Showing papers by "Zhejiang University published in 1992"

The effect of residual glassy phase in a bioactive glass-ceramic on the formation of its surface apatite layerin vitro

Abstract: A bioactive glass containing (in wt%) SiO2 48, P2O5 9.5, Na2O 20 and CaO 22.5 was transformed into a glass-ceramic through a heat treatment. The apatite formation on the surface of this glass-ceramic was examined in a simulated physiological solution. The data from X-ray diffraction, infrared reflection spectroscopy, scanning electron microscopy together with energy-dispersive X-ray analysis and composition imaging of backscattered electrons showed that the formation of the surface apatite layer depends on the relative amount of residual glassy phase in the glass-ceramic. The apatite layer was found to formin vitro on its surface if the glass-ceramic contained a residual glassy phase in a relative proportion more than a limiting volume. It lay on a layer rich in silica. However, only, a silica-rich layer was developed within the surface region of the glass-ceramic during the interaction with solution if the glass was almost completely crystallized. It is proposed that the apatite formation on the surface of the glass-ceramic is mainly caused by its residual glass. The residual glass facilitating apatite formation is considered to provide a negatively charged surface developed during its corrosion in the surrounding solution. The negatively charged surface attracts calcium ions and creates a solution within the glass — solution interface that is highly supersaturated with respect to hydroxyapatite. This leads to the formation of apatite on the surface of the glass-ceramic.

A highly robust estimator through partially likelihood function modeling and its application in computer vision

Abstract: The authors present a highly robust estimator, known as the model fitting (MF) estimator for general regression. They explain that high robustness becomes possible through partially but completely modeling the unknown log likelihood function. The partial modeling takes place by taking the Bayesian statistical decision rule and a number of important heuristics into consideration while maximizing the log likelihood function. Applications include the automatic selection of multiple thresholds, single rigid motion estimation or multiple rigid motion segmentation, and estimation from two perspective views. It is believed that the proposed MF estimator will aid in solving many robust estimation problems that demand an estimator that is either highly robust or capable of handling contaminated Gaussian mixture models. >

Influence of organic matter and its clay complexes on metolachlor adsorption on soil

Abstract: The absorption of metolachlor, 2-chloro-6′-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide was studied on three soils of various physical and chemical properties. Adsorption isotherms conformed to the Freundlich equation. The kf values increased with increasing organic carbon content of the soils. However, variations in koc values by a factor of four were observed within three natural soils. For a given soil, the koc values remained essentially unchanged after lowering the carbon content by hydrogen peroxide oxidation. These results suggest that the contribution of organic matter to total metolachlor adsorption process is influenced by association mechanisms between organic and inorganic soil constituents. Studies with mixtures of clay and organic matter indicate that the interaction between the two soil components reduces the surfaces available for metolachlor adsorption.

Investigation of silicon wafering by wire EDM

Abstract: The new technology of silicon wafering by wire electrodischarge machining (EDM) was investigated to determine its mechanism of current-conducting and material removal. Target materials were n-type single-crystal silicon ingots with the resistivity of 7–15 cmΩ. It was found that the surface potential barrier of the semiconductors had a dominating effect on EDM cutting speed. Technological experiments were performed to determine the correlation between cutting speed and machining parameters. The machined surfaces were examined by scanning electron microscopy and X-ray energy dispersive spectrometer to test the surface finish and surface impurity. The results obtained show that the technique is effective for silicon wafering.

An experimental study of two-phase turbulent coaxial jets

Abstract: The effect of solid particles on the flow structure of axisymmetric turbulent coaxial jets has been studied A laser-Doppler anemometer was used to measure the mean and fluctuation velocities of both phases, and a Malvern laser diffraction instrument was applied to measure particle size and concentration A series of velocity ratios and particle loading ratios were investigated, and the results were analysed for the effects of these ratios on the mixing characteristic and the similarity behavior of the jet The effects of particle diameter and its distribution were also studied as well as their influence on the coaxial jet behavior

Invariants and geometric phase for systems with non-hermitian time-dependent hamiltonians

Abstract: In this paper, the Lewis-Riesenfeld invariant theory is generalized for the study of systems with non-Hermitian time-dependent Hamiltonians. It is then used to study the nonadiabatic cyclic evolution and the Aharonov-Anandan phase. It is shown that the study of noncyclic evolution can be reduced to the study of cyclic evolution. The two-level dissipative system and the classical time-dependent harmonic oscillator are discussed as illustrative examples.

