气泡浓度对海洋激光雷达后向散射特性的影响

对不同浓度气泡幕水下激光雷达的后向散射特性进行了理论分析和实验研究。实验结果表明：由于水中气泡群后向散射的原因,在水下激光雷达整体后向散射信号的回波曲线上,除了水体后向散射导致的信号峰以外,还出现因气泡散射而导致的散射峰,该散射峰叠加在水体的后向散射信号峰上,其位置与水中气泡幕的位置直接相关,而其幅值则受气泡幕的浓度影响。随着气泡幕浓度的增大,其后向散射峰幅值相应增大,这一点与理论分析结果一致,而回波峰值的变化趋势则主要受水体质量的影响。     

水下运动目标激光扫描测距方法研究

相对于传统水下光电成像,水下激光扫描成像系统可以获得更远的作用距离和更好的图像质量.基于激光同步扫描技术,提出了水下运动目标的测距方法,并对测距误差进行了定量分析,为水下目标测距提供了一个新的途径.其中单探测头水下激光扫描测距方法能对合作目标进行测距,在近距离时具有较高的测距精度,双探测头水下激光扫描测距方法能对非合作...     

Polarization Properties of the Enhanced Backscattering of Light from the Fractal Aggregate of Particles

The polarized intensity enhancement of the light backscattered multiply from a fractal aggregate of particles is numerically investigated using Monte Carlo simulations. It is confirmed only for the co-polarized intensity component that an effective mean free pathlength l_D defined for a fractal medium has the same physical meaning as a mean free pathlength l for a homogeneously random medium. Furthermore, co- and crosspolarized components of the backscattering intensity enhancement decrease in accordance with θ^2.16-1.03D and θ^4-1.8D in the far-field plane and with ζ^0.93D-3.94 and ζ^1.07D-3.98 in the boundary plane between the scattering medium and the air. Therefore, the two-dimensional Fourier transform relation is satisfied only between the co-polarized intensity distributions in the far-field and the boundary planes but not the cross-polarized ones with the accuracy of the numerical simulation. Finally, we notice the applicability of the enhanced backscattering light to estimating the dimension of the absorbent fractal medium on the basis of the result that the slope of the intensity decay of the intensity peak is directly proportional to the dimension of the medium but is independent of the absorption.     

Enhancement Factor in the Light Backscattered by Fractal Aggregated Media

We investigate the phenomenon of the enhanced backscattering of light from soft sediments of fractal clusters. The clusters consist of spherical PMMA particles with the diameter of 0.4 μ, aggregated in aqueous solutions of NaCl. We found that the kinetics of aggregation, which determines the average cluster size in sediments, is controlled by the salt concentration and that the sediments are mutually self-similar media. In comparison to uniform random media, specific features for the enhancement peaks are revealed. It is found that the peak line-shape reflects the particularities of the density of scatterers in a fractal-like medium. It is shown experimentally that the enhancement factor in the light backscattered by fractal aggregated media is sensitive to the average cluster size. On this basis, we suggest a possible way to distinguish between mutually self-similar media.     

Study of the Electromagnetic Scattering from the Very Rough Fractal Sea Surface

In this paper, based on the fundamental formulae of the first-order and second-order Kirchhoff approx-imation and with consideration of the shadowing effect, the backscattering enhancement of the one-dimensional veryrough fractal sea surface with Pierson-Moskowitz spectrum is studied under the second-order Kirchhoff approximationat microwave frequency. The numerical results are compared with those of the first-order Kirchhoff approximation andintegral equation method. The dependencies of the bistatic scattering cross section and the backscattering enhancementon the incident angle, fractal dimension, and windspeed over the sea surface are analyzed in detail.     

Metal content determination in polymerization catalysts by direct methods

Metal contents in polymerization catalysts were comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) spectroscopy. Catalysts were prepared by grafting metallocene onto bare silica or onto silica chemically modified with methylaluminoxane (MAO). Catalysts were compressed as self-supporting pellets (RBS and XRF), or mounted on adhesive copper tape (XPS). The proximity of the mass of the atomic nuclei did not allow resolution by RBS of the signals corresponding to Zr and Nb, nor Si and Al in catalyst systems such as (nBuCp)₂ZrCl₂/Cp₂NbCl₂/MAO/SiO₂. On the other hand, Zr, Nb, Si and Al lines were completely resolved in an XRF spectrum. For supported metallocenes on bare silica, XPS measurement was ca. 40% higher than that obtained by RBS. Silica-supported zirconocene showed good agreement in Zr content determination by XRF and RBS.     

