激光散斑光强分布的阈化处理及其对功率谱的影响

给出了一种阈化处理激光散斑光强多灰度值分布（如２５６级灰度）的方法。采用此种处理方法，激光散斑的功率谱强度随空间频率的分布保持不变，而计算机存贮散斑图样所需的存贮空间可极大地减少。针对具体的圆形和环形散射屏引入的散斑图样，采取使处理前后的功率谱偏差最小的方法，找出了最佳的阈值。

平滑激光脉冲诱导的阈上离化

阈上离化(above-threshold ionization)是近年来发现的一种新现象。本文在基本态模型基础上利用非微扰理论研究了高斯型激光脉冲诱导的阈上离化,讨论了其特征光电子能谱随时间的演化。

包含自电离过程的阈上离化

多电子原子都存在自电离过程,本文研究了存在自电离时的阈上离化过程,利用一个简化模型得到了光电子谱的解析表达式。结果表明,自电离的存在使阈上离化过程更为复杂,导致许多新现象的产生。

激光场的空间非均匀性对阈上离化的影响

本文在基本态模型中计及激光场的空间非均匀性,得到了与实验相吻合的结果.

Threshold decision for instrument control system and its application in nuclear power plant

Threshold decision is an important function of nuclear instrument control system based on physical parameters threshold decision. Because the conventional decision methods lack correlation with time and conditions, by analyzing the existing methods, some optimized methods are adopted. Considering safety, those methods are improved in data processing algorithms, floating threshold with multiple values, association with specific working condition, etc. These measures im- prove the nuclear instrument control system in fault tolerance and fault diagnosis, especially, the shutdown number of nucle- ar power plant decreases.

A Method to Separate Effects of Oxide-Trapped Charge and Interface-Trapped Charge on Threshold Voltage in pMOSFETs Under Hot-Carrier Stress

A simple new method based on the measurement of charge pumping technique is proposed to separate and quantify experimentally the effects of oxide-trapped charges and interface-trapped charges on threshold voltage degradation in p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) under hot-carrier stress.Further,the experimental results verify the validness of this method.It is shown that,all three mechanisms of electron trapping effect,hole trapping effect and interface trap generation play important roles in p-channel MOSFETs degradation.It is noted that interface-trapped charge is still the dominant mechanism for hot-carrier-induced degradation in p-channel MOSFETs,while a significant contribution of oxide-trapped charge to threshold voltage is demonstrated and quantified.

Integration Interval Determination and Decision Threshold Optimization for Improved TRPC-UWB Communication Systems

Integration interval and decision threshold issues were investigated for improved transmitted reference pulse cluster （iTRPC-） ultra-wideband （UWB） systems. Our analysis shows that the bit error rate （BER） performance of iTRPC-UWB systems can be significantly improved via integration interval determination （IID） and decision threshold optimization. For this purpose, two modifications can be made at the autocorrelation receiver as follows. Firstly, the liD processing is performed for autocorrelation operation to capture multi-path energy as much as possible. Secondly, adaptive decision threshold （ADT） instead of zero decision threshold （ZDT）, is used as estimated optimal decision threshold for symbol detection. Performance of iTRPCUWB systems using liD and ADT was evaluated in realistic IEEE 802.15.4a UWB channel models and the simulation results demonstrated our theoretical analysis.

Quantitative analysis of influence of α-Al(MnFeCr)Si dispersoids on hot deformation and microstructural evolution of Al-Mg-Si alloys

The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.

An enhanced image binarization method incorporating with Monte-Carlo simulation

We proposed an enhanced image binarization method.The proposed solution incorporates Monte-Carlo simulation into the local thresholding method to address the essential issues with respect to complex background,spatially-changed illumination,and uncertainties of block size in traditional method.The proposed method first partitions the image into square blocks that reflect local characteristics of the image.After image partitioning,each block is binarized using Otsu’s thresholding method.To minimize the influence of the block size and the boundary effect,we incorporate Monte-Carlo simulation into the binarization algorithm.Iterative calculation with varying block sizes during Monte-Carlo simulation generates a probability map,which illustrates the probability of each pixel classified as foreground.By setting a probability threshold,and separating foreground and background of the source image,the final binary image can be obtained.The described method has been tested by benchmark tests.Results demonstrate that the proposed method performs well in dealing with the complex background and illumination condition.

