Showing papers by "Tsinghua University published in 2002"

Expected value of fuzzy variable and fuzzy expected value models

Abstract: This paper will present a novel concept of expected values of fuzzy variables, which is essentially a type of Choquet integral and coincides with that of random variables. In order to calculate the expected value of general fuzzy variable, a fuzzy simulation technique is also designed. Finally, we construct a spectrum of fuzzy expected value models, and integrate fuzzy simulation, neural network, and genetic algorithms to produce a hybrid intelligent algorithm for solving general fuzzy expected value models.

Theoretically efficient high-capacity quantum-key-distribution scheme

Abstract: A theoretical quantum key distribution scheme using Einstein-Podolsky-Rosen (EPR) pairs is presented. This scheme is efficient in that it uses all EPR pairs in distributing the key except those chosen for checking eavesdroppers. The high capacity is achieved because each EPR pair carries 2 bits of key code.

Nanotechnology: spinning continuous carbon nanotube yarns.

Abstract: Carbon nanotubes weave their way into a range of imaginative macroscopic applications. The creation of continuous yarns made out of carbon nanotubes would enable macroscopic nanotube devices and structures to be constructed1,2. Here we show that carbon nanotubes can be self-assembled into yarns of up to 30 cm in length simply by being drawn out from superaligned arrays of carbon nanotubes, and that the strength and conductivity of these yarns can be enhanced by heating them at high temperatures. Our findings should help to translate the remarkable mechanical, electrical and thermal properties of carbon nanotubes to a macroscopic scale.

Information measure for performance of image fusion

Abstract: Mutual information is proposed as an information measure for evaluating image fusion performance. The proposed measure represents how much information is obtained from the input images. No assumption is made regarding the nature of the relation between the intensities in both input modalities. The results show that the measure is meaningful and explicit.

Selected-Control Hydrothermal Synthesis of α- and β-MnO2 Single Crystal Nanowires

Abstract: A selective-control hydrothermal method has been developed in the preparation of α- and β-MnO2 single-crystal nanowires. The crystal structure and morphology of the final products can be influenced by the concentration of NH4+ and SO42-.

Design and implementation of a brain-computer interface with high transfer rates

Abstract: This paper presents a brain-computer interface (BCI) that can help users to input phone numbers. The system is based on the steady-state visual evoked potential (SSVEP). Twelve buttons illuminated at different rates were displayed on a computer monitor. The buttons constituted a virtual telephone keypad, representing the ten digits 0-9, BACKSPACE, and ENTER. Users could input phone number by gazing at these buttons. The frequency-coded SSVEP was used to judge which button the user desired. Eight of the thirteen subjects succeeded in ringing the mobile phone using the system. The average transfer rate over all subjects was 27.15 bits/min. The attractive features of the system are noninvasive signal recording, little training required for use, and high information transfer rate. Approaches to improve the performance of the system are discussed.

Synthesis of Large-Area Silicon Nanowire Arrays via Self-Assembling Nanoelectrochemistry

Abstract: Large-area silicon nanowire arrays have been prepared on a silicon wafer without the use of a template The simple method, which can be carried out near room temperature, involves the nanoelectrochemistry of silver nanowires in an aqueous HF solution containing silver nitrate This technique may be generally applicable to other semiconductors and metals The Figure shows nanodendritic silicon wires

Giant dielectric permittivity observed in Li and Ti doped NiO.

Abstract: A giant low-frequency dielectric constant ( epsilon 0 approximately 10(5)) near room temperature was observed in Li,Ti co-doped NiO ceramics. Unlike currently best-known high epsilon 0 ferroelectric-related materials, the doped oxide is a nonperovskite, lead-free, and nonferroelectric material. It is suggested that the giant dielectric constant response of the doped NiO could be enhanced by a grain boundary-layer mechanism as found in boundary-layer capacitors. In addition, there is about a one-hundred-fold drop in the dielectric constant at low temperature. This anomaly is attributed to a thermally excited relaxation process rather than a thermally driven phase transition, as for that yielding ferroelectrics.

Multiwalled carbon nanotubes as gigahertz oscillators

Abstract: The retraction energy of a multiwalled carbon nanotube with an extruded core causes the core to oscillate with respect to its fully retracted position where the van der Waals potential energy is minimized. This phenomenon, together with the available nanotechnology, leads to the creation of nanomechanical systems of operating frequency up to several gigahertz.

