Showing papers by "Shanghai University published in 2008"

Formability of ABX3 (X = F, Cl, Br, I) halide perovskites

Abstract: In this study a total of 186 complex halide systems were collected; the formabilities of ABX3 (X = F, Cl, Br and I) halide perovskites were investigated using the empirical structure map, which was constructed by Goldschmidt's tolerance factor and the octahedral factor. A model for halide perovskite formability was built up. In this model obtained, for all 186 complex halides systems, only one system (CsF–MnF2) without perovskite structure and six systems (RbF–PbF2, CsF–BeF2, KCl–FeCl2, TlI–MnI2, RbI–SnI2, TlI–PbI2) with perovskite structure were wrongly classified, so its predicting accuracy reaches 96%. It is also indicated that both the tolerance factor and the octahedral factor are a necessary but not sufficient condition for ABX3 halide perovskite formability, and a lowest limit of the octahedral factor exists for halide perovskite formation. This result is consistent with our previous report for ABO3 oxide perovskite, and may be helpful to design novel halide materials with the perovskite structure.

Acute toxicological impact of nano- and submicro-scaled zinc oxide powder on healthy adult mice

Abstract: In this work, the acute oral toxicity of 20- and 120-nm ZnO powder at doses of 1-, 2-, 3-, 4-, 5-g/kg body weight was evaluated referred to the OECD guidelines for testing of chemicals. As the results, both 20- and 120-nm ZnO belong to non-toxic chemicals according to the Globally Harmonized Classification System (GHS) for the classification of chemicals. The distribution determination showed that Zn was mainly retained in the bone, kidney and pancreas after 20- and 120-nm ZnO administration. However, the results of blood measurement suggest that the increase in blood viscosity could be induced by low and median dose of 20-nm ZnO but high dose of 120-nm ZnO. The pathological examination showed that the 120-nm ZnO treated mice had dose–effect pathological damages in stomach, liver, heart and spleen, whereas, 20-nm ZnO displayed negative dose–effect damages in liver, spleen and pancreas. Therefore, we conclude that the liver, spleen, heart, pancreas and bone are the target organs for 20- and 120-nm ZnO oral exposure. More attention should be paid on the potential toxicity induced by low dose of 20-nm ZnO oral exposure.

A Small World of Neuronal Synchrony

Abstract: A small-world network has been suggested to be an efficient solution for achieving both modular and global processing—a property highly desirable for brain computations. Here, we investigated functional networks of cortical neurons using correlation analysis to identify functional connectivity. To reconstruct the interaction network, we applied the Ising model based on the principle of maximum entropy. This allowed us to assess the interactions by measuring pairwise correlations and to assess the strength of coupling from the degree of synchrony. Visual responses were recorded in visual cortex of anesthetized cats, simultaneously from up to 24 neurons. First, pairwise correlations captured most of the patterns in the population's activity and, therefore, provided a reliable basis for the reconstruction of the interaction networks. Second, and most importantly, the resulting networks had small-world properties; the average path lengths were as short as in simulated random networks, but the clustering coefficients were larger. Neurons differed considerably with respect to the number and strength of interactions, suggesting the existence of “hubs” in the network. Notably, there was no evidence for scale-free properties. These results suggest that cortical networks are optimized for the coexistence of local and global computations: feature detection and feature integration or binding.

Quantitative function for community detection.

Abstract: We propose a quantitative function for community partition---i.e., modularity density or $D$ value. We demonstrate that this quantitative function is superior to the widely used modularity $Q$ and also prove its equivalence with the objective function of the kernel $k$ means. Both theoretical and numerical results show that optimizing the new criterion not only can resolve detailed modules that existing approaches cannot achieve, but also can correctly identify the number of communities.

