Showing papers by "Southwest University of Science and Technology published in 2007"

Dependence of flame-retardant properties on density of expandable graphite filled rigid polyurethane foam

Abstract: Different density rigid polyurethane foams (RPUF) filled with various expandable graphite loadings were fabricated by cast molding. The flame retardant properties of these composites were assessed by limiting oxygen index and horizontal and vertical burning tests. The results showed that the flame retardant efficiency got better with increase in the foam density at the fixed EG weight percent or with increase in the EG weight percent at the fixed foam density. After burning, the low density (0.065 g/cm3) pure burned RPUF produced the highly collapsed and carbonized material, while the high density (0.510 g/cm3) pure RPUF had little change in size and had reduced destruction of the material. Moreover, the scanning electronic microscope (SEM) observation showed that the higher density EG/RPUF composites had a more compact outer layer (burned layer) after burned, in which more wormlike materials composed of expanded graphite particles appeared. In addition, higher foam density led to less plastic deformation in the interface layer between the burned and the inside layers. These results indicated that a weight percent of a flame retardant additive that achieves satisfactory flame retardancy for a certain density foam cannot effectively be applied for another density foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Microwave assisted low temperature synthesis of MnZn ferrite nanoparticles

Abstract: MnZnFe2O4ferrite nanoparticles were prepared by co-precipitation method using a microwave heating system at temperature of 100 °C. X-ray diffraction reveals the samples as prepared are pure ferrite nanocrystalline phase, transmission electron microscopy image analysis shows particles are in agglomeration state with an average size of about 10 nm, furthermore, crystal size of samples are increased with longer microwave heating.

Theoretical analysis of a relativistic travelling wave tube filled with plasma

Abstract: A cold and uniform plasma-filled travelling wave tube with sinusoidally corrugated slow wave structure is driven by a finite thick annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. By means of the linear field theory, the dispersion relation for the relativistic travelling wave tube (RTWT) is derived. By numerical computation, the dispersion characteristics of the RTWT are analysed in different cases of various geometric parameters of the slow wave structure and plasma densities. Also the gain versus frequency for three different plasma densities and the peak gain of the tube versus plasma density are analysed. Some useful results are obtained on the basis of the discussion.

Carbon Nanotubes can Enhance Phase Dispersion in Polymer Blends

Abstract: A two-step method was used to prepare carbon nanotube (CNT)/ethylene-vinylacetate copolymer (EVA)/polyethylene (PE) and CNT/polycarbonate (PC)/PE composites. First, CNT-EVA and CNT-PC master batches were obtained by solution-phase processing, and second, the CNT masterbatches were melt-mixed with PE. Phase morphological observation indicates that there is a marked decrease in the size of the dispersed particles in the composites. This finding is of practical significance to develop new polymer materials based on blending concept.

Heteroepitaxial growth of ZnO on perovskite surfaces

Abstract: The microstructural properties of heteroepitaxial ZnO thin films prepared by laser molecular beam epitaxy (L-MBE) were investigated on SrTiO3 substrates and BaTiO3/SrTiO3 pseudo substrates with different orientations. The interface characteristics were in situ monitored by reflection high-energy electron diffraction (RHEED), and the epitaxial orientation relations were reconfirmed by ex situ x-ray diffraction (XRD) measurements. ZnO films grown on SrTiO3(0 0 1) and BaTiO3/SrTiO3(0 0 1) contained a poly-domain structure. For the former, the lattice mismatch was about −1.7% by four types of domain growth with the epitaxial relation of ZnO(1 1 0)||SrTiO3(0 0 1) and ZnO[−1 1 1]|| SrTiO3100. For the latter, twin domains would result in a smaller mismatch of −0.8% by the epitaxial relation of ZnO(0 0 1)||BaTiO3(0 0 1) and ZnO[1 1 0]|| BaTiO31 1 0. On SrTiO3(1 1 1) and BaTiO3/SrTiO3(1 1 1), single-domain films following the c-axial direction were observed with in-plane orientation ZnO[1 1 0]||SrTiO3[1 1 0] and ZnO[1 0 0]||BaTiO3[1 1 0], respectively. This 30° rotation in the in-plane direction of the ZnO epilayer with respect to the perovskite surfaces increased the lattice mismatch from about −2% to −14.5% after inserting BaTiO3 layers. The orientation of ZnO films could be attributed to the characteristic difference of the interface energy. It is determined entirely by interface stress and crystallographic symmetry for the growth on nonpolar (0 0 1)-orientated perovskite surfaces while the competition between elastic energy and chemical energy plays an important role for that on polar (1 1 1)-surfaces.

