Intensity Moments of Hermite-Cosh-Gaussian Laser Beams

In this paper,attention is focused on the intensity moments of the Hermite-Cosh-Gaussian (HChG) laser beams from the zero-order to the fourth-order.The frequently used parameters such as the power in bucket (PIB),the beam width,the curvature radius,the far field divergence,the M2-factor,the Rayleigh length and the kurtosis are calculated in terms of the intensity moments.Figures show the influence of the mode index and the decentered parameter,which are the critical parameters of the HChG beams.Moreover,the center of the gravity of the radiation field and the symmetry are discussed along with the propagation axis.Finally,the power fraction within the beam width defined by the second moments is illustrated with numerical method.     

Hydrolysis precipitation synthesis of monodisperse α-Fe2O3 nanorods/graphene oxide nanocomposites

A nanocomposite of graphene oxide supported by monodisperse rod-like α-Fe₂O₃ nanocrystals (GO/α-Fe₂O₃ nanocomposites) has been fabricated through a simple hydrolysis precipitation route in a water–ethanol system. The nanocomposites were characterized by X-ray diffraction, Raman spectra and transmission electron microscopy, respectively. The GO/α-Fe₂O₃ nanocomposites are GO nanosheets decorated randomly by α-Fe₂O₃ nanorods with diameters in the range of 3–5 nm and lengths of 20–30 nm, while only hollow α-Fe₂O₃ microspheres constructed by the radically oriented single-crystalline nanorods are observed in the absence of GO. Compared with pure α-Fe₂O₃ nanoparticles, α-Fe₂O₃/GO nanocomposites exhibited excellent photocatalytic activity as evident from the degradation of rhodamine B in water under UV irradiation. The superior photocatalytic activity performance of α-Fe₂O₃/GO nanocomposites could be attributed to the synergetic effect between the conducting GO nanosheets and monodisperse α-Fe₂O₃ nanorods.     

The leveling of mask and wafer in proximity nanolithography using fringe pattern phase analysis

The fringe pattern phase analysis method is proposed for the leveling of mask and wafer in proximity lithography. The tilt between mask and wafer in the space is reflected in the tilted fringe pattern. The method combining the 2-D Fourier transform and 2-D Hanning window is proposed for processing the tilted fringe pattern. The offset and angle of tilt are extracted through phase analysis. Computer simulation and experiment are both performed to verify this method. The results indicate that the tilt of the mask and wafer in the space can be extracted with high accuracy through this method.     

Magnetic Resonance Imaging Segmentation via Weighted Level Set Model Based on Local Kernel Metric and Spatial Constraint

Magnetic resonance imaging (MRI) segmentation is a fundamental and significant task since it can guide subsequent clinic diagnosis and treatment. However, images are often corrupted by defects such as low-contrast, noise, intensity inhomogeneity, and so on. Therefore, a weighted level set model (WLSM) is proposed in this study to segment inhomogeneous intensity MRI destroyed by noise and weak boundaries. First, in order to segment the intertwined regions of brain tissue accurately, a weighted neighborhood information measure scheme based on local multi information and kernel function is designed. Then, the membership function of fuzzy c-means clustering is used as the spatial constraint of level set model to overcome the sensitivity of level set to initialization, and the evolution of level set function can be adaptively changed according to different tissue information. Finally, the distance regularization term in level set function is replaced by a double potential function to ensure the stability of the energy function in the evolution process. Both real and synthetic MRI images can show the effectiveness and performance of WLSM. In addition, compared with several state-of-the-art models, segmentation accuracy and Jaccard similarity coefficient obtained by WLSM are increased by 0.0586, 0.0362 and 0.1087, 0.0703, respectively.     

带有Polak程序的抽象算法模型

In this paper, we give two algorithm models with Polak's procedure for linearly constrained optimization problem and a group of sufficiant conditions on their global convergence. Using them, it is easily seen that the convergence of algorithms in [2～5] can be proved.     