The effect of sugars and growth regulators on embryoid formation and plant regeneration from barley anther culture

Abstract: The influence of carbon source and growth regulator composition in induction medium on anther culture response was investigated using spring barley genotypes. Anthers were cultured on BAC3, Ficoll-containing medium, supplemented with one of the following carbohydrates: sucrose, maltose, cellobiosc and melibiose (6 % w/v). The use of either maltose or cellobiose resulted in a significantly higher anther response, calli and/or embryoid production and green plant regeneration compared to the incubation of anthers on a medium containing sucrose. Contrary to these results, the replacement of sucrose by melibiose in BAO medium, drastically reduced the efficiency of anther culture. As an average for the three genotypes tested, the frequency of green plants per 100 anthers plated was 9- to 22-fold higher on medium supplemented with sucrose or cellobiose than on medium containing melibiose as a sole carbohydrate. Among the growth regulators tested, the combination of auxin NAA (2 mg/l) and cytokinin BAP (1 mg/1) performed much better than the employment of auxin 2,4-D combined either with zeatin riboside or BAP as cytokinins. The beneficial effect of medium supplemented with NAA and BAP was associated with better embryoid formation compared to the other growth regulator combinations tested. The hormone-free combination gave a similar anther response and production of calli as any medium supplemented with growth regulators, but the regeneration capacity of calli produced on hormone-free medium was much lower, resulting in the drastic reduction of the number of both total and green regenerants.

Weighted learning of bidirectional associative memories by global minimization

Abstract: A weighted learning algorithm for bidirectional associative memories (BAMs) by means of global minimization, where each desired pattern is weighted, is described. According to the cost function that measures the goodness of the BAM, the learning algorithm is formulated as a global minimization problem and solved by a gradient descent rule. The learning approach guarantees not only that each desired pattern is stored as a stable state, but also that the basin of attraction is constructed as large as possible around each desired pattern. The existence of the weights, the asymptotic stability of each desired pattern and its basin of attraction, and the convergence of the proposed learning algorithm are investigated in an analytic way. A large number of computer experiments are reported to demonstrate the efficiency of the learning rule. >

Multicriterion maximum entropy image reconstruction from projections

Abstract: A solution algorithm for the image reconstruction problem with three criteria, maximum entropy, minimum nonuniformity and peakedness, and least square error between the original projection data and projection due to reconstruction is presented. Theoretical results of precedence properties which are respected by all noninferior solutions are first derived. These precedence properties are then incorporated into a multiple-criteria optimization framework to improve the computational efficiency. Comparisons of the new algorithm to the MART and MENT algorithms are carried out using computer-generated noise-free and Gaussian noisy projections. Results of the computational experiment and the efficiency of the multiobjective entropy optimization algorithm (MEOA) are reported. >

Phase Separation in 12 mol% Ceria-Doped Zirconia Induced by Heat Treatment in H2 and Ar

Abstract: The phase separation in 12 mol % CeO[sub 2]-ZrO[sub 2] ceramic heat-treated in a mixture of H[sub 2] and Ar was investigated by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman scattering. After heat treatment at temperatures above 1200[degrees] C, the tetragonal solid-solution phase separated into Zr[sub 2]Ce[sub 2]O[sub 7] and the monoclinic phase. Raman scattering measurements also provided supplementary evidence for the phase separation. XPS showed that the valence change from Ce[sup 4+] to Ce[sup 3+] predominantly occurred, whereas the reduction from Zr[sup 4+] to Zr[sup 3+] took place above 1200[degrees] C. In this paper it is concluded, that in the highly reduced sample, where the valence changes from Ce[sup 4+] (Zr[sup 4+] to Ce[sup 3+] (Zr[sup 3+]), the phase separation is noticeably promoted. Below 1000[degrees] C the phase separation was suppressed because of no appreciable valence change to trigger the phase separation.

Automatic ship classification by superstructure moment invariants and two-stage classifier

Abstract: Moment invariants have been used as descriptive feature in a variety of object recognition applications. A new descriptive scheme called superstructure moment invariants is presented. The authors calculate moment invariants only for the superstructure of a ship, which are different from the general moment invariants for the entire ship. The analysis of the theory and the statistics of the experimental results shows that the classification accuracy using superstructure moment invariants for the ship is higher than that of general ones. A modified 1-NN classifier, two stage classification is presented, which reduces the time expense and has a high classification accuracy. >

Somaclonal variation in winter wheat: frequency, occurrence and inheritance

Abstract: Plants were regenerated from immature embryo cultures of 35 winter wheat genotypes. A total of 7142 R2 spike lines from 1593 R1 plants were assessed in the field for somaclonal variants of morphological traits in 1985/86, 1986/87 and 1987/88. Selected variants were studied for their possible genetic basis. Populations of R1 plants were highly variable due mainly to the physiological disturbances resulting from the in vitro processes. Overall somaclonal variation frequencies were 14.2% on the R1 plant basis and 5.3% on the R2 spike basis. Spectra of the variants were similar in the different R2 populations with predominant variants being altered negatively in plant height, maturity, awnedness, and spike and plant types. Over 90% of the variants were observed in some spike progenies of individual regenerants, while the others appeared in all spike progenies of the regenerants and in progenies of different regenerants derived from the same explant embryos. Both uniform R2 variant families and spike lines were found in addition to the segregating variants, which constituted the majority. On average, in a variant family and line, 18 and 14% of their component lines and plants varied, respectively. Inheritability was demonstrated for the variations in both segregated and uniform variant families and spike lines. Of 134 variant selections tested, about 70% was classified inhernable. Both recessive and dominant gene mutations at one, two or three loci were evident in some of the variants as suggested by segregation data.

Influence of medicinal herbs on phagocytosis by bovine neutrophils.

