Showing papers by "Tsinghua University published in 2000"
TL;DR: The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag(+) treatment.
Abstract: To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO(3) and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both E. coli and S. aureus cells after Ag(+) treatment. The cytoplasm membrane detached from the cell wall. A remarkable electron-light region appeared in the center of the cells, which contained condensed deoxyribonucleic acid (DNA) molecules. There are many small electron-dense granules either surrounding the cell wall or depositing inside the cells. The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag(+) treatment. The slighter morphological changes of S. aureus compared with E. coli recommended a defense system of S. aureus against the inhibitory effects of Ag(+) ions.
3,811 citations
TL;DR: A converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated, which has very good current sharing characteristics even in the presence of relatively large duty cycle mismatch.
Abstract: Boost converters are widely used as power-factor corrected preregulators In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple A major design criterion then is to ensure equal current sharing among the parallel converters In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented Simulation and experimental results are also given
570 citations
TL;DR: This work describes audio and visual features that can effectively characterize scene content, present selected algorithms for segmentation and classification, and review some testbed systems for video archiving and retrieval.
Abstract: Multimedia content analysis refers to the computerized understanding of the semantic meanings of a multimedia document, such as a video sequence with an accompanying audio track. With a multimedia document, its semantics are embedded in multiple forms that are usually complimentary of each other, Therefore, it is necessary to analyze all types of data: image frames, sound tracks, texts that can be extracted from image frames, and spoken words that can be deciphered from the audio track. This usually involves segmenting the document into semantically meaningful units, classifying each unit into a predefined scene type, and indexing and summarizing the document for efficient retrieval and browsing. We review advances in using audio and visual information jointly for accomplishing the above tasks. We describe audio and visual features that can effectively characterize scene content, present selected algorithms for segmentation and classification, and review some testbed systems for video archiving and retrieval. We also describe audio and visual descriptors and description schemes that are being considered by the MPEG-7 standard for multimedia content description.
552 citations
TL;DR: In this article, the authors systematically measured emissions from 56 fuel/stove combinations in India and China, a large fraction of the combinations in use world-wide, and found that the total emissions per unit delivered energy were substantially greater from burning the solid fuels than from burning liquid or gaseous fuels, due to lower thermal and combustion efficiencies for solid-fuel and stove combinations.
479 citations
TL;DR: A review of studies of biocompatibility of diamond-like carbon (DLC) and carbon nitride (CN) coatings can be found in this article, which outlines the present level of research and suggests areas for future research, these include in vivo tests and a more detailed investigation of coating bond structure or properties.
Abstract: This paper reviews the present status of studies of biocompatibility of diamond-like carbon (DLC) and carbon nitride (CN) coatings. DLC and CN coatings, due to their novel mechanical and tribological properties, chemical inertness, electrical and optical properties, and biocompatibility, are excellent candidates for biomedical applications. A number of clinical applications for DLC are now being considered by commercial manufacturers of surgical implants. Preliminary studies have shown that DLC coating can be adherent on a range of biomaterials with desirable bulk properties, no toxicity toward living cells, no inflammatory response or loss of cell integrity, as well no cellular damage. Despite only a few reports about biocompatibility of CN coating, which, with its mechanical and chemical properties comparable with DLC, is a very attraction coating material for future biomedical applications. This paper outlines the present level of research and suggests areas for future research, these include in vivo tests and a more detailed investigation of coating bond structure or properties.
349 citations
05 Nov 2000
TL;DR: A corner block list-a new efficient topological representation for non-slicing floorplan is proposed with applications to VLSI floorplan and building block placement and the experimental results demonstrate the algorithm is quite promising.
Abstract: In this paper, a corner block list -- a new efficient topological representation for non-slicing floorplan is proposed with applications to VLSI floorplan and building block placement. Given a corner block list, it takes only linear time to construct the floorplan. Unlike the O-tree structure, which determines the exact floorplan based on given block sizes, corner block list defines the floorplan independent of the block sizes. Thus, the structure is better suited for floorplan optimization with various size configurations of each block. Based on this new structure and the simulated annealing technique, an efficient floorplan algorithm is given. Soft blocks and the aspect ratio of the chip are taken into account in the simulated annealing process. The experimental results demonstrate the algorithm is quite promising.
312 citations
TL;DR: By using this scheme, the mean square values of the symbol timing estimation error can be decreased by several orders of magnitude compared to the common correlation methods in both the AWGN and multipath fading channels.
