Constacyclic Codes over Finite Fields

An equivalence relation called isometry is introduced to classify constacyclic codes over a finite field; the polynomial generators of constacyclic codes of length $\ell^tp^s$ are characterized, where $p$ is the characteristic of the finite field and $\ell$ is a prime different from $p$

Homogeneous Weights and M\"obius Functions on Finite Rings

The homogeneous weights and the M\"obius functions and Euler phi-functions on finite rings are discussed; some computational formulas for these functions on finite principal ideal rings are characterized; for the residue rings of integers, they are reduced to the classical number-theoretical M\"obius functions and the classical number-theoretical Euler phi-functions.Comment: This paper has been published in a Chinese journal, see below; here is the English versio

Simulation Research on the Forming Process of Large Axles Rolled by Cross-Wedge Rolling

As a novel metal forming process, cross-wedge rolling (CWR) is widely used in the manufacture of large axles in the rail transportation industry. When the forming process of the axle is studied, its formability becomes one of the key issues in the metal forming process. This paper takes LZ50 axle steel as the research object. Through the application of ANSYS finite element simulation software, combined with previous research and literature, a dynamic simulation of the rolling process is carried out, and the stress, strain and temperature field of the axle steel in the forming process are analysed. The results show that with the deepening of rolling, the plastic deformation of the metal becomes increasingly obvious. When the finishing section is reached, the temperature on the surface and inside the rolled piece reaches relatively uniform distribution

Reconciling Semantic Heterogeneity in Web Services Composition

Service Oriented Computing (SOC) is a popular computing paradigm for the development of distributed Web applications. Service composition, a key element of SOC, is severely hampered by various types of semantic heterogeneity among the services. In this paper, we address the various semantic differences from the context perspective and use a lightweight ontology to describe the concepts and their specializations. Atomic conversions between the contexts are implemented using XPath functions and external services. The correspondences between the syntactic service descriptions and the semantic concepts are established using a flexible, standard-compliant mechanism. Given the naive BPEL composition ignoring semantic differences, our reconciliation approach can automatically determine and reconcile the semantic differences. The mediated BPEL composition incorporates necessary conversions to convert the data exchanged between different services. Our solution has the desirable properties (e.g., adaptability, extensibility and scalability) and can significantly alleviate the reconciliation efforts for Web services composition.This work was partially supported by the MIT Sloan China Management Education Project and grants from the National Natural Science Foundation of China (No. 60674080 and No. 60704027) and the National High-Tech R&D (863) Plan of China (No. 2007AA04Z150)

Analytical model for the photocurrent-voltage characteristics of bilayer MEH-PPV/TiO2 photovoltaic devices

The photocurrent in bilayer polymer photovoltaic cells is dominated by the exciton dissociation efficiency at donor/acceptor interface. An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO2 photovoltaic cells. The model gives an analytical expression for the exciton dissociation efficiency at the interface, and explains the dependence of the photocurrent of the devices on the internal electric field, the polymer and TiO2 layer thicknesses. Bilayer polymer/TiO2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO2, with different thicknesses of the polymer and TiO2 films, were prepared for experimental purposes. The experimental results for the prepared bilayer MEH-PPV/TiO2 cells under different conditions are satisfactorily fitted to the model. Results show that increasing TiO2 or the polymer layer in thickness will reduce the exciton dissociation efficiency in the device and further the photocurrent. It is found that the photocurrent is determined by the competition between the exciton dissociation and charge recombination at the donor/acceptor interface, and the increase in photocurrent under a higher incident light intensity is due to the increased exciton density rather than the increase in the exciton dissociation efficiency