Showing papers by "Shanghai Jiao Tong University published in 2001"

Revisitation of the localized excitations of the (2+1)-dimensional KdV equation

Abstract: In a previous paper (Lou S-y 1995 J. Phys. A: Math. Gen. 28 7227), a generalized dromion structure was revealed for the (2+1)-dimensional KdV equation, which was first derived by Boiti et al (Boiti M, Leon J J P, Manna M and Pempinelli F 1986 Inverse Problems 2 271) using the idea of the weak Lax pair. In this paper, using a Backlund transformation and the variable separation approach, we find there exist much more abundant localized structures for the (2+1)-dimensional KdV equation. The abundance of the localized structures of the model is introduced by the entrance of an arbitrary function of the seed solution. Some special types of dromion solution, lumps, breathers, instantons and the ring type of soliton, are discussed by selecting the arbitrary functions appropriately. The dromion solutions can be driven by sets of straight-line and curved-line ghost solitons. The dromion solutions may be located not only at the cross points of the lines but also at the closed points of the curves. The breathers may breathe both in amplitude and in shape.

Is All That Talk Just Noise? The Information Content of Internet Stock Message Boards

Abstract: Literally millions of messages have been posted on internet stock message boards. Financial press reports claim that these postings can move markets. We study message posting on Yahoo! Finance and Raging Bull for the firms that were in the Dow Jones Industrial Average and the Dow Jones Internet Commerce Index during the year 2000. Using computional linguistics methods we measure the bullishness of the messages. Significant predictive content was found between message posting and trading volume, between message posting and volatility, between the degree of bullishness of the messages and trading volume. These results were obtained even after taking news stories from the Wall Street Journal into account.

Performance improvement of adsorption cooling by heat and mass recovery operation

Abstract: An adsorption cooling system was developed and tested and various operation procedures have been tried. The experimental results show that the heat recovery operation between two adsorption beds will increase the COP by about 25% if compared with one adsorber basic cycle system. It was also proved that mass recovery is very effective for heat recovery adsorption cooling operation, which may help to obtain a COP increase of more than 10%. Theoretical analyses on the COP have been completed for various heat and mass recovery cycles, such as basic intermittent adsorption cycle, continuous two-adsorber heat recovery cycle, mass recovery cycle, mass recovery with sensible heat recovery, and mass recovery with both sensible heat and heat of adsorption recovery. The theoretical results are in good agreement with experimental values. Based upon the developed theoretical model, it is possible to predict the COP for various operation procedures of a real adsorption cooling system.

Mutations in IHH, encoding Indian hedgehog, cause brachydactyly type A-1.

Abstract: Brachydactyly type A-1 (BDA-1; MIM 112500) is characterized by shortening or missing of the middle phalanges (Fig. 1a). It was first identified by Farabee in 1903 (ref. 2), is the first recorded example of a human anomaly with Mendelian autosomal-dominant inheritance and, as such, is cited in most genetic and biological textbooks. Here we show that mutations in IHH, which encodes Indian hedgehog, cause BDA-1. We have identified three heterozygous missense mutations in the region encoding the amino-terminal signaling domain in all affected members of three large, unrelated families. The three mutant amino acids, which are conserved across all vertebrates and invertebrates studied so far, are predicted to be adjacent on the surface of IHH.

Communicative Language Teaching in China: Progress and Resistance

Abstract: TESOL QUARTERLY While existing test designs are being improved, organized efforts have been directed to alternative, more task-based test designs guided by contemporary language testing theories. Unlike the earlier tests, these new tests give due attention to speaking and writing. They are designed with a view to promoting learning. Formative assessment has been a means of teaching for many experienced language teachers over the years, but little research has been conducted on formative assessment in China and abroad. There seems a need for such research to complement language testing.

