Showing papers by "Zhejiang University published in 2000"

Oxygen-vacancy-related low-frequency dielectric relaxation and electrical conduction in B i : S r T i O 3

Abstract: The temperature dependence of dielectric properties and electrical conduction of $({\mathrm{Sr}}_{1\ensuremath{-}1.5x}{\mathrm{Bi}}_{x}){\mathrm{TiO}}_{3} (0.0133l~xl~0.133)$ was measured from 10 to 800 K. Three sets of oxygen vacancies related dielectric peaks (peaks A, B, and $C)$ were observed. These peaks could be greatly suppressed or eliminated by annealing the samples in an oxidizing atmosphere, and enhanced or recreated by annealing in a reducing atmosphere. The results show that the Maxwell-Wagner polarization is not the main mechanism, and the Skanavi's model also cannot be directly applied. A tentative explanation was suggested. Peak A, observed in the temperature range of 100--350 K with the activation energy for dielectric relaxation ${E}_{\mathrm{relaxA}}=0.32--0.49$ eV, is attributed to the coupling effect of the conduction electrons with the motion of the off-centered Bi and Ti ions; the conduction carriers in this temperature range are from the first ionization of oxygen vacancies ${(V}_{o}).$ Peaks B and C are also discussed.

Analysis and synthesis of nonlinear time-delay systems via fuzzy control approach

Abstract: Takagi-Sugeno (TS) fuzzy models (1985, 1992) can provide an effective representation of complex nonlinear systems in terms of fuzzy sets and fuzzy reasoning applied to a set of linear input/output (I/O) submodels. In this paper, the TS fuzzy model approach is extended to the stability analysis and control design for both continuous and discrete-time nonlinear systems with time delay. The TS fuzzy models with time delay are presented and the stability conditions are derived using Lyapunov-Krasovskii approach. We also present a stabilization approach for nonlinear time-delay systems through fuzzy state feedback and fuzzy observer-based controller. Sufficient conditions for the existence of fuzzy state feedback gain and fuzzy observer gain are derived through the numerical solution of a set of coupled linear matrix inequalities. An illustrative example based on the CSTR model is given to design a fuzzy controller.

Vortex-like excitations and the onset of superconducting phase fluctuation in underdoped La 2-x Sr x CuO 4

Abstract: Two general features of a superconductor, which appear at the critical temperature, are the formation of an energy gap and the expulsion of magnetic flux (the Meissner effect). In underdoped copper oxides, there is strong evidence that an energy gap (the pseudogap1) opens up at a temperature significantly higher than the critical temperature (by 100–220 K). Certain features of the pseudogap suggest that it is closely related to the gap that appears at the critical temperature (for example, the variation of the gap magnitudes around the Fermi surface and their maximum amplitudes are very similar2,3). However, the Meissner effect is absent in the pseudogap state. The nature of the pseudogap state, and its relation (if any) to the superconducting state are central issues in understanding copper oxide superconductivity. Recent evidence suggests that, in the underdoped regime, the Meissner state is destroyed above the critical temperature by strong phase fluctuations1,4,5,6,7 (as opposed to a vanishing of the superfluid density). Here we report evidence for vortices (or vortex-like excitations) in La2-xSrxCuO4 at temperatures significantly above the critical temperature. A thermal gradient is applied to the sample in a magnetic field. Vortices are detected by the large transverse electric field produced as they diffuse down the gradient (the Nernst effect). We find that the Nernst signal is anomalously enhanced at temperatures as high as 150 K.

