Showing papers by "Southwest University of Science and Technology published in 2010"

The β-δ-Phase Transition and Thermal Expansion of Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine

Abstract: Phase behavior of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is investigated by X-ray powder diffraction (XRD). The XRD patterns at elevated temperature show that there is a co-existing temperature range of β- and δ-phase during the phase transition process. Additionally, mechanical forces can catalyze the conversion from δ- back to β-phase. Based on the diffraction patterns of β- and δ-phase at different temperatures, we calculate the coefficients of thermal expansion by Rietveld refinement. For β-HMX, the linear coefficients of thermal expansion of a-axis and b-axis are about 1.37×10−5 and 1.25×10−4 °C−1. A slight decrease in c-axis with temperature is also observed, and the value is about −0.63×10−5 °C−1. The volume coefficient of thermal expansion is about 1.60×10−4 °C−1, with a 2.2% change from 30 to 170 °C. For δ-HMX, the linear coefficients of thermal expansion of a-axis and c-axis are found to be 5.39×10−5 and 2.38×10−5 °C−1, respectively. The volume coefficient of thermal expansion is about 1.33×10−4 °C−1, with a 2.6% change from 30 to 230 °C. The results indicate that β-HMX has a similar volume coefficient of thermal expansion compared with δ-HMX, and there is about 10.5% expansion from β-HMX at 30 °C to δ-HMX at 230 °C, of which about 7% may be attributed to the reconstructive transition.

Mechanics of advanced fiber reinforced lattice composites

Abstract: Fiber reinforced lattice composites are light-weight attractive due to their high specific strength and specific stiffness. In the past 10 years, researchers developed three-dimensional (3D) lattice trusses and two-dimensional (2D) lattice grids by various methods including interlacing, weaving, interlocking, filament winding and molding hot-press. The lattice composites have been applied in the fields of radar cross-section reduction, explosive absorption and heat-resistance. In this paper, topologies of the lattice composites, their manufacturing routes, as well as their mechanical and multifunctional applications, were surveyed.

Entanglement dynamics of two independent Jaynes-Cummings atoms without the rotating-wave approximation

Abstract: Entanglement evolution of two independent Jaynes-Cummings atoms without the rotating-wave approximation (RWA) is studied by a numerically exact approach. Previous results based on the RWA are essentially modified in the strong-coupling regime ($g\ensuremath{\geqslant}0.1$), which has been reached in the recent experiments on the flux qubit coupled to the $\mathit{LC}$ resonator. For the initial Bell state with anticorrelated spins, entanglement sudden death (ESD) is absent in the RWA but does appear in the present numerical calculation without the RWA. Aperiodic entanglement evolution in the strong-coupling regime is observed. The strong atom-cavity coupling facilitates the ESD. The sign of the detuning plays an essential role in the entanglement evolution for strong coupling, which is irrelevant in the RWA. Analytical results based on an unitary transformation are also given, which could not modify the RWA picture essentially. It is suggested that the activation of the photons may be the origin of ESD in this system.

Quantum phase transition in the sub-Ohmic spin-boson model: An extended coherent-state approach

Abstract: We propose a general extended coherent state approach to the qubit (or fermion) and multimode boson coupling systems. The application to the spin-boson model with the discretization of a bosonic bath with arbitrary continuous spectral density is described in detail, and very accurate solutions can be obtained. The quantum phase transition in the nontrivial sub-Ohmic case can be located by the fidelity and the order-parameter critical exponents for the bath exponents $sl1/2$ can be correctly given by the fidelity susceptibility, demonstrating the strength of the approach.

Analysis and application of Wireshark in TCP/IP protocol teaching

Abstract: TCP/IP is widely employed to interconnect computing facilities in today's network environments, and it is the most important content of networking elements study. This paper introduces the functions and characteristics of Wireshark, and expounds its analysis and application in TCP/IP protocol teaching by some specific examples. The practice shows that good teaching result will be received with the aid of Wireshark and it is worth popularization and application.