Literature review on solar adsorption technologies for ice-making and air-conditioning purposes and recent developments in solar technology

Abstract: The primary objective of this review is to provide fundamental understandings of the solar adsorption systems and to give useful guidelines regarding designs parameters of adsorbent bed reactors,and the applicability ofsolar adsorption both in air-conditioning and refrigeration with the improvement of the coefficient of performance. Solar adsorption heat pump and refrigeration devices are of significance to meet the needs for cooling requirements such as air-conditioning and ice-making and medical or food preservation in remote areas. They are also noiseless, non-corrosive and environmentally friendly. For these reasons the research activities in this sector are still increasing to solve the crucial points that make these systems not yet ready to compete with the well-known vapor compression system. There is an increasing interest in the development and use of adsorption chillers due to their various economic and impressive environmental benefits, enabling solar energy or waste heat to be used for applications such as district networks and cogeneration plants. Compared to adsorption systems that require heat sources with temperatures above 100°C (zeolite–water systems, activated carbon–methanol systems) or conventional compressor chillers, a silica gel/water adsorption refrigerator uses waste heat with temperature below 100°C. This creates new possibilities for utilizing low temperature energy.

Effects of Ca addition on the microstructure and mechanical properties of AZ91magnesium alloy

Abstract: The effects of Ca addition on the microstructure and mechanical properties of AZ91 magnesium alloy have been studied The results show that the Ca addition can refine the microstructure, reduce the quantity of Mg17Al12 phase, and form new Al2Ca phase in AZ91 magnesium alloy With the Ca addition, the tensile strength and elongation of AZ91magnesium alloy at ambient temperature are reduced, whereas Ca addition confers elevated temperature strengthening on AZ91 magnesium alloy The tensile strength at 150°C increases with increasing Ca content The impact toughness of AZ91magnesium alloy increases, and then declines as the Ca content increases The tensile and impact fractographs exhibit intergranular fracture features, Ca addition changes the pattern and quantity of tearing ridge, with radial or parallel tearing ridge increasing, tensile strength, elongation and impact toughness reduce

The BES upgrade

Abstract: The Beijing Spectrometer (BES) detector is a general purpose solenoid detector at the Beijing Electron Positron Collider (BEPC) in Beijing, China, that has collected large numbers of J/ψ, ψ′, Ds, D and τ events. In this paper, we describe the recent upgrade of the initial BES detector (BESI) to the improved BESII detector.

Chaotic characteristics of a one-dimensional iterative map with infinite collapses

Abstract: A one-dimensional iterative chaotic map with infinite collapses within symmetrical region [-1, O)/spl cup/(O, +1] is proposed. The stability of fixed points and that around the singular point are analyzed. Higher Lyapunov exponents of proposed map show stronger chaotic characteristics than some iterative and continuous chaotic models usually used. There exist inverse bifurcation phenomena and special main periodic windows at certain positions shown in the bifurcation diagram, which can explain the generation mechanism of chaos. The chaotic model with good properties can be generated if choosing the parameter of the map properly. Stronger inner pseudorandom characteristics can also be observed through /spl chi//sup 2/ test on the supposition of even distribution. This chaotic model may have many advantages in practical use.

X-Ray Probing of the Central Regions of Clusters of Galaxies

Abstract: The results on ASCA X-ray study of the central regions of medium-richness clusters of galaxies are summarized, while emphasizing the differences between cD and non-cD clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and cool) phases within ∼ 100kpc of a cD galaxy, where the ICM metallicity is also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal with a small metallicity gradient right of the center. The gravitational potential exhibits a hierarchical nesting around cD galaxies, while a total mass-density profile with a central cusp is indicated for a non-cD cluster, Abell 1060. The iron-mass-to-light ratio of the ICM decreases toward the center in both types of clusters, although it is radially constant in peripheral regions. The silicon-toiron abundance ratio in the ICM increases with the cluster richness, but remains close to the solar ratio around cD galaxies. These overall results are interpreted without appealing to the popular cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo structure formed around cD galaxies.