Adaptive template filter method for image processing based on immune genetic algorithm

To preserve the original signal as much as possible and filter random noises as many as possible in image processing,a threshold optimization-based adaptive template filtering algorithm was proposed.Unlike conventional filters whose template shapes and coefficients were fixed,multi-templates were defined and the right template for each pixel could be matched adaptively based on local image characteristics in the proposed method.The superiority of this method was verified by former results concerning the matching experiment of actual image with the comparison of conventional filtering methods.The adaptive search ability of immune genetic algorithm with the elitist selection and elitist crossover(IGAE) was used to optimize threshold t of the transformation function,and then combined with wavelet transformation to estimate noise variance.Multi-experiments were performed to test the validity of IGAE.The results show that the filtered result of t obtained by IGAE is superior to that of t obtained by other methods,IGAE has a faster convergence speed and a higher computational efficiency compared with the canonical genetic algorithm with the elitism and the immune algorithm with the information entropy and elitism by multi-experiments.

A method of key positioning based on laser virtual keyboard

The paper puts forward a method of virtual keyboard key positioning based on infrared laser reflection and image processing technology. In this paper, the positioning principle is introduced first. And the experimental system is established based on image acquisition, image transformation, threshold selection and binarization processing and identification of key placement. Tested in the indoor environment, the method can achieve characters input efficiently and accurately. And the key positioning has high accuracy, validity and reliability. So the method which has a high practical value provides a good theoretical basis for design of virtual keyboard application.

Enhanced dielectric permittivity of graphite oxide/polyimide composite films

Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.

Epidemic Spread in Networks Induced by Deactivation Mechanism

We have studied the topology and epidemic spreading behaviors on the networks in which deactivation mechanism and long-rang connection are coexisted. By means of numerical simulation, we find that the clustering coefficient C and the Pearson correlation coefficient r decrease with increasing long-range connection μ and the topological state of the network changes into that of BA model at the end （when μ = 1）. For the Susceptible-Infect-Susceptible model of epidemics, the epidemic threshold can reach maximum value at μ = 0.4 and presents two different variable states around μ= 0.4.

Two-dimensional cross entropy multi-threshold image segmentation based on improved BBO algorithm

In order to improve the global search ability of biogeography-based optimization(BBO)algorithm in multi-threshold image segmentation,a multi-threshold image segmentation based on improved BBO algorithm is proposed.When using BBO algorithm to optimize threshold,firstly,the elitist selection operator is used to retain the optimal set of solutions.Secondly,a migration strategy based on fusion of good solution and pending solution is introduced to reduce premature convergence and invalid migration of traditional migration operations.Thirdly,to reduce the blindness of traditional mutation operations,a mutation operation through binary computation is created.Then,it is applied to the multi-threshold image segmentation of two-dimensional cross entropy.Finally,this method is used to segment the typical image and compared with two-dimensional multi-threshold segmentation based on particle swarm optimization algorithm and the two-dimensional multi-threshold image segmentation based on standard BBO algorithm.The experimental results show that the method has good convergence stability,it can effectively shorten the time of iteration,and the optimization performance is better than the standard BBO algorithm.

Multi-dimensional and Multi-threshold Airframe Damage Region Division Method Based on Correlation Optimization

In order to obtain the image of airframe damage region and provide the input data for aircraft intelligent maintenance,a multi-dimensional and multi-threshold airframe damage region division method based on correlation optimization is proposed.On the basis of airframe damage feature analysis,the multi-dimensional feature entropy is defined to realize the full fusion of multiple feature information of the image,and the division method is extended to multi-threshold to refine the damage division and reduce the impact of the damage adjacent region’s morphological changes on the division.Through the correlation parameter optimization algorithm,the problem of low efficiency of multi-dimensional multi-threshold division method is solved.Finally,the proposed method is compared and verified by instances of airframe damage image.The results show that compared with the traditional threshold division method,the damage region divided by the proposed method is complete and accurate,and the boundary is clear and coherent,which can effectively reduce the interference of many factors such as uneven luminance,chromaticity deviation,dirt attachment,image compression,and so on.The correlation optimization algorithm has high efficiency and stable convergence,and can meet the requirements of aircraft intelligent maintenance.

