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51.
Kowalewski J Effemey M Jokisaari J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,157(2):171-177
Multiple-field (4.7, 9.4, 14.1 T) carbon-13 relaxation data are reported for hexamethylenetetramine (HMTA) in the cryosolvent D(2)O/DMSO at 243 K. Under these conditions, the reorientational motion of HMTA is outside of the extreme narrowing range and the relaxation data can be subjected to a quantitative interpretation. Because of the high symmetry of the HMTA molecule, the reorientation must be isotropic. Treating the reorientation as a small-step rotational diffusion of a rigid body, we obtain a rotational correlation time of 1.0 ns and a carbon-proton dipole-dipole coupling constant corresponding to an effective internuclear distance of 114. 2 pm. The harmonic vibrational correction to the dipole-dipole coupling constant, based on a known force field, yields an NMR estimate of the r(alpha) distance of 110.8 +/- 0.3 pm. 相似文献
52.
53.
We report lifetime measurements of the 1s 2 3d 2 D, 1s 24d 2 D, and 1s 22p 2 P states of lithium. The results τ=14.5±0.7 ns, τ=31.0±1.0 ns, and τ=27.9±1.0 ns respectively were obtained by time resolved detection of the resonance fluorescence following pulsed laser excitation. 相似文献
54.
Novel probes represented connection of pyrene as chromophore and sterically hindered amine stabilizers (HAS) in the form of esters of 2-(1-pyrenyl)acrylic acid were synthesized. HAS was in the form of parent amine (PAP) as well as stable nitroxyl radical form (PAP-NO.). Photophysics of these probes were compared with their precursor as 2-(1-pyrenyl)acrylic acid (PAA) and its methyl ester (PAM). The fluorescence spectrum of PAA strongly depends on the acidity of the solution. The spectrum in neutral methanol indicates that it originates from the anionic form –COO−. Changes of acidity or basicity of methanol solution resulted in the changes of shape, position as well as the intensity of fluorescence band. This is due to the presence of protolytic equilibria, either in the ground state or in the singlet excited state, leading to the formation of molecular form –COOH and the cationic form –COOH2+. The ester analogues did not show any changes in various pH conditions. Fluorescence of all probes depends on the polarity of solvents and the presence of oxygen. Intermolecular quenching was studied with external quenchers TEMPO and oxygen and the data were compared with the intramolecular quenching using 1′-oxo-2′,2′,6′,6′-tetramethyl-4′-piperidinyl-2-(1-pyrenyl)acrylate (PAP-NO.). 相似文献
55.
Taking into account the tetrahedral shape of a quantum-dot quantum well (QDQW) when describing excitonic states, phonon modes, and the exciton-phonon interaction in the structure, we obtain within a nonadiabatic approach a quantitative interpretation of the photoluminescence spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW. The position of the phonon peaks in the photoluminescence spectrum is attributed to interface optical phonons. We also show that the experimental value of the Huang-Rhys parameter can be obtained only within the nonadiabatic theory of phonon-assisted transitions. 相似文献
56.
We say that a family of graphs is p-quasi-random, 0<p<1, if it shares typical properties of the random graph G(n,p); for a definition, see below. We denote by the class of all graphs H for which and the number of not necessarily induced labeled copies of H in Gn is at most (1+o(1))pe(H)nv(H) imply that is p-quasi-random. In this note, we show that all complete bipartite graphs Ka,b, a,b2, belong to for all 0<p<1.Acknowledgments We would like to thank Andrew Thomason for fruitful discussions and Yoshi Kohayakawa for organizing Extended Workshop on Combinatorics in eq5 Paulo, Ubatuba, and Rio de Janeiro, where a part of this work was done. We also thank the referees for their careful work.The first author was partially supported by NSF grant INT-0072064The second author was partially supported by NSF grants DMS-9970622, DMS-0301228 and INT-0072064Final version received: October 24, 2003 相似文献
57.
Alena Juríková Kornel Csach Jozef Miškuf Václav Ocelík 《Central European Journal of Physics》2007,5(2):177-187
Creep strain recovery and structural relaxation of the amorphous metallic glass Fe40Ni41B19 after longtime loading at different annealing temperatures below the glass transition temperature have been studied using
anisothermal differential scanning calorimetry (DSC) and dilatometry (TMA). It has been demonstrated that structural relaxation
effects depend on the stress-annealing temperature of the amorphous ribbon. The structural relaxation states of the amorphous
ribbon annealed at different temperatures under and without applied stress have been compared. The activation energy spectra
were calculated from the anisothermal dilatometric measurements using the modern method based on the Fourier transformation
technique. The influence of the annealing temperature on the shape of creep strain recovery spectra has been analyzed.
相似文献
58.
Optically pure (+)-calvine, (+)-2-epicalvine, (2S,6S)-(6-pentylpiperidin-2-yl)acetic acid methyl ester and (2R,6S)-(6-pentylpiperidin-2-yl)acetic acid methyl ester, four piperidine alkaloids isolated from ladybird beetles of the genus Calvia (Coccinellidae), were synthesised from a common precursor using cyclisative Pd(II)/Cu(II)-catalysed carboamination-(methoxy)carbonylation tandem reaction of alkenylamines as a key step. The first single-crystal X-ray analysis of (+)-calvine confirmed its proposed absolute configuration to be (2S,6S) corresponding to that of natural product. 相似文献
59.
Bram Neirinck Lieve Van Mellaert Jan Fransaer Omer Van der Biest Jozef Ann Jef Vleugels 《Electrochemistry communications》2009,11(9):1842-1845
The possibility to use alternating current electrophoretic deposition (AC-EPD) to deposit living cells in the form of Staphylococcus aureus and Escherichia coli on stainless steel was assessed. The experimental results revealed that these bacteria can be successfully deposited on metallic surfaces from demineralized water and sucrose based solutions using asymmetric unbalanced electric fields. Cell viability of the deposited bacteria was influenced by the strain and deposition medium. 相似文献
60.
Heavily n‐type doped and several nanometres thick In0.485Ga0.515P layers are necessary for various devices. We studied the delta‐doping of this ternary with tellurium; the layers were grown by metalorganic vapour phase epitaxy (MOVPE), and diethyltelluride was used as the precursor. A maximum Hall sheet concentration of 2.75 × 1013 cm–2 was achieved in our samples grown at 560 °C. The Te profiles were analyzed with secondary ion mass spectrometry (SIMS), and a very narrow spectrum with a full width at half maximum of 7.5 nm was measured. This value indicates that the memory effect, referred to in the literature, was practically eliminated with appropriate growth conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献