3D modeling for effect of tool eccentricity on coupled thermal and material flow characteristics during friction stir welding

A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.

SUBSAMPLE TIME DELAY ESTIMATION BASED ON PHASE SPECTRUM OF BAND LIMITED STOCHASTIC SIGNALS

The accuracy of conventional time delay estimation （TDE） algorithms is limited by the sampling interval. A novel algorithm of subsample TDE suitable for widehand signals is presented to improve the accuracy. This algorithm applies periodogram and parabolic interpolation to the cross correlation spectrum of band limited stochastic signals, and can obtain a continuous time delay estimator. Simulations are carried out to compare the performance of the proposed algorithm with that of other subsample TDE algorithms. Results show that the proposed algorithm outperforms other algorithms and reachs the Cramer-Rao lower bound （CRLB） at a high signal- to-noise ratio. For the wideband characteristic and the randomness of the transmitting signal, the proposed algo- rithm is suitable for the low probability of intercept radars.

华南师范大学学报编辑委员会

〈正〉主任：郭宝江副主任：颜泽贤 刘伟林 赵端程委员（以姓氏笔划为序）： 邓树勋 龙庆华 关文发 许尚侠 汤在新 刘伟林 刘颂豪 吴 正 陈汉才 陈新漳 利兴民

CALCULATING ACCURATE PERIODIC MOTIONS OF HARMONICALLY FORCED PIECEWISE LINEAR OSCILLATORS

This paper presents an efficient numerical scheme for calculating the periodic motion of a harmonically forced piecewise linear oscillator very accurately. The scheme is based on the shooting technique with the traditional numerical Poincare mapping and its Jacobian replaced by the piecewise analytic ones. Thus, the scheme gets rid of the requirement of the current schemes for an assumed order of the oscillator trajectory passing through different linear regions. The numerical examples in the paper demonstrate that the new scheme, compared with the current schemes, enables one to cope with more complicated dynamics of harmonically forced piecewise linear oscillators.

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.

Periodic Boundary Value Problem for Functional Differential Equations with Impulses

Aim To investigate the periodic boundary value problem for functional differential equations with impulses. Methods The method of upper and lower solutions and the monotone iterative technique were used to establish our results. Results and Conclusion The results of the existence of maximal and minimal solutions of the periodic boundary value problem for functional differential equations with impulses are obtained.

A P.hysical Numerical Ionospheric Model and Its Simulation Results

This paper describes the construction of a one-dimensional time-dependent theoretical ionospheric model, which is based on numerical solution of continuity and momentum equations for , and NO+. The model is designed to have an option to incorporate the observational ionospheric characteristic parameters into the numerical model to indirectly determine the upper boundary condition when solving the transport equations of O+. A preliminary simulation result of the model when used to simulate the ionosphere during April 18 ~ May 10, 1998, which includes both quiet and disturbed periods, showed that the model constructed is able to reproduce the observational results reasonably well both for quiet and disturbed periods.

Asympototic Behavior of Semilinear Periodic-Parbolic Boundary Value Problem

We study a class of semilinear periodic-parabolic boundary value problem with small diffusion coefficients,give its asymptotic behavior when the diffusion cofficients go to limit zero.

Periodic Boundary Value Problems for Functional Differential Equations

The periodic boundary value problems for nonlinear functional differential equa- tions was discussed.The existence of maximal and minimal solutions was obtained when the lower and upper solutions satisfied the formal or reverse order.

An Investigation of Restarted GMRES Method by Using Flexible Starting Vectors

We discuss a variant of restarted GMRES method that allows changes of the restarting vector at each cycle of iterations.The merit of the variant is that previously generated information can be utilized to select a new starting vector,such that the occurrence of stagnation be mitigated or the convergence be accelerated.The more appealing utilization of the new method is in conjunction with a harmonic Ritz vector as the starting vector,which is discussed in detail.Numerical experiments are carried out to demonstrate that the proposed procedure can effectively mitigate the occurrence of stagnation due to the presence of small eigenvalues in modulus.

Seasonal evolution of circulation and thermal structure in the Yellow Sea

In this paper, the authors used the Princeton Ocean Model (POM) to simulate the seasonal evolu- tions of circulation and thermal structure in the Yellow Sea. The simulated circulation showed that the Yellow Sea Warm Current (YSWC) was a compensation current of monsoon-driven current, and that in winter, the YSWC became stronger with depth, and could flow across the Bohai Strait in the north. Sensitivity and control- ling tests led to the following conclusions. In winter, the direction of the Yellow Sea Coastal Current in the sur- face layer was controlled partly by tide instead of wind. In summer, a cyclonic horizontal gyre existed in the middle and eastern parts of the Yellow Sea below 10 m. The downwelling in upper layer and upwelling in lower layer were somehow similar to Hu et al. (1991) conceptual model. The calculated thermal structure showed an obvious northward extending YSWC tongue in winter, its position and coverage of the Yellow Sea Cold Water Mass in summer.

Business valuation methods selection that based on the life cycle

Based on modem financial markets becoming more and more perfect, in company stock, bonds, represented by the investment banking has permeated all aspects of life. Business valuation is the core of value management.However, companies in different stages of development have a certain stage characteristics, and therefore from the features and characteristics of the different stages of business valuation methods and the factors that affect the value of different businesses created to start, can provide investors assess the business value of new ideas.