Microbial biomass and community structure in a sequence of soils with increasing fertility and changing land use

Abstract: The microbial biomass and community structure of eight Chinese red soils with different fertility and land use history was investigated. Two community based microbiological measurements, namely, community level physiological profiling (CLPP) using Biolog sole C source utilization tests and phospholipid fatty acid (PLFA) profiles, were used to investigate the microbial ecology of these soils and to determine how land use alters microbial community structure. Microbial biomass-C and total PLFAs were closely correlated to organic carbon and total nitrogen, indicating that these soil microbial measures are potentially good indices of soil fertility in these highly weathered soils. Metabolic quotients and C source utilization were not correlated with organic carbon or microbial biomass. Multivariate analysis of sole carbon source utilization patterns and PLFAs demonstrated that land use history and plant cover type had a significant impact on microbial community structure. PLFAs showed these differences more than CLPP methods. Consequently, PLFA analysis was a better method for assessing broad-spectrum community differences and at the same time attempting to correlate changes with soil fertility. Soils from tea orchards were particularly distinctive in their CLPP. A modified CLPP method, using absorbance readings at 405 nm and different culture media at pH values of 4.7 and 7.0, showed that the discrimination obtained can be influenced by the culture conditions. This method was used to show that the distinctive microbial community structure in tea orchard soils was not, however, due to differences in pH alone.

Robust H/sub /spl infin// control of uncertain Markovian jump systems with time-delay

Abstract: This paper is concerned with the robust stochastic stabilizability and robust H/sub /spl infin// disturbance attenuation for a class of uncertain linear systems with time delay and randomly jumping parameters. The transition of the jumping parameters is governed by a finite-state Markov process. Sufficient conditions on the existence of a robust stochastic stabilizing and /spl gamma/-suboptimal H/sub /spl infin// state-feedback controller are presented using the Lyapunov functional approach. It is shown that a robust stochastically stabilizing H/sub /spl infin// state-feedback controller can be constructed through the numerical solution of a set of coupled linear matrix inequalities.

Time dependence of piezoresistance for the conductor-filled polymer composites

Abstract: The piezoresistance and its time dependence of conductor-filled polymer composites have been investigated. To reveal the origin of the time dependence of piezoresistance, the creep of the polymer matrix is also studied. Based on the interparticle separation change under the applied stress, a model has been developed to predict the piezoresistance and its time dependence. By analyzing this model, the influences of applied stress, filler particle diameter, filler volume fraction, matrix compressive modulus, potential barrier height, and the matrix creep behavior on the piezoresistance and its time dependence are interpreted quantitatively. These predicted results are compared with the experimental data obtained on the polymer composites filled with conductor fillers, and good agreements were obtained. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2739–2749, 2000

Sorption of Phenol, p-Nitrophenol, and Aniline to Dual-Cation Organobentonites from Water

Abstract: A series of dual-cation organobentonites are synthesized by replacing the metal ions in bentonite with both long-chain alkyl quaternary ammonium cations, such as dodecyltrimethylammonium (DTMA), benzyldimethyltetradecylammonium (BDTDA), cetyltrimethylammonium (CTMA), octodecyltrimethylammonium (OTMA), and short-chain alkyl quaternary ammonium cations, such as tetramethylammonium (TMA). The influential factors, mechanisms and characteristics of polar and ionizable organic contaminants, such as p-nitrophenol, phenol, and aniline, and sorption to dual-cation organobentonites from water are investigated systematically and described quantitatively. The sorption properties are affected by treatment conditions, such as pH, amount of organobentonite, and shaking time; structure of organobentonites, such as interlayer spacings and organic carbon contents; and the properties of organic compounds, such as solubility and octanol−water coefficient partition. Sorption isotherms of p-nitrophenol, phenol, and aniline are...

Methods of constructing core collections by stepwise clustering with three sampling strategies based on the genotypic values of crops.

Abstract: A genetic model with genotype×environment (GE) interactions for controlling systematical errors in the field can be used for predicting genotypic values by an adjusted unbiased prediction (AUP) method. Mahalanobis distance, calculated based on the genotypic values, is then applied to measure the genetic distance among accessions. The unweighted pair-group average, Ward’s and the complete linkage methods of hierarchical clustering combined with three sampling strategies are proposed to construct core collections in a procedure of stepwise clustering. A homogeneous test and t-tests are suggested for use in testing variances and means, respectively. The coincidence rate (CR%) for range and the variable rate (VR%) for the coefficient of variation are designed to evaluate the property of core collections. A worked example of constructing core collections in cotton with 21 traits was conducted. Random sampling can represent the genetic diversity structure of the initial collection. Preferred sampling can keep the accessions with special or valuable characteristics in the initial collection. Deviation sampling can retain the larger genetic variability of the initial collection. For better representation of the core collection, cluster methods should be combined with different sampling strategies. The core collections based on genotypic values retained larger genetic variability and had superior representatives than those based on phenotypic values.