Studies on alcohol sensing mechanism of ZnO based gas sensors

Abstract: Nanosized ZnO powder was synthesized by using a chemical precipitation method, and loaded with different dopants through impregnation. The as-prepared ZnO powder was characterized by XRD and TEM. The characterization results show that the as-prepared sample is wurtzite polycrystalline ZnO, the mean grain size is 30–40 nm, and there are three types of adsorbed oxygen (O 2 − , O 2 2− , and O 2− ) on the surface of the sample. The as-prepared ZnO powder shows excellent gas responses to alcohol and acetaldehyde, but no response to ethene. The sensing mechanism of ZnO was further studied with the help of gas chromatography (GC) associated with a fixed-bed reactor. The studies show that acetaldehyde, carbon dioxide and water are the only oxidation products of C 2 H 5 OH over ZnO. The gas response to C 2 H 5 OH is strongly dependent on the conversion ratio of C 2 H 5 OH to acetaldehyde. In addition, among all the dopants tested, Ru is the optimal dopant which can increase the response to C 2 H 5 OH, but cannot increase the conversion ratio of C 2 H 5 OH to acetaldehyde. Thus we suggest that the gas sensing mechanism of ZnO to C 2 H 5 OH is the mode controlled by chemisorption of negatively charged oxygen, and the sensitizing role of Ru in the ZnO sensor belongs to the electronic sensitization mechanism.

The template-free synthesis of square-shaped SnO(2) nanowires: the temperature effect and acetone gas sensors.

Abstract: Square-shaped single-crystalline SnO2 nanowires and their sphere-like hierarchical structures were synthesized successfully with a template-free hydrothermal approach. It was found that an intermediate phase—Na2Sn(OH)6—is first produced because it is slow to dissolve in ethanol/water media. The intermediate phase gradually decomposes and converts into SnO2 at temperatures higher than 200 °C. The reaction temperature also affects the microstructure of SnO2 nanomaterials. Uniform square-shaped SnO2 nanowires, which form sphere-like hierarchical structures in 100% structure yield, can be produced at 285 °C on a large scale. The diameter of the nanowires shows a decrease accompanying the increase of the reaction temperature. The temperature effect could be a result of the faster and oriented growth of SnO2 nanowires along their direction at higher temperature. Chemical sensors constructed with square-shaped SnO2 nanowires exhibit excellent stability, good sensitivity and selectivity, as well as a quick response and short recovery times under exposure to acetone gas in practical applications.

Template-Free Synthesis, Controlled Conversion, and CO Oxidation Properties of CeO2 Nanorods, Nanotubes, Nanowires, and Nanocubes

Abstract: A general large-scale synthesis of single-crystalline and uniform CeO2 nanorods was first realized without templates by a precipitation method at room temperature and pressure. Such nanorods have an aspect ratio of ca. 3 nm with a diameter of ca. 8 nm and a large BET specific area of 128.2 m2/g. On the basis of this, the controlled conversion of the as-prepared nanorods into nanotubes, nanowires, and nanocubes through hydrothermal reactions has been realized. Further experimental results show that the growth of nanorods is a function of the base concentration, temperature, and time. In addition, particle size measurements demonstrate that the primary nanorods grow by Ostwald ripening. It is found that CeO2 growth is faster at higher base concentration and temperature due to the accelerated ripening. During the synthesis, the formation of Ce(OH)3 intermediate species and their transformation into CeO2 have been dynamically demonstrated and are regarded as the key factors responsible for the evolution of shape. The CO oxidation properties of CeO2 nanorods, nanowires, nanotubes, and nanocubes were investigated, and CeO2 nanotubes have the best performance due to the large BET surface area and the novel inner surface. In addition, CeO2 nanorods aged for 9 d also have an excellent catalytic performance for CO oxidation due to the exposed crystal surface (110) of CeO2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Reliable multi-objective optimization of high-speed WEDM process based on Gaussian process regression

