Table of Content

20 May 2000, Volume 36 Issue 3

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π₁-finite-index Maps from 3-manifolds Covered by Torus Bundles over S^１

HUANG Hong

2000, 36(3):  342-346. 

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It is proved that any π₁-finite-index map from a closed orientable 3-manifold covered by a torus bundle over S¹ to a closed aspherical orientable irreducible 3-manifold is homotopic to a covering map, and is of non-zero degree. This verifies a special case of the conjecture that any π₁-surjective map between closed aspherical 3-manifolds having the same rank on π₁ must be of non-zero degree.

On Several Problems of Statistical Learning Theory

DUAN Zhisheng,HUANG Lin

2000, 36(3):  347-357. 

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It is proved that the UCEM property of a family of measurable functions F implies that F is totally bounded; the UCEMUP property and PAC learnability still preserve when the family of probabilities is replaced by its closure. And a concept class C is constructed to show that every PAC algorithm of C would require a super-polynomial number of samples. Finally, the learnability of a concept class C with respect to the probability measures P and its convex hull C(P) is discussed and a mistake of [1] is corrected.

Probabilistic Approach to Robust Controller Synthesis

SONG Chunlei,WANG Long,HUANG Lin

2000, 36(3):  358-364. 

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A probabilistic approach to robust controller synthesis for a class of linear and multilinear interval control system involving real parameter uncertainty is presented, it is mainly based on some important results on robust stability analysis and design as well as probabilistic ideas. Examples in the paper show that this approach is feasible and very effective.

Transient Axisymmetric Elastic Waves in Finite Orthotropic Cylindrical Shells

TIAN Jiayong,SU Xianyue

2000, 36(3):  365-372. 

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The equations of motion governing the axisymmetric elastic deformation of finite orthotropic cylindrical shells, involving the effect of transverse shear and rotational inertia, are derived. By applying the Reverberation Method, the displacement and the resultant forces of the shell in the phase space are expressed. Then the transient waves in the finite orthotropic cylindrical shell subjected to the axisymmetric impact are obtained by using inverse Laplace transforms. Furthermore, the transient solutions are decomposed to the generalized ray integrals and computed numerically.

Adaptive Grid Technique and Its Application to Shock Problems

KANG Hongwen,WANG Pengyun,XU Xiangde

2000, 36(3):  373-380. 

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Adaptive grid techniques through a variational approach are applied to two shock problems with exact solutions. More grid points are redistributed in the shock regions in response to numerical solution and thus the shock can be captured successfully. The results show the techniques have excellent qualities in improving accuracy of numerical solution and reducing CPU time.

Quasi-stationary State of Convective Boundary Layer over Heterogeneous Flat Surfaces

CAI Xuhui,CHEN Jiayi

2000, 36(3):  388-397. 

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Large-eddy simulations are carried out for the adjustment of convective boundary layer (CBL) over heterogeneous surfaces. Simulations are confined for zero mean-wind and flat terrain. Surface heat-flux is set varying in x-direction with its average to be 0.15K·ms^-1 and varying magnitude 0.05K·ms^-1. Wavelengths or scales of surface heterogeneity are less than 20km. Simulation results show that CBLs do reach a quasi-stationary state correspondent to specified surfaces, after a long enough evolution. In this transition process and after that, horizontal statistics, i.e. mean potential temperature and vertical heat-flux, show profiles little differences to those over homogeneous flat surface. Main effect of surface heterogeneity is to increase kinetic energy in CBL and the increase concentrates in the direction of surface heterogeneity. The time of CBL spent to reach its first peak of mean kinetic energy, t_c, and dimensionless kinetic energy of CBL in its stationary state, E_eq, could be two scales for the adjustment process. Results show that, qualitatively, the larger scale of surface heterogeneity, the higher value of dimensionless kinetic energy E_eqcould be reached, meanwhile the longer transition time t_c is needed.

Numrical Calculation of the Tidal Stress Field inside the Homogeneous Spherical Elastical Earth Model

WU Qingpeng

2000, 36(3):  398-404. 

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The displacement vectors caused by the tide-generating force are different for different points inside the earth, hence tidal strain and stress fields are formed inside the earth. In the study of the relations between the earthquake and the earth tide, it is necessary to know the time and space distributions of the tidal stress field inside the earth. Homogeneous spherical elastic earth model is the first approximation of the real earth in the approach to study the earth tide, this paper gives a numerical method to calculate the stress field for such an earth model.

The Transition Mechanism of the Flow Regimes and Its Control of Gas-liquid Two-phase Flow in Vertical Pipes

SUN Baojiang,YAN Dachun

2000, 36(3):  381-387. 

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It is studied that the formation mechanism of Taylor bubble and its control method in gas-liquid two-phase flow, which affects the pressure balance and mechanical driving efficiency in the flow of petroleum engineering. Experiments show that the formation of Taylor bubble in gas-liquid two-phase flow is due to the intensive congregation and amalgamation of small bubbles driven by void fraction waves and that the highly turbulent flow is able to restrain this formation. Thus, the flow regime transition may be checked by increasing the flow turbulence and controlling the disturbed frequency.

