2016 Vol. 9, No. 5
In order to research on the influence of imaging depth on photoacoustic tomography, the multiple linear array detectors is used for detection imaging at limited-view. Both simulation and experimental results show that the reconstructed image qualities are better as the absorber is closer to the detectors. Image distortion becomes obvious when the ratio of detectors size to the imaging depth is less than 1. We also demonstrated that the image distortion can be significantly reduced by rotating the multiple linear array detectors. This study helps the design of scanning strategy and the evaluation of reconstructed images.
Aiming at the deficiency of the current image fusion process, combining with good directional sensitivity and parabolic scaling properties of Finite Discrete Shearlet Transform(FDST), a new image fusion algorithm based on FDST is proposed. Firstly, the registration multi sensing images are decomposed by FDST, and the low frequency sub-band coefficients and high frequency sub-band coefficients of different scales and directions are obtained. The fusion principle of low frequency sub-band coefficients is based on the method of combining the differences between global attribute and each pixel with region spatial frequency matching degree. As for high frequency sub-band coefficients, sum of the directional weight contrast can be adopted as the fusion rule, which combines with the relative region average gradient and relative region variance. Finally, the low frequency information and high frequency information are reconstructed to image by Finite Discrete Shearlet Inverse Transform. The results indicate that the algorithm proposed in this paper has a good subjective visual effect, and its quality indexes has been increased averagely by 0.9%、3.8%、3.1%, 2.6%、3.8%、2.9% and 1.5%、125%、59% respectively compared with other fusion algorithms, which shows that the algorithm is superior to other fusion algorithms.
In order to solve the problem of the time consuming of the super-resolution reconstruction algorithm based on dictionary learning, a method of super-resolution image reconstruction based on sparse threshold model is proposed. First of all, the over-complete dictionary couple based on the theory of joint dictionary by method of sparse threshold is obtained. And then, the sparse representation of feature block image is represented by sparse threshold OMP algorithm. Then, the initial super-resolution image is reconstructed by the high resolution dictionary. Finally, the global optimization of the initial super-resolution image is improved by the modified iterative back projection algorithm, which can improve the quality of reconstructed image. The experimental results show that the average peak signal to noise ratio(PSNR) is 30.1dB; the average structure self-similarity(SSIM) is 0.9379; the average computation time is 10.2s. This method can improve not only the speed of super-resolution reconstruction, but also the quality of reconstructed high resolution images.
Aiming at the problem of low recognition rate in the existing pedestrian re-identification algorithm using single low-level feature, a new method by fusing low-level and mid-level features is proposed, which identifies person in a coarse to fine strategy. First, the pedestrian is recognized roughly by color and texture features. Then, the human body is divided into three parts, including head, main body and leg. Head is ignored for its few useful information. A mid-level dictionary method is proposed and the dictionary is trained using patches from main body and leg, and then mid-level feature is computed for fine recognition. Fusing mid-level and low-level features can be not only discriminative but also representative. The experimental results indicate that the proposed method can increase nAUC by 6.3% compared with the existing methods, which is more robust to occlusion and background adhesion.
The polarization characters of the material are connected with its complex refractive index, roughness of the surface and the observation conditions. In order to apply polarization detection technology to achieve the target's quantitative retrieval, firstly, the polarization characters of two typical objects(a kind of green paint and quartz glass) are measured in this paper, and an analysis on the relationship between DOP and detection zenith angle is carried out. Then, considering the influence of the roughness, the refractive index and extinction coefficient are quantified inversed for the first time based on the experimental data and the PG model describing objects' polarization properties. Finally, comparison is made between the inverse result and the reference data. The result shows that the relative error of the refractive index for the quartz glass is 4.9449% and the relative error of refractive index and extinction coefficient for the green paint is 11% and 21.5589% respectively. By considering the roughness of the objects, this method can retrieve the complex refractive index more accurately and it also provides the gist for polarization detection used in quantitative inversion.
A set of processing device is designed to collect the melt particles during laser cutting zirconia ceramic. The melt particles morphology including quantity, shape, mean dimeter, standard deviation, and distribution are studied using the image processing software of Imagine-Pro Pluse(IPP). Various cutting experiments with different ceramic thicknesses(0.8mm, 1.0mm, 1.5mm and 3mm) are taken based on controlling of vapor-to-melt ratio. Results of IPP observation show that, with the ceramic thickness increased, the percentage of spherical molten particles is declined from 99.21% to 89.81%, while the cakey and dumbbell shaped molten particles are ascended from 0.79% to 7.44% and 0 to 2.75% respectively, and the mean and standard deviation of spherical melt particles diameter also are enlarged. Simultaneously, with the increasing of mean and standard deviation of spherical particle diameter, the roughness of kerf surface is deteriorated from 2.287μm to 5.946μm. The establishment of geometric model reveals the connection between the form of removal molten particles and cutting quality. The larger the percentage of spherical molten particles, the smaller the mean diameter and standard deviation, and then the better the cutting quality. The high quality cutting sheet is achieved finally.
A kind of all solid state Mid-IR laser system with high quality and high efficiency is built. Firstly, we use diode laser as the pump source, Tm3+:YAP crystal as the gain medium, to build a NIR laser with the wavelength of 1.97 μm. Secondly, we use NIR laser as the pump source, a self-made Cr2+:ZnSe single crystal as the gain medium, to build an all solid state Mid-IR laser. Finally, we test the quality and efficiency of output laser, and comparison of the theoretical output efficiency of the laser with the actual parameters is carried out. The experimental results show that light-light conversion efficiency of the all solid state Mid-IR laser is 17.2%; slope efficiency is 20%; the beam quality(M2) of the highest output at 3 W are respectively 1.7 and 1.73 in x and y direction; the Gaussian beam is circular.