Abstract: The paper discusses the development of reliable multi-objective optimization based on Gaussian process regression (GPR) to optimize the high-speed wire-cut electrical discharge machining (WEDM-HS) process, considering mean current, on-time and off-time as input features and material remove rate (MRR) and Surface Roughness (SR) as output responses. In order to achieve an accurate estimation for the nonlinear electrical discharging and thermal erosion process, the multiple GPR models due to its simplicity and flexibility identify WEDM-HS process with measurement noise. Objective functions of predictive reliability multi-objectives optimization are built by probabilistic variance of predictive response used as empirical reliability measurement and responses of GPR models. Finally, the cluster class centers of Pareto front are the optional solutions to be chosen. Experiments on WEDM-HS (DK7732C2) are conducted to evaluate the proposed intelligent approach in terms of optimization process accuracy and reliability. The experimental result shows that GPR models have the advantage over other regressive models in terms of model accuracy and feature scaling and probabilistic variance. Given the regulable coefficient parameters, the experimental optimization and optional solutions show the effectiveness of controlling optimization process to acquire more reliable optimum predictive solutions.

Zn-doped TiO2 nanoparticles with high photocatalytic activity synthesized by hydrogen–oxygen diffusion flame

Abstract: Zn-doped TiO2 nanoparticles with high photocatalytic activity were synthesized by the hydrogen–oxygen diffusion flame method and the photocatalytic degradation mechanism of rhodamine B dye under visible light irradiation were elaborated. The Zn dopants presented in the form of small ZnO nuclei dispersing randomly on the surface of anatase TiO2 nanoparticles. It is found that the photosensitized degradation activity can be enhanced by doping an appropriate amount of Zn. The improved activity by Zn doping can be attributed to the appropriate energetic position between ZnO and the excited state of dye, which enhanced the electron injection into the conduction band of TiO2 by capturing electron, subsequently promoted the formation of reactive oxygen species. Hence, the enhanced photodegradation of dyes under visible irradiation can be realized.

High aspect ratio In2O3 nanowires: Synthesis, mechanism and NO2 gas-sensing properties

Abstract: Flexural In 2 O 3 nanowires with high aspect ratios were synthesized via a hydrothermal–annealing route. The as-synthesized In 2 O 3 nanowires had diameters of 30–50 nm and length up to several microns. Various reaction parameters, such as the kind of reagents, the time of hydrothermal treatment, annealing time and annealing temperature, were investigated by a series of control experiments. The as-synthesized In 2 O 3 nanowires showed excellent gas-sensing properties to NO 2 in terms of sensor response and selectivity.

Metal-organic frameworks constructed from 2,4,6-Tris(4-pyridyl)-1,3,5-triazine.

Abstract: Five new metal-organic frameworks based on 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) ligand have been hydrothermally synthesized. Reaction of tpt and AgNO 3 in an acidic solution at 180 degrees C yields {[Ag(Htpt)(NO3)]NO(3).4H2O}n (1).Ag(I) is trigonally coordinated by two pyridyl nitrogen and one nitrato oxygen to form a 1D zigzag chain. Reaction of tpt with CuSO4 affords {[Cu2(tpt)2(SO4)2(H2O)2].4H2O}n (2). Copper(II) is bonded to two pyridyl nitrogen, two sulfato oxygen, and two water oxygen atoms to form an elongated octahedral geometry. Each H2O ligand bridges two copper(II), whereas sulfate bridges copper(II) via micro-1,3 and micro-1,1 fashions. The copper(II)-sulfate-H2O2D layers are linked by bidentate tpt to form a 3D polymeric structure. Reaction of Cu(SO4)2, tpt, and 1,2,4,5-benzenetetracarboxylic acid (H4btec) in the presence of piperidine gives [Cu(tpt)(H2btec)1/2]n (3). Copper(I) is located in a trigonal-pyramidal coordination environment and coordinated by three pyridyl nitrogen of tpt in a plane, whereas a carboxylate oxygen is coordinated to the copper(I) axially. The tpt-Cu forms a layer, and the layers are linked through H 2btec2- to form a 2D double-layered coordination polymer. Replacing CuSO4 with ZnI2 in the synthesis gives {[Zn(tpt)(btec)1/2].H2O}n (4). Zinc(II) is in a distorted tetrahedral geometry and linked through bidentate tpt and exotetradentate btec4- to form a 2D coordination grid. Reaction of tpt with CuCN leads to the assembly of a 3D metal-organic framework [Cu3(CN)3(tpt)]n (5). Copper(I) is trigonally coordinated by one pyridyl nitrogen and two cyanides to form an intriguing honeycomb architecture. Luminescence study shows that 1, 3, 4, and 5 have blue fluorescence, which can be assigned to be ligand-centered emissions. Thermal analysis shows that all of these complexes are quite stable, and especially for 4, the framework is stable up to 430 degrees C.