Synthesis and Characterization of Lanthanide Hydroxide Single‐Crystal Nanowires

Abstract: Nanowires represent a class of quasi-one-dimensional materials, in which carrier motion is restricted in two directions so that they usually exhibit significant photochemical, photophysical, and electron-transport properties which differ from that of bulk or nanoparticle materials.[1±11] In the last decade, many important materials have been prepared in the form of nanorods or nanowires to generate some unexpected properties[2±5] based on which, many new potential applications have been explored. For example, wellcontrolled and monodisperse CdSe nanorods can be used in solar cells,[2] and can form liquid-crystal phases with orientational order and positional disorder in organic solvents;[3] single-crystalline, well-defined ZnO nanowires can serve as natural resonance cavities, and well-aligned ZnO nanowire arrays may serve as room-temperature ultraviolet nanolasers.[4] Along with chemical composition and crystal structure, shape and dimensionality are now regarded as particularly important factors that influence the chemical and/or physical properties of materials. As a consequence of their unique electronic structures and the numerous transition modes involving the 4f shell of their ions, lanthanide compounds usually have outstanding optical, electrical, and magnetic properties,[12±22] and have been widely used as high-quality phosphors,[12] up-conversion materials,[13] catalysts,[14] and time-resolved fluorescence (TRF) labels for biological detection.[15] There have been extensive studies regarding lanthanide chemistry at bulk or atomic levels,[16±19] and the synthesis of lanthanide monothiooxides,[20] lanthanide-doped oxides or sulfides, organolanthanide compounds, the complexation behavior of lanthanide ions or atoms,[16,17] and the emission phenomena from lanthanides when bound to biomolecules (including calcium-binding proteins and nucleic acids).[18,19] Very recently, the synthesis of lanthanide oxide[21] and fluoride[22] nanoparticles with enhanced luminescence and photomagnetic properties has also been reported. However, to the best of our knowledge, few studies have focused on the synthesis of nanowires or nanorods of lanthaniderelated compounds. Such materials would be of great significance because of the possible novel properties induced by their reduced dimensionality. Herein, we report the synthesis of lanthanide hydroxide nanowires (La(OH)3, Pr(OH)3, Nd(OH)3, Sm(OH)3, Eu(OH)3, Gd(OH)3, Dy(OH)3, Tb(OH)3, Ho(OH)3, Tm(OH)3, and YbOOH) through a facile solution-based hydrothermal synthetic pathway. The synthesis of Ln(OH)3 nanowires was based on the preparation of colloidal Ln(OH)3 at room temperature, with subsequent hydrothermal treatment at 180 8C for about 12 h. Figure 1A shows typical XRD patterns for La(OH)3 nanowires. All of the reflections could be readily indexed to the hexagonal phase (space group P63/m (no. 176)) of La(OH)3

General scheme for superdense coding between multiparties

Abstract: Dense coding or superdense coding in the case of high-dimension quantum states between two parties and multiparties is studied in this paper. We construct explicitly the measurement basis and the forms of the single-body unitary operations corresponding to the basis chosen, and the rules for selecting the one-body unitary operations in a multiparty case.

Carbon nanotube-modified electrodes for the simultaneous determination of dopamine and ascorbic acid.

Abstract: The voltammetric separation of dopamine and ascorbic acid was studied with cyclic voltammetry at two kinds of carbon nanotube-modified electrodes (coated and intercalated) The anodic peak difference reached 270 mV under the present conditions The separation mechanism and effect factors were carefully studied Using various types of surfactants as coating dispersants of carbon nanotubes, it was demonstrated that the charge nature of the surfactants had a strong effect on the electrochemical behavior of dopamine and ascorbic acid When the oxidation solution of carbon nanotubes was changed from the most commonly used mixed concentrated nitric acid and sulfuric acid (1 + 3 v/v) to dilute nitric acid and to hydrochloric acid, the anodic peak separation value of dopamine and ascorbic acid increased significantly, and it was shown that carboxylic acid groups attached to the carbon nanotubes were an adverse factor for the discrimination of DA from AA These results indicated that the resolution of DA and AA was mainly attributable to the stereo porous interfacial layer formed from aggregated pores and inner cavities of the carbon nanotubes The modified electrodes exhibited an attractive ability to measure DA and AA simultaneously and showed good stability and reproducibility

Stem cell pluripotency and transcription factor Oct4.

Abstract: Mammalian cell totipotency is a subject that has fascinated scientists for generations. A long lasting question whether some of the somatic cells retains totipotency was answered by the cloning of Dolly at the end of the 20th century. The dawn of the 21st has brought forward great expectations in harnessing the power of totipotentcy in medicine. Through stem cell biology, it is possible to generate any parts of the human body by stem cell engineering. Considerable resources will be devoted to harness the untapped potentials of stem cells in the foreseeable future which may transform medicine as we know today. At the molecular level, totipotency has been linked to a singular transcription factor and its expression appears to define whether a cell should be totipotent. Named Oct4, it can activate or repress the expression of various genes. Curiously, very little is known about Oct4 beyond its ability to regulate gene expression. The mechanism by which Oct4 specifies totipotency remains entirely unresolved. In this review, we summarize the structure and function of Oct4 and address issues related to Oct4 function in maintaining totipotency or pluripotency of embryonic stem cells.

