Showing papers by "Harbin Institute of Technology published in 2004"
TL;DR: In this paper, the mechanical properties of nano-Fe2O3 and nano-SiO2 cement mortars were experimentally studied and the experimental results showed that the compressive and flexural strengths measured at the 7th day and 28th day of the cement mortar mixed with the nano-particles were higher than that of a plain cement mortar.
Abstract: The mechanical properties of nano-Fe2O3 and nano-SiO2 cement mortars were experimentally studied. The experimental results showed that the compressive and flexural strengths measured at the 7th day and 28th day of the cement mortars mixed with the nano-particles were higher than that of a plain cement mortar. Therefore, it is feasible to add nano-particles to improve the mechanical properties of concrete. The SEM study of the microstructures between the cement mortar mixed with the nano-particles and the plain cement mortar showed that the nano-Fe2O3 and nano-SiO2 filled up the pores and reduced CaOH2 compound among the hydrates. These mechanisms explained the supreme mechanical performance of the cement mortars with nano-particles.
1,052 citations
TL;DR: In this paper, pure and La doped TiO 2 nanoparticles with different La content were prepared by a sol-gel process using Ti (OC 4 H 9 ) 4 as raw material, and also were characterized by XRD, TG-DTA, TEM, XPS, DRS and Photoluminescence (PL) spectra.
515 citations
TL;DR: In this paper, the mechanical properties and self-monitoring capability of nano-SiO2 or nano-Fe2O3 were experimentally studied and compared with that of plain cement paste.
443 citations
20 Dec 2004
TL;DR: In this paper, the output-feedback stabilisation problem is solved for discrete-time systems with time-varying delay in the state, and a stability condition is first proposed, which is dependent on the minimum and maximum delay bounds.
Abstract: The output-feedback stabilisation problem is solved for discrete-time systems with time-varying delay in the state. A stability condition is first proposed, which is dependent on the minimum and maximum delay bounds. Based on this easily verifiable stability condition, the problems of stabilisation by static and dynamic output-feedback controllers are solved within the linear matrix inequality (LMI) framework. Since the obtained conditions for the existence of admissible controllers are not expressed as strict LMI conditions, the cone complementary linearisation procedure is exploited to solve the nonconvex feasibility problem. In addition, the obtained results, including stability analysis, static output-feedback stabilisation and dynamic output-feedback stabilisation are further extended to discrete time-delay systems with norm-bounded uncertain parameters. Numerical examples are also presented to illustrate the applicability of the developed results.
419 citations
TL;DR: Two different backstepping neural network (NN) control approaches are presented for a class of affine nonlinear systems in the strict-feedback form with unknown nonlinearities and the controller singularity problem is avoided perfectly in both approaches.
Abstract: In this paper, two different backstepping neural network (NN) control approaches are presented for a class of affine nonlinear systems in the strict-feedback form with unknown nonlinearities. By a special design scheme, the controller singularity problem is avoided perfectly in both approaches. Furthermore, the closed loop signals are guaranteed to be semiglobally uniformly ultimately bounded and the outputs of the system are proved to converge to a small neighborhood of the desired trajectory. The control performances of the closed-loop systems can be shaped as desired by suitably choosing the design parameters. Simulation results obtained demonstrate the effectiveness of the approaches proposed. The differences observed between the inputs of the two controllers are analyzed briefly.
404 citations
TL;DR: In this paper, a delay-dependent approach to robust H/sub/spl infin// filtering is proposed for linear discrete-time uncertain systems with multiple delays in the state.
Abstract: A delay-dependent approach to robust H/sub /spl infin// filtering is proposed for linear discrete-time uncertain systems with multiple delays in the state. The uncertain parameters are supposed to reside in a polytope and the attention is focused on the design of robust filters guaranteeing a prescribed H/sub /spl infin// noise attenuation level. The proposed filter design methodology incorporates some recently appeared results, such as Moon's new version of the upper bound for the inner product of two vectors and de Oliveira's idea of parameter-dependent stability, which greatly reduce the overdesign introduced in the derivation process. In addition to the full-order filtering problem, the challenging reduced-order case is also addressed by using different linearization procedures. Both full- and reduced-order filters can be obtained from the solution of convex optimization problems in terms of linear matrix inequalities, which can be solved via efficient interior-point algorithms. Numerical examples have been presented to illustrate the feasibility and advantages of the proposed methodologies.
