Showing papers by "Tsinghua University published in 2004"

Colloidal carbon spheres and their core/shell structures with noble-metal nanoparticles.

Abstract: Colloidal microand nanospheres have been of continuous research interest, since their intrinsic properties can be finely tuned by changing parameters such as diameter, chemical composition, bulk structure, and crystallinity. Up to now, they have found a broad range of applications in fields such as drug delivery, biodiagnostics, combinatorial synthesis, and photonic band-gap crystals (PBG). The success of these applications strongly depends on the availability of colloidal spheres with tightly controlled size and surface properties. However, until now, only amorphous silica and some colloidal polymer spheres can be routinely prepared with satisfactorily narrow size distributions. As-prepared colloidal nanoand microspheres usually have relatively inert surfaces, which make surface modification almost unavoidable before use as supports or templates.

Online Consumer Review: Word-of-Mouth as a New Element of Marketing Communication Mix

Abstract: Online consumer product review is an emerging market phenomenon that is playing an increasingly important role in consumers' purchase decisions. This paper examines a fundamental issue concerning online consumer review, i.e., the functions such reviews have for an online marketer. We argue that online consumer reviews, a type of product information created by users based on personal usage experience, can serve as a new element of marketing communications mix and work as free sales assistants to help consumers identify the products that best match their idiosyncratic usage conditions. For many products, this marketing function is impossible or very costly for traditional marketing communications to achieve. However, this new communication mode does not come without cost because it eliminates a seller's control over the content of product information accessible to consumers, and because consumer reviews may not be fully informative.We examine four specific strategic issues: (1) when an online seller should provide consumer reviews to its customers, (2) how a seller's decision to supply consumer reviews interacts with its product assortment strategy, (3) how the seller's strategy regarding the supply of consumer reviews interacts with its traditional marketing communication strategy, and (4) what timing is best for the seller to offer consumer review information for a product.Our results show that supplying online consumer reviews can benefit or hurt an online seller depending on product characteristics, the informativeness of the review, the seller's product assortment strategy, the seller's product value for the partially matched consumers, and consumer heterogeneity in product consumption expertise. We also show that the seller's decision to provide consumer reviews will increase its incentive to offer more complete product information to consumers through its traditional marketing communications. Finally, we discover that offering consumer review information too early leads to a lower profit.An empirical study based on data from online sellers in different product categories provides some preliminary support for our theory.

Secure direct communication with a quantum one-time pad

Abstract: Quantum secure direct communication is the direct communication of secret messages without first producing a shared secret key. It may be used in some urgent circumstances. Here we propose a quantum secure direct communication protocol using single photons. The protocol uses batches of single photons prepared randomly in one of four different states. These single photons serve as a one-time pad which is used directly to encode the secret messages in one communication process. We also show that it is unconditionally secure. The protocol is feasible with present-day technique.

Efficient multiparty quantum-secret-sharing schemes

Abstract: In this work, we generalize the quantum-secret-sharing scheme of Hillery, Bu\ifmmode \check{z}\else \v{z}\fi{}ek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Bu\ifmmode \check{z}\else \v{z}\fi{}ek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph∕0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically $100%$ in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information.

An integrated framework for customer value and customer‐relationship‐management performance: a customer‐based perspective from China

Abstract: In the modern customer‐centred era, customer value is a strategic weapon in attracting and retaining customers. Delivering superior customer value has become a matter of ongoing concern in building and sustaining competitive advantage by driving customer‐relationship‐management (CRM) performance. However, related studies are rather divergent, the key dimensions of customer value remain unclear, and there is no agreement on the evaluation of CRM performance. This paper develops an integrative framework for customer value and CRM performance based on the identification of the key dimensions of customer value. Emphasising the customer equity‐based view, the paper explores the decomposed effects of customer value on CRM performance in terms of relationship quality and customer behaviours. In doing so, a structural equation model is developed using the partial least square method supported by an empirical investigation of customers in China.

