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61.
A study of the flexibility parameter of Ptitsyn-Eizner for flexible polymers has been carried out; it has been found that λ depends on polymer-solvent interactions. The λ values for various flexible polymers under theta conditions, in which it is only a characteristic of chain flexibility, have been found. This parameter varies in the same way as the rigidity coefficient, σ. Finally, λ has been found to vary linearly with temperature. 相似文献
62.
The hydrodynamic stability of a low speed, plane, non-isothermal laminar wall jet at a constant temperature boundary condition was investigated theoretically and experimentally. The mean velocity and temperature profiles used in the stability analysis were obtained by implementing the Illingworth–Stewartson transformation that allows one to extend the classical Glauert solution to a thermally non-uniform flow. The stability calculations showed that the two unstable eigenmodes coexisting at moderate Reynolds numbers are significantly affected by the heat transfer. Heating is destabilizing the flow while cooling is stabilizing it. However, the large-scale instabilities associated with the inflection point of the velocity profile still amplify in spite of the high level of the stabilizing temperature difference. The calculated stability characteristics of the wall jet with heat transfer were compared with experimental data. The comparison showed excellent agreement for small amplitudes of the imposed perturbations. The agreement is less good for the phase velocities of the sub-harmonic wave and this is attributed to experimental difficulties and to nonlinear effects. 相似文献
63.
The fracture characteristics, Young’s modulus and Vickers hardness of nanocrystalline materials obtained from the amorphous precursor Co66Fe4Mo2Si16B12 by thermal treatments at two different temperatures (slightly and well below the crystallization temperature) have been studied. The results show that these nanocrystalline materials are very brittle and the plastic flow involved in the fracture process practically disappears in the case of the material obtained at the temperature slightly below the crystallization one. In addition, an interesting nanolamellar structure has been observed in this sample. 相似文献
64.
M. Quintana E. Haro-poniatowski N. Batina 《Applied Physics A: Materials Science & Processing》2004,79(4-6):903-906
The effect of an inert gas pressure on the structure of selenium thin films has been systematically investigated in the pulsed laser deposition process. The ablated material is deposited on Au (111) gold thin films for its characterization by atomic force microscopy (AFM). Analysis of the surface morphology shows that instead of the formation of a uniform Se thin film on top of Au (111) terraces, as it occurs in high vacuum, the film grows as two dimensional ellipsoid shaped aggregates. The size of these Se aggregates increases significantly with the gas pressure and reaches a maximum at pressures of 1.5 Torr, and subsequently decreases with further increase of the gas pressure. This effect is probably due to the fact that the kinetic energy of the impinging species decreases as pressure increases, thus impeding diffusion on the substrate surface. However, further increase in the pressure prevents the Se species from being deposited on the substrate resulting in a decrease in size of the aggregates. PACS 81.07; 68.37.P; 81.16.M 相似文献
65.
J. R. Quintana R. Stubersfield C. Price Issa Katime 《Journal of Polymer Science.Polymer Physics》1990,28(9):1565-1570
The structure of stereocomplex aggregates formed from isotactic and syndiotactic poly (methyl methacrylate)s was studied in tetrahydrofuran (THF) by transmission electron microscopy (TEM). We have found that the primary stereocomplex particles are nearly spherical and, as the complexation advances, the particles lengthen. Eventually aggregates branch to form a three-dimensional network. 相似文献
66.
G. de Angelis T. Martinez A. Gadea N. Marginean E. Farnea E. Maglione S. Lenzi W. Gelletly C.A. Ur D.R. Napoli Th. Kroell S. Lunardi B. Rubio M. Axiotis D. Bazzacco A.M. Bizzeti Sona P.G. Bizzeti P. Bednarczyk A. Bracco F. Brandolini F. Camera D. Curien M. De Poli O. Dorvaux J. Eberth H. Grawe R. Menegazzo G. Nardelli J. Nyberg P. Pavan B. Quintana C. Rossi Alvarez P. Spolaore T. Steinhart I. Stefanescu O. Thelen R. Venturelli 《The European Physical Journal A - Hadrons and Nuclei》2001,12(1):51-55
Gamma ray transitions de-exciting states in the N = Z nucleus 70Br have been identified for the first time using the GASP and EUROBALL arrays coupled with ancillary detectors. The level
scheme of 70Br has been established by means of particle-gated γ-γ and γ-γ-γ coincidences. The Coulomb energy differences between isobaric
analogue states in 70Br and 70Se show a deviation from the expected behaviour which could be related to dripline effects.
Received: 18 July 2001 / Accepted: 25 September 2001 相似文献
67.
Ya Zou Víctor Bonal Sergio Moles Quintero Dr. Pedro G. Boj Dr. José M. Villalvilla Dr. José A. Quintana Dr. Guangwu Li Shaofei Wu Dr. Qing Jiang Dr. Yong Ni Prof. Juan Casado Prof. María A. Díaz-García Prof. Jishan Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15037-15044
Perylene-fused, aggregation-free polycyclic aromatic hydrocarbons with partial zigzag periphery ( ZY-01 , ZY-02 , and ZY-03 ) were synthesized. X-ray crystallographic analysis reveals that there is no intermolecular π–π stacking in any of the three molecules, and as a result, they show moderate-to-high photoluminescence quantum yield in both solution and in the solid state. They also display the characteristic absorption and emission spectra of perylene dyes. ZY-01 and ZY-02 with a nearly planar π-conjugated skeleton exhibit amplified spontaneous emission (ASE) when dispersed in polystyrene thin films. Solution-processed distributed feedback lasers have been fabricated using ZY-01 and ZY-02 as active gain materials, both showing narrow emission linewidth (<0.4 nm) at wavelengths around 515 and 570 nm, respectively. In contrast, ZY-03 did not show ASE and lasing, presumably due to its highly twisted backbone, which facilitates nonradiative internal conversion and intersystem crossing. 相似文献
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