390 citations
TL;DR: In this paper, a nonlinear control method and based on Lyapunov stability theory to design controller to synchronize two identical chaotic systems or two different chaotic systems was introduced. But the technique was applied to two identical Lu systems and two different Lu systems.
367 citations
TL;DR: An innovative watermarking scheme based on genetic algorithms (GA) in the transform domain is proposed, which is robust againstWatermarking attacks, and the improvement in watermarked image quality with GA.
340 citations
TL;DR: In this article, the authors examined the performance of a Si film vacuum on a Ni foil and found that it has a Li insertion capacity over 2000 mAh/g with cycleability over 1000 cycles, but a great issue was its difficulty to obtain a sufficiently thicker Si film capable of high current charge/discharge.
335 citations
TL;DR: In this paper, the robust H"2 and H"~ filtering problem for linear discrete-time systems with polytopic parameter uncertainty was studied and a matrix inequality condition was proposed to provide additional free parameters as compared to existing characterizations.
325 citations
TL;DR: This paper shows that an appropriate assignment of feature-weight can improve the performance of fuzzy c-means clustering and is given by learning according to the gradient descent technique.
TL;DR: A thin film of Si was vacuum-deposited onto a 30μm thick Ni foil from a source of n-type of Si, the film thickness examined being 200-1500
01 Dec 2004
TL;DR: A new face and palmprint recognition approach that first uses a two-dimensional separability judgment to select the DCT frequency bands with favorable linear separability, and extracts the linear discriminative features by an improved Fisherface method and performs the classification by the nearest neighbor classifier.
Abstract: In the field of image processing and recognition, discrete cosine transform (DCT) and linear discrimination are two widely used techniques. Based on them, we present a new face and palmprint recognition approach in this paper. It first uses a two-dimensional separability judgment to select the DCT frequency bands with favorable linear separability. Then from the selected bands, it extracts the linear discriminative features by an improved Fisherface method and performs the classification by the nearest neighbor classifier. We detailedly analyze theoretical advantages of our approach in feature extraction. The experiments on face databases and palmprint database demonstrate that compared to the state-of-the-art linear discrimination methods, our approach obtains better classification performance. It can significantly improve the recognition rates for face and palmprint data and effectively reduce the dimension of feature space.
TL;DR: In this article, the state of the art and key technologies concerned with equipment, process control, simulation, etc. are explored in detail, and conclusions are drawn concerning possible future developments in hydroforming technology.
TL;DR: In this article, the phase equilibria in the Ni-Al-Pt system and the influences of alloy composition on the formation, growth and spallation behavior of the resulting TGO scales formed during isothermal and thermal cycling tests at 1150°C were investigated.
Abstract: Thermal barrier coating (TBC) systems, needed for higher thrust with increased efficiency in gas turbines, typically consist of an alumina-scale forming metallic bond coat and a ceramic topcoat. The durability and reliability of TBC systems are critically linked to the oxidation behavior of the bond coat. Ideally, the bond coat should oxidize to form a slow-growing, non-porous and adherent thermally grown oxide (TGO) scale layer of α-Al2O3. The ability to promote such ideal TGO formation depends critically on the composition and microstructure of the bond coat, together with the presence of minor elements (metal and non-metal) that with time diffuse into the coating from the substrate during service. An experimental program was undertaken to attain a more detailed fundamental understanding of the phase equilibria in the Ni-Al-Pt system and the influences of alloy composition on the formation, growth and spallation behavior of the resulting TGO scales formed during isothermal and thermal cycling tests at 1150°C. Additional studies were conducted to determine the influence of platinum on interdiffusion behavior in the Ni-Al system, and how this influence would impact coating/substrate interdiffusion. It will be shown that platinum has a profound effect on the oxidation and interdiffusion behaviors, to the extent that novel advanced coating systems can be developed. Introduction The demand for improved performance in high-temperature mechanical systems has led to increasingly severe operating environments, particularly for the components in advanced gas-turbine engines. Future improvements in gas-turbine performance will require even higher operating efficiencies, longer operating lifetimes, reduced emissions and, therefore, higher turbine operating temperatures. Advanced cooling schemes coupled with thermal barrier coatings (TBCs) can enable the current families of nickel-base superalloys to meet the materials needs for the engines of tomorrow. Thermal barrier coating systems currently provide average metal temperature reductions of about 80°C, while potential benefits are estimated to be greater than 170°C. However, lack of reliability, more than any other design factor, limits the general use of TBC systems for gas turbines. Commercial