Mechanical properties of human enamel as a function of age and location in the tooth.

Abstract: Aging and the related changes in mechanical behavior of hard tissues of the human body are becoming increasingly important. In this study the influence of aging on the mechanical behavior of human enamel was evaluated using 3rd molars from young (18 ≤ age ≤ 30 years) and old (55 ≤ age) patients. The hardness and elastic modulus were quantified using nanoindentation as a function of distance from the Dentin–Enamel Junction (DEJ) and within three different regions of the crown (i.e. cervical, cuspal and inter-cuspal enamel). Results of the evaluation showed that the elastic modulus and hardness increased with distance from the DEJ in all three regions examined, regardless of patient age. The largest increases with distance from the DEJ occurred within the cervical region of the old enamel. Overall, the results showed that there were no age-dependent differences in properties of enamel near the DEJ. However, near the tooth’s surface, both the hardness (p < 0.025) and elastic modulus (p < 0.0001) were significantly greater in the old enamel. At the surface of the tooth the average elastic modulus of “old” enamel was nearly 20% greater than that of enamel from the young patients.

Fragile Watermarking With Error-Free Restoration Capability

Abstract: This paper proposes a novel fragile watermarking scheme capable of perfectly recovering the original image from its tampered version. In the scheme, a tailor-made watermark consisting of reference-bits and check-bits is embedded into the host image using a lossless data hiding method. On the receiver side, by comparing the extracted and calculated check-bits, one can identify the tampered image-blocks. Then, the reliable reference-bits extracted from other blocks are used to exactly reconstruct the original image. Although content replacement may destroy a portion of the embedded watermark data, as long as the tampered area is not too extensive, the original image information can be restored without any error.

An amplitude-frequency study of turbulent scaling intermittency using Empirical Mode Decomposition and Hilbert Spectral Analysis

Abstract: Hilbert-Huang transform is a method that has been introduced recently to decompose nonlinear, nonstationary time series into a sum of different modes, each one having a characteristic frequency. Here we show the first successful application of this approach to homogeneous turbulence time series. We associate each mode to dissipation, inertial range and integral scales. We then generalize this approach in order to characterize the scaling intermittency of turbulence in the inertial range, in an amplitude-frequency space. The new method is first validated using fractional Brownian motion simulations. We then obtain a 2D amplitude-frequency representation of the pdf of turbulent fluctuations with a scaling trend, and we show how multifractal exponents can be retrieved using this approach. We also find that the log-Poisson distribution fits the velocity amplitude pdf better than the lognormal distribution.

Hydrogen-Generation Materials for Portable Applications

Abstract: Unlike traditional batteries, small fuel cells have a high energy density and can work uninterruptedly, being better energy suppliers for portable devices. Such devices require an economically viable fuel. Recent findings showed that metal Al particle surfaces could be modified by fine ceramic oxide grains through a ceramic processing procedure, and the modified Al powder could continuously react with pure water and generate hydrogen under ambient conditions. The reaction of Al with water produces as much as 3.7–4.8 wt% hydrogen, and the reaction byproducts are chemically neutral. Metal Al is cheap and hydrogen generation from the reaction between surface-modified Al particles and water is a simple process. These features make this new process a cost-efficient way of generating hydrogen for small fuel cells in comparison with other portable hydrogen-generation materials and technologies. In this paper, the state of the art of portable hydrogen-generation materials is surveyed, and the ceramic oxide-modified Al–hydrogen technology and its potential are highlighted.