Clinical value of cancer cells joint detection in peripheral blood plasma of thyroid cancer patients

We aimed to detect cytokeratin 19 （CK19） and polymorphic epithelial mucin 1 （MUC1） expression in peripheral blood of thyroid cancer patients, and investigate the clinical value of it as a diagnostic marker for circulating blood micrometastases. Methods： The flow cytometry （FCM） was used to detect and analyze CK19 and MUC1-expressing cells in peripheral blood of 491 thyroid cancer patients. Results： CK19 and MUC1 expression showed no statistically significant difference with gender and age in thyroid cancer patients （P 〉 0.05）, while had statistically significant difference with tumor size, lymph node stage and distant metastasis （P 〈 0.01）. The expression of CK19 and MUC1 were positively correlated （r = 0.628, P = 0.00）. Conclusion： CK19 is closely related to MUC1 expression, tumor size, extent of invasion and distant metastasis in peripheral blood of thyroid cancer patients. The circulating blood CK19 and MUC1 tests can help predict thyroid cancer micrometastases and prognosis.

Period-Doubling Cascades and Strange Attractors in Extended Duffing-Van der Pol Oscillator

The dynamical behavior of the extended Duffing-Van der Pol oscillator is investigated numerically in detail. With the aid of some numerical simulation tools such as bifurcation diagrams and Poinearé maps, the different routes to chaos and various shapes of strange attractors are observed. To characterize chaotic behavior of this oscillator system, the spectrum of Lyapunov exponent and Lyapunov dimension are also employed.

Early Development of Silvetia babingtonii(Fucales, Phaeophyceae)

Silvetia babingtonii is a potentially economic brown alga for sources of food and high-value added utilization. So far, sporeling nursery and field cultivation has not been successful. The lack of knowledge on development and life cycle of this alga hinder the development of techniques for the sporeings and cultivation. In this study, internal structure of oogonium and antherium of S. babingtonii was observed with hematoxylin and eosin staining and through microscope. Meanwhile, early development from zygotes to juvenile sporelings was studied at 20℃ under 60–100 μmol photons m-2 s-1. Zygotes germinated and divided into thallus and rhizoid cells. The larger thallus cells further divided and developed into juvenile sporelings; while the smaller rhizoid cells divided and elongated into rhizoid hairs. These findings documented the life cycle of S. babingtonii and provided fundamental knowledge for sporeling nursery in the near future.

On the Solutions of xn＋1=f（xn）/xn-1Where fis Piecewise Linear

Our goal in this paper is to examine the long-term behavior of solutions of the following difference equation xn＋1=f（xn）/xn-1 wherefis piecewise linear, and the initial values x-1 and xoare non-zero real numbers. We examine the boundedness, periodicity, and the existence of oscillatory solutions.

Diagnostic and monitoring values of circulating AFPmRNA and HS-GGT for hepatocellular carcinoma

Objective: Early finding of hepatocellular carcinoma(HCC) and monitoring of its metastasis are of the utmost importance. The objectives of this study were to investigate the values of circulating hepatoma-specific gamma-glutamyl transferase(HS-GGT) fraction and α-fetoprotein mRNA(AFP-mRNA) from peripheral blood mononuclear cells(PBMCs) in diagnosis or monitoring metastasis of HCC. Methods: Total RNA was extracted from hepatomas or PBMCs of patients, synthesized to AFP-cDNA through random primers and reverse transcriptase, amplified by using a nested PCR assay, and confirmed by sequencing. Simultaneity, the HS-GGT activities were quantitatively determined in sera of patients. The comprehensive assessments of two markers were investigated in HCC patients. Results: The amplified fragments of AFP-mRNA were identical to original designed ones(159 bp) and confirmed by sequencing. The lowest sensitivity was 2 ng/L of total RNA. The incidences of AFP-mRNA and HS-GGT were 60.4%(113 of 187) and 84.5%(158 of 187) in the HCC group, and their significantly higher(P < 0.01) than that in any of other groups. The high frequencies of HS-GGT and AFP-mRNA were 78.2% and 56.4% in the HCC patients with AFP < 50 ng/mL. All positive of AFP-mRNA was found in HCC patients with extrahepatic metastasis. No significant correlation was found between tumor size and AFP-mRNA or HS-GGT. The total incidence of combined AFP-mRNA and HS-GGT detection was 93.6 % for HCC diagnosis. Conclusion: HS-GGT and AFP-mRNA are specific markers for HCC diagnosis or differentiation, especially the former for early finding and the later for monitoring metastasis of HCC.

The Prediction Analysis of Customer Lifetime Value in Business to Business Enterprise

The measurement of customer assets value has become a significant task in the field of marketing. Although a series of achievements have been formed, the deeper research is still needed in the following aspects： how to build parameter estimation model of various variables based on the interaction among customer assets elements and how to get the scientific and available measured data. In order to solve these problems, this paper, based on the characteristics of customer relationship in Business to Business （B to B） enterprise and the analysis of the variable factors in the interactive models will systematically and practically use the seemingly unrelated regression method to construct three main parameters estimation models in the customer assets measurement model, and prove the feasibility of the model through a case study. Research results show that measurement model system constructed by this method solves the problem of interaction and germination among parameters influencing factors. At the same time, factors concentration simplifies data sources to ensure the reliability and objectivity of the data, and thus improve the accuracy and feasibility of the estimation of customer assets value.

Spatial Distribution of Return Period in China Based on b-value Obtained by Using a New Method

The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using some complete samples of the earthquakes occurred during the last two centuries (1800 - 1999). The A-value of the Gutenberg-Richter relation was estimated by using those data samples. Taking into account the fact that the b-value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposing on the whole area studied and their distribution were examined. The results show that the b values increase smoothly from 0.4 to 0.93. Furthermore, keeping the b values obtained fixed, the a value distribution was also examined. In order to display more detailed information about the seismicity, smaller cell surface (10000 km2) for the calculation of the a value has chosen. The mean return period for different magnitudes was also calculated for each small cell.