Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:The spin polarized transport through double quantum dots embedded in one arm of an A-B ring coupled to ferromagnetic leads has been studied in this paper. The Keldysh nonequilibrium Green function method is used to calculate the total tunneling current, the spin up current, the spin down current and the spin accumulation. The magnitude of them can be modulated by adjusting the polarization, the bias voltage and the magnetic flux in parallel and antiparallel configuration. With the spin-polarization strength P increasing, the total tunneling current decreases in both parallel and antiparallel configuration, and the tunneling for spin up and spin down electrons are different in two configurations. By tuning the magnetic flux, obvious interference between the two different paths can be observed. The spin accumulation in both QDs in antiparallel configuration is also investigated, and increases with the increase of P.
Abstract:CuInS2 thin film, CuIn11S17 thin film and a mixture of both were formed on ITO glass substrates by sulfurizing Cu-In-S precursors which were electrodeposited in the electrolytes solutions with different Cu2+ concentrations. The properties of the thin films were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM) and energy dispersive spectroscopy (EDS). The experiment results indicate that while keeping the In3+ and S2O32- concentrations fixed, the concentration of Cu2+ has significant influence on the chemical composition, morphology and crystal structure of the resulting thin films. With a proper Cu2+ concentration, a single-phase polycrystalline CuInS2 thin film can be achieved with ideal stoichiometry and a suitable band gap of 1.5 eV, which will be used as the absorber layer of a thin film solar cell in further work.
Abstract:The mechanism of stripe noise was analyzed. An algorithm for eliminating stripe noise in one frame time was proposed. The algorithm obtains the extreme value of every row pixels by traversing all pixels of a frame in local window and computes noise gain and offset parameters through the succession of adjacent row pixels. By setting adaptive threshold value, eliminating the influences of image edges and system noise, we can achieve the precise gain and offset parameters and complete the eliminating algorithm for stripe noise. The experiment and theoretical analysis indicate that our algorithm can eliminate stripe noise effectively in one frame time.
Abstract:The absorption edge and IR transmission of the as-grown and annealed Cd1-xMnxTe wafer were investigated. The Cd1-xMnxTe crystal was grown by the vertical Bridgman method, from which several (111) face monocrystalline wafers with area of 30 mm×40 mm were sliced. The wafer was annealed under Cd atmosphere. The cut-off wavelength of the absorption edge obtained from the NIR transmission spectra indicates that the Mn composition within the as-grown wafer is in the range of 0.1887≤x≤0.2039, and the Mn variation is about 0.0152 and 0.0013 in the axial and radial directions of the wafer, respectively. The absorption coefficient of Cd1-xMnxTe (x=0.2) deduced from the absorption edge of the NIR transmission spectrum ranges from 2.5 to 55 cm-1. The FT-IR spectra in the wavenumber range 4000~500 cm-1 show that the IR transmittance of the as-grown wafer is in the range of 45%~55%. Annealing does not change the positions of absorption edge, which shows that the annealing treatment has no effect on the Mn composition of the wafer. IR transmittance of the annealed wafer increases to above 61% in the wavenumber range of 4000~500 cm-1, which is close to the theoretical value of 65%.
Abstract:This review gives an introduction to the discovery and fabrication of the graphene, back-gated and top-gated GFET with the possible tunable band-gap of 0~250 meV at room temperature for middle and far infrared detector application, radio frequency GFET application and other advanced high k gate oxides integration processes.
Abstract:For the thermal images obtained with scan, it happens frequently that the interframe micro-displacement in vertical direction is no longer equivalent to accurate half-pixel. An approximating recursive technique, dealing with the dislocation at different direction, is introduced to reconstruct the image with high resolution. By analyzing the error distribution caused by the approximating recursion, a sub-pixel processing algorithm to reduce the error is proposed. The algorithm uses neighboring pixel to approximate the boundary, and the statistical principle is used to minimize the error introduced by the approximation. The obtained sub-pixel image is highly similar to the original image. All the simulation results and experiment data show that the performance of the algorithm proposed in this paper is obviously better than that of over-sampling and approximating recursive reconstruction. The algorithm is simple and effective. A real time processing is easily achieved. The realization of the algorithm has great significance in improving the technological performance of scanning thermal imaging system.
