变“默算”为“声算”

《中小学数学》(小学版)2004年第11期刊登了湖南省桂阳县教育局教研室刘建军老师撰写的《小学生计算出错的原因及矫正策略》，

The anti-correlation method for removing harmonic distortion in vibroseis slip-sweep data

The slip-sweep technique is one of the high-efficiency, high-fidelity, and environmental vibroseis seismic prospecting techniques which consists of a vibrator group sweeping without waiting for the previous group＇s sweep to terminate. The cycle time can be reduced drastically and hence the production efficiency can be increased significantly but harmonic distortion of one sweep will leak into the record of the other sweep. In this paper, we propose an anti-correlation method for removing harmonic distortion in vibroseis data. This method is based on decomposition of the ground force signal into fundamental and harmonic components. Then the corresponding anti-correlation operator can be computed to estimate the energy of each harmonic after correlating the vibroseis data with the corresponding harmonic component. Finally, the vibroseis harmonic noise to be removed can be obtained by subtracting the extracted harmonic noise from the traces of the previous group＇s sweep. The advantage of the proposed method is that it can process both uncorrelated and correlated vibroseis seismic data. Moreover, the algorithm is simple, stable, and computationally fast. Especially, the significant contribution of this method is a considerable reduction in the harmonic without any alteration of the desired signals. The method was tested on both synthetic and field data sets to validate the good harmonic noise suppression results.

Seismic data reconstruction based on CS and Fourier theory

Traditional seismic data sampling follows the Nyquist sampling theorem. In this paper, we introduce the theory of compressive sensing （CS）, breaking through the limitations of the traditional Nyquist sampling theorem, rendering the coherent aliases of regular undersampling into harmless incoherent random noise using random undersampling, and effectively turning the reconstruction problem into a much simpler denoising problem. We introduce the projections onto convex sets （POCS） algorithm in the data reconstruction process, apply the exponential decay threshold parameter in the iterations, and modify the traditional reconstruction process that performs forward and reverse transforms in the time and space domain. We propose a new method that uses forward and reverse transforms in the space domain. The proposed method uses less computer memory and improves computational speed. We also analyze the antinoise and anti-aliasing ability of the proposed method, and compare the 2D and 3D data reconstruction. Theoretical models and real data show that the proposed method is effective and of practical importance, as it can reconstruct missing traces and reduce the exploration cost of complex data acquisition.

Experimental studies on pillar failure characteristics based on acoustic emission location technique

Acoustic emission （AE） technique is a useful tool for investigating rock damage mechanism, and is used to study the temporal-spatial evolution process of microcracks during the similar pillar material experiment. A combined AE location algorithm was developed based on the Least square algorithm and Geiger location algorithm. The pencil break test results show that the location precision can meet the demand of microcrack monitoring. The 3D location of AE events can directly reflect the process of initiation, propagation and evolutionary of microcracks. During the loading process, stress is much likely concentrated on the area between pillar and roof of the specimen, where belongs to danger zone of macroscopic failure. When rock reaches its plastic deformation stage, AE events begin to decrease, which indicates that AE quiet period can be seen as precursor characteristic of rock failure.

NUMERICAL SIMULATION OF SUPERSONIC AXISYMMETRIC FLOW OVER MISSILE AFTERBODY WITH JET EXHAUST USING POSITIVE SCHEMES

Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the 2-D conservation laws.Comparisons between the numerical results and the experimental measurements show excellent agreements.The computed results are in good agreement with the numerical solutions obtained by using third order accurate RKDG finite element method.The results show larger gradient at discontinuous points compared with those obtained by second order accurate TVD schemes.It indicates that the presented method is efficient and reliable for solving the axisymmetric jet with external freestream flows,and shows that the method captures shocks well without numerical noise.