Abstract: Orthogonal frequency division multiplexing (OFDM) is an effective modulation technique for high-rate and high-speed transmission over frequency selective fading channels. However, OFDM systems can be extremely sensitive and vulnerable to synchronization errors. In this paper, we present a scheme for performing timing recovery that includes symbol synchronization and sampling clock synchronization in OFDM systems. The scheme is based on pilot subcarriers. In the scheme, we use a path time delay estimation method to improve the accuracy of the correlation-based symbol synchronization methods, and use a delay-locked loop (DLL) to do the sampling clock synchronization. It is shown that by using this scheme, the mean square values of the symbol timing estimation error can be decreased by several orders of magnitude compared to the common correlation methods in both the AWGN and multipath fading channels. In addition, the scheme can track the symbol timing drift caused by the sampling clock frequency offsets.
297 citations
TL;DR: The strength and Young's modulus of the composites in tensile tests overlapped the lower range of values reported for bone, and the composite showed biodegradability that was partly through a multinucleated giant cell mediated process.
Abstract: Several types of calcium phosphate/collagen composites, including noncrystalline calcium phosphate/collagen, poorly crystalline carbonate-apatite (PCCA)/collagen, and PCCA + tetracalcium phosphate/collagen composites, were prepared through the mineralization of collagen matrix. The type I collagen was presoaked with a PO(3-)(4) containing solution and then immersed in a Ca(2+) containing solution to allow mineral deposition. The solution of 0.56 M sodium dibasic phosphate (Na(2)HPO(4)) with a pH of nearly 14 was metastable and its crystallization produced Na(2)HPO(4) and sodium tripolyphosphate hexahydrate (Na(5)P(3)O(10)). 6H(2)O), leading to a controlled release of orthophosphate ions during the subsequent mineral precipitation. The development of the composites was investigated in detail. The mineral contributed up to 60-70% of the weight of the final composites. The strength and Young's modulus of the composites in tensile tests overlapped the lower range of values reported for bone. When implanted in muscle tissue, the composite showed biodegradability that was partly through a multinucleated giant cell mediated process. In a bone explant culture model it was observed that bone-derived cells deposited mineralizing collagenous matrix on the composite.
290 citations
TL;DR: In this article, an alloy of palladium and silver dispersed on Al2O3 has been used for the selective hydrogenation of acetylene, but the selectivity of Pd-Ag catalyst is higher and less impaired by temperature increase than that of pure metal Pd catalyst.
Abstract: An alloy of palladium and silver dispersed on Al2O3 has been used for the selective hydrogenation of acetylene. The activity of Pd–Ag catalyst is lower than that of pure metal Pd catalyst. But the selectivity of Pd–Ag catalyst is higher and less impaired by temperature increase than that of Pd catalyst. X-ray diffraction (XRD) indicates that metal Pd and Ag can form an alloy on the surface of alumina. X-ray photoelectron spectroscopy (XPS) shows that the Pd–Ag alloy is formed with enrichment of Ag on the surface. Results of hydrogen adsorption isotherm, temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) reveal that the bulk of palladium of Pd–Ag catalyst adsorbed a small amount of hydrogen, which is desorbed at a higher temperature than that in the case of Pd catalyst.
264 citations
TL;DR: A nitrate-citrate gel was prepared from metal nitrates and citric acid by sol-gel process, in order to synthesize Ni 0.25 Cu 0.50 Fe 2 O 4 ferrite as discussed by the authors.
262 citations
TL;DR: In this paper, the strain energies in straight and bent single-walled carbon nanotubes (SWNTs) are calculated by taking account of the total energy of all the occupied band electrons.
Abstract: The strain energies in straight and bent single-walled carbon nanotubes (SWNT's) are calculated by taking account of the total energy of all the occupied band electrons. The obtained results are in good agreement with previous theoretical studies and experimental observations. Young's modulus and the effective wall thickness of SWNT's are obtained from the bending strain energies of SWNT's with various cross-sectional radii. The repulsion potential between ions contributes the main part of Young's modulus of SWNT's. The wall thickness of the SWNT comes completely from the overlap of electronic orbits and is approximately of the extension of the $\ensuremath{\pi}$ orbit of carbon atom. Both Young's modulus and the wall thickness are independent of the radius and the helicity of SWNT, and insensitive to the fitting parameters. The results show that continuum elasticity theory can serve well to describe the mechanical properties of SWNT's.
TL;DR: In this paper, the atlases of the global conditioning index and the global stiffness index are obtained in the solution space to optimize the link lengths of 3-DOF SPMs; the dexterity and stiffness maps of the manipulators are presented to analyze the operational performance.