Efficient ray-tracing methods for propagation prediction for indoor wireless communications

Abstract: The application of several ray-tracing techniques, in combination with the uniform theory of diffraction, is presented for efficient prediction of propagation in the UHF (communication) band in an indoor environment First, we improve the computational efficiency of the two-dimensional (2D) ray-tracing method by reorganizing the objects in an indoor environment into irregular cells Second, by making use of the two-dimensional ray-tracing results, a new three-dimensional (3D) propagation-prediction model is developed, which can save 99% of the computation time of a traditional three-dimensional model This new hybrid model is more accurate than two-dimensional models, and more efficient in computing the path loss to any point in the building than traditional three-dimensional models In this model, reflection and refraction by layered materials, and diffraction for the corners of the walls, are considered A patched-wall model is used to improve the accuracy of prediction in the method Finally, a comparison between simulation and measurements shows good agreement

Effects of bismuth and antimony additions on the microstructure and mechanical properties of AZ91 magnesium alloy

Abstract: The effects of bismuth and antimony additions on the microstructure and mechanical properties of AZ91 alloy have been studied. Results show that a small amount of bismuth or antimony additions to AZ91 increases the yield strength and creep resistance significantly at elevated temperatures up to 200°C. The highest creep resistance has been obtained from the alloy with combined additions of bismuth and antimony. The activation energies of the steady-state creep for AZ91-based alloys studied were close to that of pure magnesium self-diffusion, indicating that dislocation climb is responsible for the creep mechanism under the present conditions. Microstructural observations reveal that the additions of bismuth or antimony have the effect of refining the b (Mg17Al12) precipitates in as-cast alloys and suppressing discontinuous precipitation of the b phase effectively during the aging process. Some rod-shaped Mg3Bi2 or Mg3Sb2 particles distributed mainly at grain boundaries have been observed in the alloys with bismuth or antimony additions. Both Mg3Bi2 and Mg3Sb2 have a high thermal stability and play important roles in improving creep resistance of the alloys at elevated temperatures. © 2001 Elsevier Science B.V. All rights reserved.

Characteristics and fabrication of NiTi/Si diaphragm micropump

Abstract: A novel micropump actuated by NiTi/Si composite diaphragm was described in this paper. The driving principle, microfabrication processes and characteristics of the pump were reported. The pump is composed of a deformable chamber and two silicon flap check valves. The outer dimension of the pump is 6 mm ×6 mm ×1.5 mm , with the diaphragm size of 3 mm ×3 mm ×20 μm. The fabrication processes include silicon micromachining and AuSi eutectic bonding. By using the recoverable force of NiTi thin-film and biasing force of silicon membrane, the actuation diaphragm realized reciprocating motion effectively. Experimental results show that the pump has superior performance, such as high pumping yield (up to 340 μl/min), high working frequency (up to 100 Hz), and long fatigue life time (more than 4×107 working cycles).

Structural forms of cubic BC 2 N

Abstract: Superhard cubic boron-carbonitrides $(c\ensuremath{-}{\mathrm{BC}}_{2}\mathrm{N})$ are studied with the use of the ab initio pseudopotential density functional method. The total energy, lattice constant, bulk and shear moduli, and electronic band structures as well as the electron density of states are calculated for all the possible $c\ensuremath{-}{\mathrm{BC}}_{2}\mathrm{N}$ structures in an eight-atom zinc-blende-structured cubic unit cell. The results obtained provide a plausible explanation for recent experimental observations as well as a possible path to synthesis of the materials.

In Situ FTIR Spectroscopic Study of the Conformational Change of Isotactic Polypropylene during the Crystallization Process

Abstract: The conformational change of isotactic polypropylene (iPP) during the crystallization process has been carefully studied by Fourier transform infrared (FTIR) spectroscopy. The experimental measurements show that the iPP melt system is stable when the persistence length of helical sequences is less than 12 monomer units. As soon as the helix length exceeds 12 monomer units, the 31 helix conformation extends quickly and then crystallization occurs. These results are discussed in terms of Imai's microphase separation theory. It can be found that the experimental observation agrees very well with Imai's theory.