Abstract:A third harmonic little-orbit gyrotron oscillator is investigated theoretically in order to develop high power and efficiency terahertz (THz) radiation sources. Mode competition with different electron-beam parameters have been investigated in a 0.52 THz third harmonic TE37 mode gyrotron oscillator, which can generate 3.7kW of RF power at resonant magnetic field 6.98T. In addition, a high magnetic compression ratio magnetron injection gun (MIG) with 65 kV/2.5 A has been developed. PIC simulation results show that the velocity ratio of electron beam is 1.24, the average beam radius in the cavity is 0.35 mm. The spread of perpendicular and parallel velocities are 6.1% and 6.6%, respectively.
Abstract:Based on in situ data in Chao Lake from October 15th 2009 to October 16th 2009, two algorithms named Gons and Simis were used to estimate phytoplankton pigment (Chlorophyll-a, Chla; Phycocyanin, PC). Results showed that both Gons and Simis algorithms can be used in waters with algae, but not in waters while algal blooms formed. For the pigment absorption at 665 nm (aph(665)), Gons can provide a better result than Simis. Simis algorithm can be used to estimate PC, while related parameters were re-calibrated. Therefore, it is necessary and significant to validate and develop the algorithms to estimate Chla and PC in Chao Lake.
Abstract:To effectively retrieve large-scale daily soil moisture, this study proposed a model-level integrated approach termed co-inversion of visible, infrared and passive microwave remote sensing data. Specifically, the MODIS data are used to derive soil moisture base, and the AMSR-E data are employed to estimate daily variation of land surface soil moisture over a large area. The soil moisture information over the large area is then estimated by integrating these two parts: base and variation. Improvements inherent in the proposed approach enable daily 1 km×1 km soil moisture estimation of the entire study area, even when some areas were covered with clouds. Verification with ground truthing data in Xinjiang, China shows that the co-inversion of thermal and passive microwave remotely sensed data can achieve better estimation of soil moisture than each single data source or model. The square correlation coefficient is 0.86 and RSME is 3.99 when the estimated soil moisture is compared with the ground truthings. The results proved that the co-inversion model outperformed either the MODIS or AMSR-E inversion of soil moisture over large areas, and can meet the needs of Xinjiang's soil moisture monitoring.
Abstract:The information quality of the IIM hyperspectral data has been assessed from the aspects of signal-to-noise ratio and comentropy for the further applications of the IIM data. As the assessment results show, the information of the IIM data has a good quality as a whole. The quality of the information at the middle bands are much better than that at both ends of the bands. Corresponding to reflectance of plagioclase and the pyroxene, the peak in the spectrum centered around 750 nm exhibits high value of SNR and comentropy. This result is of great importance for retrieving elements and minerals on the lunar surface. However, the absorption valley, centered around 930 nm, exhibits poor information quality. Although the information quality of the first nine bands has an obvious trend of rising, the noise should be reduced carefully before use because of the low quality of them as a whole. Moreover, the information quality of the first band and the last one is too poor to use.
Abstract:Infrared probes composed of different hollow fibers were designed, fabricated, and optimized. Remote measuring system using the probe was set up with a Fourier Transform Infrared Spectrometer (FTIR). The experimental results showed that the transmission efficiency reached 17.6% when tapered fiber was used as the receiving fiber in the probe. Infrared spectral features were measured for films such as polycarbonate (PC) and Poly vinylidene fluoride (PVDF), as well as liquid-phase films such as ethanol and toluene. Quantitative measurements were carried out for the mixed liquid of ethanol and toluene using the characteristic absorption peak of toluene at the wavenumber of 1605 cm-1. A number of mixed liquid with various concentration ranging from 5% to 50% were made to build the quantitative model and evaluate the effect of the measurement. The results showed that RMSEP was 3.356 and the correlation coefficient was 0.9200. The system can be used in remote sensing of spectral features for solid and liquid phase films.