Synthesis of PLA-co-PGMA Copolymer and its Application in the Surface Modification of Bacterial Cellulose

Abstract: Nature fibers have been developed for the reinforcement of polymers. The main disadvantage of the natural fibers to be used as reinforcement is their hydrophilic nature. In this paper, a novel copolymer of polylactide and glycidyl methacrylate (PLA-co-PGMA) was prepared by free radical polymerization and used to modify the cellulose surface. The characterization of the PLA-co-PGMA copolymers was conducted by Fourier transform infrared (FTIR) and gel permeation chromatography. Modified bacterial cellulose (BC) with the copolymer was characterized by FTIR and contact angle measurements. Interfacial thermodynamic properties were studied. The results suggested that PLA-co-PGMA was efficient in modifying the BC nanofibril surface and in improving the compatibility of PLA/cellulose composites.

Crystal State of 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB) Undergoing Thermal Cycling Process

Abstract: The present report aims to discuss the crystal state variation of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) suffering from thermal cycling process. In this study, in situ X-ray powder diffraction (XRD) was employed to determine thermal expansion and crystal fragmentation, primarily attributed to its crystal state variation. The results showed that the change of crystal volume mainly stemmed from the thermal expansion at the c axis of crystal lattice, and TATB crystal had the same thermal expansion coefficients at a and b axes. It was also demonstrated that crystal fragmentation occurred during this process, and more auto-repair happened in the [002] plane of TATB than other planes. These results will have an implication on the process of TATB-based materials.

Two Conservative Difference Schemes for the Generalized Rosenau Equation

Abstract: Numerical solutions for generalized Rosenau equation are considered and two energy conservative finite difference schemes are proposed. Existence of the solutions for the difference scheme has been shown. Stability, convergence, and priori error estimate of the scheme are proved using energy method. Numerical results demonstrate that two schemes are efficient and reliable.

Preparation and Characterization of Bacterial Cellulose/Polylactide Nanocomposites

Abstract: Nanocomposite consisting of two biocompatible materials, bacterial cellulose (BC) and polylactide was prepared. To improve the compatibility, maleic anhydride (MA) was first grafted onto BC nanofibers. Mechanical tests showed that the tensile strength and modulus of the composites increased, especially the composites including BC nanofibers modified with MA. Differential scanning calorimetry showed the thermal behaviors changed due to the addition of BC. The morphology of the composites suggested that the grafting of MA made BC nanofibers well disperse into polylactide matrix and the interfacial adhesion between BC and polylactide was improved. This research proposes novel avenues to tailor the dispersion of BC nanofibers into the thermoplastic matrix to produce nanocomposites and improve the compatibility of reinforcement and matrix.

Study on the flavor contribution of phospholipids and triglycerides to pork

Abstract: For investigating the flavor contribution of phospholipids and triglycerides to pork, the longissimus muscle of Rongchang (RC) and PIC (bred by PIC Company of England) pig were selectively removed of intramuscular triglycerides or total intramuscular lipids. After cooking, the flavor of different samples was compared by sensory evaluation, gas chromatographymass spectrometry (GC-MS), and electronic nose. The results showed that removing triglycerides had little effect on the aroma of the cooked meat, but when total intramuscular lipids were removed a remarkable difference was observed. The control samples covaried strongly with some lipid-derived products, and the petroleum ether defatted samples also positively related to these compounds, but to a lesser extent, both of them negatively covaried with chloroform-methanol extracted samples which associated with some Maillard reaction products. Moreover the flavor difference between 2 breeds would decrease when triglycerides were removed, and reduce further when phospholipids and triglycerides were removed simultaneously. These results suggested that intramuscular lipids especially phospholipids contributed significantly to pork flavor, the flavor difference between 2 breeds resulted mainly from different intramuscular lipids content and composition.

Trajectory tracking sliding mode control of ball and plate system

Abstract: This paper proposes a position tracking control scheme for the ball and plate system. At first, the property of the ball and plate control system is analyzed, and the path tracking control problem is divided into subproblems of ball position control and plate angle control. Afterwards, a path tracking sliding mode control algorithm is proposed for the ball position control based on dynamic model of the ball motion system and basic principle of sliding mode control, asymptotical stability of the close-loop system is proved mathematically through Lyapunov stability theory as well. The proposed sliding mode control algorithm eliminates the effect of time-varying uncertain friction while the ball is rolling on the plate surface, and thus the path tracking precision is improved. Finally, control performance of the proposed sliding mode control algorithm is validated by simulation experiment.