Transgenic rice plants with a synthetic cry1Ab gene from Bacillus thuringiensis were highly resistant to eight lepidopteran rice pest species.

Abstract: To fully explore the resistance potential of transgenic rice produced by Agrobacterium-mediated transformation, an elite line KMD1 was assessed for its resistance to eight lepidopteran rice pest species KMD1 contained a synthetic cry1Ab gene from Bacillus thuringiensis under the control of a maize ubiquitin promoter It was derived from a commercial japonica Chinese rice variety Xiushui 11, and bred true for both agronomic traits and a cry1Ab gene when the bioassays were done in 1998 in the R5 generation The eight lepidopteran pest species were: four Pyralidae species: Chilo suppressalis (striped stem borer, SSB), Scirpophaga incertulas (yellow stem borer, YSB), Cnaphalocrocis medinalis (leaf folder), Herpitogramma licarisalis; two Noctuidae: Sesamia inferens (pink stem borer, PSB) and Naranga anescens; one Stayridae: Mycalesis gotama; and one Hesperiidae, Parnara guttata In laboratory bioassays, 100% mortality was observed in all insect species when their newly hatched or third-instar larvae were fed KMD1 leaf tissues, whereas only 965% of the neonates and none of the third-instar larvae died when fed the leaf tissues of non-transgenic control Moreover, the leaf area of control tissues consumed in four days by stem borers was 20 to 40 times higher than that of KMD1 tissues, and the area of control tissues eaten by leaf-feeding species was 120 to 180 times greater than that of the transgenic tissues Under natural infestation, no KMD1 plant was visibly damaged by the SSB, YSB and leaf folder in field evaluation On the other hand, 80, 93 and 887% of control plants were injured by SSB, YSB, and leaf folder, respectively These data disclosed that the transgenic line was highly resistant to a broad spectrum of lepidopteran insect species and could be useful in insect resistance breeding programs

Actively clamped bidirectional flyback converter

Abstract: An actively clamped bidirectional flyback converter is proposed. The converter's operation is examined in detail. All switches in the converter have zero-voltage-switching characteristics. A low-frequency behavior model and small-signal transfer functions are derived. It is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter. It is expected that such bidirectional converters will find wide applications in the interconnection of multiple sources of DC power to a common bus (e.g., in a DC uninterruptible power supply). Simulation and experiment results are also presented.

Improvement of bioactivity of H2O2/TaCl5‐treated titanium after subsequent heat treatments

Abstract: Commercially pure titanium was treated with a H2 O2/3mM TaCl5 solution at 80°C for various periods and a titania gel layer was formed on the surface. This gel remained amorphous when heating for 1 h below 200°C and transformed to anatase after heating between 300° and 600°C. The anatase titania gel layers were found to be bioactive as to deposit carbonate ion-incorporated apatite within 1 day of immersion in the Kokubo solution, whereas the amorphous layers did not deposit apatite within 7 days. The apatite particles were found to nucleate preferentially inside the cracks prevailing in the thicker gel layers of 1-h chemically treated specimens. After immersing for 2 days, the titanium specimens were almost completely covered by apatite. Elimination of peroxide radicals from the titania gel and formation of anatase upon subsequent heating are considered to be responsible for the enhanced ability of apatite deposition. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 52, 171–176, 2000.