Investigation of copper patinas using ion beam analysis and scanning electron microscopy

Ion beam analysis (IBA) techniques were applied successfully to the investigation of non‐corroded and artificially corroded patina layers grown on copper substrates in order to explore their potential use in the study of degradation phenomena of copper and copper alloys subjected to chemical treatment and exposed to selected environmental conditions. Rutherford backscattering spectroscopy (RBS) with deuterons as projectiles and the nuclear reactions ¹⁶O(d,p)¹⁷O and ³²S(p,p′γ)³²S were applied to the investigation of the depth distribution of oxygen and sulphur in near‐surface layers of synthetic patina consisting of mineral phases corresponding to chalcanthite as well as to cuprite + chalcanthite and antlerite + brochantite + chalcanthite. Electrochemical techniques (potentiodynamic polarization and cyclic voltammetry in 0.5 M Na₂SO₄) were used for artificial acceleration and study of the corrosion processes, and scanning electron microscopy (SEM/EDS) was used for examination of the surface morphology of the samples. A patinated roof sample from the Vienna Hofburg also was investigated using the same techniques. The measurement showed that IBA can provide valuable information for the study of patina near‐surface layers of thickness up to a few micrometres and indicated that cuprite was the mineral phase primarily formed on the copper substrates and the main component of the interface between the patina layer and the metallic substrate. The investigated copper patinas looked rather heterogeneous and were characterized by high porosity. Mixed patinas exhibited considerable stability to further corrosive attack. Copyright © 2005 John Wiley & Sons, Ltd.     

Cathodoluminescence study of defects in thermal treatment of zinc titanate thin films deposited by a cosputtering process

The effects of thermal treatment of polycrystalline ZnO–TiO₂ systems on their luminescence emission and phase properties were investigated using ex situ cathodoluminescence and backscattering electron microscopy. The main features of the spectrum are a blue band at 2.75 eV for the phase of TiO and a complex visible band at 2.18 eV for the phase of ZnO, whose peak intensity depends on the annealing temperature. The spectrum intensity is dominated by the ZnO phase when annealing temperature was 720°C, which is attributed to abnormal grain growth. Competition is observed between the broad band peaked at 2.18 eV and visible band peaked at 2.75 eV as the annealing temperature changed (820°C‐920°C). The cathodoluminescence density is gradually governed by the TiO₂ phase, and the emission in polychromatic and monochromatic imaging is stronger equally at 920°C. The nucleation of the TiO₂ and ZnO grains is present in the backscattering electron images as well.     

Medium energy,heavy and inert ion irradiation of metallic thin films: studies of surface nano‐structuring and metal burrowing

In context to the ion induced surface nanostructuring of metals and their burrowing in the substrates, we report the influence of Xe and Kr ion‐irradiation on Pt:Si and Ag:Si thin films of ~5‐nm thickness. For the irradiation of thin films, several ion energies (275 and 350 keV of Kr; 450 and 700 keV of Xe) were chosen to maintain a constant ratio of the nuclear energy loss to the electronic energy loss (S_n/S_e) in Pt and Ag films (five in present studies). The ion‐fluence was varied from 1.0 × 10¹⁵ to 1.0 × 10¹⁷ ions/cm². The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images show ion beam induced systematic surface nano‐structuring of thin films. The surface nano‐structures evolve with the ion fluence. The RBS spectra show fluence dependent burrowing of Pt and Ag in Si upon the irradiation of both ion beams. At highest fluence, the depth of metal burrowing in Si for all irradiation conditions remains almost constant confirming the synergistic effect of energy losses by the ion beams. The RBS analysis also shows quite large sputtering of thin films bombarded with ion beams. The sputtering yield varied from 54% to 62% by irradiating the thin films with Xe and Kr ions of chosen energies at highest ion fluence. In the paper, we present the experimental results and discuss the ion induced surface nano‐structuring of Pt and Ag and their burrowing in Si. Copyright © 2016 John Wiley & Sons, Ltd.     

Sputtering of bismuth thin films under MeV Cu heavy ion irradiation: Experimental data and inelastic thermal spike model interpretation.

The sputtering of bismuth (Bi/Si) thin films deposited onto silicon substrates and irradiated by swift Cu^q+ heavy ions (q = +4 to +7) was investigated by varying both the ion energy over the 10 to 26‐MeV range and the ion fluence ϕ from 5.1 × 10¹³ cm⁻² to 3.4 × 10¹⁵ cm⁻². The sputtering yields were determined experimentally via the Rutherford backscattering spectrometry technique using a 2‐MeV He⁺ ion beam. The measured sputtering yields versus Cu⁷⁺ ion fluence for a fixed incident energy of 26 MeV exhibit a significant depression at very low ϕ‐values flowed by a steady‐state regime above ~1.6 × 10¹⁴ cm⁻², similarly to those previously pointed out for Bi thin films irradiated by MeV heavy ions. By fixing the incident ion fluence to a mean value of ~2.6 × 10¹⁵ cm⁻² in the upper part of the yield saturation regime, the measured sputtering yield data versus ion energy were found to increase with increasing the electronic stopping power in the Bi target material. Their comparison to theoretical predicted models is discussed. A good agreement is observed between the measured sputtering yields and the predicted ones when considering the contribution of 2 competitive processes of nuclear and electronic energy losses via, respectively, the SRIM simulation code and the inelastic thermal spike model using refined parameters of the ion slowing down with reduced thermophysical proprieties of the Bi thin films.