Optical properties and highly efficient laser oscillation of Nd:YAG ceramics

Optical absorption, emission spectra have been measured for polycrystalline Nd-doped Y₃Al₅O₁₂ ceramics. Fluorescence lifetimes of 257.6 μs, 237.6 μs, 184.2 μs and 95.6 μs have been obtained for 0.6%, 1%, 2% and 4% neodymium-doped YAG ceramics, respectively. For the first time, highly efficient laser oscillation at 1064 nm has been obtained with this kind of ceramics. Slope efficiency of 53% has been achieved on a uncoated 4.8-mm thick 1% Nd:YAG ceramics sample. Optical to optical conversion efficiency is 47.6%. Laser oscillation has also been obtained with a 2% Nd:YAG ceramics. The optical properties and laser output results have been compared with that of Nd:YAG single crystal grown by the Czochralski method. Almost identical results have been achieved including laser experiments results. But fabrication of Nd:YAG ceramics is much easier compared to the single-crystal growth method. And also large size (now of about 400 mm diameter×5 mm is available) and high-concentration (>1%) Nd:YAG ceramics can be fabricated. The results show that this kind of Nd:YAG ceramics is a very good alternative to Nd:YAG single crystal. Received: 20 April 2000 / Published online: 16 August 2000     

Influence of NH beam bombarding energy on structural characterization and cell attachment of CNx coating

The carbon nitride (CN_x) coating with its novel properties will be excellent candidate for biomedical applications. CN_x coatings were prepared on the surface of Ti–6Al–4V by ion-beam-assisted deposition (IBAD) with different NHⁿ⁺ beam bombarding energies at low substrate temperature. The coatings were characterized by Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. The result showed that the wear-resistance of CN_x coatings was better at higher beam bombarding energy. The cell attachment tests also gave interesting results that CN_x coatings exhibited low macrophage attachment and provide desirable surface for the normal cellular growth and morphology of the fibroblasts. Structural analysis showed that NHⁿ⁺ beam bombardment at the energies of 300–400 eV could result in more nitrogen concentration and fraction of sp³CN bonds in the structure of CN_x coatings, which may be responsible for the improvement in the wear-resistance and the cell attachment.     

Ag-mediated charge transfer from electron-doped SrTiO3 to CO and NO: A first-principles study

Ag-mediated charge transfer from electron-doped SrTiO₃ to molecules CO and NO has been studied through the first-principles calculations based on density functional theory (DFT). Evaluation of Fukui functions indicates that Ag atom on SrTiO₃ (001) surface is presented as an active reduction and oxidation site. It shows that Ag prefers to mediate the charge transfer from electronically excited SrTiO₃ to target species. It illustrates that electron initially transfers from electron-doped SrTiO₃ to Ag, i.e., Ag is negatively charged. Interfacial charge transfer induces dipole moment and changes the surface work function. SrO-termination of SrTiO₃ (001) surface has weak activity to CO and NO while CO and NO can be strongly adsorbed on the negatively charged Ag atom. Negatively charged Ag donates its charge to the molecules. Charge occupies the molecule π_2p* orbital, which is responsible for the activation of the molecular bonds. Evidence that deposited metals on photocatalyst surface can efficiently separate the photogenerated electron-hole pairs has been addressed in this study.     

Study on optical gain of one-dimensional photonic crystals with active impurity

Localized fields in the defect mode of one-dimensional photonic crystals with active impurity are studied with the help of the theory of spontaneous emission from two-level atoms embedded in photonic crystals.Numerical simulations demonstrate that the enhancement of stimulated radiation, as well as the phenomena of transmissivity larger than unity and the abnormality of group velocity close to the edges of photonic band gap, are related to the negative imaginary part of the complex effective refractive index of doped layers. This means that the complex effective refractive index has a negative imaginary part, and that the impurity state with very high quality factor and great state density will occur in the photonic forbidden band if active impurity is introduced into the defect layer properly. Therefore, the spontaneous emission can be enhanced, the amplitude of stimulated emission will be very large and it occurs most probably close to the edges of photonic band gap with the fundamental reason, the group velocity close to the edges of band gap is very small or abnormal.