DIAGNOSTIC CHECKING FOR TIME SERIES MODELS USING NONPARAMETRIC APPROACH

In time series modeling, the residuals are often checked for white noise and normality. In practice, the useful tests are Ljung Box test. Mcleod Li test and Lin Mudholkar test. In this paper, we present a nonparametric approach for checking the residuals of time series models. This approach is based on the maximal correlation coefficient ρ 2 * between the residuals and time t . The basic idea is to use the bootstrap to form the null distribution of the statistic ρ 2 * under the null hypothesis H 0:ρ 2 * =0. For calculating ρ 2 * , we proposes a ρ algorithm, analogous to ACE procedure. Power study shows this approach is more powerful than Ljung Box test. Meanwhile, some numerical results and two examples are reported in this paper.

The Algorithms of Adaptive Active Noise Control Systems in a Duct

On the basis of the theory of adaptive active noise control(AANC) in a duct, this article discusses the algorithms of the adaptive control, compares the algorithm characteristics using LMS, RLS and LSL algorithms in the adaptive filter in the AANC system, derives the recursive formulas of LMS algorithm. and obtains the LMS algorithm in computer simulation using FIR and IIR filters in AANC system. By means of simulation, we compare the attenuation levels with various input signals in AANC system and discuss the effects of step factor, order of filters and sound delay on the algorithm's convergence rate and attenuation level.We also discuss the attenuation levels with sound feedback using are and IIR filters in AANC system.

Contrast-enhanced ultrasonography assessment of gastric cancer response to neoadjuvant chemotherapy

AIM:To quantitatively assess the ability of double contrast-enhanced ultrasound(DCUS) to detect tumor early response to pre-operative chemotherapy.METHODS:Forty-three patients with gastric cancer treated with neoadjuvant chemotherapy followed by curative resection between September 2011 and February 2012 were analyzed.Pre-operative chemotherapy regimens of fluorouracil + oxaliplatin or S-1 + oxaliplatin were administered in 2-4 cycles over 6-12 wk periods.All patients underwent contrast-enhanced computed tomography(CT) scan and DCUS before and after two courses of pre-operative chemotherapy.The therapeutic response was assessed by CT using the response evaluation criteria in solid tumors(RECIST 1.1) criteria.Tumor area was assessed by DCUS as enhanced appearance of gastric carcinoma due to tumor vascularity during the contrast phase as compared to the normal gastric wall.Histopathologic analysis was carried out according to the Mandard tumor regression grade criteria and used as the reference standard.Receiver operating characteristic(ROC) analysis was used to evaluate the efficacy of DCUS parameters in differentiating histopathological responders from non-responders.RESULTS:The study population consisted of 32 men and 11 women,with mean age of 59.7 ± 11.4 years.Neither age,sex,histologic type,tumor site,T stage,nor N stage was associated with pathological response.The responders had significantly smaller mean tumor size than the non-responders(15.7 ± 7.4 cm vs 33.3 ± 14.1 cm,P < 0.01).According to Mandard's criteria,27 patients were classified as responders,with 11(40.7%) showing decreased tumor size by DCUS.In contrast,only three(18.8%) of the 16 non-responders showed decreased tumor size by DCUS(P < 0.01).The area under the ROC curve was 0.64,with a 95%CI of 0.46-0.81.The effects of several cut-off points on diagnostic parameters were calculated in the ROC curve analysis.By maximizing Youden's index(sensitivity + specificity-1),the best cut-off point for distinguishing responders from non-responders was determined,which had optimal sensitivity of 62.9% and specificity of 56.3%.Using this cut-off point,the positive and negative predictive values of DCUS for distinguishing responders from non-responders were 70.8% and 47.4%,respectively.The overall accuracy of DCUS for therapeutic response assessment was 60.5%,slightly higher than the 53.5% for CT response assessment with RECIST criteria(P = 0.663).Although the advantage was not statistically significant,likely due to the small number of cases assessed.DCUS was able to identify decreased perfusion in responders who showed no morphological change by CT imaging,which can be occluded by such treatment effects as fibrosis and edema.CONCLUSION:DCUS may represent an innovative tool for more accurately predicting histopathological response to neoadjuvant chemotherapy before surgical resection in patients with locally-advanced gastric cancer.

