed the free energy of the peptide as a function of its position relative to the tunnel exit and also studied the properties of the conformational ensemble, when the peptide's position is restricted at different points along the tunnel. Confining the peptide within a sufficiently wide tunnel stabilizes the folded state. The protein then remains folded as it moves towards the tunnel exit. However, when the diameter D of the tunnel is below a certain critical value D(c), confinement destabilizes the folded state and forces the peptide to assume an extended configuration. In this case, as the peptide progresses towards the tunnel exit and eventually leaves the tunnel, it goes through a series of compact, misfolded conformations and eventually folds when it gets close to the exit. The critical tunnel diameter D(c) is comparable to the width of ribosomal tunnels. Our results suggest that co-translational folding is probably not universal, but rather a protein-specific phenomenon. 相似文献
453.
Vadim V. Bardin Dmitrii V. Trukhin Nicolay Yu. Adonin Vladimir F. Starichenko 《Journal of fluorine chemistry》2004,125(10):1431-1435
Dehalogenation of perhalogenated cyclohexanes C6Cl6F6, 1-azacyclohexenes C5Cl4F5N and bicyclo[4.4.0]dec-1(6)-enes C10Cl8F8 in the vapour phase over iron filings at 350-500 °C and in solution with Zn and additivities (Cu, NiCl2·6H2O + bpy) at 80 °C (heterogeneous reaction) or with P(NEt2)3 at 20 °C (homogeneous reaction) was studied. In all cases, perfluoroarenes, chloroperfluoroarenes and dichloroperfluoroarenes (benzenes, naphthalenes and pyridines) were obtained in good overall yield. 相似文献
454.
Dmitrii P. Krut’ko Maxim V. Borzov Edward N. Veksler Andrei V. Churakov 《Journal of organometallic chemistry》2005,690(17):4036-4048
Synthetic routines for a new ligand C5Me4CH2CH2PMe2 (2b) in forms of its Li- (2b-Li), Na- (2b-Na) salts and in the CH-form (2b-H), as well as for silanes Me3Si-C5H4CH2CH2PMe2 (3a) and Me3Si-C5Me4CH2CH2PMe2 (3b) have been developed. On the basis of it, new half-sandwich [η5:η1-κP-C5H4CH2CH2PMe2]ZrCl3 (4a), [η5:η1-κP-C5Me4CH2CH2PMe2]ZrCl3 (4b) and sandwich [η5-C5Me4CH2CH2PMe2]2ZrCl2 (5), [η5-C5Me4CH2CH2PMe2][η5-C5Me5]ZrCl3 (6) complexes of Zr(IV) have been prepared and characterized. Along with them, the first example of X-ray structurally characterized dinuclear Zr(IV) complex incorporating both sandwich (6) and half-sandwich (4b) moieties linked one to another by means of Zr ← P coordination bond 7, has been described. Formation of an analogously organized trinuclear complex 8, built from one sandwich fragment of 5 and two half-sandwich fragments of 4b was proved by NMR spectroscopy methods. Molecular structures of half-sandwich complexes in their solvent-free dimeric forms (4a and 4b) and as 1:1 adducts with THF (4a-THF and 4b-THF) along with those of dinuclear complex 7 have been established by X-ray diffraction analyses. The dynamic behavior for di- and trinuclear complexes 7 and 8, due to the intermolecular dissociation-coordination of the Me2P-groups in THF-d8 solutions has been studied by variable-temperature NMR spectroscopy. 相似文献
455.
456.
Liang S Lee CH Kozhushkov SI Yufit DS Howard JA Meindl K Rühl S Yamamoto C Okamoto Y Schreiner PR Rinderspacher BC de Meijere A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(7):2012-2018
Epoxidation of bullvalene (1) with a neutralized solution of Oxone gave racemic trisepoxide rac-6 in 93 % isolated yield. Its structure was examined by X-ray crystallography. The two enantiomers of 6 were separated by preparative HPLC and exhibited specific rotations of [alpha](25)(D)= +160, [alpha](25)(365)= +567 (c=0.946, CHCl(3)) for the firstly eluted and [alpha](25)(D)= -157, [alpha](25)(365)= -554 (c=0.986, CHCl3) for the secondly eluted enantiomer of 6. The geometry of (+)-6 and the absolute configuration of (-)-6 were determined by X-ray crystal structure analysis and anomalous diffraction, respectively. According to this, (-)-6 possesses (3R,5S,7S,9R,11R,13S)- and (+)-6 has (3S,5R,7R,9S,11S,13R)-configuration. Upon treatment with BF(3)Et(2)O at -78 degrees C, trisepoxide rac-6 rearranges with retention of the skeletal three-membered carbocycle to give the cage trisether rac-8, as proved by X-ray crystal structure analysis, in virtually quantitative yield. Enantiomers of rac-8 were separated by preparative HPLC and exhibited specific rotations of [alpha](25)(D)= +49, [alpha](25)(365)= +170 (c=1.01, CHCl3) (firstly eluting) and [alpha](25)(D)= -46, [alpha](25)(365)= -160 (c=1.02, CHCl(3)) (secondly eluting enantiomer). The absolute configuration of (-)-8 was determined by anomalous diffraction to be (1R,3R,7R,9R,11R,13R). DFT computations at the TD-B3 LYP/6-31+G(d,p)//B3 LYP/6-31+G(d) level of theory for (3R,5S,7S,9R,11R,13S)-6 and (1R,3R,7R,9R,11R,13R)-8 predicted specific rotations of -206.7 and -83.4, respectively. Acid-catalyzed isomerization of the enantiomerically pure (+)-6 proceeded without racemization to give exclusively (-)-8, and (-)-6 provided only (+)-8. Thus, this isomerization occurs with ring opening of the three C--O bonds in the epoxide moieties in the alpha-position relative to the three-membered carbocycle rather than in the beta-position. 相似文献
457.
Dmitrii V. Pasechnik 《Geometriae Dedicata》1993,46(2):161-164
The aim of this note is to present a series of examples of finite geometries with diagram, whereq=2
k
and GQ-residues are of typeT*
2
(
). 相似文献
458.
E. G. Zinoviev 《Journal of Mathematical Sciences》2008,154(3):301-303
Ideals and factor rings of the so-called csp-rings are described, and modules over such rings are considered.
__________
Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 13, No. 3, pp. 35–38, 2007. 相似文献
459.
Yu. M. Zinoviev 《Theoretical and Mathematical Physics》2008,157(1):1399-1419
We propose a new system of vacuum expectation values for quantum fields. For finite series, these distributions satisfy the
linear Wightman axioms.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 157, No. 1, pp. 41–63, October, 2008. 相似文献
460.
Laser sources with unique properties can be produced using a combination of nonlinear Brillouin gain in single-mode optical fibre (SMOF) and gain in erbium-doped fibre (EDF). Narrow bandwidth nonlinear gain from stimulated Brillouin scattering in SMOF determines the wavelength of operation, and gain in EDF allows efficient operation and large power extraction. Various cascading schemes based on the Brillouin/erbium fibre laser (BEFL) as well as distinctive multi-wavelength versions of the BEFL were proposed, being able to produce 10GHz combs of over 30 lines at 1550 nm. These multi-wavelength sources may be of use in future dense wavelength-division multiplexing systems. We explore fundamental aspects of BEFLs configured to generate multiple wavelengths with particular focus on the effects of the Brillouin and EDF pumps on the number of lines and the relationship between the intensities of the individual lines in the comb. 相似文献