NbC as grain growth inhibitor and carbide in WC–Co hardmetals

Abstract: WC–NbC–12 wt%Co hardmetals with 0.45–60 wt%NbC were prepared by solid state pulsed electric current sintering (PECS), also known as spark plasma sintering (SPS), for 2 min at 1240 °C and conventional sintering (CS) for 1 h at 1420 °C. The role of NbC as grain growth inhibitor and major carbide addition was investigated in terms of the densification behaviour, the microstructure and mechanical properties. Experimental work revealed that the addition of more than 5 wt%NbC inhibits pressure assisted solid-state densification compared to WC–Co based hardmetals. The addition of NbC limits WC grain growth during PECS and conventional sintering, whereas substantial (Nb, W)C grain growth was observed in the hardmetals with ⩾0.9 wt%NbC addition. The influence of the NbC content on the hardness, strength and toughness of the WC–NbC–12 wt%Co hardmetals was explained in terms of WC grain growth inhibition and the formation of coarse (Nb, W)C grains.

Derivative voltammetric direct simultaneous determination of nitrophenol isomers at a carbon nanotube modified electrode

Abstract: Cyclic voltammetry was used to investigate the electrochemical reduction of nitrophenol isomers at a glassy carbon electrode modified with carbon nanotubes, and a derivative voltammetric technique was adopted to improve the resolution and enhance the determination sensitivity. In 0.1 mol L−1 HAc–NaAc buffer solution (pH 5.0), the modified electrode showed a good electrocatalytic response towards nitrophenol isomers. Through a derivative technique, the peak currents increased significantly and the reduction peaks of nitrophenol isomers could be separated, so the method could be applied to direct simultaneous determination without preseparation. The linear calibration ranges were 4.0 × 10−6 to 2.0 × 10−3 mol L−1 for o-nitrophenol, 1.0 × 10−5 to 1.0 × 10−3 mol L−1 for m-nitrophenol and 2 × 10−6 to 4.0 × 10−3 mol L−1 for p-nitrophenol, with detection limits of 5.0 × 10−7, 6.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively.

Role of mast cells in acupuncture effect: a pilot study.

Abstract: To better understand the therapeutic effectiveness of acupuncture, questions about the underlying mechanisms need to be addressed. Here we describe the impact of manual stimulation by an acupuncture needle of zusanli (stomach 36 [ST36]) on analgesia in rats. The analgesic effect was more pronounced after stimulation of ST36 than after stimulation of a sham point near the acupuncture point. At the same time, we determined in tissue slices the density of mast cells in the acupuncture points and nearby points, as well as the degree of degranulation before and after stimulation. We found that the density of mast cells from the ST36 of rats was higher than that from a nearby sham point. In addition, acupuncture resulted in a remarkable increase in degranulation of the mast cells. Pretreatment of the acupuncture point with disodium chromoglycate not only counteracted the phenomenon of degranulation but also reduced analgesic effect of acupuncture. Our experiments on inhibition of degranulation of mast cells in tissue from acupuncture points demonstrates the possible role of mast cells in acupuncture effects.

One-Step Synthesis of Hierarchical Cantaloupe-like AlOOH Superstructures via a Hydrothermal Route

Abstract: Hierarchical cantaloupe-like and hollow microspherical AlOOH superstructures were successfully synthesized on a large scale via a one-step hydrothermal route. The as-obtained superstructures were characterized by several techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and nitrogen adsorption/desorption measurement. The as-obtained superstructures, consisting of closely packed nanorods in an ordered fashion, have an average horizontal axis of ca. 2.5 µm and a longitudinal axis of ca. 1.5 µm. The as-obtained cantaloupe-like AlOOH superstructures have Brunauer–Emmett–Teller (BET) surface area of about 55.5 m2/g. The possible formation mechanism of the cantaloupe-like AlOOH superstructures is proposed and discussed.