Iterative Approximation to Convex Feasibility Problems in Banach Space

Abstract: The convex feasibility problem (CFP) of finding a point in the nonempty intersection is considered, where is an integer and each is assumed to be the fixed point set of a nonexpansive mapping , where is a reflexive Banach space with a weakly sequentially continuous duality mapping. By using viscosity approximation methods for a finite family of nonexpansive mappings, it is shown that for any given contractive mapping , where is a nonempty closed convex subset of and for any given the iterative scheme is strongly convergent to a solution of (CFP), if and only if and satisfy certain conditions, where and is a sunny nonexpansive retraction of onto . The results presented in the paper extend and improve some recent results in Xu (2004), O'Hara et al. (2003), Song and Chen (2006), Bauschke (1996), Browder (1967), Halpern (1967), Jung (2005), Lions (1977), Moudafi (2000), Reich (1980), Wittmann (1992), Reich (1994).

Parameters localisation of coherently distributed sources based on sparse signal representation

Abstract: A robust and low-complexity parameters estimation method, which combines TLS-ESPRIT and sparse signal representation (SSR) to estimate the parameter of coherently distributed sources is presented. The central direction-of-arrivals are estimated by TLS-ESPRIT based on approximate rotational relationship between two identical uniform linear arrays (ULAs), and angular spreads are given by basis selection method using SSR. Hence the method is a low-complex estimator that does not need a search in one or two-dimensional parameter space. And it owns more robustness in estimating angular spread than one-dimensional distributed source parameter estimator (DSPE). In addition, our method can estimate parameters of the sources with different angular signal distribution functions, which DSPE cannot work. The simulation results prove the effectiveness of our method.

Three New Limonoids from Cipadessa cinerascens

Abstract: Three new limonoids, cipadesins D-F (1-3), together with 8,15-dibydroxy-13E-labdane, beta-sitosterol and P-daucosterol, were isolated from the leaves and bark of Cipadessa einerascens. Their structures were elucidated by spectral evidence. X-Ray crystallographic analysis confirmed the structure of 1.

Solitary Wave Interactions in Granular Media

Abstract: We numerically study the interactions of solitary waves in granular media, by considering a chain of beads, which repel upon contact via the Hertz-type potential, V∝δn, with 5/2≤ n≤3 and δ≥0, δ being the bead–bead overlap. There are two collision types of solitary waves, overtaking collision and head-on collision, in the chain of beads. Our quantitative results show that after collision the large solitary wave gains energy and the small one loses energy for overtaking type while the large one loses energy, and the small one gains energy for head-on type. The scattering effects decrease with n for overtaking collision whereas increase with n for head-on collision.

Temperature Dependence of Electric Properties of [Bi0.5(Na1-xAgx)0.5]1-yBayTiO3 Ceramics

Abstract: The temperature dependence of the piezoelectric and dielectric properties of lead-free piezoelectric ceramics, namely, [Bi0.5(Na1-xAgx)0.5]1-yBayTiO3 (abbreviated as BNBTy–xAg, x=0–6 mol % and y=0–10 mol %), was investigated, and the features of the depolarization temperature (Td) of the ceramics were discussed. The temperature dependence of the piezoelectric properties shows that the piezoelectric constant (d33) decreases sharply and that the piezoelectricity almost disappears at Td for all of the ceramic samples. With an increase in the amount of Ag+, the Td of the BNBT6–xAg ceramics decreases. Moreover, the Td of the BNBTy–4Ag ceramics decreases with an increase in the amount of Ba2+ up to 6 mol %, and then increases with a further increase in the amount of Ba2+. Furthermore, the temperature dependence of the dielectric properties shows that the characteristic of the diffuse phase transition is more evident for the compositions near the morphotropic phase boundary (MPB).

Variational PDE based image restoration using neural network

Abstract: Two variational partial differential equations as regularisation terms are proposed for the image restoration model based on the modified Hopfield neural network. One is based on a harmonic model and the other is based on a total variation model. The performance of these regularisation terms is analysed from the viewpoint of nonlinear diffusion. It can be shown that the two proposed restoration models have edge-preserving performance superior to that of the traditional restoration model. Two algorithms have been proposed on the basis of the harmonic restoration model and the total variation model. Experimental results show that the proposed algorithms are more effective than the traditional algorithm.

Lower ground state due to counter-rotating wave interaction in a trapped ion system

Abstract: We consider a single ion confined in a trap under the radiation of two travelling waves of lasers. In the strong-excitation regime and without the restriction of the Lamb-Dicke limit, the Hamiltonian of the system is similar to a driving Jaynes-Cummings model without the rotating wave approximation ( RWA). The approach we developed enables us to present complete eigensolutions, which makes it possible to compare with the solutions under the RWA. We find that the ground state in our non-RWA solution is energetically lower than the counterpart under the RWA. If we have the ion in the ground state, it is equivalent to a spin dependent force on the trapped ion. Discussion is given for the difference between the solutions with and without the RWA, and for the relevant experimental test, as well as for the possible application to quantum information processing.

