Showing papers by "Xi'an Jiaotong University published in 1994"

Phase-unwrapping algorithm for the measurement of three-dimensional object shapes.

Abstract: A new phase-unwrapping algorithm is described that uses two phase images with different precision in the unwrapping; this technique can produce an approximately correct unwrapping in the presence of discontinuities. We introduce it into the measurement of a three-dimensional object shape and also present the experimental results.

The net reproductive value and stability in matrix population models

Abstract: The net reproductive value n is defined for a general discrete linear population model with a nonnegative projection matrix. This number is shown to have the biological interpretation of the expected number of offspring per individual over its life time. The main result relates n to the population's growth rate (i.e. the dominant eigenvalue >. of the projection matrix) and shows that the stability of the extinction state (the trivial equilibrium) can be determined by whether n is less than or greater than 1. Examples are given to show that explicit algebraic formulas for n are often derivable, and hence available for both numerical and parameter studies of stability, when no such formulas for>. are available.

Comments on "Theoretical analysis of evolutionary algorithms with an infinite population size in continuous space. I. Basic properties of selection and mutation" [with reply]

Abstract: This paper aims at establishing fundamental theoretical properties for a class of "genetic algorithms" in continuous space (GACS). The algorithms employ operators such as selection, crossover, and mutation in the framework of a multidimensional Euclidean space. The paper is divided into two parts. The first part concentrates on the basic properties associated with the selection and mutation operators. Recursive formulae for the GACS in the general infinite population case are derived and their validity is rigorously proven. A convergence analysis is presented for the classical case of a quadratic cost function. It is shown how the increment of the population mean is driven by its own diversity and follows a modified Newton's search. Sufficient conditions for monotonic increase of the population mean fitness are derived for a more general class of fitness functions satisfying a Lipschitz condition. The diversification role of the crossover operator is analyzed in Part II. The treatment adds much light to the understanding of the underlying mechanism of evolution-like algorithms. >

Survival advantages of multicellular spheroids vs. monolayers of HepG2 cells in vitro.

Abstract: Mammalian cells grow in three-dimensions (3-D) in vivo. Commonly used two-dimensional (2-D) cell cultures are inadequate to recreate the biological microenvironment of tumor cells. The potentially different outcomes from 2-D and 3-D culture systems may have a significant impact on the relevance of experimental findings. The purpose of this study was to characterize the human hepatoma cell line HepG2 in 2-D and 3-D cultures. HepG2 cells in 2-D and 3-D cultures were treated with cisplatin, 5-fluorouracil, and adriamycin and were analyzed by scanning electron microscopy and transmission electron microscopy. Cell cycle progression and apoptosis were detected by flow cytometry. Inhibition of cell proliferation was quantified by MTT assay. The expression of E-cadherin, CD44v6, VEGF, KDR, endostatin, Bax, and cytochrome-c were analyzed by immunohistochemical (IHC) staining. As compared to the 2-D monolayer culture, the 3-D multicellular spheroids (MCS) of HepG2 cells featured a greater fraction of cells in G1 phase and were organized with more abundant cell-cell adhesion. In addition, cells in MCS were significantly less apoptotic in maintenance culture media and were more resistant to drug-induced apoptosis. E-cadherin, CD44v6, VEGF, KDR, endostatin, and cytochrome-c levels were increased in MCS as compared to 2-D cell cultures. In coclusion, MCS conferred differ-entiated phenotypes including increased cell-cell adhesion and G1 phase cell cycle arrest, enhanced cellular resistance to apoptosis, and upregulated angiogenic potential. Based on our data, a multicellular morphological hierarchy may sustain the growth/survival advantages of cancer cells in vivo. Therefore, a 3-D culture system should be the preferred technique for cancer biology investigation.

Asymmetric bidirectional associative memories

Abstract: Bidirectional associative memory (BAM) is a potentially promising model for heteroassociative memories. However, its applications are severely restricted to networks with logical symmetry of interconnections and pattern orthogonality or small pattern size. Although the restrictions on pattern orthogonality and pattern size can be relaxed to a certain extent, all previous efforts are at the cost of increase in connection complexity. In this paper, a new modification of the BAM is made and a new model named asymmetric bidirectional associative memory (ABAM) is proposed. This model not only can cater for the logical asymmetry of interconnections but also is capable of accommodating a larger number of non-orthogonal patterns. Furthermore, all these properties of the ABAM are achieved without increasing the connection complexity of the network. Theoretical analysis and simulation results all demonstrate that the ABAM indeed outperforms the BAM and its existing variants in all aspects of storage capacity, error-correcting capability and convergence. >

Silicon 1*2 digital optical switch using plasma dispersion

Abstract: The first silicon 1×2 digital optical waveguide switch which relies on free-carrier plasma dispersion and waveguide-vanishing effect is demonstrated. Operation is demonstrated at a wavelength of 1.3µm.