A mini-review on ammonia decomposition catalysts for on-site generation of hydrogen for fuel cell applications

Abstract: Due to the drive for better environmental protection and energy conversion efficiency, on-site generation of CO x -free hydrogen from ammonia decomposition for fuel cell applications has attracted much attention. The development of high performance solid catalysts is essential for the supply of such hydrogen from ammonia. In this mini-review, we provide a summary of the reaction kinetics of catalytic ammonia decomposition. Comparisons are then made among the catalysts that have different active components, supports, and promoters. According to the works reported in the literature and our recent research results, Ru is the most active catalyst, carbon nanotubes (CNTs) are the most effective support, and KOH is the best promoter. An increase in Ru dispersion results in better catalytic performance. Both support basicity and conductivity are important criteria for a NH 3 decomposition catalyst of high efficiency; and it seems possible to generate novel advanced support, such as oxide-CNTs nanocomposite materials, that bears such characteristics. Also, proper removal of the electron-withdrawing entities that originate from the precursors of active component, support or promoter can be effective in enhancing the catalytic activity of a Ru catalyst.

Potent neutralization of severe acute respiratory syndrome (SARS) coronavirus by a human mAb to S1 protein that blocks receptor association

Abstract: Effective prophylaxis and antiviral therapies are urgently needed in the event of reemergence of the highly contagious and often fatal severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) infection. We have identified eight recombinant human single-chain variable region fragments (scFvs) against the S1 domain of spike (S) protein of the SARS-CoV from two nonimmune human antibody libraries. One scFv 80R efficiently neutralized SARS-CoV and inhibited syncytia formation between cells expressing the S protein and those expressing the SARS-CoV receptor angiotensin-converting enzyme 2 (ACE2). Mapping of the 80R epitope showed it is located within the N-terminal 261–672 amino acids of S protein and is not glycosylation-dependent. 80R scFv competed with soluble ACE2 for association with the S1 domain and bound S1 with high affinity (equilibrium dissociation constant, Kd = 32.3 nM). A human IgG1 form of 80R bound S1 with a 20-fold higher affinity of 1.59 nM comparable to that of ACE2 (Kd = 1.70 nM), and neutralized virus 20-fold more efficiently than the 80R scFv. These data suggest that the 80R human monoclonal antibody may be a useful viral entry inhibitor for the emergency prophylaxis and treatment of SARS, and that the ACE2-binding site of S1 could be an attractive target for subunit vaccine and drug development.

Highly Sensitive WO3 Hollow-Sphere Gas Sensors

Abstract: In this paper, we describe how WO(3) hollow spheres have been synthesized in solution phase by the controlled hydrolysis of WCl(6) using novel carbon microspheres as the templates. All of the products were characterized by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized spheres had large diameters of about 400 nm and thin shells of about 30 nm composed of numerous small nanocrystals. Prompted by the porous structure and small crystal size of the shell wall, we constructed WO(3) hollow-sphere gas sensors and found that these sensors had good sensitivity to alcohol, acetone, CS(2), and other organic gases.

The Cross-Section of Volatility and Expected Returns

Abstract: We examine the pricing of aggregate volatility risk in the cross-section of stock returns Consistent with theory, we find that stocks with high sensitivities to innovations in aggregate volatility have low average returns In addition, we find that stocks with high idiosyncratic volatility relative to the Fama and French (1993) model have abysmally low average returns This phenomenon cannot be explained by exposure to aggregate volatility risk Size, book-to-market, momentum, and liquidity effects cannot account for either the low average returns earned by stocks with high exposure to systematic volatility risk or for the low average returns of stocks with high idiosyncratic volatility

Comparative study on lipase-catalyzed transformation of soybean oil for biodiesel production with different acyl acceptors