Adsorption refrigeration research in Shanghai Jiao Tong University

Abstract: The research work on adsorption refrigeration in Shanghai Jiao Tong University (SJTU) started in 1993, various adsorption refrigeration cycles have been investigated, such as continuous heat recovery cycle, mass recovery cycle, thermal wave cycle, convective thermal wave cycle, cascade multi effect cycle, hybrid heating and cooling cycle etc. Several prototype adsorption refrigeration systems have been developed and tested, typical examples are continuous heat regenerative adsorption ice maker using spiral plate adsorbers, adsorption heat pump using novel heat exchanger as adsorbers, solar powered adsorption ice maker, solar powered hybrid system of water heater and adsorption refrigerator, waste heat driven air conditioning system for automobiles. Reasonable experimental results have been obtained, it was found that with a heat source temperature of 100°C, the refrigerator can obtain specific refrigeration power for 5.2 kg-ice/day per kg activated carbon in one adsorber, the heat pump can reach a specific cooling power for more than 150 W/kg-adsorbent with a COP close to 0.5, the adsorption solar ice maker yields 5–7 kg-ice per day per square meter solar collector, the hybrid solar water heater and ice maker is capable of heating 60 kg water up to about 90°C and meanwhile yields ice making about 5 kg per day with a 2 m 2 solar collector. The adsorption mechanisms of adsorption refrigeration pairs and also the thermo-physical properties have been also studied in SJTU, which are very helpful for adsorption refrigeration researches. This paper shows the various aspects researched in SJTU.

Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM.

Abstract: The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been studied in two heat transfer systems: recirculating cooling water and pool boiling systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasing fluid velocity for the cooling water system, whereas in the presence of inhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decreases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results show that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FTIR analyses demonstrate that for the CaCO3 formed in the pool boiling system, the content of vaterite increases with the increase of inhibition effects. The metastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. The step morphology has been observed by atomic force microscopy. It is shown that the step space on the CaCO3 surface increases in the presence of inhibitors. Moreover, with the increase in inhibition effect, both the step space and the fractal dimension increase. Step bunching is also found and discussed in this paper. C ∞ 2001 Academic Press

A short-time multifractal approach for arrhythmia detection based on fuzzy neural network

Abstract: The authors have proposed the notion of short-time multifractality and used it to develop a novel approach for arrhythmia detection. Cardiac rhythms are characterized by short-time generalized dimensions (STGDs), and different kinds of arrhythmias are discriminated using a neural network. To advance the accuracy of classification, a new fuzzy Kohonen network, which overcomes the shortcomings of the classical algorithm, is presented. In the authors' paper, the potential of their method for clinical uses and real-time detection was examined using 180 electrocardiogram records [60 atrial fibrillation, 60 ventricular fibrillation, and 60 ventricular tachycardia]. The proposed algorithm has achieved high accuracy (more than 97%) and is computationally fast in detection.

Microstructure and tensile properties of in situ (TiB+TiC)/Ti6242 (TiB:TiC=1:1) composites prepared by common casting technique

Abstract: In the present work, (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 were produced by common casting and hot-forging technology utilizing the SHS reactions between titanium and B4C, C powder. The microstructures of composites were examined using optical microscopy (OM) and transmission electron microscopy (TEM). The X-ray diffraction (XRD) was used to identify the phases that were present in the composites. There are three phases — TiB, TiC and titanium matrix alloy. TiB grows in short-fiber shape, whereas TiC grows in dendritic, equiaxed or near-equiaxed shape. TiB whiskers were made to align the longitudinal direction and TiC dendritic was broken up after hot-forging. The reinforcements are distributed uniformly in matrix alloy. The interfaces between reinforcements and titanium matrix alloy are very clean. The tensile strength (yield strength and ultimate tensile strength) and the Young's modulus improve with the addition of TiB whiskers and TiC particles although some reduction in ductility is observed. (TiBw+TiCp)/Ti6242 composites with TiB:TiC=4:1 will fracture on a lower level of applied stain due to deformation restraint of TiB whiskers on titanium matrix alloy. The (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 show higher tensile strength and ductility. The addition of graphite not only improves the tensile strength and the Young's modulus but also increases the ductility. The improved Young's moduli and increased tensile strengths of the composites are explained using shear lag and rule-of mixtures theories. The Young's moduli of the composites were found in good agreement with that calculated from Tsai–Halpin equation applied for discontinuous-reinforced composites.