Experimental study on heat transfer and pressure drop characteristics of four types of plate fin-and-tube heat exchanger surfaces

Abstract: In this paper, air side heat transfer and pressure drop characteristics of twelve three-row plate fin-and-tube heat exchanger cores of four types of fin configurations have been experimentally investigated. The heat transfer and friction factor correlations for the twelve cores are provided in a wide range of Reynolds number. It is found that in the range of Reynolds number tested, the Nusselt number of the slotted fin surface is the largest and that of the plain plate fin is the lowest while the Nusselt numbers of two types of wavy fins are somewhere in between.

The influence of brazing conditions on joint strength in Al2O3/Al2O3 bonding

Abstract: The brazing of alumina ceramic to itself was performed using Ag57Cu38Ti5 filler alloy. The bonding was carried out in a vacuum of 7 × 10−3 Pa, and the joining conditions were at 1073, 1123, 1173, 1223, 1273 and 1323 K for 1.8ks under a pressure of 0.01 MPa, at 1123 K with a pressure of 0.01 MPa for 0, 0.3, 0.9, 1.8, 2.7 and 3.6 ks, and at 1123 K for 1.8 ks with pressures of 0, 0.01, 0.05, 0.10, 0.15, 0.20 and 0.30 MPa, to determine the effects of joining temperature, pressure and holding time on the joint strength. The joint strength was measured by shear tests. The interface microstructures and fractured surfaces after testing were observed by scanning electron microscopy (SEM). It was shown that the shear strength of Al2O3/Al2O3 joints was largely affected by the joining conditions; it first increased and then decreased with increasing joining temperature, pressure and holding time and depended mainly on the strength of interfacial reaction layer itself and the interface bonding strength between the reaction layer and the ceramic. The maximum joint strength was obtained when the reaction occurred under a suitable temperature, pressure and time, and the reaction layer thickness was about 2 μm. SEM observations revealed that there were four types of fracture and each kind corresponded to a different strength.

CuO-doped ZnCr2O-4-LiZnVO4 thick-film humidity sensor

Abstract: The crystalline structure, surface morphology and humidity-sensitive characteristics of CuO-doped Zn-Cr-2O4-LiZnVO4 thick films are investigated. The experimental results show that a humidity sensor made from the thick film exhibits a high long-term stability (<±%RH/Year), appropriated humidity sensitivity (≈103) and short response time (<10 s). It could be used as a commercial humidity sensor. In addition, a preliminary conduction mechanism and the effect of CuO on the humidity are discussed.

Selective stimulation of smaller fibers in a compound nerve trunk with single cathode by rectangular current pulses

Abstract: Electrical stimulation of unmyelinated nerve fibers is analyzed, using point sources in a simple volume conductor model and a dynamic Hodgkin-Huxley model of nerve fiber. The excitation and blocking threshold of single cathode stimulation with an indifference anode at infinity are calculated by solving difference equations with axons of different diameters. The relation between the blocking threshold and the pulsewidth of single cathode stimulation is also calculated. The results suggest a method of selectively stimulating the smaller fibers in a compound nerve trunk. Two kinds of stimulation electrodes are designed to test this method. Both of them are proven to yield results in accordance with the authors' model by the animal experiments on a toad's sciatic nerve trunk. It is possible to excite the smaller fibers without exciting the larger ones in a compound nerve trunk by properly controlling the stimulus intensity. The method is likely to be used in both physiological experiments and neural prostheses. >

Penny-shaped crack in transversely isotropic piezoelectric materials

Abstract: Using a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials, we obtain the so-called general solution in which the displacement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order. In order to analyse the mechanical-electric coupling behaviour of penny-shaped crack for above materials, another form of the general solution is obtained under cylindrical coordinate system by introducing three quasi-harmonic functions into the general equations obtained above. It is shown that both the two forms of the general solutions are complete. Furthermore, the mechanical-electric coupling behaviour of penny-shaped crack in transversely isotropic piezoelectric media is analysed under axisymmetric tensile loading case, and the crack-tip stress field and electric displacement field are obtained. The results show that the stress and the electric displacement components near the crack tip have (r−1/2) singularity.

A general solution and the application ofspace axisymmetric problem inpiezoelectric mate rial

Abstract: According to the structure feature of the governing equations of space axisymmetric problem in transversely isotropic piezoelectric material, using the method of introducing potential function one by one, in this paper we obtain the so-called general solution of displacement and electric potential function denoted by unique potential function which satisfies specific partiality equations. As an applying example of the general solution, we solve problem of semi-infinite body made of piezoelectric material, on the surface of the semi-infinite body a concentrative force is applied, and get the analytic formulations of stress and electric displacement components. The general solution provided by this paper can be used as a tool to analyse the mechanical-electrical coupling behavior of piezoelectric material which contains defects such as cavity, inclusion, penny-shape crack, and so on. The result of the solved problem can be used directly to analyse contact problems which take place between two piezoelectric bodies or piezoelectric body and elastic body.

A Chain Decomposition Algorithm for the Proof of a Property on Minimum Weight Triangulations

Abstract: In this paper, a chain decomposition algorithm is proposed and studied. Using this algorithm, we prove a property on minimum weight triangulations of points in the Euclidean plane, which shows that a special kind of line segments must be in the minimum weight triangulations and in the greedy triangulation of a given point set.

