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排序方式: 共有80条查询结果,搜索用时 31 毫秒
61.
David Cavaill Claire Levelut Rmy Vialla Ren Vacher Eric Le Bourhis 《Journal of Non》1999,260(3):235-241
Brillouin light scattering allows the measurement of sound velocity and elastic moduli in transparent materials. The ability to select a small scattering volume and to use specific scattering configurations gives important information about the gradient and anisotropy of mechanical properties. Brillouin experiments are often used to measure the second-order elastic constants. When a high accuracy in frequency measurements is achieved, Brillouin scattering may allow the determination of third-order elastic constants in pre-stressed media. Hence, Brillouin scattering provides in principle, a method for the analysis of stress fields in tempered glasses. In order to validate the technique, samples of float soda-lime–silica glass submitted to controlled stresses by four-point flexion were investigated. The results show the expected profile for the velocity of sound waves propagating in directions parallel and perpendicular to the surface of the samples, respectively. They allow the determination of several third-order elastic constants of the investigated glass. This technique was applied to several samples of tempered glass corresponding to different values of the surface stress. The main result is the observation of the expected general trend, namely, through the thickness of the sample, a parabolic variation of the sound velocity whose amplitude increases with the magnitude of the surface stress. 相似文献
62.
P. Doussineau A. Levelut 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):13-21
Aging, memories after temperature sweeps (double ramp and double jump) and memories after electric field sweeps (double ramp
and double jump) were studied as a function of frequency. The experiments were performed at low temperatures in the ferroelectric
phase of two potassium niobo-tantalate crystals K Ta1-xNbxO3 with the niobium concentration x close to 0.02. Five complex quantities are defined, which respectively characterize these five phenomena. The main feature
is that isothermal aging and memories after temperature sweeps have exactly the same frequency dependence while after electric
field sweeps the frequency dependence is clearly different. Additionally, the role of the characteristics of the sweeps (amplitudes,
rates of changes, durations) on these memories were measured. The observed behaviours are discussed in term of a model which
attributes the time dependent effects to growth and reconformation of ferroelectric domains and takes into account that the
domain wall motion is hindered by pinning sites. The difference in the frequency dependences against the nature of the swept
parameters shows that the distribution of the reconformation time is sensitive to the biasing electric field.
Received 28 May 2001 and Received in final form 10 October 2001 相似文献
63.
The short- and long-range structure of a series of single and mixed aluminophosphate glasses with the general composition [xNa(2)O (46 - x)Li(2)O], [yAl(2)O(3) (54 - y)P(2)O(5)] is analyzed using (31)P and (27)Al magic-angle spinning (MAS) NMR as well as small-angle X-ray scattering. These series of glasses allow analyzing both the effect of alumina incorporation in these glasses, for small alumina content (y = 0, 4, 8), and the structural changes associated with the so-called mixed alkali effect (x = 0, 11.5, 23, 34.5, 46). Our results indicate that aluminum is mainly octahedrally coordinated in these glasses and that there is most likely some segregation of the Al(OP)(6) species. In the pure phosphate glasses, we observe a "classical" continuous variation of the structural properties with the relative alkali content, but in the aluminophosphate, both local and long-range structural results reveal for the first time some nonlinear change as a function of the relative alkali content. 相似文献
64.
J. F. Berret P. Doussineau A. Levelut W. Schön 《Zeitschrift für Physik B Condensed Matter》1988,70(4):485-490
Dielectric measurements have been performed at 1 and 10 GHz in (KBr)1–x
(KCN)
x
mixed crystals for cyanide concentrationsx=0.25 andx=0.50 in the temperature rangeT=1.7–150 K. The maxima of the real and imaginary parts of the dielectric constant falls into the Arrhenius straight lines obtained at lower frequencies. These dipolar lines cross over the so-called quadrupolar (acoustic) lines, in contradiction with theoretical predictions on the nature of the freezing. We also present a qualitative model which reinterprets the dipolar and quadrupolar freezings in terms of an individual and a collective processes.Associated with the Centre National de la Recherche Scientifique 相似文献
65.
A. Moudden A. M. Levelut M. Pineri 《Journal of Polymer Science.Polymer Physics》1977,15(10):1707-1719
The telechelic polybutadiene–methacrylic acid copolymer (Hycar CTB) containing 2 mole percent acid and neutralized (5–100%) by alkali ions, Na+, K+, and Cs+, has been studied by small-angle x-ray scattering. Salt groups form clusters, and the average value of the radii of gyration is approximately 8 Å; this value seems to be independent of the nature of the cation and the degree of neutralization. The existence of a low-angle maximum in the scattering intensity gives evidence of a mean distance of 80 Å between clusters in the fully neutralized sample. This distance increases slightly with a decreasing degree of neutralization. A more precise analysis of the small-angle scattering curve gives further information on the cluster structure: the ionic groups may form small bilayer disks while the polymer chains maintain a regular distance of 80 Å between the disks. 相似文献
66.
X-ray investigations on a homologous series of mesogenic azo compounds complexed with palladium (II)
A. M. Levelut M. Veber O. Francescangeli S. Melone M. Ghedini F. Neve F. P. Nicoletta R. Bartolino 《Liquid crystals》1995,19(2):241-249
The X-ray diffraction experimental data concerning a homologous series of p-alkyl-p'-alkoxy-azobenzene cyclopalladated chloro-bridged dimers, both as powder and monodomain samples, are reported. These results, compared with those obtained for the parent non-metallated materials, suggest a model for the molecular arrangement wherein the alkoxy and alkyl chains are roughly coplanar with the palladium-containing rigid core and, depending on the chain length, bent towards each other. 相似文献
67.
68.
69.
Handzy DO Bauer W Daffin FC Gaff SJ Gelbke CK Glasmacher T Gualtieri E Hannuschke S Huang MJ Kunde GJ Lacey R Li T Lisa MA Llope WJ Lynch WG Martin L Montoya CP Pak R Peaslee GF Pratt S Schwarz C Stone N Tsang MB Vander Molen AM Westfall GD Yee J Yennello SJ 《Physical review letters》1995,75(16):2916-2919
70.