Abstract: Twenty-six herbal preparations made from 24 medicinal herbs, categorized as antipyretics in Chinese materia medica, were tested in vitro to determine their effects upon phagocytosis of 32P-labelled Staphylococcus aureus by neutrophils isolated from bovine blood and milk. The percentage of phagocytosis was determined after incubating (1 hour at 37 degrees C) 1.25 x 10(7) neutrophils, 1 x 10(8) 32P-labelled S. aureus and 10% skimmed milk with herbal solutions. Concentrations of herbal preparations tested were 100%, 10% and 1% (v/v). When compared with PBSS (0.01 M phosphate buffered saline solution) controls, most of the herbs at high concentrations inhibited phagocytosis while at lower concentrations phagocytosis was increased. All 26 herbal preparations significantly increased blood neutrophil activity at their proper concentrations. The most active herbs in promoting blood neutrophil phagocytosis were observed for Herba verbenae, Flos chrysanthemi, Flos lonicerae, Radix sophorae flavescentis, Herba houttuyniae, Radix isatidis, Herba patriniae, Berberini sulfatis at the lowest concentration and for Folium hibisci at the high concentration with the increased percentage of more than 40.0% in comparison with PBSS control. Of the 19 herbal preparations tested with milk neutrophils, 18 herbs greatly increased phagocytosis at suitable concentrations. The most active preparations in stimulating milk neutrophil functions included Folium hibisci, Flos chrysanthemi, Radix bupleuri, Radix stellariae, Herba houttuyniae, Herba senecionis scandentis, Caulis lonicerae and Flos lonicerae which increased phagocytosis by over 35.0%.

Synthesis and photoconductivity study of phthalocyanine polymers. III. PVK‐CuPC(NO2)2

Abstract: Cu–dinitro–diamino phthalocyanine was synthesized and converted to the diazonium salt. Polyacrylamide bonded CuPc(NO2)2 [PAA–CuPc(NO2)2] (I) was synthesized by hot polymerization of acrylamide and this diazonium salt. Polymer(I) is water soluble and contains about 7 mol % CuPc(NO2)2 rings, which are covalently bonded to PAA. Polymer(I) shows good photoconductivity, which is much better than that of the corresponding phthalocyanine monomers. By doping with iodine (I2), the photosensitivity of polymer(I) is increased, which through fluorescence analysis is explained by the fact that a charge–transfer complex (CTC) of polymer(I) with I2 is formed. The influence of interface layer (IFL) and charge–transportation material (CTM) on the photoconductivity of polymer(I) were also studied.

Thyristor switch model for power electronic circuit simulation in modified SPICE 2

Abstract: Modifications to the commercially available SPICE 2 program that allow the accurate simulation of thyristor circuits are discussed. A near-ideal switch model of a thyristor is developed using resistive components, thus eliminating the problems associated with transistor models. The simulator SPICE 2G.6 is modified and a new input format for the thyristor is implemented. Examples of simulations with the new model agree closely with theoretical and experimental investigations. >

Adsorption of CO on ordered alloy surfaces.

Abstract: The adsorption of CO on two ordered alloy surfaces, Cu{001}c(2\ifmmode\times\else\texttimes\fi{}2)-Pd and Ni{001}c(2\ifmmode\times\else\texttimes\fi{}2)-Al, has been studied by high-resolution electron-energy-loss spectroscopy. For Cu{001}c(2\ifmmode\times\else\texttimes\fi{}2)-Pd, CO molecules are bonded only in on-top positions of Pd atoms at 240 K; at 135 K, CO molecules are bonded in on-top positions of Pd atoms also for low coverage, and CO adsorbed both in on-top positions of Pd and Cu atoms for high coverage. For oxygen-contaminated Ni{001}c(2\ifmmode\times\else\texttimes\fi{}2)-Al, CO molecules are bonded in on-top positions of Ni atoms and fourfold bridge positions between two Ni and two Al atoms, and the dissociation of CO has been observed at room temperature and low temperatures. The CO-dissociation rate is proportional to the degree of oxygen contamination on the surface.

General analytic solution of dynamic response of beams with nonhomogeneity and variable cross-section

Abstract: In this paper, a new method, the step-reduction method, is proposed to investigate the dynamic response of the Bernoulli-Euler beams with arbitrary nonhomogeneity and arbitrary variable cross-section under arbitrary loads. Both free vibration and forced vibration of such beams are studied. The new method requires to discretize the space domain into a number of elements. Each element can be treated as a homogeneous one with uniform thickness. Therefore, the general analytical solution of homogeneous beams with uniform cross-section can be used in each element. Then, the general analytic solution of the whole beam in terms of initial parameters can be obtained by satisfying the physical and geometric continuity conditions at the adjacent elements. In the case of free vibration, the frequency equation in analytic form can be obtained, and in the case of forced vibration, a final solution in analytical form can also be obtained which is involved in solving a set of simultaneous algebraic equations with only two unknowns which are independent of the numbers of elements divided. The present analysis can also be extended to the study of the vibration of such beams with viscous and hysteretic damping and other kinds of beams and other structural elements with arbitrary nonhomogeneity and arbitrary variable thickness.