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 capacitancevoltage (CV) measurements of GaNbased Schottky diodes were carried out in the frequency range of 0.3～1.5MHz. Anomalous peaks and negative value of capacitance were observed in the CV plots of Au/iGaN Schottky diodes under forward bias, while neither of them was seen in the plots of Au/iAl0.45Ga0.55N Schottky diodes. Based on the parameters extracted from the currentvoltage (IV) and CV plots of GaN and Al0.45Ga0.55N Schottky diodes, the peak and negative capacitance are ascribed to the capture and loss of interface charges. These processes are greatly suppressed when there exists a huge series resistance in the diode.
Abstract:Time resolved optical properties of CdSe tetrapod nanocrystals where studied. The results show that the decays of photoluminescence (PL) intensities for tetrapods in solution and on insulating silicon substrate can be well fitted by a biexponential function. Based on the emissionenergy dependence of carrier lifetimes, the fast and slow PL decays of CdSe tetrapods are attributed to the recombination of delocalized carriers and the localized carriers in the localized states, respectively. By comparing the amplitude ratio of the fastdecay component to the slowdecay component for samples in solution with those on silicon, it is concluded that the slow PL decay is associated with the recombination of localized carriers in the surface defects of CdSe tetrapods.
Abstract:Environmental data synthesis method is one of the effective ways to solve small sample performance reliability estimation problem for complex electronic equipments. The most important part of this method is how to estimate the environmental factors. However, the existing estimation methods have the shortage of lower estimation precision and more difficulty in modeling. In view of these situations, an evaluation method for environmental factors based on circuit simulation was proposed. Firstly, the Pspice schematic of equipment (i.e. the physics modeling of equipment) was protracted. Then, the transient analysis, MonteCarlo analysis and temperature analysis of Pspice software were used to attain the performance simulation data. Thirdly, environmental factors can be acquired for discretional environment situations by combining with the related theory of accelerated performance testing. Finally, an example of steady voltage power was provided and the validity and practicability of the proposed method were confirmed.
Abstract:PbZr0.4Ti0.6O3 multilayers with 16 periods have been grown on the glass substrates coated by transparent tin oxide doped with fluorine by using chemical solution deposition, and the micro-structures and optical properties of the multilayers have been investigated. The scanning electron microscope images show that the multilayers exhibit a smooth, dense and crack-free surface morphology, and a layered structure consisting of dense and porous PbZr0.4Ti0.6O3 layers. The X-ray diffraction curves of the PbZr0.4Ti0.6O3 multilayers show a single perovskite structure. The room temperature reflectance and transmittance spectra in the wavelength range of 350-900 nm display an optical reflection-band centered at 450 nm, with a peak reflectivity of 91% and a 41 nm stop-band width, and a transmission valley at 450 nm with the same band-width as the reflection band. The minimum of the transmittance is less than 6% in the valley. This investigation is helpful to enlarge the application scale of ferroelectric multilayers.
Abstract:〗An eightway power amplifier at Kaband was designed, fabricated and measured. Measured results show that the maximum combined output power is 4.2W (continuous wave) at 26.5GHz. The power combining efficiency is higher than 60% over the interested frequency range (25.1～28.4GHz) and it can reach to 72.5% at 26.4GHz. The foundational cell of this amplifier is a double antipodal flexible substrate integrated waveguide (FSIW) including symmetrical dovetail taper transition structure. A number of dovetail tapers of these cells are stacked together and plugged along narrow wall into a couple of normal waveguides, a broadband power divider/combiner is then simply implemented with low insertion loss. The results demonstrate that this technique can be applied in broadband power combining amplifiers at millimeterwave frequencies.
