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61.
Chati F Léon F Décultot D Maze G 《The Journal of the Acoustical Society of America》2011,129(4):1899-1904
This paper revisits the vanishing of the transverse component of the particle displacement vector in free surfaces of an isotropic homogeneous plate, for both symmetric and antisymmetric Lamb waves. Drawing on well-known analytical expressions from Viktorov's book [(1967) Rayleigh and Lamb Waves: Physical Theory Applications, Chap. II, pp. 67-121], two distinct frequency-thickness product expressions, in cases where this vanishing occurs, are derived: one for the symmetric modes and another for the antisymmetric modes. At these frequency-thickness products, phase and group velocities have appreciable values which are discussed herein. It appears that these velocities depend on the transverse bulk wave velocity only. This is the specific condition of the Lame? modes. Moreover, theoretical and experimental investigations of displacements in the surface of a plate in air have been carried out. The theoretical part shows that the normal and transverse displacements have, respectively, a local maximum and a local minimum in the vicinity of these frequency-thickness products. The experimental part corroborates the presence of the local maximum of the S(0) Lamb mode for various materials. 相似文献
62.
Farid Ammar Khodja Assia Benabdallah Manuel González-Burgos Luz de Teresa 《Comptes Rendus Mathematique》2014,352(5):391-396
We consider two parabolic equations coupled by a matrix A(x)=q(x)A0, where A0 is a Jordan block of order 1, and controlled by a single localized function, or by a single boundary control. The support of the coupling coefficient, q , and the control domain may be disjoint. We exhibit an explicit minimal time of null-controllability, T0(q)∈[0,+∞]. 相似文献
63.
64.
Nadine Tachon Farid Jahouh Michel Delmas Joseph H. Banoub 《Rapid communications in mass spectrometry : RCM》2011,25(18):2657-2671
We have identified compounds obtained from the SARA fractions of bitumen by using atmospheric pressure photoionization mass spectrometry and low‐energy collision tandem mass spectrometric analyses with a QqToF‐MS/MS hybrid instrument. The identified compounds were isolated from the maltene saturated oil and the aromatic fractions of the SARA components of a bitumen. The QqToF instrument had sufficient mass resolution to provide accurate molecular weight information and to enhance the tandem mass spectrometry results. The APPI‐QqToF‐MS analysis of the separated compounds showed a series of protonated molecules [M + H]+ and molecular ions [M]+? of the same mass but having different chemical structures, in the maltene saturated oil and the aromatic SARA fractions. These isobaric ions were a molecular ion [M2]+? at m/z 418.2787 and a protonated molecule [M5 + H]+ at m/z 287.1625 in the saturated oil fraction, and molecular ions [M6]+? at m/z 418.1584 and [M7]+? at m/z 287.1285 in the aromatic fraction. The identification of this series of chemical compounds was achieved by performing CID‐MS/MS analyses of the molecular ions [M]+? ([M1]+? at m/z 446. 2980, [M2]+? at m/z 418.2787, [M3]+? at m/z 360.3350 and [M4]+? at m/z 346.2095) in the saturated oil fraction and of the [M5 + H]+ ion at m/z 287.1625 also in the saturated oil fraction. The observed CID‐MS/MS fragmentation differences were explained by proposed different breakdown processes of the precursor ions. The presented tandem mass spectrometric study shows the capability of MS/MS experiments to differentiate between different classes of chemical compounds of the SARA components of bitumen and to explain the reasons for the observed mass spectrometric differences. However, greater mass resolution than that provided by the QqToF‐MS/MS instrument would be required for the analysis of the asphaltene fraction of bitumen. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
65.
The track etch rates of
10
20
Ne-ion in cellulose nitrate (LR-115) have been measured for different temperatures and the activation energy is determined.
The experimental results show that both the track etch rate and the normalized track etch rate depend on the energy loss as
well as on etching temperature. The maximum etched track length of
10
20
Ne-ion agrees with the theoretically computed range. The experimental results show that there is no sharp threshold, at least
in CN(LR-115). 相似文献
66.
67.
Virtual adjustable sources are introduced in equivalent network representation of boundary conditions. For this purpose, integral equations are to be solved simple application of analog Kirchoff’s and Ohm’s laws. These adjustable sources represent generalized trial quantities. In order to illustrate this proposed approach, equivalent network representation of lossy planar transmission lines with arbitrary metallization thickness is presented. 相似文献
68.
Daniel C. Bertolet Jung-Kuei Hsu Farid Agahi Kei May Lau 《Journal of Electronic Materials》1990,19(9):967-974
In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness
(h
c) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In0.11Ga0.89As, in which the QW layers are under biaxialcompression, and Al0.35Ga0.65As/GaAs0.82P0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature
photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed
onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall
results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra,
signifying that even layers that have exceededh
c and have undergone partial relaxation are thermodynamically stable against further dislocation propagation. 相似文献
69.
Belkacem Manser Idir Belaidi Abderrachid Hamrani Sofiane Khelladi Farid Bakir 《Comptes Rendus Mecanique》2019,347(2):141-165
A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to or . 相似文献
70.
Hossein Eshghi Ali Javid Amir Khojastehnezhad Farid Moeinpour Fatemeh F. Bamoharram Mehdi Bakavoli Masoud Mirzaei 《催化学报》2015,(3)
A novel magnetic acidic catalyst comprising Preyssler (H14[NaP5W30O110]) heteropoly acid support‐ed on silica coated nickel ferrite nanoparticles (NiFe2O4@SiO2) was prepared. The catalyst was character... 相似文献