The graphene oxide(GO) is synthesized by the improved Hummer method. The fluorescence quenching mechanism of graphene oxide by Fe3+(0.5, 1, 2 mmol/L) in detail is studied using the time-resolved spectrometry probe system. From the steady photoluminescence emitting spectra, the fluorescence intensity of GO decreased dramatically as the Fe3+ concentration increased. From the time-resolved fluorescence spectra and femtosecond transient absorption spectra, the dynamic decay curves have no extinctive changes for GO with different Fe3+ concentrations. It is proved that the fluorescence quenching mechanism of GO by Fe3+ is mainly ascribed to the static fluorescence quenching.
Critical components in optical devices and optical measuring systems are mainly produced through the ultra-high precision machining. Aluminium alloys have been proven to be advantageous and very commonly used in the photonics industry. This ever-increasing use and demand in optics have led to the development of newly modified grades of aluminium alloys produced by rapid solidification in the foundry process. The newer grades are characterised by the finer microstructures and can improve mechanical and physical properties. Their main inconvenience currently lies in their having a very limited machining database as there is not enough adequate research contributions on their performance in terms of machinability when diamond turned. This paper investigates the machinability of rapidly solidified aluminium RSA 905 by varying diamond cutting parameters and measuring the diamond tool wear over a cutting distance of 4 km. The machining parameters varied were cutting speed, feed rate and depth of cut. The results show that the cutting speed is the most influential parameter on the diamond tool wear. The highest tool wear of 12.2 μm was achieved at the spindle speed of 500 rpm, the feed rate of 25 mm/min and the depth of cut of 15 μm. The lowest tool wear of 2.45 μm was recorded at the spindle of 1750 rpm speed, the feed rate of 5 mm/min and the depth of cut of 5 μm. Generally, a combination of higher cutting speeds, lower feed rates and smaller depths of cut caused less diamond tool wear. Statistical analysis was performed to develop a model for the diamond tool wear. Wear maps were generated from the model to identify zones where the cutting parameters produced the least wear. The results prove the rapidly solidified aluminium is a superior alternative to traditional aluminium alloys and can also provide a reference for machinists using this material.
After thorough studies on the sensing principle, the tolerance for aberration and the spectrum quality, a simplified and integrated optical readout technology has been put forward and developed, to realize the miniaturization, integration and lightweight of the optical readout focal plane array(FPA) infrared imaging system. First, based on the thermal-mechanical effect of FPA, the working principle of optical readout FPA infrared imaging system is introduced. Secondly, in view of the large size, heavy weight and complicated structure of the conventional system, a novel optical readout system with the characteristics of high integration is presented. Then, after analyzing and discussing the aberration tolerance of optical readout infrared FPA imaging system, the optical readout system containing a special-shaped prism is simulated and designed. Finally, an optical readout infrared FPA imaging system integrated with optics, mechanics, electronics and computer technology is designed and realized. The system prototype is implemented and the experimental results indicate that the size of the optical readout infrared FPA imaging system is reduced to 175mm×83mm×105mm, on the premise of guaranteeing the image quality and sensitivity. The optical readout FPA infrared imaging system with a special-shaped prism as the core component can effectively reduce the volume, weight and power consumption of the imaging system, and promote the system's industrial application.
Taking the X-51A for example, the detectability of airship infrared detection system to hypersonic vehicle in near space is researched. Firstly, the infrared radiation models of hypersonic vehicle in near space and its background are established in different wavebands, changed with the altitude of hypersonic vehicle. After considering the effects of earth curvature, altitude of hypersonic vehicle and airship, band selectivity of the atmospheric infrared transmission and so on, the three dimensional atmospheric transmittance model of infrared transfer is built. Based on the above models, the detecting distance model of the airship infrared detection system is set up. By simulation, the infrared radiation intensities in three wavebands of hypersonic vehicle in different flight states are obtained, changed with the altitude of hypersonic vehicle, and the detectability of airship infrared detection system to hypersonic vehicle in different simulation situations are also obtained. The results show that the effective detection range of the airship infrared detection system to the hypersonic target can reach 100 kilometers. When the flight state of the hypersonic vehicle is confirmed, with the increase of the altitude of the target, the detection range of the airship infrared detection system increases first and then decrease. At the same time, compared with that in long wave band, the detection range in medium and short wave band is greater. Based on the conclusion, we propose that the deployment of the near space airship should be as far as possible in the altitude above 18km.
In order to estimate the SiC mirror surface figure under the space zero-gravity environment, extracting zero-gravity surface figure of SiC mirror by orientation reversal under ground environment was studied. Firstly, the principle of extracting zero-gravity surface figure by orientation reversal is introduced. Secondly, the effect of orientation reversal on mirror surface figure is analysed by finite element analysis software. Then, according to the flow chart, mirror surface figure of 0° and 180° conditions are tested successively, and the zero-gravity surface figure is obtained by average two measurements. The data indicate that the RMS value of the ground zero-gravity surface figure of mirror is 12.3nm, which meets the design requirement. Last, data credibility is analysed and confirmed. The obtained results indicate the mirror surface figure in the zero-gravity environment of space, which has important significance for optical fabrication and alignment of mirror.