Kinetics of photocatalytic degradation of aniline in water over TiO2 supported on porous nickel

Abstract: The photocatalytic degradation of aniline was studied in annular photoreactor, with 2×6 W (Emax=365 nm) UV lamp as light source, borosilicate glass as wave filter and titanium dioxide immobilized on porous nickel as catalysts. Parameters such as the initial concentration, flow rate, initial pH, dissolved oxygen, electrolyte, hydrogen peroxide addition, temperature and external potential bias affecting the degradation rate of aniline were studied. The results showed that photocatalysis is an effective process for the degradation of aniline. The activated energy for the photocatalytic degradation of aniline is 6.13 kJ mol−1. The initial quantum yield is 1.89% for aniline 1.10×10−4 mol l−1. Total mineralization requires a much longer illumination time than the disappearance of anilines. The external potential bias can largely improve the efficiency of photocatalytic degradation of aniline. The degradation kinetic of aniline can be described by Langmuir–Hinshelwood equation.

Variation of Langmuir adsorption constant determined for TiO2-photocatalyzed degradation of acetophenone under different light intensity

Abstract: The Langmuir–Hinshelwood (L–H) kinetic model has been used to describe semiconductor photocatalysis. In this report, the L–H rate constant (kL–H)and the Langmuir adsorption constant (K) have been determined under different light intensity for the photocatalytic degradation of poorly adsorbed acetophenone over TiO2 of Degussa P25 in aqueous medium (pH 6.2). The result shows that K decreases when the irradiation is performed at higher light intensity, while kL–H increases expectedly. It is also demonstrated that the initial time interval selected for the initial rate calculation is quite critical to the final determination for the constants.

QTLs and epistasis for aluminum tolerance in rice (Oryza sativa L.) at different seedling stages

Abstract: To investigate the genetic background for aluminum (Al) tolerance in rice, a recombinant inbred (RI) population, derived from a cross between an Al-sensitive lowland indica rice variety IR1552 and an Al-tolerant upland japonica rice variety Azucena, was used in culture solution. A molecular linkage map, together with 104 amplified fragment length polymorphism (AFLP) markers and 103 restriction fragment length polymorphism (RFLP) markers, was constructed to map quantitative trait loci (QTLs) and epistatic loci for Al tolerance based on the segregation for relative root length (RRL) in the population. RRL was measured after stress for 2 and 4 weeks at a concentration of 1mM of Al3+ and a control with a pH 4.0, respectively. Two QTLs were detected at both the 2nd and the 4th weeks on chromosomes 1 and 12 from unconditional mapping, while the QTL on chromosome 1 was only detected at the 2nd stress week from conditional mapping. The effect of the QTL on chromosome 12 was increased with an increase of the stress period from 2 to 4 weeks. The QTL on chromosome 1 was expressed only at the earlier stress, but its contribution to tolerance was prolonged during growth. At least one different QTL was detected at the different stress periods. Mean comparisons between marker genotypic classes indicated that the positive alleles at the QTLs were from the Al-tolerant upland rice Azucena. An important heterozygous non-allelic interaction on Al tolerance was found. The results indicated that tolerance in the younger seedlings was predominantly controlled by an additive effect, while an epistatic effect was more important to the tolerance in older seedlings; additionally the detected QTLs may be multiple allelic loci for Al tolerance and phosphorus-uptake efficiency, or for Al and Fe2+ tolerance.

Sorption Behavior of p-Nitrophenol on the Interface between Anion−Cation Organobentonite and Water

Abstract: A series of anion−cation organobentonite are prepared by incorporating both cationic surfactant bromide dodecyltrimethylammonium (DTMAB) and anionic surfactant sodium dodecyl sulfate (SDS) to bentonite. The results indicate that the organic carbon contents of the organobentonites are proportional to the amounts of anionic and cationic surfactants in bentonite. The amount of organic pollutant removed from water depends greatly on the amount of SDS and DTMAB in the bentonite. Partition and adsorption contributions to the sorption amount of p-nitrophenol on organobentonites are described quantitatively. The mixed surfactants on anion−cation organobentonites excellently created partition mediums for organic pollutants in water. The removal rate of organic pollutants from water is improved by synergistic solubilization in both anionic and cationic surfactant moieties of the organobentonites. The effect of synergistic solubilization results mainly from partition at higher concentrations or adsorption at lower c...