Abstract: Methyl acetate, a novel acyl acceptor for biodiesel production has been developed, and a comparative study on Novozym 435-catalyzed transesterification of soybean oil for biodiesel production with different acyl acceptors was conducted and reported in this paper. Methanol has a serious negative effect on enzymatic activity. A molar ratio of methanol to oil of above 1:1 leads to serious inactivation of the enzyme. However, when methyl acetate was used as the acyl acceptor, a yield of 92% of methyl ester could be obtained with a molar ratio of methyl acetate to oil of 12:1, and methyl acetate showed no negative effect on enzymatic activity. Additionally, with crude soybean oil as the oil source and methanol as acyl acceptor, a much lower methyl ester yield was obtained than that with refined soybean oil, while with methyl acetate as acyl acceptor, an equally high yield of methyl ester (92%) was achieved for both soybean oils. Lipase loses its activity very rapidly during repeated experiments with methanol as the acyl acceptor, while there is almost no detected loss in lipase activity, even after being continuously used for 100 batches, when methyl acetate was used for biodiesel production. Moreover, the by-product triacetylglycerol is an important chemical with a higher value than glycerol, and this novel acyl acceptor seems very promising for lipase-catalyzed large-scale production of biodiesel.

Hierarchically biomimetic bone scaffold materials: Nano-HA/collagen/PLA composite†

Abstract: A bone scaffold material (nano-HA/ collagen/PLA composite) was developed by biomimetic synthesis. It shows some features of natural bone both in main composition and hierarchical microstructure. Nano-hydroxyapatite and collagen assembled into mineralized fibril. The three-dimensional porous scaffold materials mimic the microstructure of cancellous bone. Cell culture and animal model tests showed that the composite material is bioactive. The osteoblasts were separated from the neonatal rat calvaria. Osteoblasts adhered, spread, and proliferated throughout the pores of the scaffold material within a week. A 15-mm segmental defect model in the radius of the rabbit was used to evaluate the bone-remodeling ability of the composite. Combined with 0.5 mg rhBMP-2, the material block was implanted into the defect. The segmental defect was integrated 12 weeks after surgery, and the implanted composite was partially substituted by new bone tissue. This scaffold composite has promise for the clinical repair of large bony defects according to the principles of bone tissue engineering.

Pilot-assisted wireless transmissions: general model, design criteria, and signal processing

Abstract: Pilot-assisted transmission (PAT) multiplexes the known symbols with the information bearing data. These pilot symbols and the specific multiplexing scheme are known at the receiver and can be exploited for channel estimation, receiver adaptation, and optimal decoding. Even though PAT has been used for many practical reasons, there still remains a need for an optimal design. The theory and methodology for the design of an optimal PAT have emerged, but much still remains unknown. In this article, the author has presented an overview of PAT. A general PAT model is given as well as the review of the common design criteria. The information theoretic and signal processing issues were also discussed.

A real-time articulated human motion tracking using tri-axis inertial/magnetic sensors package

Abstract: A basic requirement in virtual environments is the tracking of objects, especially humans. A real time motion-tracking system was presented and evaluated in this paper. System sensors were built using tri-axis microelectromechanical accelerometers, rate gyros, and magnetometers. A Kalman-based fusion algorithm was applied to obtain dynamic orientations and further positions of segments of the subject's body. The system with the proposed algorithm was evaluated via dynamically measuring Euler orientation and comparing with other two conventional methods. An arm motion experiment was demonstrated using the developed system and algorithm. The results validated the effectiveness of the proposed method.

Fast rotation invariant multi-view face detection based on real Adaboost

Abstract: In this paper, we propose a rotation invariant multi-view face detection method based on Real Adaboost algorithm. Human faces are divided into several categories according to the variant appearance from different viewpoints. For each view category, weak classifiers are configured as confidence-rated look-up-table (LUT) of Haar feature. Real Adaboost algorithm is used to boost these weak classifiers and construct a nesting-structured face detector. To make it rotation invariant, we divide the whole 360-degree range into 12 sub-ranges and construct their corresponding view based detectors separately. To improve performance, a pose estimation method is introduced and results in a processing speed of four frames per second on 320/spl times/240 sized image. Experiments on faces with 360-degree in-plane rotation and /spl mnplus/90-degree out-of-plane rotation are reported, of which the frontal face detector subsystem retrieves 94.5% of the faces with 57 false alarms on the CMU+MlT frontal face test set and the multi-view face detector subsystem retrieves 89.8% of the faces with 221 false alarms on the CMU profile face test set.