advanced TBC systems are typically two-layered, consisting of a ceramic topcoat and an underlying metallic bond coat. The properties of the ceramic topcoat are such that it has a low thermal conductivity, high oxygen permeability, and a relatively high coefficient of thermal expansion. The topcoat is also made “strain tolerant” by depositing a structure that contains numerous pores and/or pathways. The consequently high oxygen permeability of the topcoat imposes the constraint that the metallic bond coat must be resistant to oxidation attack. The bond coat should therefore be sufficiently rich in aluminum to form a protective, thermally grown oxide (TGO) scale of α-Al2O3. In addition to imparting oxidation resistance, the TGO serves to bond the ceramic topcoat to the substrate/bond coat system. Notwithstanding, it is generally found that spallation and/or cracking of the growing TGO scale is the ultimate failure mechanism of Materials Science Forum Online: 2004-08-15 ISSN: 1662-9752, Vols. 461-464, pp 213-222 doi:10.4028/www.scientific.net/MSF.461-464.213 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:01:32) commercial TBCs, particularly EB-PVD TBCs [1-3]. Thus, improving the adhesion and integrity of the interfacial TGO scale is critical to the development of more reliable TBCs. Current bond coats are typically either an MCrAlY overlay (where M = Ni,Co, or both) or a platinum-modified diffusion aluminide (β-NiAl-Pt). The composition and phase constitutions of such bond coats vary. Both the MCrAlY and NiAl-Pt types of coating were originally developed to enhance long-term oxidation and corrosion protection of turbine components rather than specifically as bond coats. The oxidation resistance provided by these coatings allowed alloy developers to maximize the high-temperature mechanical properties of nickel-base superalloys. The original coatings required a high aluminum content in order to ensure re-healing of the Al2O3 scale after repeated cracking and spalling during service. In the case of TBC systems, however, Al2O3 healing after scale spallation is not an important requirement for ceramic topcoat adhesion. This is because the adhesion, and therefore the reliability, of a TBC system is dictated primarily by the first spallation event of the TGO scale. As a consequence, the currently used bond coats do not necessarily possess optimum compositions and/or structures for prime reliant TBC systems. In assessing a given bond coat system, it is also important to realize that its composition and structure change with time in service due to both TGO-scale growth and interdiffusion with the substrate. The occurrence of coating/substrate interdiffusion decreases the concentration of aluminum in the coating, thereby reducing the ability of the coating to sustain exclusive Al2O3-scale growth, particularly in the event of localized detachment and/or microcracking, and introduces unwanted elements (e.g., sulfur and titanium) which can promote oxide-scale spallation [4]. A further consequence of coating/substrate interdiffusion, particularly for the next generation of superalloys with up to 6 wt.% rhenium, is the formation of topologically close-packed (TCP) phases in the region of the original coating/substrate interface, which can be deleterious to the mechanical properties of the superalloy substrate. The results presented in this paper are from a larger US Office of Naval Research sponsored study that is concerned with gaining a more detailed fundamental understanding of the influences of alloy composition and microstructure on the adhesion/spallation resistance of TGO scales for the purpose of improving the reliability and durability of advanced TBC systems. An experimental approach was taken initially, from which the important chemical and microstructural factors governing TGO growth and adhesion were determined. The starting point for this study was a determination of the (partial) Ni-Al-Pt phase diagram, which to date has only been shown to be speculative [5] (see Fig.1). Oxidation and interdiffusion experiments were then conducted on the various Ni-Al-Pt bulk alloys processed to determine the potential effects of phase constitution and Pt content on overall coating performance. Experimental Procedures Ni-Al-Pt alloys were prepared by argon arc melting high-purity pieces of the constituents. To ensure homogenization and equilibration, all alloys were annealed at 1100 ̊C or 1150 ̊C for at least one week in a flowing argon atmosphere and then quenched in water to retain their high-temperature structure. The alloys were then cut into coupon samples and polished to a 600-grit finish for the further testing. The equilibrated alloy samples were first analyzed using X-ray diffraction (XRD) for phase identification and then prepared for metallographic analyses by cold mounting them in an epoxy resin followed by polishing to a 0.5 μm finish. Microstructure observations were initially carried out on etched samples using an optical microscope. Concentration profiles were obtained from unetched (i.e., re-polished) samples by either energy (EDS) or wavelength (WDS) dispersive spectrometry, with the former utilizing a scanning electron microscope (SEM) and the latter an 214 High Temperature Corrosion and Protection of Materials 6
TL;DR: Polymers 2-4 display strong fluorescent emissions in the solid state at room temperature and the effects of temperature on the hydrothermal reaction system of btx and CdSO(4) and found that different products can be obtained at different temperatures.