Impurity-induced ferroelectric relaxor behavior in quantum paraelectric SrTiO 3 and ferroelectric BaTiO 3

Abstract: We report that ``ferroelectric relaxor'' behavior is induced by doping Bi in quantum paraelectric ${\mathrm{SrTiO}}_{3},$ and doping Ce in typical ferroelectric ${\mathrm{BaTiO}}_{3}.$ The present results show that the ``ferroelectric relaxor'' state may exist no matter whether the matrix is ferroelectric or paraelectric, however, the relaxor behavior is the dynamic response of the polar clusters induced in the system.

QTL mapping for the paste viscosity characteristics in rice (Oryza sativa L.)

Abstract: In order to understand the genetic basis of the paste viscosity characteristics (RVA profile, which is tested on the Rapid Visco Analyser) of the rice grain, we mapped QTLs for RVA profile parameters using a DH population derived from a cross between an indica variety, Zai-Ye-Qing 8 (ZYQ8), and a japonica variety, Jing-Xi 17 (JX17). Evidence of genotype-by-environment interaction was found by comparing the mapped QTLs between two locations, Hainan (HN) and Hangzhou (HZ). A total of 20 QTLs for six parameters of the RVA profiles were identified at least one location. Only the waxy locus (wx) located on chromosome 6 was detected significantly at both environments for five traits, i.e. hot paste viscosity (HPV), cool paste viscosity (CPV), breakdown viscosity (BDV), consistency viscosity (CSV) and setback viscosity (SBV). This locus explained 19.5%–63.7% of the total variations at both environments, suggesting that the RVA profiles were mainly controlled by the wx gene. HPV, CPV, BDV, CSV and SBV were also controlled by other QTLs whose effects on the respective parameter were detected only in one environment, while for the peak viscosity (PKV), only 2 QTLs, 1 at HN,the other at HZ, were identified. These results indicate that RVA profiles are obviously affected by environment.

An analysis of loop seal operations in a circulating fluidized bed

Abstract: The operation of a loop seal in a circulating fluidized bed is studied on the basis of pressure balance of the circulation loop. The sharp-crested theory of free surface flow is applied to analyze the solids flow rate through a loop seal. Factors, which influence the solids flow rate through the loop seal, include loop seal air velocity, initial bed inventory, standpipe size, loop seal slit size and particle size. The solids flow could occur only between two limiting values of each of those parameters. The analysis also presented pressure distributions along the loop for different circulation rates. Results from above theoretical analyses were compared with experimental results. A good agreement between the results confirmed the validity of the present analysis.

The effects of promoter and curing process on exfoliation behavior of epoxy/clay nanocomposites

Abstract: The effects of a catalyst and coupling agent as well as a curing process on exfoliation behavior of CH3(CH2)15NH3+–montmorillonite clay in an anhydride-cured epoxy–clay system have been investigated by XRD, DSC, and TEM. The results have shown that the organoclay is easily intercalated by the epoxy precursor during the mixing process, and the clay galleries continue to expand during the curing process, but the Na+–montmorillonite clay is not intercalated during either the mixing or the curing process. The results also suggest that in the cured system without any promoter although partial exfoliated clay layers have already formed, an amount of the intercalation structure still remains. Although addition of a promoter or coupling agent into the cured system significantly lowers the maximum reaction temperature, and during the curing process the layered organoclay can be gradually broken into nanoscale structures, in which no d001 diffraction peaks are observed, the complete exfoliation is achieved at gel time or before. The possible mechanism for the complete exfoliation is discussed on the thermodynamic and kinetic point of view. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 808–815, 2000

Comparative evaluation of the in vitro micronucleus test and the comet assay for the detection of genotoxic effects of X-ray radiation.