Effect of surface roughness on femtosecond laser ablation of 4H-SiC substrates

Ablation threshold is an important concept in the study of femtosecond laser micro-and nano-machining.In this paper,the ablation experiments of three kinds of surface roughness 4H-Si C substrates irradiated by femtosecond laser were carried out.The feature thresholds were systematically measured for three surface roughness Si C substrates and found in the modification and annealing regions ranging from coincidence(R_(a)=0.5 nm)to a clear demarcation(R_(a)=5.5 nm),eventually being difficult to identify the presence of the former(R_(a)=89 nm).Under multi-pulse laser irradiation,oriented ripple structures were generated in the annealing region,where deep subwavelength ripples(about 110 nm,Λ≈0.2λ)can be generated above substrates with surface roughness higher than 5.5 nm.We investigated the effect of surface roughness on the ablation morphology,ablation threshold,and periodic structures of femtosecond laser ablation of 4H-Si C substrates,while the ablation threshold was tended to decrease and stabilize with the increase of pulse number N≥500.

RADIATION EFFECT ON FLUORINATED SiO_2 FILMS

A systematic investigation of γ radiation effects in gate SiO2 as a function of thefluorine ion implantation conditions was performed. It has been found that thegeneration of interface states and oxide trapped charges in fluorinated MOSFETsdepends strongly on implantation conditions. The action of F in oxides is theconjunction of positive and negative effects. A model by forming St--F bonds tosubstitute the other strained bonds which easily become charge traps under irradiationand to relax the bond stress on St / SiOZ interface is use'd for experimental explanation.

Response of fuzzy clustering on different threshold determination algorithms in spectral change vector analysis over Western Himalaya, India

Abstract： Change detection is a standard tool to extract and analyze the earth＇s surface features from remotely sensed data. Among the different change detection techniques, change vector analysis （CVA） have an exceptional advantage of discriminating change in terms of change magnitude and vector direction from multispectral bands. The estimation of precise threshold is one of the most crucial task in CVA to separate the change pixels from unchanged pixels because overall assessment of change detection method is highly dependent on selected threshold value. In recent years, integration of fuzzy clustering and remotely sensed data have become appropriate and realistic choice for change detection applications. The novelty of the proposed model lies within use of fuzzy maximum likelihood classification （FMLC） as fuzzy clustering in CVA. The FMLC based CVA is implemented using diverse threshold determination algorithms such as double-window flexible pace search （DFPS）, interactive trial and error （T＆E）, and 3x3-pixel kernel window （PKW）. Unlike existing CVA techniques, addition of fuzzy clustering in CVA permits each pixel to have multiple class categories and offers ease in threshold determination process. In present work, the comparative analysis has highlighted the performance of FMLC based CVA overimproved SCVA both in terms of accuracy assessment and operational complexity. Among all the examined threshold searching algorithms, FMLC based CVA using DFPS algorithm is found to be the most efficient method.

Remaining useful life estimation based on Wiener degradation processes with random failure threshold

Remaining useful life(RUL) estimation based on condition monitoring data is central to condition based maintenance(CBM). In the current methods about the Wiener process based RUL estimation, the randomness of the failure threshold has not been studied thoroughly. In this work, by using the truncated normal distribution to model random failure threshold(RFT), an analytical and closed-form RUL distribution based on the current observed data was derived considering the posterior distribution of the drift parameter. Then, the Bayesian method was used to update the prior estimation of failure threshold. To solve the uncertainty of the censored in situ data of failure threshold, the expectation maximization(EM) algorithm is used to calculate the posteriori estimation of failure threshold. Numerical examples show that considering the randomness of the failure threshold and updating the prior information of RFT could improve the accuracy of real time RUL estimation.

An adaptive waveform-detection threshold joint optimization method for target tracking

The joint optimization of detection threshold and waveform parameters for target tracking which comes from the idea of cognitive radar is investigated for the modified probabilistic data association(MPDA)filter.The transmitted waveforms and detection threshold are adaptively selected to enhance the tracking performance.The modified Riccati equation is adopted to predict the error covariance which is used as the criterion function,while the optimization problem is solved through the genetic algorithm(GA).The detection probability,false alarm probability and measurement noise covariance are all considered together,which significantly improves the tracking performance of the joint detection and tracking system.Simulation results show that the proposed adaptive waveform-detection threshold joint optimization method outperforms the adaptive threshold method and the fixed parameters method,which will reduce the tracking error.The average reduction of range error between the adaptive joint method and the fixed parameters method is about 0.6 m,while that between the adaptive joint method and the adaptive threshold only method is about 0.3 m.Similar error reduction occurs for the velocity error and acceleration error.