Abstract:By coupling leaf with canopy radiation transfer model, a modified vegetation index was explored to extract the vegetation water content in order to monitor the vegetation water content from remote sensing data. Some vegetation indices for the vegetation leaf water content, such as NDVI, WI, NDWI, MSI, CSI and NDII, were analyzed and compared based on the hyperspectral data simulated by PROSAIL. The results show that the water content can not be estimated by NDVI, and CSI is not an ideal tool. The rest four indices WI, NDWI, NDII, and MSI can generate relatively good results with the correlation coefficients square between the estimation and real value being all about 0.76. Then, sensitivity factors were analyzed for NDWI extracting the water content, and the results show that NDWI and MCARI have a good linear relationship. This method can better remove the interference of LAI. The correlation coefficient square between the estimation and real value has been improved to 0.97, which is increased by 27% compared to the foregoing value. The estimated residual is reduced from 0.0156 to 0.00535, a reduction of 65% compared to NDWI method.
Abstract:The applications of remote sensing depend more and more on the particular futures in the spectrum of ground objects. To obtain the spectral characteristics of arid area, the spectrum of delta oasis of Wigan and Kuqa rivers located in the North of Tarim Basin were collected and studied. The spectral data of typical geotargets such as salinealkaline ground, silver sand ground, cotton ground, Tamarix, Alhagi, sparsifolia, Phragmites australis, Halostachys, caspica etc. as well as water body were acquired by the ASD Fieldspec HH spectrometer. These data were then analyzed. The method of moving average, which may depress partially the highfrequency components of the spectrum, was used to eliminate the noise in the spectrum. The spectrum technology of the derivative was implemented to remove the environmental noise and distinguish overlapped spectrum. Finally after continuum removal, spectral curves with highlighted absorption and reflection features were obtained. With these data, the spectral library of primary geosurface features for the delta oasis of Weigan and Kuqa rivers has been built up with the aid of ENVI software. It can provide services for the vegetation surveys, vegetation classification, and environmental monitoring in this area.
Abstract:A relatively simple optical method based on Seidel aberration theory was presented for the design of mechanically compensated infrared reflective zoom systems with 4 mirrors. This research includes the study of image formation rules by a single mirror, the concept of the mechanical compensation method in zoom systems, and the derivation of analytical formulae for the Seidel aberration coefficients. The advantage of this method is that it allows the designer to achieve the initial structure parameters of the optical system (radii of curvature and separations between mirrors, etc.) by solving a set of Seidel aberration coefficient functions. Two design examples of 4mirror zoom systems were given. The results show that the proposed method is feasible in the design of infrared reflective zoom systems with large zoom ratios.
Abstract:The relation between the polarization index and the liquid density can be established in term of refractive index. USB2000 spectroscopy was used to obtain the hyperspectral polarization information of brine with different concentrations, and the briny density was calculated. It is found that the optimum wavelength bands of light incident at different angles are different for brine with different concentrations. The precision of the briny density calculated in the best bands is the highest. The best bands become wider when incident angle approaches the Brewster angle, which can satisfy the demand of the present remote sensing technology. The results provide a new scientific basis for monitoring the density of water by using remote sensing technology.
Abstract:Considering hyperspectral images with multiband and large data amount, a novel fusion algorithm of hyperpsectral multiband images based on pulse coupled neural networks (PCNN) was proposed. Firstly, the original PCNN model was expanded according to the multiinput characteristics of the hyperspectral images, and a multichannel PCNN model was applied to fuse the multiple input images in a nonlinear manner. Then, the modified variable threshold exponent increasing attenuation model was proposed to improve fusion effect and reduce time complexity by analyzing the characteristics and shortage of the traditional variable threshold attenuation model. Finally, the fusion image with a certain degree of enhancement effect was obtained by the time matrix which recorded the ignition time. The experiment results show that the proposed algorithm outperforms the traditional fusion algorithms based on principle component analysis (PCA) and wavelet transform.
Abstract:The traditional hyperspectral image unmixing algorithm involves the extraction of endmember and the estimation of abundance values for each endmember. Although many models usually provide acceptable unmixing results, the bias may be great in those pixels where an unknown endmember exists. Therefore, a hyperspectral image unmixing algorithm based on support vector data description (SVDD) was proposed. First, hyperspectral image datas were classified into two parts,i.e., innerclass and outerclass. The datas in the innerclass were considered as the pixels mixed by known endmember datas entirely, and the datas in outerclass included unknown endmembers. The boundary between the two classes was considered as points mixed by known and unknown endmember datas. Then, unmixing operation was carried out. Experimental results on synthetic and real hyperspectral data demonstrate that this method reduces effectively the influence of the existing unknown endmembers on unmixing results, and unmixing component with unknown endmember can be given. The results unmixed by the proposed algorithm are hardly affected by unknown endmembers and are superior to that of direct unmixing.
