H∞ control for uncertain Markovian jump systems with mode-dependent mixed delays

We study the problem of H_∞ control for a class of Markovian jump systems with norm-bounded parameter uncertainties and modedependent mixed delays including discrete delays and distributed delays in this paper. Our aim is to present a new delay-dependent control approach such that the resulting closed-loop system is robust mean-square (MS) exponentially stable and satis?es a prescribed H_∞ performance level, irrespective of the parameter uncertainties. Such delay-dependent approach does not require system transformation or free-weighting matrix. A numerical example shows that the results are less conservative and more e?ective.     

Robust control for uncertain singular systems with time-varying delay

We study the problem of L2-L∞, control for a class of uncertain singular systems with time-delay and norm-bounded parameter uncer- tainties in this paper. A new delay-dependent robust stability criterion is obtained in terms of linear matrix inequalities （LMIs）. Based on this criterion, a state feedback controller is designed to guarantee that the closed-loop system is regular, impulse free and stable with a prescribed L2-L∞ performance satisfied for all admissible parameter uncertainties. A simulation example is included to illustrate the effectiveness of the proposed method.     

H∞ control for uncertain Markovian jump systems with mode-dependent mixed delays

We study the problem of H∞ control for a class of Markovian jump systems with norm-bounded parameter uncertainties and mode-dependent mixed delays including discrete delays and distributed delays in this paper. Our aim is to present a new delay-dependent control approach such that the resulting closed-loop system is robust mean-square （MS） exponentially stable and satisfies a prescribed H∞ performance level, irrespective of the parameter uncertainties. Such delay-dependent approach does not require system transformation or free-weighting matrix. A numerical example shows that the results are less conservative and more effective.     

Robust fault tolerant control of uncertain time-delay linear systems

Robust fault tolerant control for a class of time-delay linear systems with parameter uncertainties is studied, and a time-delay related state feedback control is proposed. On the basis of Lyapunov method , we prove that the proposed control law has integrity against sensor and/or actuator failures if the correspondent sufficient condition can be satisfied. A heuristic algorithm is also provided to facilitate the realization of the fault tolerant control. Finally, a simulation example is presented to show the effectiveness of the proposed approach.     

碲镉汞吸收缘以上E1和E2峰的指认

The fundamental reflectivity spectrum of HgCdTe have been investigated.The feature of the spectra is the presence of E₁ and E₂ peaks in the fundamental absorption region.The lower energy peak can be split into a doublet (E₁ and E₁＋Δ₁）.A three-dimensional saddle point is used to fit the E₁ and E₁+Δ₁ critical point and some simulated calculation is done for E₂ at X point.The calculated results are compared with the measured results and prominent features of the dielectric spectra are identified with critical-point transitions at the Λ and X points in the Brillouin zone.     

Canonical Huffman code based full-text index

Full-text indices are data structures that can be used to find any substring of a given string. Many full-text indices require space larger than the original string. In this paper, we introduce the canonical Huffman code to the wavelet tree of a string T[1..n]. Compared with Huffman code based wavelet tree, the memory space used to represent the shape of wavelet tree is not needed. In case of large alphabet, this part of memory is not negligible. The operations of wavelet tree are also simpler and more efficient due to the canonical Huffman code. Based on the resulting structure, the multi-key rank and select functions can be performed using at most nH₀+|Σ|（lglgn+lgn-lg|Σ|）+O（nH₀） bits and in O(H0) time for average cases, where H0 is the zero-th order empirical entropy of T. In the end, we present an efficient construction algorithm for this index, which is on-line and linear.     

Molecular cloning and characterization of a cotton phosphoenolpyruvate carboxylase gene

Phosphoenolpyruvate carboxylase (PEPC) plays diverse physiological functions during plant development. In this study, a new phosphoenolpyruvate carboxylase gene GhPEPC2 is isolated from cotton (Gossypium hirsutum cv. zhongmian 35) by RACE-PCR. The cloned cDNA of GhPEPC2 is 3,364 bp in length, and has an open reading frame of 2,913 bp, encoding for 971 putative amino acids with a calculated molecular mass of 110.6 kD and pI of 5.56. The deduced amino acid sequence of GhPEPC2 shares high similarity with other reported plant PEPCs. Southern blot analysis indicates that the cotton PEPC exists as a small gene family and the GhPEPC2 might have two copies in the cotton genome. The semi-quantitative RT-PCR reveals that GhPEPC2 constitutively expresses in all the tissues of cotton and accumulated highly in roots, flowers and embryos but relatively low in stems and fibers. In addition, the recombinant GhPEPC2 has been purified by expressing it in E. coli and the catalytic properties of it were also investigated. The results showed that GhPEPC2 is a typical C₃ PEPC with a higher K_m (83.6 μM) and lower V_max (8.0 μmol min^-1 mg^-1) compared with the C₃ PEPCs previously reported.     