TL;DR: In this paper, a Hermite type collocation method is proposed, in which both PDEs and prescribed traction boundary conditions are imposed on prescribed traction boundaries, which improves the accuracy significantly.
Abstract: Meshless methods based on collocation with radial basis functions (RBFs) are investigated in detail in this paper. Both globally supported and compactly supported radial basis functions are used with collocation to solve partial differential equations (PDEs). Using RBFs as a meshless collocation method to solve PDEs possesses some advantages. It is a truly mesh-free method, and is space dimension independent. Furthermore, in the context of scattered data interpolation it is known that some radial basis functions have spectral convergence orders. This study shows that the accuracy of derivatives of interpolating functions are usually very poor on boundary of domain when a direct collocation method is used, therefore it will result in significant error in solving a PDE with Neumann boundary conditions. Based on this fact, a Hermite type collocation method is proposed in this paper, in which both PDEs and prescribed traction boundary conditions are imposed on prescribed traction boundary. Numerical studies shows that the Hermite type collocation method improve the accuracy significantly.
TL;DR: In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its DC link capacitor dynamics included, and four principal control strategies for UPFC series element main control and their impacts on system stability are discussed.
Abstract: In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its DC link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC-network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly.
TL;DR: A review of the up-to-date experimental studies on amorphization transition, which results in the formation of amorphous alloys or metallic glasses, by ion irradiation of multiple metal layers in the binary metal systems is presented in this paper.
Abstract: This review attempts to present first a brief summary of the up-to-date experimental studies on amorphization transition, which results in the formation of amorphous alloys or metallic glasses, by ion irradiation of multiple metal layers in the binary metal systems Secondly, based on the framework of Miedema’s theory, thermodynamic modeling of metallic glass formation is described with consideration of the significant role of interfacial free energy of the multilayers in amorphization Thirdly, results of molecular dynamics simulations for some representative systems are presented to show the calculation of the intrinsic glass-forming ability from interatomic potential of the binary metal systems
TL;DR: In this article, the authors used the Nernst-Einstein equation to calculate the diffusion coefficient of chloride ions of high-performance concrete (HPC), analyzing and discussing the property of resistance to chloride ion of HPC with fly ash or blast furnace slag.
TL;DR: A new model for portfolio selection is proposed in which the expected returns of securities are considered as variables rather than as the arithmetic means of securities, to describe the return and risk of a portfolio more accurately.
TL;DR: In this article, the authors proposed a new method for randomizing the Halton sequence using the von Neumann-Kakutani transformation, which combines the potential accuracy advantage of Halton sequences in multi-dimensional integration with the practical error estimation advantage of Monte Carlo methods.
TL;DR: The accumulation of TOC in the supernatant of the bioreactor and its degradation after 5 months of operation proved to be inhibitory towards the metabolic activity of the activated sludge, as well as contributing to the poor membrane permeability of the mixed liquor.
TL;DR: New sufficient conditions for simplified fuzzy systems and linear TS fuzzy systems as universal approximators are given, respectively and a comparative study on existing sufficient conditions is carried out with numeric examples.
Abstract: Universal approximation is the basis of theoretical research and practical applications of fuzzy systems. Studies on the universal approximation capability of fuzzy systems have achieved great progress in recent years. In this paper, linear Takagi-Sugeno (TS) fuzzy systems that use linear functions of input variables as rule consequent and their special case, named simplified fuzzy systems that use fuzzy singletons as rule consequent, are investigated. On condition that overlapped fuzzy sets are employed, new sufficient conditions for simplified fuzzy systems and linear TS fuzzy systems as universal approximators are given, respectively. Then, a comparative study on existing sufficient conditions is carried out with numeric examples.
TL;DR: It is found that both CAP and CPL have excellent nerve cell affinity, defined as the ability to promote nerve cell to grow and function normally, and those two materials may be promising for the repair of the nervous system.
Abstract: Reparation of the central nervous system (CNS) is important because when it is impaired its recovery is difficult and concomitant malfunction of other parts of body occurs. In our previous studies, chitosan was found to be a good material supporting nerve repair. The purpose of this article was to study the ability of chitosan and some chitosan-derived materials to facilitate the growth of nerve cells. Those materials were chitosan, glutaraldehyde-crosslinked chitosan, glutaraldehyde-crosslinked chitosan-gelatin conjugate, a chitosan-gelatin mixture, chitosan coated with polylysine (CAP), and a chitosan-polylysine mixture (CPL). Gelatin and polylysine were used as controls. After nerve cells (gliosarcoma cells and normal cerebral cells) were grown on those materials, their attachment, spread, and growth were observed. The adsorption of some extracellular matrix molecules such as laminin and fibronectin on the materials and the role the molecules play in nerve cell attachment and spreading were also studied by enzyme-linked immunosorbent assay and MTT method. We found that both CAP and CPL have excellent nerve cell affinity, defined as the ability to promote nerve cell to grow and function normally. Those two materials may be promising for the repair of the nervous system. Materials precoated with laminin, fibronectin, and serum were analyzed for their nerve cell affinity. Results suggest that after being precoated with laminin and fibronectin solution or serum, all material have better nerve cell affinity.
