Showing papers by "Zhejiang University published in 1997"

Stochastic Averaging of Quasi-Integrable Hamiltonian Systems

Abstract: A stochastic averaging method is proposed to predict approximately the response of quasi-integrable Hamiltonian systems, i.e., multi-degree-of-freedom integrable Hamiltonian systems subject to lightly linear and (or) nonlinear dampings and weakly external and (or) parametric excitations of Gaussian white noises. According to the present method an n-dimensional averaged Fokker-Planck-Kolmogrov (FPK) equation governing the transition probability density of n action variables or n independent integrals ofmotion can be constructed in nonresonant case. In a resonant case with a resonant relations, an (n +α)-dimensional averaged FPK equation governing the transition probability density of n action variables and a combinations ofphase angles can be obtained. The procedures for obtaining the stationary solutions of the averaged FPK equations for both resonant and nonresonant cases are presented. It is pointed out that the Stratonovich stochastic averaging and the stochastic averaging of energy envelope are two special cases of the present stochastic averaging. Two examples are given to illustrate the application and validity of the proposed method.

Viscosity and Density of H2O + NaCl + CaCl2 and H2O + KCl + CaCl2 at 298.15 K

Abstract: The viscosity and density of water + sodium chloride + calcium chloride solutions and water + potassium chloride + calcium chloride solutions were measured over the entire concentration range at 298.15 K. The recently extended Jones−Dole equation still functions well for these systems up to a high concentration. It has been empirically found that when a seventh term of molarity was further added to the extended Jones−Dole equation, the viscosity for calcium chloride solutions and the mixed electrolyte solutions with larger ionic strengths could be excellently represented up to their saturated concentrations. In consideration of the large solubility of calcium chloride and furthermore of its large ionic strength and of its large viscosity−concentration coefficient, it could be supposed that the extented Jones−Dole equation in this work should fit many aqueous electrolyte solutions to their rather high concentrations or just to the saturated concentrations. In low concentrations, the calculated viscosity va...

The Topoligical Sphere Theorem for Complete Submanifolds

Abstract: A topological sphere theorem is obtained from the point of view of submanifold geometry. An important scalar is defined by the mean curvature and the squared norm of the second fundamental form of an oriented complete submanifold Mn in a space form of nonnegative sectional curvature. If the infimum of this scalar is negative, we then prove that the Ricci curvature of Mn has a positive lower bound. Making use of the Lawson–Simons formula for the nonexistence of stable k-currents, we eliminate Hk (Mn, Z) for all 1 ` k ` n − 1.We then observe that the fundamental group of Mn is trivial. It should be emphasized that our result is optimal.

Thermal conductivities of some organic solvents and their binary mixtures

Abstract: The thermal conductivity of 12 pure organic solvents, acetone, acetonitrile, acrylonitrile, carbon tetrachloride, chloroform, 1,2-dichloroethane, ethanol, ethyl acetate, heptane, tetrahydrofuran, toluene, and water, and eight binary mixtures, acetone + ethanol, acetone + ethyl acetate, ethanol + heptane, ethanol + carbon tetrachloride, ethyl acetate + ethanol, heptane + acetone, heptane + toluene, and water + ethanol, were measured by an absolute transient hot-wire method at some selected temperatures from 253.15 K to 303.15 K. A correlation previously developed was used to calculate the thermal conductivity. The agreement between the experimental and the calculated thermal conductivities is satisfactory.

Body mass index and the risk of cancers of the gastric cardia and distal stomach in Shanghai, China.

Abstract: The divergent incidence patterns of gastric cardia and distal stomach cancers suggest different etiologies. Although obesity has recently been linked to cardia cancer in Western populations, its association with distal stomach cancer remains unclear. This study examined the relation of anthropometric measurements to risk by subsites of stomach cancer in a Chinese population. We identified 1124 population-based cases of stomach cancer, ages 20-69 years, newly diagnosed between December 1988 and November 1989 in Shanghai, China. Controls (n = 1451) were randomly selected from permanent Shanghai residents and frequency-matched to cases by age and sex. Information on demographic characteristics, height and weight, diet, smoking, and other exposures was obtained by trained interviewers in person. The body mass index (BMI) was calculated as weight in kilograms divided by height in square meters and categorized into quartiles based on the distribution among controls. Odds ratios and 95% confidence intervals were estimated using logistic regression models, simultaneously adjusting for age, education, income, cigarette smoking (men only), alcohol drinking (men only), intake of total calories, and chronic gastric diseases. For gastric cardia cancer, the odds ratios among men were 1.4, 1.5, and 3.0 in the second, third, and fourth quartiles of usual BMI (P for trend, < 0.01). Among women, elevated risks also were associated with excess weight, but the gradient in risk was not smooth. Risk patterns for usual body weight, maximum BMI, and minimum BMI were similar to those found for usual BMI. For distal stomach cancer, no association with usual BMI was observed among men, but a slightly elevated risk was seen among women. Our observations in China support recent findings in Western populations that obesity contributes to the risk of gastric cardia cancer, especially among men.

