Showing papers by "Yanshan University published in 2005"
TL;DR: In this paper, the optical properties of high-pressure phase ZnO in NaCl and C2 Cl structures were investigated using the ab initio pseudopotential density functional method, in which the Perdew-Burke-Eruzerhof form of the generalized gradient approximation available in the CASTEP code together with plane wave basis sets for expanding the periodic electron density.
Abstract: We present a detailed investigation on optical properties of high-pressure phase ZnO in $B1$ (NaCl) and $B2$ (CsCl) structures, including dielectric function, refractive index, absorption, and electron energy-loss spectrum. Theoretical calculations are performed using the ab initio pseudopotential density functional method, in which we employ the Perdew-Burke-Eruzerhof form of the generalized gradient approximation available in the CASTEP code together with plane wave basis sets for expanding the periodic electron density. Both structures are optimized under the respective structural phase transition pressures; for the $B1$ structure it is $9\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, which has been verified to be in agreement with theory [Jaffe et al., Phys. Rev. B 62, 1660 (2000)] and experiment [Desgreniers, Phys. Rev. B 58, 14102 (1998)], while for the $B2$ structure a transition pressure of $256\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is predicted in theory [Jaffe et al., Phys. Rev. B 62, 1660 (2000)]. We find that their electronic structures and optical properties under high pressure are quite different from those under ambient pressure.
320 citations
TL;DR: It is proved that the constructed controller can render the closed-loop system asymptotically stable and based on Lyapunov stability theory, it is shown that the designed observer and controller are independent of the time delays.
Abstract: In this note, the problem of robust output feedback control for a class of nonlinear time delayed systems is considered. The systems considered are in strict-feedback form. State observer is first designed, then based on the observed states the controller is designed via backstepping method. Both the designed observer and controller are independent of the time delays. Based on Lyapunov stability theory, we prove that the constructed controller can render the closed-loop system asymptotically stable. Simulation results further verify the effectiveness of the proposed approach.
243 citations
TL;DR: The results calculated by a new ionicity Scale, a population ionicity scale, indicate that the maximum ionicity among those boron-boron bonds is larger than that of bor on-nitrogen bonds in the III-V compound cubic BN.
Abstract: First-principles calculations are used to investigate ionicities of boron-boron bonds in B(12) icosahedra. It is observed that the geometrical symmetry breaking of B(12) icosahedra results in the spatial asymmetry of charge density on each boron-boron bond, and further in the ionicity of B(12) icosahedra. The results calculated by a new ionicity scale, a population ionicity scale, indicate that the maximum ionicity among those boron-boron bonds is larger than that of boron-nitrogen bonds in the III-V compound cubic BN. It is of great importance that such an ionicity concept can be extended to boron-rich solids and identical atom clusters.
199 citations
05 Nov 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a hyperbolic-sine Arrhenius-type equation was used to characterize the dependence of the peak stress on deformation temperature and strain rate.
Abstract: Hot compression tests at different temperatures and strain rates were performed on Inconel 718 solution treated as well as solution treated and then aged at 900 °C for 1–24 h in order to investigate the effect of the δ phase on hot deformation behavior. A hyperbolic-sine Arrhenius-type equation was used to characterize the dependence of the peak stress on deformation temperature and strain rate. In the case of Inconel 718 with a large amount of the δ phase, the apparent activation energy was determined to be 458 kJ/mol, which was slightly higher than the activation energy of 443 kJ/mol for solution treated Inconel 718. The γ″/γ′ phases present in Inconel 718 prior to hot deformation enhanced the peak stress, but did not affect the peak strain. The δ phase present in Inconel 718 not only decreased the peak strain and the peak stress, but also promoted the flow softening after the peak stress.
162 citations
TL;DR: In this article, an improved pyrolysis route was proposed to synthesize turbostratic carbon nitride from melamine, which was performed in two steps: first, the temperature was maintained at 300 ◦C in order to realize the primary condensation (melamine → melam) as complete as possible; and then it was risen to 650 ¼C to perform the advanced condensation.