Experimental research of reinforced concrete buildings struck by debris flow in mountain areas of western China

Abstract: It’s very important to simulate impact load of debris flow effectively and to investigate dynamic response of architectures under dynamic impact of debris flow, which are necessary to design disaster mitigation construction. Firstly, reinforced concrete domestic architectures in mountain areas of western China had been chosen as main architecture style. The bearing load style and the destructed shape of reinforced framed construction impacted by discontinuous viscous debris flow were studied systematically. Secondly, Jiangjia Ravine debris flow valley in Yunnan Province, China had been chosen as research region. Utilizing based data from fieldwork and practical survey, the authors simulated and calculated theoretically impact force of discontinuous viscous debris flow. Thirdly, an impact data collecting system (IMHE IDCS) was designed and developed to fulfill designed simulation experiments. Finally, a series of impact test of researched structure models had been fulfilled. During experiment, the destructed shape and course of models were observed and the dynamic displacement data and main natural frequency data of models were collected and analyzed.

Processing and phase separation of LSMO-based multiferroic composite ceramics

Abstract: In this paper, the effect of processing conditions on phase separation and crystal structure of ( x ) La 0.625 Sr 0.375 MnO 3 –(1 − x ) LuMnO 3 composite system was studied by XRD and SEM. The results confirm that there is a solid solution of monoclinic phase of space group P112 1 /a in this system, i.e. (La 0.625 Sr 0.375 ) x Lu 1− x MnO 3 is formed for x = 0.980–1.0. For 0 x ≤ 0.975, the immiscibility region shows clear separation of both La-rich and Lu-rich phases. The optimal preparation conditions were found for this system: sintering at 1250 and 1350 °C for samples of monoclinic La-rich phase and for the immiscibility region, respectively.

Changes in Thermostability of Photosystem II and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll a/b Protein Complexes

Abstract: We studied the difference in thermostability of photosystem II (PSII) and leaf lipid composition between a T-DNA insertion mutant rice (Oryza sativa L.) VG28 and its wild type Zhonghua 11. Native green gel and SDS-PAGE electro-phoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSII photochemistry (Fv/ Fm) and oxygen-evolving activity of PSII in leaves significantly decreased with increasing temperature. However, the PSII activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of 16:1t and a marked increase in the content of 18:3 compared with the wild type. The effects of lipid composition and unsaturation of membrane lipids on the thermostability of PSII are discussed.

Nonlinear Integral Inequalities in Two Independent Variables and Their Applications

Abstract: This paper generalizes results of Cheung and Ma (2005) to more general inequalities with more than one distinct nonlinear term From our results, some results of Cheung and Ma (2005) can be deduced as some special cases Our results are also applied to show the boundedness of the solutions of a partial differential equation

Study of mechanical behavior and reinforcing measures of middle rock wall of parallel tunnel with small interval

Abstract: Applying 2D elastoplastic numerical calculation method and under the conditions of surrounding rocks of grades Ⅲ,Ⅳand Ⅴ,the characteristics of stress and deformation of middle rock wall in parallelly laid twin tunnel are studiedThe findings show that the stress and deformation of middle rock wall are adverse due to the parallel tunnel with smaller interval;and these locations are very critical for design,construction and monitoring measurementsAt the same time,the effects of different buried depths and different reinforcing measures of rock wall on stress and deformation of the tunnels with small interval,are also studied,so as to provide guidance for design of support,selection of excavation method,reinforcing method of rock wall and monitoring plans

Morphology development of high‐density rigid polyurethane foam upon compression by on‐line scanning electronic microscope

Abstract: The high-density rigid polyurethane foam (RPUF) was obtained by airtight cast molding. The morphology development during the compressive fracture process of RPUF was observed on-line by a scanning electronic microscope (SEM). In the early stage of loading, the deformation of samples came from the tiny shape change in the cells' windows. As the load increases, some creases were formed in some cell windows in the vertical direction of loading, and the creases enlarged and resulted in the cracks across the whole cells. Moreover, during the deformation process, a failure band was formed in the weakest position. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Finite Element Modal Analysis Theory and Application

Abstract: The basic theory of finite element modal analysis was discussed briefly in this paper,and the method how to build properly finite element model of body in white was recited.Through calculation and analysis,nature frequency and modal shape were found.Results were compared with those from experience.At last,the feasibility of adopted method of modeling and analysis was validated.