Artificial neural network aided design of catalyst for propane ammoxidation

Abstract: An artificial neural network (BP network) is applied to design a VSbWSn (P, K, Cr, Mo)/SIAL catalyst for acrylonitrile synthesis via propane. The conversion of propane and selectivity of acrylonitrile can be calculated as functions of the catalyst components by the BP network to be trained. After training, the network can simulate the catalytic system very well. If one takes the conversion of propane and selectivity of acrylonitrile as the two sub-objectives, a model for this catalytic system can be given as:Max(y1=X C3 ), Max(y2=S ACN ), y= F(W,X in ), 0≤y1≤1.0, 0≤y2≤1.0. A better catalyst could be found through optimization for propane ammoxidation to acrylonitrile. The best yield of acrylonitrile is 55.0%, which is higher than those reported in the literature.

Kinetics of Simultaneous Saccharification and Lactic Acid Fermentation Processes

Abstract: After pretreatment of corn cob by dilute acid, the lignocellulosic residue was used as raw materials for the simultaneous saccharification and lactic acid fermentation (SSLF). Because of the same optimal temperature and pH requirement as well as the anaerobic condition, the lactic acid fermentation is perfectly compatible with enzymatic hydrolysis of cellulosic materials. In the SSLF processes, the final concentration of lactic acid reached 33.97g/L with a conversion ratio of 79% based on the consumed cellulose. A mathematical model is suggested to simulate the SSLF process with good agreement.

Exponential stability and analyticity of abstract linear thermoelastic systems

Abstract: This paper develops an abstract framework for analysis of linear thermoelastic systems. Linear semigroup theory is used to establish the well-posedness. Sufficient conditions for the exponential stability and analyticity of the associated semigroups for the thermoelastic systems are obtained via the frequency domain method and a contradiction argument. The results are applied to linear thermoelastic rods, beams and plates of homogeneous and nonhomogeneous material with various boundary conditions.

On the extension of the α-sialon phase area in yttrium and rare-earth doped systems

Abstract: The extension of the α-sialon phase area in Y, Yb, Dy and Nd doped sialon systems has been mapped out on the basis of element analysis of individual α-sialon grains. The α-sialon-forming area expands with decreasing size of the M ion in MxSi12−(m+n)Alm+nOnN16−n. The maximum n value, nmax is 1.0 for M = Nd and 1.2 for the other dopants. The m value varies from 1.0 in all systems studied to a value of 2.75 in the Yb-α-sialon system, indicating that the substitution of AlO units for SiN in α-sialon is more restricted than substitution of AlN for SiN. It is shown that the lattice expansion of the α-sialon phase with increasing content of M ions is due to the substitution of AlN units for SiN, while the lattice parameters are not at all or only very slightly dependent on the ionic radius of the M ion. Based on the elemental analysis of individual α-sialon grains and the lattice parameters obtained, the following empirical relation between the sizes of the a and c axes and the m and n values of the α-sialon phase was obtained: a( A ) = 7.752 + 0.036 m + 0.02 n c( A ) = 5.620 + 0.031 m + 0.04 n

Properties and applications of filled conductive polymer composites

Abstract: The electrical properties of polymers filled with different types of conducting particles are reviewed. Following a theoretical description of a general effective media (GEM) equation, the experimental conductivity–volume fraction data for thermoplastic filled with vanadium oxide particles as well as thermosetting polymer composites, are fitted to the equation. The calculated property-related parameters in the equation are discussed. The electrical conductivity of the composites is combined with an extremely large positive temperature coefficient (PTC) effect, depending on the filler type (V2O3 or carbon black), as well as on its distribution and volume fraction. Both melting and recrystallization behaviour are responsible for the PTC effect. Due to a conductive filamentary network across the medium, a localized thermal effect comes into existence, leading to self-heating of the body. This gives the composites potential application, for example, in plastic welding. Preliminary experimental results are reported. ©1997 SCI

Preparation, Characterization and Biodegradable Characteristics of Poly(D,L-lactide-co-1,3-trimethylene carbonate)

Abstract: Poly(D,L-lactide-co-1,3-trimethylene carbonate) (PLCA) has been synthesized by ring-opening polymerization of 1,3-trimethylene carbonate (CA) and D,L-lactide (LA) using stannous octoate as catalyst. The copolymers were characterized by 1H nuclear magnetic resonance (NMR), 13C NMR and differential scanning calorimetry. Water content and static contact angle of distilled water on the polymer surface were used to evaluate hydrophobicity of the polymers. It was found that the hydrophobicity increased with increasing CA fractions in the copolymers. Biodegradation experiments were conducted in vitro and in vivo. The results indicated that the biodegradation behaviour changed from surface to bulk degradation when the LA content exceeded 30mol% in the copolymers. These properties of PLCA may be useful in protein delivery systems. © of SCI.