Abstract: Since the theoretical calculations predicted that the hardness of C3N4 covalent compound might be comparable to or even higher than that of diamond [1, 2], many attempts have been made to synthesis this novel substance. Due to the great thermodynamic stability of N2, however, the ideal structural transition from precursor to crystalline carbon nitride is difficult to realize. In most cases, only amorphous products with low nitrogen content were obtained [3]. To solve this problem, it is good to prepare carbon nitride in graphitic or turbostratic form firstly, and then using it as precursor to synthesize other carbon nitride crystalline phases. Therefore, graphitic C3N4 have recently attracted more attention. Through different routes, graphitic C3N4 has been synthesized [4–6]. For previous work, the claimed graphitic-like C3N4 with unique (002) diffraction peak has the turbostratic structure actually [7–10], for the lake of other peaks in their XRD patterns. Meanwhile, the (002) spacing of those obtained turbostratic carbon nitrides are in the range of 0.32–0.33 nm. The graphitic C3N4 predicted by Teter and Hemley [11] can be described as a perfect de-ammonation polycondensate of melamine, therefore, melamine was often chosen as the carbon nitride precursor to synthesize graphitic C3N4 by electrodeposition [6] and solvothermal method [7]. Pyrolysis of melamine was investigated [12] in 1988, however, the authors focused their attention only on its thermal behavior, and they didn’t consider the possibility as potential candidate for carbon nitrides after complete polycondensate. Recently, pyrolysis of melamine under high pressure was studied at the temperatures up to 700 ◦C [13]. Obvious nitrogen loss made the attempt unsuccessful. In this letter, we report an improved pyrolysis route to prepare turbostratic carbon nitride from melamine. The pyrolysis was performed in two steps: first, the temperature was maintained at 300 ◦C in order to realize the primary condensation (melamine → melam) as complete as possible; and then it was risen to 650 ◦C to perform the advanced condensation. In the experimental, melamine was pyrolyzed in a quartz tube with a diameter of 35 mm, and an outer-thimble-shape heater was used. Melamine was placed at the middle of the quartz tube. The pyrolysis was conducted at 300 ◦C for 1 hr, then at 600◦ for 2 hr in atmosphere; after milling, the obtained powder was maintained at 300 ◦C for 0.5 hr, then at 650 ◦C for 1 hr in vacuum. Finally, a kind of brown carbon nitride powder was obtained. The chemical composition was analyzed by using elemental analyzer (LECO, CHN-1000) and EDX (EDAX INC., Phoenix). The product was characterized by X-ray diffraction (XRD) with Cu-Kα radiation (JEOL, ROTEX JRX-12), fourier transfer infrared (FTIR) spectroscopy (Bruker, EQUINOX55), scanning electron microscopy (SEM) (TOPCON, SM520), and transmission electron microscopy (TEM) coupled with selected area diffraction (SAED) (JEOL, JEM-2010) and thermogravimetry (TG) (NETZSCH, STA449C/6/G). The composition of the product characterized by elemental analysis and EDX is listed in Table I. SEM observation found that the particles dimension ranged from 5 μm to 20 μm. Most of the particles show the flake-like morphology. Fig. 1 shows a typical XRD pattern of the product. There is a single main peak at the position of 27.62 ◦, which suggests that the product was turbostratic. Its corresponding d-spacing is 0.321 nm similar to the (002) plane of the turbostratic/graphitelike carbon nitrides obtained in previous work [9, 14]. The FTIR spectrum of the prepared turbostratic carbon nitride and melamine are shown in Fig. 2. The IR spectrum of melamine presents three absorption bonds: 3000–3650 cm−1, 1100–1700 cm−1, and the last one centered at about 810 cm−1. The 3000– 3650 cm−1 band is assigned to N H stretching vibration modes, the 1100–1650 cm−1 band corresponds to the stretching vibrations related to C N, C N, and is generally associated with the skeletal stretching vibrations of these aromatic rings. The absorption at 810 cm−1 is characteristic of out-of-plane bending modes of these rings. The 460–850 cm−1 band is linked to the C NH2 group and the ring breadth or bending vibration modes [15]. Comparing the FTIR spectrum of the turbostratic carbon nitride with that of melamine, it reveals that after pyrolysis, the previous strong absorption peaks in the range of 3000–3650 cm−1 have disappeared, only a board absorption bond is left, which suggest that most of the N H bonds have been destroyed during the de-ammonation condensation. While the increased number of absorption peaks ranging from 1100 to 1700 cm−1 implies the condensation of 1,3,5-s-triazine rings making the related chemi-
127 citations
TL;DR: In this article, a low-carbon Mn-Mo-Nb pipeline steel designed for acicular ferrite microstructure was investigated and three independent TTT curves for isothermal phase transformation, namely, polygonal ferrite-pearlite transformation, massive ferrite transformation and bainitic transformation, respectively.