Manifold-ranking based image retrieval

Abstract: In this paper, we propose a novel transductive learning framework named manifold-ranking based image retrieval (MRBIR) Given a query image, MRBIR first makes use of a manifold ranking algorithm to explore the relationship among all the data points in the feature space, and then measures relevance between the query and all the images in the database accordingly, which is different from traditional similarity metrics based on pair-wise distance In relevance feedback, if only positive examples are available, they are added to the query set to improve the retrieval result; if examples of both labels can be obtained, MRBIR discriminately spreads the ranking scores of positive and negative examples, considering the asymmetry between these two types of images Furthermore, three active learning methods are incorporated into MRBIR, which select images in each round of relevance feedback according to different principles, aiming to maximally improve the ranking result Experimental results on a general-purpose image database show that MRBIR attains a significant improvement over existing systems from all aspects

Color-based road detection in urban traffic scenes

Abstract: Road detection is a key issue for autonomous driving in urban traffic. In this paper, after a brief overview of existing methods, we present a road-area detection algorithm based on color images. This algorithm is composed of two modules: boundaries are first estimated based on the intensity image and road areas are subsequently detected based on the full color image. In the first module, an edge image of the scene is analyzed to obtain the candidates for the left and right road borders and to delimit the area that will subsequently be used to compute the mean and variance of the Gaussian distribution, assumed to be obeyed by the color components of road surfaces. The second module effectively extracts the road area and reinforces boundaries that most appropriately fit the road-extraction result. The combination of these modules can overcome basic problems due to inaccuracies in edge detection based on the intensity image alone and due to the computational complexity of segmentation algorithms based on color images. Experimental results on real road scenes have substantiated the effectiveness of the proposed method.

Cloning and Functional Analysis of a Novel DREB1/CBF Transcription Factor Involved in Cold-Responsive Gene Expression in Zea mays L.

Abstract: ;The transcription factors DREB1s/CBFs specifically interact with the DRE/CRT cis-acting element (core motif: G/ACCGAC) and control the expression of many stressinducible genes in Arabidopsis. We isolated a cDNA for a DREB1/CBF homolog, ZmDREB1A in maize using a yeast one-hybrid system. The ZmDREB1A proteins specifically bound to DRE and the highly conserved valine at the 14th residue in the ERF/AP2 DNA binding domain was a key to determining the specific interaction between this protein and the DRE sequence. Expression of ZmDREB1A was induced by cold stress and slightly increased by highsalinity stress. This gene was also transiently expressed by mechanical attack. ZmDREB1A activated the transcription of the GUS reporter gene driven by DRE in rice protoplasts. Overexpression of ZmDREB1A in transgenic Arabidopsis induced overexpression of target stress-inducible genes of Arabidopsis DREB1A resulting in plants with higher tolerance to drought and freezing stresses. This indicated that ZmDREB1A has functional similarity to DREB1s/CBFs in Arabidopsis. The structure of the ERF/ AP2 domain of ZmDREB1A in maize is closely related to DREB1-type ERF/AP2 domains in the monocots as compared with that in the dicots. ZmDREB1A is suggested to be potentially useful for producing transgenic plants that is tolerant to drought, high-salinity and/or cold stresses.

Blur detection for digital images using wavelet transform

Abstract: With the prevalence of digital cameras, the number of digital images increases quickly, which raises the demand for image quality assessment in terms of blur. Based on the edge type and sharpness analysis, using the Harr wavelet transform, a new blur detection scheme is proposed in this paper, which can determine whether an image is blurred or not and to what extent an image is blurred. Experimental results demonstrate the effectiveness of the proposed scheme.

Thermal Expansion of Single Wall Carbon Nanotubes

Abstract: We have developed an analytical method to determine the coefficient of thermal expansion (CTE) for single wall carbon nanotubes (CNTs). We have found that all CTEs are negative at low and room temperature and become positive at high temperature. As the CNT diameter decreases, the range of negative CTE shrinks. The CTE in radial direction of the CNT is less than that in the axial direction for armchair CNTs, but the opposite holds for zigzag CNTs. The radial CTE is independent of the CNT helicity, while the axial CTE shows a strong helicity dependence.