Case 27 thermal infrared anomaly precursor of impending earthquakes

Abstract: People have already recognized the temperature increase anomaly before earthquakes, and studies have been made on this phenomenon (Wu, 1980;Wu et al., 1982;Geng, 1985). With the method of fixed-point network observation, only the timing temperature data limited to some sites can be obtained instead of dynamic evolution data of the temperature in a large area within the seismogenic range. However, it is advantageous to use the thermal infrared (IR) radiation measured by Meteosat to detect the ground temperature, because of the data accuracy, large area coverage, large amount of information, and the capability of capturing the time-space dynamic variation of the temperature increase before earthquakes. However relevant works on the relationship of the thermal IR anomaly measured by Meteosat to seismic activity are only found published in the Soviet Union (Gornuy et al., 1988). The authors used the thermal IR anomaly measured by Meteosat to monitor and tried to predict the earthquake of October 18, 1989 in Datong, Shanxi Province and other shocks, and obtained preliminary ideas and methods for carrying out predictions in this way.

Green's functions for a two-phase infinite piezoelectric plane

Abstract: First, on the basis of the governing equations of piezoelectric materials, a displacement function is introduced and the general solutions are derived. Second, by employing the generalized Almansi's theorem, these solutions are further simplified, i.e. all physical quantities are expressed in three displacement functions i (i = 1,2,3), which satisfy, respectively, three similar harmonic secondorder partial differential equations. Then the Green's functions for point forces and point charge acting in the interior of a twophase infinite piezoelectric plane are given using the method of mirror image source. The paper is concluded by a discussion of some special cases, in which the point force and charge solutions for an infinite uniform piezoelectric plane and for a halfplane with free or fixed straight boundary are given.

Deposition of self-polarized PZT films by planar multi-target sputtering

Abstract: A planar multi target sputtering approach was used to deposit self polarized PZT films on TiO2/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays By using elevated substrate temperatures of about 450°C “in situ” growth of tetragonal PZT could be achieved The films exhibited pyroelectric currents without poling The pyroelectric coefficient was 2×10−4 C/m2K, the dielectric constant was 300 and dielectric loss tan δ was 001 The self polarization disappears after heating the sample to 600°C Stresses were studied in the thin film processing for the bottom electrode and the PZT film The TiO2/Pt electrode is under high tensile stress of 900 MPa after preparation PZT has a small compressive stress of -60 MPa, the whole TiO2/Pt/PZT stack has a tensile stress of +80 MPa This low stress level together with the self polarization and the good electrical properties makes the films suitable for the use in pyroelectric detector arrays

Absorption spectra of rare-earth-doped α-sialon ceramics

Abstract: Abstracts are not published in this journal

On the extension of the α-SiAlON solid solution range and anisotropic grain growth in Sm-doped α-SiAlON ceramics

Abstract: α-SiAlON samples of the overall composition SmxSi12−(m+n)Alm+nOnN16 − m, with m and n in the ranges 0.6 ≤ m ≤ 1.44 and 1.3 ≤ n ≤ 1.7 (m = 3x), were prepared by a hot-pressing technique at 1800 and 1700 °C. Based on X-ray powder diffraction studies and elemental analysis of individual α-SiAlON grains in the obtained ceramic compacts, the extension of the Sm-doped α-SiAlON solid solution range was mapped out. The m-value was found to vary between 0.89 and 1.52 while n was always less than 1.23. Elongated α-SiAlON grains were found preferentially in compacts having overall compositions located slightly outside the oxygen-rich border-line of the homogeneity region of the Sm-doped α-SiAlON phase, i.e. for m ≈ 1.2 and n ≈ 1.3. We also noticed that elongated α-SiAlON grains were formed preferentially perpendicular to the pressure applied in the sintering procedure. All samples exhibited HV10-values in the range 21–22 GPa and KIC-values in the range 4.0–4.7 M Pa m 1 2 .

Vector-entropy optimization-based neural-network approach to image reconstruction from projections

Abstract: In this paper we propose a multiobjective decision making based neural-network model and algorithm for image reconstruction from projections. This model combines the Hopfield's model and multiobjective decision making approach. We develop a weighted sum optimization based neural-network algorithm. The dynamical process of the net is based on minimization of a weighted sum energy function and Euler's iteration, and apply this algorithm to image reconstruction from computer-generated noisy projections and Siemens Somatson DR scanner data, respectively. Reconstructions based on this method is shown to be superior to conventional iterative reconstruction algorithms such as the multiplicate algebraic reconstruction technique (MART) and convolution from the point of view of accuracy of reconstruction. Computer simulation using the multiobjective method shows a significant improvement in image quality and convergence behavior over the conventional algorithms.