Quantum phase transitions in coupled two-level atoms in a single-mode cavity

Abstract: The dipole-coupled two-level atoms (qubits) in a single-mode resonant cavity are studied by extended bosonic coherent states. The numerical solution is presented. The first-order quantum phase transitions may occur in finite systems, in contrast to the original Dicke model. This system also exhibits a second-order quantum phase transition from the normal to the superradiant phase, as in the original Dicke model. Finite-size scaling for several observables---such as average fidelity susceptibility, order parameter, and concurrence---is performed for different interatomic interactions. The scaling exponents obtained suggest that interatomic interactions do not change the universality class.

Aflp analysis of genetic diversity in populus cathayana rehd originating from southeastern qinghai-tibetan plateau of china

Abstract: The wide geographical and climatic distribution of Populus cathayana Rehd indicates that there is a large amount of genetic diversity available, which can be exploited for conservation, breeding programs and afforestation schemes. In our study, genetic diversity was evaluated in the natural populations of P. cathayana originating from southern and eastern areas of the Qinghai-Tibetan Plateau of China by means of AFLP markers. For four primer combinations, a total of 175 bands were obtained of which 173 (98.9%) were polymorphic. Six natural populations of P. cathayana possessed different levels of genetic diversity, high level of genetic differentiation existed among the populations (G(ST)=0.489) of P. cathayana. Individuals cluster and PCO analysis based on Jaccard's similarity coefficient also showed evident population genetic structure with high level of population genetic differentiation. The long evolutionary process coupled with genetic drift within populations, rather than contemporary gene flow, are the major forces shaping genetic structure of P. cathayana populations. Moreover, there was no correspondence between geographical and genetic distances in the populations of P. cathayana, seldom gene exchange among the populations and different selection pressures may be the causes. Our findings of different levels of genetic diversity within populations and high level of genetic differentiation among the populations provided promising condition for further breeding and conservation programs.

All-Electron Scalar Relativistic Calculation on the Adsorption of Carbon Monoxide onto Small Gold Clusters

Abstract: An all-electron scalar relativistic calculations on Au n CO (n = 1–10) clusters have been performed by using density functional theory with the generalized gradient approximation at the PW91 level. Our results reveal that all Au n CO clusters prefer to keep the planar structures like pure Au n cluster and the Au n structures in all Au n CO clusters are only changed slightly. The carbon monoxide molecule prefers to occupy the on-top and single fold coordination site and small gold cluster would like to bond with carbon. The adsorptions in AuCO, Au6CO, Au9CO and Au10CO clusters are relatively weaker than the adsorptions in other Au n CO clusters. After adsorption of carbon monoxide, the Au–Au interaction is strengthened and the C–O interaction is weakened. The VIPs, HLGs, HOMO and LUMO energy levels for Au n CO clusters have obvious odd–even oscillation. The even-numbered Au n CO cluster is relatively more stable than the adjacent odd-numbered Au n CO cluster electronically and chemically. The odd–even alteration of magnetic moments is observed in Au n CO (n = 1–10) clusters and may be served as the material with tunable code capacity of “0” and “1” by adsorbing carbon monoxide molecule onto odd or even-numbered gold cluster.

Modeling of Learning Inference and Decision-Making Engine in Cognitive Radio

Abstract: Cognitive radio (CR) is an intelligent wireless communication system and the core of it is the cognitive engine. Cognitive engine is expected to implement cognitive learning, inference, decision-making through the artificial intelligence technology to decide a specific radio configuration (i.e. carrier frequency, modulation type, power, etc.) according to the changing of environment. In this paper, a cognitive radio learning inference and decision-making engine based on Bayesian network (BN) is proposed to obtain the optimum configuration rules adapt to the variation of the environment with the learning and inference algorithm of Bayesian network. Simulation results show the feasibility and validity of modeling the cognitive learning inference and decision-making engine with Bayesian network.