New sigma point filtering algorithms for nonlinear stochastic systems with correlated noises

New sigma point filtering algorithms, including the unscented Kalman filter （UKF） and the divided difference filter （DDF）, are designed to solve the nonlinear filtering problem under the condition of correlated noises. Based on the minimum mean square error estimation theory, the nonlinear optimal predictive and correction recursive formulas under the hypothesis that the input noise is correlated with the measurement noise are derived and can be described in a unified framework. Then, UKF and DDF with correlated noises are proposed on the basis of approximation of the posterior mean and covariance in the unified framework by using unscented transformation and second order Stirling＇s interpolation. The proposed UKF and DDF with correlated noises break through the limitation that input noise and measurement noise must be assumed to be uneorrelated in standard UKF and DDF. Two simulation examples show the effectiveness and feasibility of new algorithms for dealing with nonlinear filtering issue with correlated noises.

Numerical Study on Flow-induced Noise for a Steam Stop-valve Using Large Eddy Simulation

The noise induced by the fluctuant saturated steam flow under 250 °C in a stop-valve was numerically studied.The simulation was carried out using computational fluid dynamics（CFD） and ACTRAN.The acoustic field was investigated with Lighthill＇s acoustic analogy based on the properties of the flow field obtained using a large-eddy simulation that employs the LES-WALE dynamic model as the sub-grid-scale model.Firstly,the validation of mesh was well conducted,illustrating that two million elements were sufficient in this situation.Secondly,the treatment of the steam was deliberated,and conclusions indicate that when predicting the flow-induced noise of the stop-valve,the steam can be treated as incompressible gas at a low inlet velocity.Thirdly,the flow-induced noises under different inlet velocities were compared.The findings reveal it has remarkable influence on the flow-induced noises.Lastly,whether or not the heat preservation of the wall has influence on the noise was taken into account.The results show that heat preservation of the wall had little influence.

Multipurpose audio watermarking algorithm

To make audio watermarking accomplish both copyright protection and content authentication with localization, a novel multipurpose audio watermarking scheme is proposed in this paper. The zero-watermarking idea is introduced into the design of robust watermarking algorithm to ensure the transparency and to avoid the interference between the robust watermark and the semi-fragile watermark. The property of natural audio that the VQ indices of DWT-DCT coefficients among neighboring frames tend to be very similar is utilized to extract essential feature from the host audio, which is then used for watermark ex-traction. And, the chaotic mapping based semi-fragile watermark is embedded in the detail wavelet coefficients based on the instantaneous mixing model of the independent component analysis (ICA) system. Both the robust and semi-fragile watermarks can be extracted blindly and the semi-fragile watermarking algorithm can localize the tampering accurately. Simulation results demonstrate the effectiveness of our algorithm in terms of transparency, security, robustness and tampering localization ability.

Endoscopic ultrasound features of gastric schwannomas with radiological correlation:A case series report

Gastric schwannomas are rare mesenchymal tumors of the gastrointestinal tract.They are usually misdiagnosed as other submucosal tumors preoperatively.Experience of the imaging features of gastric schwannomas is extremely limited.In this report,we summarize the features of a series of endoscopic ultrasound(EUS) images of gastric schwannomas in an effort to improve the diagnosis and differential diagnosis rate.We retrospectively reviewed the endosonographic features of four patients with gastric schwannomas and their computed tomography imaging results.Gastric schwannomas had heterogeneous hypoechogenicity or isoechogenicity,and a well-demarcated margin.The tumors originated from the fourth layer.Cystic changes and calcification were uncommon.Marginal hypoechoic haloes were observed in two patients.The results described here were different from those of previous studies.In the EUS evaluation,the internal echogenicity of gastric schwannomas was heterogeneous and low,but slightly higher than that of muscularis pro-pria.These features might help us differentiate gastric schwannomas from other submucosal tumors.Further investigation is needed to differentiate these mesenchymal tumors.

Thermal conductivity of dielectric nanowires with different cross-section shapes

Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, axe carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, tim thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circulax cross-section.

Ultrasonic attenuation estimation based on time-frequency analysis

The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.