Abstract:A new image reconstruction algorithm was proposed based on the TV norm minimization model. Then using the under sampling fusion information, combined with the image reconstruction algorithm, a fusion model based on compressed sensing is proposed. Numerical results show that the proposed image reconstruction method can reduce the sampling number required to some extent compared with the traditional algorithm. The proposed fusion model has good performance for many kinds of images.
Abstract:Good performance has been obtained by extending traditional image denoising algorithm from local computation model to non-local one with non-local means algorithm. For synthesis aperture radar (SAR) image, however, the similarity measured by observations and isotropic window is not robust and without direction, which is bad for capturing the structure of image. In this paper, Non-subsample Shearlet feature and directional neighborhood based non-local means algorithm are proposed. Experimental results demonstrated that the improved non-local means algorithm can not only remove the speckle, but also preserve the geometrical structure information which is essential for understanding and interpretation of SAR image.
Abstract:An unsupervised band selection algorithm for hyperspectral imagery based on maximal information is proposed in this paper. The objective of the method is to preserve the maximal information from original data in the selected bands. The bands with less information are removed one by one from the original data. K-L divergence is used to quantify the information amount and its distribution over all the dataset is considered to judge the specific band which needs to be removed. Compared with traditional methods, the proposed approach has an explicit physical meaning and its computational process is very simple. It is an unsupervised method and can perform automatically.
Abstract:In order to realize the FLIR and visual image registration effectively, an automatic registration algorithm based on sensor parameters and the refined CPD algorithm was proposed. Firstly, geometric rectification based on the attitude angle and height parameters was carried out to eliminate the rotation and scale discrepancies between the FLIR and visual images. Then the edges of visual image and rectified infrared image were extracted and a refined CPD algorithm was proposed for point set registration, the similarity transformation was adopted for fine image registration. Finally, the experiments on real FLIR data show that the proposed algorithm can realize the registration of infrared and visual images effectively and the registration precision can be around one pixel.
Abstract:Generally, most of adaptive nonuniformity correction algorithms have the ghosting artifact problem. In this paper, the cause of ghosting artifacts in Neural Network nonuniformity correction (NN-NUC) algorithm for infrared focal plane array (IRFPA) was studied. Based on the analysis, a novel algorithm for eliminating the ghosting artifact was proposed, which replaces the linear spatial average filter in the NN-NUC algorithm with the partial differential equation (PDE)-based nonlinear filter to estimate the desired image. The comparison experiment using real IRFPA infrared image shows that the proposed algorithm can effectively remove the ghosting artifact. Compared with several deghosting algorithms, the proposed algorithm converges much faster.
Abstract:An improved test method was introduced. Compared with the traditional one, it could be more precision and impersonal. Nevertheless it is easy to implement and anti-influence of fabricated process. Through the test process with the microbolometers fabricated, this test method is reliable and precision.
Abstract:We built up a transient thermal multilayer model for heating of human skin with high power millimeter waves by finite volume method (FVM) based on Pennes’ bioheat transfer equation. We analyzed the calculated results and compared them with the experimental ones. The errors were no more than 1 ℃, especially at the incident power densities of 284 and 853 mW/cm2. The computing results agreed closely with the experimental ones. The veracity and reliability of finite volume model were validated. We charted the temperature changes with depth in the energy penetration depth at different radiation intensity of steady state. It was found that the maximum temperature spot caused by millimeter wave was not on the skin surface, but at some spot in subcutaneous. The difference in temperature between these two spots could be more than 1 ℃. The effect of blood perfusion rate on the temperature of skin surface was further analyzed. The change of blood perfusion rate had little effect on the temperature of skin surface in the temperature range studied in this paper.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335