Modified effective Hamiltonian for degenerate Raman process

Abstract: A modified effective Hamiltonian for degenerate Raman interaction in the far off-resonant case is put forward to include effects of Stark shift. It is found that the modified effective Hamiltonian is more suitable in studying the system than the well known effective Hamiltonian.

Natural convection in a square enclosure with an internal isolated vertical plate

Abstract: Numerical computations were performed for the average Nusselt number at an internal vertical plate situated in a square enclosure, with the inner plate and the bounding wall of the enclosure maintained at uniform but different temperatures. Natural convection occurred in the air which occupied the enclosure space. The position of the inner vertical plate within the enclosure was varied parametrically. The plate height-cavity height ratio was 0.513. For narrow distance between the inner plate and the bounding wall the inner plate Nusselt number was enhanced. Aside from this, the plate average Nusselt number was remarkably insensitive to the plate position. The effect of the Rayleigh number on the velocity and temperature fields and local Nusselt numbers are also discussed. The agreement between the predicted flow pattern forRa=1.1×106 and the flow visualization result was reasonably good.

Orientation dependence of cyclic deformation in high purity titanium single crystals

Abstract: Cyclic deformation was studied in a series of high purity titanium single crystals with different orientations. The multiple step test method was employed in low cycle fatigue with a closed-loop electro-hydraulic servo-controlled Instron machine and cyclic stress-strain curves were obtained. The surface morphology of the fatigued specimens was observed with scanning electron microscopy, and dislocation structure was analysed with transmission electron microscopy. The results show that the cyclic responses and microstructures of titanium single crystals are sensitive to orientation. In the crystals oriented near the center of the (0001) stereographic projection, single slip and/or cross slip occur, planar dipole arrays and dislocation loops exist, and the cyclic strain hardening rate is low; whereas for crystals, in which orientations are favorable for double and multiple slip, cell structure is found and the cyclic strain hardening rate is high. Cyclic twins with different morphologies and fine structures are observed in almost all specimens, and the higher the content of twins, the higher is the strain hardening rate. Stacking faults are found in fatigued titanium especially in the region of twins in spite of the high stacking fault energy.

A new vapor-pressure equation

Abstract: A new vapor-pressure equation which has only three adjustable parameters and has a simple form is established consistent with the renormalization-group theory of critical phenomena. The equation presented here is valid over the entire range from the triple point to the critical temperature for a chemically diverse set of compounds and does an excellent job representing data. The new equation also has a great advantage over all of the previous vapor-pressure equations in that it can be used to extrapolate extraordinarily from the usual range in which data are available both to the critical point and to the triple point. Furthermore, it reflects physical properties of the substance based upon the known physical behavior. Satisfactory results are presented for 44 simple, quantum, hydrobonding, nonpolar and polar substances, refrigerants, associating compounds, and others.

Permanence of populations in a polluted environment.

Abstract: Studies of several population-toxicant models are discussed. Under the hypothesis that the exogenous input of toxicant into the environment is periodic in time, the conditions for permanence of populations are obtained.

Loading mode dependence of deformation microstructure in a high-purity titanium single crystal oriented for difficult glide

Abstract: A special high-purity titanium single crystal was prepared to study the effect of loading mode on deformation microstructure Six rectangularly sectioned specimens were cut from the same single crystal The loading axis of the specimens was parallel to the C-axis of the crystal, and the wide surface was parallel to the prism plane {10 1 &}, with the narrow surface {1 2 10} Mechanical tests were conducted within the chamber of a scanning electron microscope JSM35C using a specially designed apparatus with closed-loop computer control Five loading modes were used: monotonic tension, tension-tension fatigue, and tension-compression fatigue with three different stress amplitudes The surface appearance of the specimens was registered with SEM periodically, and the cyclic twins as well as persistent slip bands were identified using trace analysis technique The substructures of the tested specimens were examined with a transmission electron microscope on foils cut from the specimens parallel to the wide surface The dislocation structures of specimens tested in different modes were observed, and the slip systems and twinning modes for each case are discussed

The model of interaction between arc and AgMeO contact materials

Abstract: Based on switching experiments with cylindrical contacts of different diameters by high-speed camera observations and SEM micrographs, the effects of phase change, viscosity, and surface tension on erosion losses of AgMeO contact materials are analysed during arcing in the current range up to 1000 A rms. The erosion model of AgMeO is used for expressing the heat-force function during arc-electrode interaction and the liquid-solid, liquid-gas boundary corresponding to upper and lower erosion limits, respectively, for the reason that erosion is composed of two modes: evaporation and minute molten droplets losses. Furthermore, supposing the arc column is a hypothetical point heat source in middle of the gap, a new erosion mathematical model is established by finite differential method, and the results coincide well with those of experiments. >

Highway transportation comprehensive evaluation

Abstract: This paper elaborates the principle and method of comprehensive evaluation of highway transportation, deeply analyses, directed by the thought of system engineering, the highway transportation system, establishes the index system of highway transportation comprehensive evaluation. In addition, it gives, on the above basis, the methods of AHP and IDS as well as adopting the index system to evaluate comprehensively highway transportation comprehensive highway transportation system.