Abstract: Four novel cadmium−btx (btx = 1,4-bis(triazol-1-ylmethyl)benzene) coordination polymers [Cd(btx)2(NO3)2]n (1), [Cd(btx)2Cl2]n (2), [Cd(btx)(SO4)(H2O)2]n (3), and [Cd(btx)(S2O7)(H2O)]n (4) have been prepared by hydrothermal reaction (140 or 180 °C) and characterized. Both 1 and 2 have two-dimensional rhombohedral grid structures, 3 possesses a two-dimensional rectangular grid structure, and 4 displays a three-dimensional framework, which is formed by btx bridging parallel layers. To the author's best knowledge, polymer 4 is the first Cd(II) polymer in which the Cd(II) ion is eight-coordinated in a hexagonal bipyrimidal geometry. In addition, we studied the effects of temperature on the hydrothermal reaction system of btx and CdSO4 and found that different products can be obtained at different temperatures. Furthermore, polymer 3 possesses a very strong third-order NLO absorptive effect with an α2 value of 1.15 × 10-9 m W-1. Polymers 2−4 display strong fluorescent emissions in the solid state at room temper...
TL;DR: A novel algorithm for the automatic classification of low-resolution palmprints is proposed, using a set of directional line detectors to extract the principal lines of the palm in terms of their characteristics and their definitions in two steps.
TL;DR: In this article, the microstructural evolution during cold rolling of IF-steel up to reductions of 90% has been investigated using scanning and transmission electron microscope techniques, and the deformation microstructures consist of similar features to those already identified in several FCC metals, namely cell blocks showing a pattern of subdivision on two levels.
TL;DR: Using Kalman filtering theory, a new multi-sensor optimal information fusion algorithm weighted by matrices is presented in the linear minimum variance sense, which is equivalent to the maximum likelihood fusion algorithm under the assumption of normal distributions.
TL;DR: Rod-shaped CuO nanostructures were successfully synthesized by a one-step annealing process in air using copper plates as starting material as mentioned in this paper, and phase analysis was carried out using X-ray diffraction, transmission electron microscopy and micro-Raman scattering and the results confirmed the nanorods as single phase CuO.
TL;DR: The results indicate that for the group of phenol and chlorophenols studied, the presence of an increasing number of chlorine substituent atoms corresponds to an increasing reactivity of the undissociating compound, and a decreasing reactivities of the dissociated compound.
TL;DR: A novel computerized tongue inspection method aiming to address the problems of traditional tongue diagnosis, which is concerned with the identification of syndromes rather than with the connection between tongue abnormal appearances and diseases.
Abstract: Tongue diagnosis is an important diagnostic method in traditional Chinese medicine (TCM). However, due to its qualitative, subjective and experience-based nature, traditional tongue diagnosis has a very limited application in clinical medicine. Moreover, traditional tongue diagnosis is always concerned with the identification of syndromes rather than with the connection between tongue abnormal appearances and diseases. This is not well understood in Western medicine, thus greatly obstruct its wider use in the world. In this paper, we present a novel computerized tongue inspection method aiming to address these problems. First, two kinds of quantitative features, chromatic and textural measures, are extracted from tongue images by using popular digital image processing techniques. Then, Bayesian networks are employed to model the relationship between these quantitative features and diseases. The effectiveness of the method is tested on a group of 455 patients affected by 13 common diseases as well as other 70 healthy volunteers, and the diagnostic results predicted by the previously trained Bayesian network classifiers are reported.
