排序方式: 共有23条查询结果,搜索用时 15 毫秒
1.
R. Raschell I. -G. Marino P. P. Lottici D. Bersani A. Lorenzi A. Montenero 《Optical Materials》2004,25(4):419-423
Photorefractive gratings have been obtained with 632.8 nm writing beams in organic–inorganic SiO2-based films. The hybrid glass is prepared by a sol–gel technique, starting from organic Si precursors, and contains Disperse Red 1 (DR1), carbazole units and 2,4,7-trinitro-9-fluorenone (TNF). The photorefractive gain, which has been found unexpectedly even without poling field, has been determined through an asymmetric energy exchange by two-beam coupling measurements. The effects of the polarization of the writing beams and of a circularly polarized photoisomerizing radiation during the erasure of the grating have been interpreted in terms of an orientational contribution to the grating formation. 相似文献
2.
Hydroxy- and fluorapatite films on Ti alloy substrates: Sol-gel preparation and characterization 总被引:6,自引:0,他引:6
M. Cavalli G. Gnappi A. Montenero D. Bersani P. P. Lottici S. Kaciulis G. Mattogno M. Fini 《Journal of Materials Science》2001,36(13):3253-3260
In this paper we describe the preparation of hydroxyfluorapatite (HFA) and fluorapatite (FA) films deposited on titanium alloys by means of the dip-coating method starting from a sol-gel prepared colloidal solution. These materials are compared with hydroxyapatite (HA) films prepared via sol gel and commercial films prepared by means of plasma spray. The film characterization from the point of view of the composition and crystallinity, performed by means of XRD, FTIR and Raman Spectroscopies, has shown a good purity degree, and compositional homogeneity for the sol-gel materials, though traces of carboxy-hydroxy apatite were found. Also, the samples exhibit a good crystallinity. SEM pictures, taken on HA coating deposited via sol-gel, revealed a homogeneous surface structure and optimum features to set up a good prosthesis-tissue interface. 相似文献
3.
Lottici V. Luise M. Marselli M. Reggiannini R. 《Communications, IEEE Transactions on》2004,52(9):1532-1537
Many frequency-recovery algorithms for orthogonal frequency-division multiplexing systems are geared to recover offsets up to half the distance of the subcarriers. If the error is larger, an ambiguity of an integer number of subcarrier spacings is left. This paper develops a blind algorithm for ambiguity resolution that works effectively over frequency-selective radio channels. Simulation results show a sizable improvement over existing techniques, expecially at high signal-to-noise ratios. 相似文献
4.
In this paper, we introduce a low-complexity carrier phase estimation algorithm to be integrated into the data decoder of a turbo-coded modem employing a linear modulation. The estimator is based on a pseudo-maximum-likelihood approach and makes iterative use of soft decisions provided by the soft-in/soft-out decoders within the overall turbo-decoding scheme. In doing so, iterative decoding and carrier phase recovery go together iteration after iteration in a "soft decision-directed" mode. This allows performing reliable blind phase estimation and almost ideal coherent detection for values of the signal-to-noise ratio down to a few decibels only, and without the need to resort to narrowband phase-locked loops with large acquisition time. Performance in terms of mean estimated value, root mean-squared estimation error, and overall decoder bit-error rate as derived by simulation are also reported. 相似文献
5.
Iron-Titanium mixed oxides in powders and thin films on glass substrates have been prepared at different composition by using the sol-gel method. The thermal evolution, revealing the formation of different crystalline phases, has been followed by means of the micro-Raman spectroscopy. Pseudobrookite was the only crystalline phase found involving both iron and titanium. The differences in the thermal behavior between powders and films and the influence of iron as impurity in the crystallization process of the titania were also studied. 相似文献
6.
Raman scattering characterization of gel-derived titania glass 总被引:5,自引:0,他引:5
The preparation by the sol-gel method of bulk vitreous TiO2 is reported and its transformation both by controlled thermal treatment and by laser-induced heating in the anatase and rutile crystalline forms is studied by Raman spectroscopy. The results are compared with those existing for amorphous TiO2 thin films. The dependence of the Raman frequencies and linewidths on the incident laser power is presented and the Raman spectrum of the brookite (a third naturally occurring form of TiO2) is also reported as a comparison. 相似文献
7.
G Bisagni G Cocconi G Ceci V De Lisi B Di Blasio R Lottici R Passalacqua C Finardi 《Canadian Metallurgical Quarterly》1994,5(1):93-94
A 54-year-old woman presented a lesion on the dorsum of the right hand. Routine laboratory tests were normal or negative. Histological examination revealed mucin deposits in the reticular dermis. The lesion cleared within 1 year without any treatment but biopsy. This case does not fit the diagnostic criteria of any known cutaneous mucinoses. 相似文献
8.
Holographic diffraction gratings have been obtained in Disperse Red 1 (DR1)-doped silica and ORganically MOdified SILanes thin films (ORMOSILs), produced by tetraethylorthosilicate (TEOS) and 3-(triethoxysilyl)propyl isocyanate (ICPTEOS) as precursors for the sol–gel process. For the DR1 + TEOS film, the grating is associated to an irreversible bleaching of the dye and may be detected by a Raman micro-spectroscopy mapping. For films based on ICPTEOS, a transient phase diffraction grating is created by the photoinduced birefringence. Two characteristic relaxation times of the birefringence grating have been measured. 相似文献
9.
Iari‐Gabriel Marino Pier Paolo Lottici Carlo Razzetti Angelo Montenero Marco Rocchetti Maurizio Toselli Michele Marini Francesco Pilati 《Packaging Technology and Science》2008,21(6):329-338
Polymeric films (low‐density polyethylene and oriented polypropylene) for packaging applications coated with organic–inorganic nanocomposite hybrids have been prepared by sol‐gel process. Tetraethoxysilane and two different organic phases, polyvinyl alcohol and a diblock copolymer polyethylene‐polyethylene glycol were used as precursors. Information about the hydrolysis and polycondensation degrees was obtained by investigating the vibrational features of the coatings by means of attenuated total reflectance‐Fourier transform infrared and Raman spectroscopies. Through a new polariscopic imaging technique, the bi‐dimensional maps of the optical anisotropy of the samples, both as‐prepared and under mechanical strain, were obtained. The maps showed inhomogeneous retardation and nearly flat azimuth distributions. The anisotropy properties of the samples depended mainly on the substrates and were not influenced by the coatings, while the optical transmission was slightly better for the tetraethoxysilane‐polyvinyl alcohol sample. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
10.
Adaptive pre- and post-compensation of nonlinear distortions for high-level data Modulations 总被引:1,自引:0,他引:1
In this letter, we show how different signal processing techniques can be combined to optimize the performance of a typical wideband nonlinear satellite link with spectrally efficient high-level modulation techniques. In particular, we follow two concurrent approaches: on one side, we pursue signal optimization in the form of special amplitude and phase shift keying (APSK) constellations to reduce the effect of nonlinear distortions, while on the other, we analyze the feasibility of adaptive data predistortion (DP) at the transmitter and adaptive nonlinear equalization (NLE) at the receiver. We demonstrate that the use of such optimized constellations relieves the complexity of the nonlinearity compensation techniques, and we also show that by clever adoption of these techniques the sensitivity to nonlinear distortion of both uncoded and turbo coded quadrature amplitude modulation and APSK constellations is greatly reduced. 相似文献