URBAN AIR POLLUTION IN CHINA: Current Status, Characteristics, and Progress

Abstract: ▪ Abstract China is rapidly developing as evidenced by enhanced urbanization and industrialization and greatly increased energy consumption. However, these have brought Chinese cities a variety of urban air pollution problems in recent decades. During the 1970s, black smoke from stacks became the characteristic of Chinese industrial cities; in the 1980s, many southern cities began to suffer serious acid rain pollution; and recently, the air quality in large cities has deteriorated due to nitrous oxides (NOx), carbon monoxide (CO), and photochemical smog, which are typical of vehicle pollution. Some cities now have a mixture of these. Urban air pollution influences both the health of citizens and the development of cities. To control air pollution and protect the atmospheric environment, the Chinese government has implemented a variety of programs. This paper first reviews the current status of air quality in Chinese cities, especially key cities, then describes the characteristics of some major urban air ...

Development of a gas sensor utilizing chemiluminescence on nanosized titanium dioxide.

Abstract: A gas-sensing mode based on chemiluminescence generated on the surface of nanosized materials is proposed in the present work. Seven nanosized materials were tested, and chemiluminescence was detected from six of them during the catalytic oxidation of organic vapors in air. The luminescence characteristics of ethanol and acetone vapors passing through the surface of TiO2 chosen were studied with a chemiluminescence-based detection system. The linear range of chemiluminescence intensity versus concentration of organic compounds is 40-400 microg/mL for ethanol and 20-200 microg/mL for acetone dissolved in water, respectively. X-ray powder diffraction and Raman spectrometry were used to investigate the changes in catalytic activity of TiO2 after a 60-h reaction at 380 degrees C. The results showed that the carbon deposited on the surface of TiO2, decreasing the catalytic activity, but can be removed in air by controlling the temperature at 500 degrees C for 3 h. Regenerability and no consumption of sensor substrate signify the long lifetime of the gas sensor.

Single-walled and multiwalled carbon nanotubes viewed as elastic tubes with the effective Young's moduli dependent on layer number

Abstract: The complete energy expression of a deformed single-walled carbon nanotube (SWNT) is derived in the continuum limit from the local density approximation model proposed by Lenosky et al [Nature (London) 355, 333 (1992)] and is shown to be consistent with the classic shell theory by which Young's modulus, the Poisson ratio, and the effective wall thickness of SWNT's are obtained as $Y=470 \mathrm{TPa},$ $\ensuremath{ u}=034,$ and $h=075 \mathrm{\AA{}},$ respectively The elasticity of a multiwalled carbon nanotube (MWNT) is investigated as the combination of the above SWNT's of layer distance $d=34 \mathrm{\AA{}}$ and the effective Young's modulus of the MWNT is found to be an apparent function of the number of layers, N, varying from 470 to 104 TPa for $N=1$ to $\ensuremath{\infty}$

Music type classification by spectral contrast feature

Abstract: Automatic music type classification is very helpful for the management of digital music databases. In this paper, the octave-based spectral contrast feature is proposed to represent the spectral characteristics of a music clip. It represented the relative spectral distribution instead of average spectral envelope. Experiments show that the octave-based spectral contrast feature performs well in music type classification. Another comparison experiment demonstrates that the octave-based spectral contrast feature has a better discrimination among different music types than mel-frequency cepstral coefficients (MFCC), which is often used in previous music type classification systems.

Structure-directing coordination template effect of ethylenediamine in formations of ZnS and ZnSe nanocrystallites via solvothermal route.

Abstract: ZnS and ZnSe precursors (ZnS x 0.5en and ZnSe x 0.5en, en = ethylenediamine) were prepared via a solvothermal process using ethylenediamine as solvent. Phase-pure hexagonal wurtzite ZnS and ZnSe products were obtained by annealing the precursors in argon stream at temperatures above 350 degrees C. The role of ethylenediamine as a structure-directing coordination molecular template responsible for the morphologies of the annealed products was discussed. This work provided further insights into the solvent coordination molecular template (SCMT) mechanism previously proposed to explain the growth mechanism of CdE (E = S, Se, Te) nanorods in ethylenediamine (Inorg. Chem. 1999, 38, 1382). The as-prepared precursors as well as the annealed products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorbance spectroscopy (IR), thermogravimetric analysis (TGA), X-ray fluorescence (XRF) analysis, and combustion analysis for C, N, H contents.

Dissipative particle swarm optimization

Abstract: A dissipative particle swarm optimization is developed according to the self-organization of dissipative structure The negative entropy is introduced to construct an opening dissipative system that is far-from-equilibrium so as to driving the irreversible evolution process with better fitness The testing of two multimodal functions indicates it improves the performance effectively