The Comparison Study of Two Turbulence Parameterization in Meso-scale Numerical Weather Forecasting

SUN Aidong,XU Yumao

2000, 36(3):  405-413. 

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The non-local turbulence parameterization, i.e., transilient theory was used in the host model MM4 to simulate the turbulent activities of the atmosphere. The control models are the standard MM4 using the Blackadar high resolution boundary scheme, the bulk boundary scheme, the KUO cumulus parameterization scheme and explicit clouds. Results of comparison indicate that although some oversea study of the transilient theory succeeded in a degree, if the transilient theory is to be used in model MM4, substantial improvement of the expression of the vertical mixing potential is necessary, or an empirical filter should be applied to ameliorate the result of forecasting. Although the location of rainfall is the same as the host model, the expression used in many researches had the tendency of over-mixing, leading to the decreasing of rainfall.

The Study of Ionospheric TEC during the Flare on Nov 22, 1998 by Means of 4 GPS Receivers over China

ZHANG Donghe,XIAO Zuo

2000, 36(3):  414-420. 

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By means of 4 dual-frequency GPS receivers over china, the TEC in the ionosphere during solar flare on Nov 22, 1998 is calculated. The results indicate that the flare, the X-ray level of which is X3.7, cause obvious TEC enhancements in the ionosphere, the largest TEC enhancement caused by the flare is about 1.25 TECU. The characteristic of this method to study such ionospheric disturbances caused by flares is analyzed. It is concluded that this method can be used to study the ionosphere disturbances caused by solar flare, and can get more ionospheric disturbances information because of the special satellite constellation.

Ultra-high Density Data Storage on A Novel All-organic Complex Thin Film

LI Jianchang,XUE Zengquan,HOU Shimin,LIU Weimin,WU Quande

2000, 36(3):  421-427. 

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A novel all-organic complex thin film, tetrathiofulvalene/m-nitrobenzylidene propanedinitrile(TTF/m-NBP), was grown by a vacuum hot-wall deposition. The film was characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. It was found that large scale single crystal TTF/m-NBP film can be obtained by this method. Atomic resolution surface images were observed both with atomic force microscope(AFM) and scanning tunneling microscope(STM). High density data storage was realized by applying voltage pulses between the STM tip and the substrate. The diameter of the small recording marks is about 1.2nm. The I-V characteristic analyses showed that the recording mechanism may be mainly due to the charge transfer between the electron donor TTF and the electron acceptor m-NBP molecules induced by the applied pulse voltage.

The Thumbnail Mechanism of Web Search Services

CUI Peng,MA Zhigang,DONG Shihai

2000, 36(3):  428-437. 

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The net citizen are not satisfied with the accuracy of the search results that the current Web search services return. The goal of this paper is to develop a machanism that can improve the usefulness of Web search services. The authors defined a new concept“thumbnail", that is an information unit in Web search services. The authors made the researches on the application of thumbnail in Web search services and developed a practical system WebThumb that supports thumbnail machanism.

Generalized Pareto Distribution and Analysis of Stock Price Returns

PAN Jiazhu,DING Meichun

2000, 36(3):  295-306. 

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Some properties of the generalized Pareto distribution are discussed. Then GP model is used to analyze the returns to Shanghai stock index, Shenzhen stock index and the stock prices of two specific companies. A quantitative indicator of extreme changes in stock index and stock price is mentioned. The estimation of Value-at-Risk is also discussed.

A Model of Attention-based Image Recognition and Its Application in Face Detection

WANG Shuguang,CHENG Minde

2000, 36(3):  307-315. 

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An attention-based image recognition model is proposed. When analyze complex visual field or pattern, visual attention mechanism is used to detect saliency features in the image and drive the fixation point to scan the saliency features sequentially. During each fixation, the local pattern at the fixation point is memorized or matched. There are two parts in the memory of a complex pattern, the memory of local patterns that constitute the complex pattern and the memory of space relations between local patterns. Corresponding to memory process, the recognition process also contains two parts, the matching of local patterns and the matching of space relations between local patterns. An object is recognized only when there are enough numbers of local patterns is matched and the space relations between these local patterns are correct. This model is used in face detection in complex background. The results shows that the model can solves the problem of invariant recognition with respect to shift, rotation and scale, and the computing is fast and robust. This model likes human's vision system and is applicable.

An Edgeworth Expansion of A Sum of Extreme Values

WANG Dongfa,CHENG Shihong

2000, 36(3):  316-330. 

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Under the condition of second order generalized regular variation,the asymptotic expansions for the distribution of the sums of extreme values are obtained.

Difference Sets in Groups of Order 4p⁴

WAN Zhaoze

2000, 36(3):  331-341. 

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Let G be a group of order 4p⁴, N be a normal subgroup of G and D be a hypothetical Menon difference set in G, by investigating the intersection numbers, some necessary conditions are gotten.