TL;DR: In this paper, the authors showed that catalytic stability depends greatly on the preparation method of the support precursor and showed that the catalyst prepared by impregnation of ultra-fine Zr(OH)4 (6nm) particles with nickel nitrate showed high and extremely stable activity for syngas production.
Abstract: CO2 reforming of CH4 was studied at 1030 K over Ni/ZrO2 catalysts with different preparations. It was shown that catalytic stability depends greatly on the preparation method of the support precursor. The catalyst prepared by impregnation of ultra-fine Zr(OH)4 (6 nm) particles with nickel nitrate showed high and extremely stable activity for syngas production. In contrast, the nickel catalyst prepared using bigger Zr(OH)4 particles deactivated rapidly. Also, the nickel catalyst made from co-precipitation of ultra-fine nickel–zirconium hydroxide (7 nm) was not resistant to coke deposition during the reaction.
TL;DR: In this article, the authors used the molecular dynamics computational technique to investigate the thermal conductivity of solid thin films in the direction perpendicular to the film plane and found that the calculated values are roughly 30 percent higher than anticipated.
Abstract: This study uses the molecular dynamics computational technique to investigate the thermal conductivity of solid thin films in the direction perpendicular to the film plane. In order to establish a benchmark reference, the computations are based on the widely used Lennard-Jones argon model due to its agreement with experimental liquid-phase data, its physically meaningful parameters, and its simple two-body form. Thermal conductivity increases with film thickness, as expected from thin-film experimental data and theoretical predictions. The calculated values are roughly 30 percent higher than anticipated. Varying the boundary conditions, heat flux, and lateral dimensions of the films causes no observable change in the thermal conductivity values. The present study also delineates the conditions necessary for meaningful thermal conductivity calculations and offers recommendations for efficient simulations. This work shows that molecular dynamics, applied under the correct conditions, is a viable tool for calculating the thermal conductivity of solid thin films. More generally, it demonstrates the potential of molecular dynamics for ascertaining microscale thermophysical properties in complex structures.
19 Jun 2000
TL;DR: In this article, an n-gram-based model was proposed to predict the next document in the Web using path profiles of users from very large data sets to predict users' future requests.
Abstract: As an increasing number of users access information on the Web, there is a great opportunity to learn from the server logs to learn about the users' probable actions in the future. We present an n-gram based model to utilize path profiles of users from very large data sets to predict the users' future requests. Since this is a prediction system, we cannot measure the recall in a traditional sense. We, therefore, present the notion of applicability to give a measure of the ability to predict the next document. Our model is based on a simple extension of existing point-based models for such predictions, but our results show for n-gram based prediction when n is greater than three, we can increase precision by 20% or more for two realistic Web logs. Also we present an efficient method that can compress our model to 30% of its original size so that the model can be loaded in main memory. Our result can potentially be applied to a wide range of applications on the Web, including pre-sending, pre-fetching, enhancement of recommendation systems as well as Web caching policies. Our tests are based on three realistic Web logs. Our algorithm is implemented in a prediction system called WhatNext, which shows a marked improvement in precision and applicability over previous approaches.
TL;DR: In this article, a search for the Standard Model Higgs boson in the data sample collected with the ALEPH detector at LEP, at centre-of-mass energies up to 209 GeV, was performed.
TL;DR: The kinetics study demonstrated that the biodegradation of three phthalates conformed to the first-order model with respect to their concentrations, and appeared to be related to the length of the alkyl-side chains.
TL;DR: In this article, an experimental adsorption cooling system driven by the waste heat of a diesel engine was described, where Zeolite 13×13×13 water was used as the working pair and a finned double-tube heat exchanger is used as an adsorber.
TL;DR: In this article, a method was developed to estimate the spatial and temporal distribution of vehicle emissions and concentrations in Beijing based on the limited database, and the vehicle sources were treated as both line sources and area sources to make full use of the available data.
TL;DR: Based on the investigations of crystal structure of nacre using SEM, TEM and XRD, it is proposed that there exists a domain structure of crystal orientation in the nacre as discussed by the authors.