Abstract: The genotoxic effects of X-ray radiation on human lymphocytes were measured using the single cell gel electrophoresis (SCGE) assay (comet assay) and the cytokinesis-blocked micronucleus (CBMN) test; both were carried out in vitro on isolated human lymphocytes in order to compare the relationship and sensitivity of these two detecting methods. The radiation-doses were 0.00, 0.02, 0.05, 0.10, 0.25, 0.50, 1.00 and 2.00 Gy. In the comet assay, the average comet length (38.6±0.8 μm) of 0.05 Gy was significantly longer than that (29.4±1.1 μm) of 0 Gy (P 0.05). The lowest dose, which induced significant increase of average MN and MNC, was 0.25 Gy. The average MN and MNC rates increased with radiation-dose. The results showed that there was correlation between SCGE and CBMN, and the sensitivity of SCGE was significantly higher than that of CBMN.

Different tolerance to light stress in NO3-- and NH4+-grown Phaseolus vulgaris L.

Abstract: NH4+-grown plants are more sensitive to light stress than NO3−-grown plants, as indicated by reduced growth and intervenal chlorosis of French bean (Phaseolus vulgaris L.). Measuring the time course of Fv/Fm ratios under photoinhibitory light regimes did not reveal any difference in PS II damage between NO3−- and NH4+-grown plants, in spite of some indications of higher energy quenching in NO3−-grown plants. Also, a direct action of NH4+ as an uncoupler at the thylakoid membrane could be excluded. Instead, biochemical analysis revealed enhanced lipid peroxidation and higher activity of scavenging enzymes in NH4+-grown plants indicating that these plants make use of metabolic pathways with stronger radical formation. Evidence for higher rates of photorespiration in NH4+-grown plants came from experiments showing that electron flux and O2 evolution were decreased by SHAM in NH4+-grown plants, and by antimycin A in NO3−-grown plants. Further, the comparison of electron flux and of photoacoustic measurements of O2 evolution suggested that in NH4+-grown plants the Mehler reaction was also increased, at least in the induction phase. However, the major cause of N form-dependent stress sensitivity is assumed to be in the coupling between photosynthesis and respiration, i.e., NO3−-grown plants can utilize the TCA cycle for the generation of C skeletons for amino acid synthesis, thus improving the ATP: reductant balance, whereas NH4+-grown plants have enhanced rates of photorespiration.

Seasonal abundance of the parasitoid complex associated with the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) in Hangzhou, China.

Abstract: An investigation of insect parasitoids of the diamondback moth, Plutella xylostella (Linnaeus), in brassica vegetable crops in the suburbs of Hangzhou was conducted during five periods from 1989 to 1997. Eight species of primary parasitoids were recorded: Trichogramma chilonis Ishii, Cotesia plutellae Kurdjumov, Microplitis sp., Oomyzus sokolowskii Kurdjumov, Diadromus collaris (Gravenhorst), Itoplectis naranyae (Ashmead), Exochus sp. and Brachymeria excarinata Gahan. Seven species of hyperparasitoids were also collected. Rates of parasitism of eggs of P. xylostella were usually very low. However, rates of parasitism of larvae and pupae were substantial and showed two peaks each year, around June-July and September-November respectively. Rates of parasitism during peaks were usually 10-60% and reached over 80% on a few occasions. Cotesia plutellae, O. sokolowskii and D. collaris were the major larval, larval-pupal and pupal parasitoids respectively. In the field, C. plutellae was active throughout the year. Oomyzus sokolowskii was active from May to October, entered a quiescent pupal stage in October-November to overwinter and did not emerge until next April-May. Diadromus collaris was recorded from April to July and October. Rates of parasitism of P. xylostella in radish and mustard fields were usually higher than those in cabbage and Chinese cabbage fields in the same locality. Negative correlations of parasitism rates between C. plutellae and O. sokolowskii indicate a competitive relationship for host larvae between these two larval parasitoids.