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991.
Structural noise is a very important limitation to the visibility of flaw echoes in ultrasonic testing and evaluation of highly scattering materials. In order to enhance the signal-to-noise ratio, different algorithms have been developed. One of these techniques is based on filtering the spectrum low band of the received echo to obtain a significant improvement of the defect visibility. Based on this idea, in this work a new time-frequency technique is presented. In this method, block-processing autoregressive techniques are used to estimate the instantaneous center frequency of the traveling wave. From this information, a time-frequency filter is designed tuned at half the estimated instantaneous center frequency. Experimental results and the comparison with the non-time-frequency filtering technique are also included, showing that the proposed method has an excellent performance on SNR enhancement. 相似文献
992.
993.
The mass spectra of a series of substituted 3-methyl-4-benzylideneamine-5-styrylisoxazoles are reported and discussed. The spectra of these isoxazoles show a characteristic fragmentation pattern different from the 5-styryl-4-nitroisoxazoles. Perhaps this is due to the presence of the Schiff base at position 4. 相似文献
994.
Nagel SB Mickelson PG Saenz AD Martinez YN Chen YC Killian TC Pellegrini P Côté R 《Physical review letters》2005,94(8):083004
We report photoassociative spectroscopy of 88Sr(2) in a magneto-optical trap operating on the 1S0-->3P1 intercombination line at 689 nm. Photoassociative transitions are driven with a laser red detuned by 600-2400 MHz from the 1S0-->1P1 atomic resonance at 461 nm. Photoassociation takes place at extremely large internuclear separation, and the photoassociative spectrum is strongly affected by relativistic retardation. A fit of the transition frequencies determines the 1P1 atomic lifetime (tau=5.22+/-0.03 ns) and resolves a discrepancy between experiment and recent theoretical calculations. 相似文献
995.
Peña V Sefrioui Z Arias D Leon C Santamaria J Martinez JL Te Velthuis SG Hoffmann A 《Physical review letters》2005,94(5):057002
We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa2Cu3O7 layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures. 相似文献
996.
Tz. Kokalova W. von Oertzen S. Torilov S. Thummerer M. Milin A. Tumino G. de Angelis E. Farnea A. Gadea D. R. Napoli Th. Kröll N. Marginean T. Martinez M. Axiotis S. M. Lenzi C. Ur P. Papka M. Rousseau 《The European Physical Journal A - Hadrons and Nuclei》2005,23(1):19-31
We have studied the emission of light unbound clusters, 8Be and 12C * (0+2), in the reactions 18O + 13C {31} Si {23} Ne + 8Be and 28Si + 24Mg {52} Fe {40} Ca + 12C * (0+2). The -ray spectra obtained in coincidence with 8Be and 12C * (0+2) emission have been studied relative to the statistical emission of two or three -particles. The angular-momentum-to-energy balance of the cluster emission is compared with that of multiple- emission. The properties of the energy spectra of the binary process and the population of the residual nuclei by cluster emission are discussed. It is observed that cluster emission carries away less excitation energy on average than the sequential emission of the individual components. 相似文献
997.
R.?A.?DiazEmail author R.?Martinez C.?E.?Sandoval 《The European Physical Journal C - Particles and Fields》2005,41(3):305-310
Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the e-
mixing is much more constrained than the others, and the decays proportional to such a vertex are usually very suppressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the Bd,s0 mesons and from
. We emphasize that although the Bd0-
mixing restricts severely the d-b mixing vertex, the upper bound for this vertex could still give a sizable contribution to the decay
with respect to the standard model contribution, from which we see that such a vertex could still play a role in the phenomenology.Received: 16 September 2004, Published online: 26 April 2005PACS:
12.60.Fr, 12.15.Mm, 12.15.Ff, 11.30.Hv 相似文献
998.
A.?G.?DiasEmail author R.?Martinez V.?Pleitez 《The European Physical Journal C - Particles and Fields》2005,39(1):101-107
Some 3-3-1 models predict the existence of a non-perturbative regime at the TeV scale. We study in these models and their supersymmetric extensions, the energy at which the non-perturbative limit and a Landau-like pole arise. An order of magnitude for the mass of the extra neutral vector boson,
, present in these models is also obtained.Received: 12 October 2004, Revised: 1 November 2004, Published online: 21 December 2004PACS:
12.60.Cn, 12.60.Jv 相似文献
999.
Sentets S Rodriguez Martinez Mdel C Vendier L Donnadieu B Huc V Lugan N Lavigne G 《Journal of the American Chemical Society》2005,127(42):14554-14555
An uncommon synergism in the concerted action of OH- and PR3 toward the simple Ru(II) complex Ru(CO)3Cl2(thf) allows a highly efficient reduction of the metal in ethanol or acetonitrile solution at 0 degrees C, with selective production of the corresponding Roper's-type Ru(0) complexes Ru(CO)2(PR3)3 in high yields within 10 min. 相似文献
1000.
Poulter AJ Zeman J Maude DK Potemski M Martinez G Riedel A Hey R Friedland KJ 《Physical review letters》2001,86(2):336-339
Magneto infrared absorption measurements have been performed in a highly doped GaAs quantum well which has been lifted off and bonded to a silicon substrate, in order to study the resonant polaron interaction. It is found that the pinning of the cyclotron energy occurs at an energy close to that of the transverse optical phonon of GaAs. This unexpected result is explained by a model taking into account the full dielectric constant of the quantum well. 相似文献