TL;DR: In this article, the authors investigated the effect of delay on the dynamics of Chen's system with delayed feedback and showed that when the delay passes through certain critical values, chaotic oscillation is converted into a stable steady state or a stable periodic orbit.
Abstract: Time-delayed feedback has been introduced as a powerful tool for control of unstable periodic orbits or control of unstable steady states. In the present paper, regarding the delay as parameter, we investigate the effect of delay on the dynamics of Chen's system with delayed feedback. We first consider the effect of delay on the steady states, and then investigate the existence of local Hopf bifurcations. By using the normal form theory and center manifold argument, we derive the explicit formulas determining the stability, direction and other properties of bifurcating periodic solutions. Finally, we give several numerical simulations, which indicate that when the delay passes through certain critical values, chaotic oscillation is converted into a stable steady state or a stable periodic orbit.
TL;DR: In this article, the optimum performance in electrocatalytic activity for oxygen evolution reaction in alkaline media was obtained on the Co+Ni mixed oxide deposited from the solution containing Co{sup 2+}/Ni{sup2+} ratio of 1:1.
TL;DR: In this article, a photoreduction method was used to modify ZnO nanoparticles by depositing Pd on their surfaces with a photo-degradation method, and the effect of Pd content on SPS responses was discussed from the point of the electronic energy level.
TL;DR: In this article, a gas-solid two-fluid flow model is presented, which treats the kinetic and frictional stresses of particles additively, and the effects of inclined angle of conical base on the distributions of particle velocities and concentrations in the spout, annulus and fountain zones were numerical studied.
TL;DR: In this paper, the influence of plating parameters on the content of the co-deposited Al 2 O 3 particles in Co-Ni alloys was investigated, and it was shown that the presence of Al 2O 3 particles greatly improves the hardness and the wear resistance of composite coatings.
Abstract: Composite coatings of Co–Ni–Al 2 O 3 were studied by electrolytic codeposition of Co–Ni alloys and Al 2 O 3 from a sulfamate electrolyte containing Al 2 O 3 particles. The influence of plating parameters on the content of the co-deposited Al 2 O 3 particles in Co–Ni alloys was investigated. The maximum value of co-deposited Al 2 O 3 can be achieved at a particle content of 80 g l −1 in bath, a current density of 3 A dm −2 , a pH of 4.5, and a stirring rate of 100 rpm. In the process of codeposition, cathodic polarization increases with the increase of Al 2 O 3 concentration in bath and cobalt ions in electrolyte caused the reduction of polarization while nickel ions do not change the polarization behavior. Surface morphology and microstructure of Co–Ni–Al 2 O 3 coatings were determined by means of scanning electron microscopy, atomic force microscopy and X-ray diffraction. It was found that the phase structure of solid solution cannot be varied by codeposition of Al 2 O 3 particles in Co–Ni alloys, and it only influences the growth and orientation of crystal planes. It was shown that the presence of Al 2 O 3 particles in deposit greatly improves the hardness and the wear resistance of composite coatings. However, the codeposition of Al 2 O 3 increases the tensile internal stress of Co–Ni–Al 2 O 3 deposit. The coefficient of thermal expansion and the thermal conductivity of Co–Ni–Al 2 O 3 composite coatings are varied with the increase of Co contents and the temperature.
TL;DR: In this paper, the authors focus on polymer nanocomposites and their syntheses, properties and future applications, several of these application will be successful in the near future, and propose a new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation.
Abstract: This paper focuses on polymer nanocomposites and their syntheses, properties and future applications, several of these application will be successful in the near future. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in-situ intercalative polymerization and melt intercalation. The whole range of polymer matrices covered, i.e., thermoplastics, thermosets and elastomers. Small addition—typically less than 6 wt%—of these nanoscale inorganic fillers promote concurrently several properties of the polymer materials, including tensile characteristics, heat distortion temperature, scratch resistance, gas permeability resistance, and flame retardancy.
TL;DR: In this paper, the authors developed a distributed mathematical model of the airside heat exchanger under frosting in an air source heat pump water heater/chiller (ASHPWHC) unit and evaluated the impacts of frosting on the operational performance of an ASHPWHC unit.