Effects of electrolysis on Microcystis aeruginosa in water

Microcystis aeruginosa (blue-green algae) is of concern in relation to drinking water because of its ability to produce toxins and odors that can significantly impair water quality. The drinking water contaminated with toxic cyanobacteria could cause the death of the domestic and wild animals and the cases of human illness. To minimize the threat, the treatment of eutrophicated water containing algae (M.aeroginosa) was conducted via electrochemical oxidation process, with titanium based anode coated with RuO₂ in this study. The research showed that the electrochemical oxidation process was effective in inhibiting the growth of the algae such as M.aeruginosa. The electrolysis parameters such as: electrolysis time, current density, and electrodes distance were analyzed by the orthogonal collocation method. The results showed the electrolysis time was the dominant factor for the inhibition of the algal growth. The optimal operating conditions were: current density of 10 mA/cm² and the electrodes distance of 6 cm. The inhibitive efficiency was 92.64% with the electrolysis time of 40 minutes. The preliminary mechanism of this process was also explored and proposed in this paper.     

CFD simulation of fluidization quality in the three-dimensional fluidized bed

Multiphase computational fluid dynamics (CFD) has become an alternative method to experimental investigation on predicting the fluid dynamics in gas-solid fluidized beds. The model of Brandani and Zhang, which contains additional terms in both the gas- and solid-phase momentum equations, is employed to explore homogenous fluidization of Geldart type A particles and bubbling fluidization of Geldart type B particles in three-dimensional gas-fluidized beds. In this model, only a correlation for drag force is necessary to close the governing equations. Two kinds of solids, i.e., fine alumina powder (d_p=60 μm and ρ_p=1500 kg/m³) and sand (d_p=610 μm and ρ_p=2500 kg/m³), are numerically simulated in a rectangular duct of 0.2 m (long) ×0.2 m (wide) ×0.5 m (high). The results show good agreement with the classic theory of Geldart.     

Fabrication of MgB2 superconducting films by different methods

MgB₂ superconducting films have been successfully fabricated on single crystal MgO(111) and c-AL₂O₃ substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transition temperature of 38.4 K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with the zero resistance transition temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J_c of 10⁷ A/cm² at 15 K in zero field for the thin film and of 10⁵ A/cm² for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100 μΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO.     

Fabrication of MgB2 superconducting films by different methods

MgB₂ superconducting films have been successfully fabricated on single crystal MgO(111) and c-AL₂O₃ substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transition temperature of 38.4 K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with the zero resistance transition temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J_c of 10⁷ A/cm² at 15 K in zero field for the thin film and of 10⁵ A/cm² for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100 μΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO.     

高温变形时Al67Mn8Ti25的动态回复和动态再结晶

The deformation microstructure of Ll₂-structure Al₆₇Mn₈Ti₂₅ compound after tension at high temperature was investigated by TEM. The results show that dynamic recovery occurs and there exist a high density of dislocations, dislocation walls and unstable networks within the grains after deformation at 1 173 K and a strain rate of 8.35×10^-5 s^-1. At 1 173 K and a strain rate of 3.34×10^-5s^-1, dynamic recrystallization took place and the deformation microstructures were fine recrystallized grains with stable sub-boundaries in the specimen. Owing to difficulties in the dislocation motion and the process concerned with atom diffusion, the dynamic recovery and dynamic recrystallization occur only at rather higher temperature and lower strain rates, and only under this condition can the appreciate tensile ductility be obtained for this compound.     