110 citations
TL;DR: In this paper, the influence of the concentration of Co 2+ ions in the electrolyte and electrolysis parameters, such as the cathodic current density, the temperature as well as electrolyte jet speed, on the chemistry and microstructure of Ni-Co-deposit alloys were investigated.
106 citations
TL;DR: It is shown that the stability and stabilization with some required performance can be established for the closed loop control system if there exists a DPLKF and that the DPLkF and the corresponding controller can be obtained by solving a set of linear matrix inequalities (LMIs).
Abstract: Based on a novel delay-dependent piecewise Lyapunov-Krasovskii functional (DPLKF), this paper presents delay-dependent stability analysis and synthesis methods for discrete-time Takagi-Sugeno (T-S) fuzzy systems with time delays. It is shown that the stability and stabilization with some required performance can be established for the closed loop control system if there exists a DPLKF and that the DPLKF and the corresponding controller can be obtained by solving a set of linear matrix inequalities (LMIs). New algorithms have also been developed to obtain the maximum value of the allowable constant delay and the suboptimal performance upper bound. An example is finally presented to demonstrate the efficiency and advantage of the proposed methods
104 citations
TL;DR: It is tested that LBP can alleviate insulin resistance and the effect of LBP is associated with increasing cell-surface level of glucose transporter 4 (GLUT4) in skeletal muscle of NIDDM rats, and the mechanism may be involved in increasingcell- surface level of GLut4, improving GLUT4 trafficking and intracellular insulin signaling.
Abstract: Lycium barbarum is one of the traditional oriental medicines. It has been reported to reduce blood glucose levels. In this study, the effect of Lycium barbarum polysaccharide (LBP) on the improvement of insulin resistance and lipid profile was studied in rats, a model for non-insulin dependent diabetes mellitus (NIDDM). The rats were divided into three groups: control, NIDDM control, and NIDDM+LBP. Diabetes model groups were made by feeding high-fat diet and subjecting to i.p. streptozotocin (50 mg/kg). LBP treatment for 3 weeks resulted in a significant decrease in the concentration of plasma triglyceride and weight in NIDDM rats. Furthermore, LBP markedly decreased the plasma cholesterol levels and fasting plasma insulin levels, and the postprandial glucose level at 30 min during oral glucose tolerance test and significantly increased the Insulin Sensitive Index in NIDDM rats. In the present study, we have tested that LBP can alleviate insulin resistance and the effect of LBP is associated with increasing cell-surface level of glucose transporter 4 (GLUT4) in skeletal muscle of NIDDM rats. Under insulin stimulus, GLUT4 content in plasma membrane in NIDDM control rats was significantly lower than that of control (p<0.01), and GLUT4 content in the plasma membrane in NIDDM+LBP rats was higher than that of NIDDM control rats (p<0.01). In conclusion, LBP can ameliorate insulin resistance, and the mechanism may be involved in increasing cell-surface level of GLUT4, improving GLUT4 trafficking and intracellular insulin signaling.
81 citations
TL;DR: In this article, a discrete method is developed for analyzing the free vibration problem of orthotropic rectangular plates with variable thickness, which is obtained by transforming the differential equations into integral equations and using numerical integration.