Prediction of Soil Erosion on Different Underlaying Surface in Construction Period of Xichang to Panzhihua Expressway

Abstract: In order to investigate the behavior of soil erosion on the slope of the different underlaying surface during construction, the experiment with natural rainfall on Xichang-Panzhihua highway was conducted, to quantify the runoff and soil loss. The results show that: (1) the main type of soil erosion is gully erosion, the amount of soil erosion caused by gully erosion is higher than that by surface erosion. (2) The principal factor causing soil erosion on the slope of the embankment is individual amount of precipitation, the width of the embankment and rain intensity. (3) The principal factor causing soil erosion on the cutting slope is individual amount of precipitation, the width of the cutting slope and rain intensity. (4) The principal factor causing soil erosion on the slope of the dumped soil area is individual amount of precipitation, the width of the flat roof and rain intensity. There are well linear relationships between the amount of soil erosion and the principal factor, and their correlation coefficient are 0.935 7-0.999 8.

Cross-sectional analysis of ferroelectric domains in PZT capacitors via piezoresponse force microscopy

Abstract: Ferroelectric domains have been investigated on the cross-section of Pb(Zr0.55Ti0.45)O3 (PZT) thin film capacitors by scanning probe microscopy. The static domain images on the cross-section were obtained by the lateral piezoresponse force microscopy (LPFM) method, in which the ac voltage used to induce the converse piezoelectric effect was applied between the conductive tip and the bottom electrode. The polarization component normal to the substrate could be characterized via both d33 and d15 piezoelectric coefficients, which resulted in a high resolution of LPFM images. After a variable dc bias was applied between the top and the bottom electrodes, the variations of domain image on the cross-section were recorded by the LPFM immediately. Upon the application of low bias, new domain sites appeared near the PZT/Pt interface opposite to the initial polarization. Forward stretch of new domains was facilitated under the dc field approaching the coercive field Ec. Under a very high field (about three times of the Ec), the sidewise expansion of columnar domains was observed. However, the domains were only partially switched even though a very high field was applied. The observed domain growth process indicated a lower energy barrier for nucleation compared with that of domain wall motion. Possible reasons for the incomplete switching are the substantial influences of the interface and depolarization in thin film capacitors.

Run-time Monitoring of Energy Consumption in Wireless Sensor Networks

Abstract: As sensor nodes are commonly battery-operated, energy consumption is a major concern in most wireless sensor networks. Run-time monitoring of energy consumption in sensor nodes is crucial to obtaining the network-wide distribution of remaining energy. In this paper, we present a computation-efficient approach to the run-time monitoring of energy consumption of MICA2 nodes running TinyOS applications. A standalone TinyOS module is developed to capture both low-level events and high level commands to track the state transitions of individual hardware components of the nodes. The energy consumption of the nodes is estimated with a power model adjusted regularly according to the readings of supply voltage. The lifetime of the nodes is predicted by linear extrapolation of their current energy consumption estimates.

Effect of nano-silicon dioxide on hydration and hardening of portland cement

Abstract: The hydration and hardening of cement-based materials containing nano-silicon dioxide of 5% (in mass) were investigated by microcalorimeter, X-ray diffraction, differential thermal analysis, scanning electron microscope, and nitrogen adsorption. The results show that nano-silicon dioxide can consume large amounts of Ca(OH)2 due to its high pozzolanic activity, so that hydration can be accelerated, the evolution rate of hydration heat in the early period can be increased, the microstructure can be improved and harden cement paste gets more homogeneous and dense. Nano-silicon dioxide can increase water requirement of normal consistency, shorten setting time and enhance com- pressive strength of cement-based materials, especially at middle period and later period.

Design and Performance of Miniature Rogowski Coil for Heavy Current Measurement

Abstract: A kind of miniature Rogowski coil which measures high frequency and heavy current is introduced,and the principle of work of Rogowski coil is analyzed.The influence of non-uniform laying of the miniature Rogowski coil,including the biased laying and the inclined laying on the electric current survey performance is discussed.In order to reduce the influence of the coil laying on the capriciousness,the coil may be wound thread or increased evenly from the integral coefficient.The Rogowski coil of the hollow multi-layer circles reduces the coil stray capacity in the manufacture process.The design project of coil is proposed,the current waveform is tested by using many kinds of structures of the coil,and the massive test data are obtained.Through comparing the overseas standard electric current test and head test data of the probe,the current coil design is improved unceasingly.The test using magnetic material can enhance the coil actually from the integral criterion function,but the used magnetic material should have saturation induction density and consider its working band.