Abstract:In order to investigate a fast and efficient method determining the freshness of bee pollen, visible and nearinfrared (VisNIR) reflectance spectroscopy with least squaressupport vector machines (LSSVM) was applied to determine storage period of bee pollen. The Camellia bee pollens stored for 4~50(47) days at room temperature were investigated. Spectra were collected by an ASD Fieldspec spectrometer as the input variables to build the LSSVM model. Results show that the prediction performance of LSSVM model is better than partial least square (PLS) and principal component regression (PCR). Its correlation coefficient of prediction set (rp) is 0.996, standard error of prediction (SEP) is 1.310, and root mean square error of prediction (RMSEP) is 1.308. It is concluded that VisNIR spectroscopy with LSSVM is a feasible method to determine the storage period of bee pollen. Moreover, the results for different storage periods were compared. It is shown that the storage periods between 11~50 can be well determined by LSSVM.
Abstract:〗A method to determine some physical and chemical indices of tobacco flavor and fragrance simultaneously and rapidly was established. Prediction models of four indices including refraction index, pH, relative density, and total volatile constituents were founded by using Fourier transform nearinfrared (FTNIR) spectroscopy. The effect of spectra pretreatment on models was studied. At the same time, reliability and repeatability of the predicted results of these models were evaluated. Results show that these models are applicable to different flavors and fragrances, and can predict simultaneously four indexes including refraction index, pH, relative density, and total volatile constituents. The values of RMSEP are 0.00182, 0.374, 0.00393 and 3.04, respectively. Therefore, the qualities of tobacco flavor and fragrance can be controlled rapidly without any damage by FTNIR.
Abstract:Faraday rotation induced when electromagnetic wave penetrates through ionosphere is the major source for the cross polarization in observed Stokes brightness temperature with a polarimetric microwave radiometer. Faraday rotation correction employing TEC (total electron content) data generated by IRI (international reference ionosphere) model can not meet polarization rotation correction accuracy in some low latitude regions. To improve the correction accuracy, the following two methods were used: 1.integrating Faraday rotation angle along observation path and 2.correcting Faraday rotation by using TEC data released by IGS. Analysis results show that the first method is hardly helpful to improve the correction accuracy, while the second one can improve Faraday rotation correction accuracy considerably. By using TEC data, the correction method can satisfy the correction accuracy of polarization rotation angles which a polarimetric microwave radiometer demands.
Abstract:Millimeter wave(MMW)/infrared (IR) sensor is a key technology for composite guidance system of missiles. Aimming to solve the problems that there were linear errors in the algorithm of squareroot unscented Kalman filter (SRUKF) and it was difficult to obtain the importance density function for the algorithm of particle filter(PF), a squareroot unscented Kalman particle filter (SRUKPF) algorithm with the sequential fusion was presented by combining SRUKF with PF. The main idea of this algorithm was to calculate the state transition matrix and the error covariance matrix by SRUKF, and to construct the importance density function by the sequential fusion of particle filter. Thus, the importance density function could integrate the latest observation into system state transition density, and the proposal distribution could be more in line with the distribution of real states. To demonstrate the effectiveness of this model, simulations were carried out based on tracking algorithm for the surfacetoair missile with MMW/IR sensor.The results show that this technique can overcome the flaw that it is hard to get the optimization importance density function in the particle filter, and it can significantly improve the accuracy of state estimation for the system with multisensors.
Abstract:The spatial response matrix in all directions needs to be measured for the traditional radiometer array calibration algorithm, and the reversed image can be blurred by missing partial spatial information. To solve this problem, an improved calibration algorithm with partial spatial information missing was proposed. Experimental results for the real scene show that the image blur can be restrained effectively by the improved calibration algorithm
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335