The strain ampli tude-controlled cyclic fatigue behavior of Al2O3 fiber reinforced Al–Si alloy composite at elevated temperatures

The strain amplitude-controlled fatigue characteristics of an Al–Si casting alloy and itscomposite reinforced with 17 vol% Al₂O₃ fibers (Al–Si/Al₂O₃) are studied at three different temperatures. Both the alloy and the composite showed different degrees of cyclic softening at elevated temperatures. Increasing the temperature, fatigue damage of either the alloy or the composite occurred with varying mode from brittle fracture of silicon particles to their separation from the aluminum matrix. This is explained by the different thermal expansion coefficients of silicon particles and the aluminum matrix. The reinforcement Al₂O₃ fibers in the composite showed a similar damage behavior with those silicon particles despite temperature variation     

Design Criterion for Fixture Layout Based on the State Space Model in Multistation Assembly Processes

The fixture layout is crucial to assure the product quality in a multistation assembly process （MAP）. A well-designed fixture layout will make the final product＇s variability be insensitive to the fixture variation inputs. As the basis of the fixture layout design, the design criterion plays an important role in the effectiveness of a solution and the optimization efficiency. In this paper, an effective and efficient design criterion is proposed for the fixture layout with a fixed reference point （FRP） in an MAP. First of all, a state space model for the individual port＇s variation propagation and accumulation is developed, which is the mathematical foundation of the proposed criterion. Then, based on this model, a novel design criterion used to evaluate the performance of the fixture layout is proposed for the fixture layout with an FRP. Finally, a method extracted from the proposed design criterion is developed for quick fixture layout design. A four-station assembly process is used to validate the effectiveness and efficiency of the proposed models and methods.     

Robust direct adaptive fuzzy control for nonlinear MIMO systems

For a class of nonlinear multi-input multi-output systems with uncertainty, a robust direct adaptive fuzzy control scheme was proposed. The feedback control law and adaptive law for parameters were derived based on Lyapunov design approach. The overall control scheme can guarantee that the tracking error converges in the small neighborhood of origin, and all signals of the closed-loop system are uniformly bounded. The main advantage of the proposed control scheme is that in each subsystem only one parameter vector needs to be adjusted on-line in the adaptive mechanism, and so the on-line computing burden is reduced. In addition, the proposed control scheme is a smooth control with no chattering phenomena. A simulation example was proposed to demonstrate the effectiveness of the proposed control algorithm.     

Si3N4-MgO-CeO2陶瓷烧结过程中的致密化与相变

Silicon nitride ceramics show great potential for wide applications. It is difficult to densify silicon nitride due to its covalent nature of bonding. A new sintering aid with combination of MgO and CeO₂ was used in the present study. The effects of MgO-CeO₂ on densification and phase transformation during sintering of Si₃N₄ were discussed. For Si₃N₄-MgO-CeO₂ ceramics,a lot of liquid phase existed at 1450℃,and densification process took place rapidly from 1550℃ to 150℃;the phase transformation from α-Si₃N₄ to β-Si₃N₄ took place rapidly from 1550℃ to 1660℃,the phase transformation process lags behind the densification process. The nonpressure sintered Si₃N₄-MgO-CeO₂ ceramics achieved a bending strength of 948MPa. MgO-CeO₂ can be considered as an effective sintering aid for Si₃N₄.     

Mechanism of electrochemical evolution of chlorine and oxygen at Ti/SnO2-IrO2 anode

The mechanisms of chlorine and oxygen electrochemical evolution at a novel Ti/SnO₂-IrO₂ anode were investigated using cyclic voltammetry and steady state current?potential measurements. For this study a laboratory constructed model cell was employed. Firstly, controlled potential electrolysis of 0.1 mol/L NaCl was performed and chlorine was observed to evolve at potential +1.2 V. The pH values of the solution decreased during electrolysis over the potential range of +1.0 V?+2.0 V, suggesting that oxygen evolution may involve in the reactions. Electrolysis with a de?oxygenated NaCl solution at a fixed potential of +2.0 V confirmed that O2 is one of the products generated at the anode. Further electrolysis of NaCl solution was conducted under steady state conditions. A potential?current density plot was constructed over the potential range of +1.00 V?+1.28 V. The slope of the plot at Tafel section was found to be 41 mV/decade. These results indicate that chlorine evolution at the anode is achieved via an intermediate layer formed by electrosorption of oxygen and chlorine on the electrode surface.     

Bridging properties of the debonded interface with frictional sliding

A theoretical model simulating the properties of frictional bridging is presented and relatively perfect stress solutions for the fiber and matrix are obtained. Based on the energy equilibrium in the process of interfacial debonding, an expression for the energy release rate G is derived to explore the interfacial fracture properties. By introducing an interfacial debonding criterion G≥Γ_i, a method for determining the critical debond length is proposed and the bridging constitutive relationship is also obtained. Numerical calculations are conducted for the fiber-reinforced composite SCS-6/T_i-6Al-4V and the results are also compared with those obtained by using other existing models.