SAR STEREO IMAGING ALGORITHM BASED ON CAPON SPECTRUM ESTIMATION

This letter presents a novel approach for the Synthetic Aperture Radar (SAR) stereo imaging based on the Capon spectrum estimation technique. In order to deal with nonuniform sampling space and lead to super resolution in the elevation direction, Capon approach is used to focus the SAR data on a certain height. Results obtained on simulated data demonstrate the feasibility of the Capon based algorithm. Compared with the classical Fast Fourier Transform (FFT), the Capon based algo-rithm shows better resolution quality.

Time-domain CFD computation and analysis of acoustic attenuation performance of water-filled silencers

The multi-dimensional time-domain computational fluid dynamics(CFD) approach is extended to calculate the acoustic attenuation performance of water-filled piping silencers. Transmission loss predictions from the time-domain CFD approach and the frequency-domain finite element method(FEM) agree well with each other for the dual expansion chamber silencer, straight-through and cross-flow perforated tube silencers without flow. Then, the time-domain CFD approach is used to investigate the effect of flow on the acoustic attenuation characteristics of perforated tube silencers. The numerical predictions demonstrate that the mean flow increases the transmission loss, especially at higher frequencies, and shifts the transmission loss curve to lower frequencies.

Interactive Genetic Algorithms with Fitness Adjustment

Noises widely exist in interactive genetic algorithms. However, there is no effective method to solve this problem up to now. There are two kinds of noises, one is the noise existing in visual systems and the other is resulted from user’s preference mechanisms. Characteristics of the two noises are presented aiming at the application of interac- tive genetic algorithms in dealing with images. The evolutionary phases of interactive genetic algorithms are determined according to differences in the same individual’s fitness among different generations. Models for noises in different phases are established and the corresponding strategies for reducing noises are given. The algorithm proposed in this paper has been applied to fashion design, which is a typical example of image processing. The results show that the strategies can reduce noises in interactive genetic algorithms and improve the algorithm’s performance effectively. However, a further study is needed to solve the problem of determining the evolution phase by using suitable objective methods so as to find out an effective method to decrease noises.

An Improved Underwater Acoustic Network Localization Algorithm

Underwater sensor network can achieve the unmanned environmental monitoring and military monitoring missions.Underwater acoustic sensor node cannot rely on the GPS to position itself,and the traditional indirect positioning methods used in Ad Hoc networks are not fully applicable to the localization of underwater acoustic sensor networks.In this paper,we introduce an improved underwater acoustic network localization algorithm.The algorithm processes the raw data before localization calculation to enhance the tolerance of random noise.We reduce the redundancy of the calculation results by using a more accurate basic algorithm and an adjusted calculation strategy.The improved algorithm is more suitable for the underwater acoustic sensor network positioning.

Multiple sub-array beamspace CAATI algorithm for multi-beam bathymetry system

This paper extends CAATI （Computed Angle-of-Arrival Transient Imaging） technique of Multi-angle Swath Bathymetry Sidesean Sonar （MSBSS） into Multi-Beam Bathymetry Sonar （MBBS） and presents a new Multiple Sub-array Beamspaee - CAATI （MSB-CAATI） algorithm. The method not only can achieve high resolution seafloor mapping in the whole wide swath, but also can work well in complex acoustic environments or geometries. Simulation results and processing results of sea-experiment data prove the validity and superiority of the algorithm.

Robust Digital Non-Linear Self-Interference Cancellation in Full Duplex Radios with Maximum Correntropy Criterion

Full duplex radio increases the frequency efficiency but its performance is limited by the self-interference （SI）. We first analyze the multiple noises in the full duplex radio system and model such noises as an α - stable distribution. Then we formulate a novel non-Gaussian SI problem. Under the maximum correntropy criterion （MCC）, a robust digital non-linear self-interference cancellation algorithm is proposed for the SI channel estimation. A gradient descent based algorithm is derived to search the optimal solution. Simulation results show that the proposed algorithm can achieve a smaller estimation error and a higher pseudo signal to interference plus noise ratio （PSINR） than the well-known least mean square （LMS） algorithm and least square （LS） algorithm.