67 citations
TL;DR: A new rate-based active queue management algorithm, called Yellow, is proposed, which outperforms the recently proposed AQM algorithms in terms of link utilization, packet loss and robust performance through extensive simulations.
TL;DR: In this paper, the problem of control for a class of chaotic systems is considered and the corresponding controller which renders the closed-loop system asymptotically stable is constructed.
Abstract: In this paper, the problem of control for a class of chaotic systems is considered. The nonlinear functions of chaotic systems are not necessarily to satisfy the Lipsichtz conditions, but bounded by a polynomial with the gains unknown. Employing adaptive method, the corresponding controller which renders the closed-loop system asymptotically stable is constructed. The designed controller is robust with respect to certain class of disturbances in the chaotic systems. Simulations on unified chaotic systems and Arneodo chaotic system are performed and the results verify the validity of the proposed techniques.
25 Jan 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a parameterized die design system for CWR has been developed based on the expertise experiences, in which the optimized selection of the key factors of dies can be achieved automatically.
Abstract: Some research progresses of the cross wedge rolling (CWR) technique were summarized in this paper. Firstly, a parameterized die design system for CWR has been developed based on the expertise experiences, in which the optimized selection of the key factors of dies can be achieved automatically. Secondly, some empirical equations for recrystallization evolutions and transformation used in the simulation were obtained using the Gleeble-3500 thermomechanical simulator. Finally, using the die design system, a three-dimensional (3D) solid model was generated and imported into the finite element analysis software. Then, by the aid of the microstructural evolution models established, a 3D non-linear finite element model for modeling the CWR process was developed with the thermal, mechanical and microstructural phenomena coupled. Through simulation, the distributions of different field-variables, such as strains, temperature and grain size and so on, were obtained. Compared the calculated results with experimental data, the consistency is demonstrated.
TL;DR: In this paper, the effects of anodic current density (ja) and the ratio of cathodic to anodic (jc/ja) on the mechanical and corrosion resistance properties of MAO coatings have been studied by microhardness and pitting corrosion tests, respectively.
TL;DR: A decentralized adaptive feedback controller is designed, which is independent of the delays, and Lyapunov-Krasovskii approach is employed to show that the corresponding closed-loop system is asymptotically stable.
TL;DR: In this article, a semi-empirical model for the hardness is employed to predict the hardness of nitride spinels and related compounds, showing that the influence of the electronic density, the bond strength, and the ionicity on the hardness decrease monotonously in the order of
Abstract: The nitride spinels are of considerable interest. The structural parameters of the nitride spinels have been calculated by first-principles. A semiempirical model for the hardness is employed to predict the hardness of nitride spinels and related compounds. The studies show that the influence of the electronic density, the bond strength, and the ionicity on the hardness of $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{A}}_{3}{\mathrm{N}}_{4}$ ($\mathrm{A}=\mathrm{C}$, Si, Ge) all decrease monotonously in the order of $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$, $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}$, and $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Ge}}_{3}{\mathrm{N}}_{4}$. The origin of superhardness in the group-IV nitride spinels results mainly from ${\mathrm{A}}^{t}{\mathrm{N}}_{4}$ tetrahedral units rather than on ${\mathrm{A}}^{o}{\mathrm{N}}_{6}$ octahedral units. The detailed studies of the nitride poly-morphs experimentally detected and theoretically proposed indicate that the increasing of coordination cannot always result in the increasing of hardness. It has to be emphasized that the relation between the coordination numbers and hardness has to be applied with care.
TL;DR: The microstructure of Al88Ni7Y5 solidified under 6.0 GPa has been analyzed by X-ray diffraction, metallography and SEM.
TL;DR: This paper addresses the problem of identifying the property of the singularity loci of a class of 6/6-Gough-Stewart manipulators in which the moving and base platforms are two similar semiregular hexagons, and derives a cubic polynomial expression in the moving platform position parameters, which represents the constant-orientation singulary locus of the manipulator.
Abstract: In this paper we address the problem of identifying the property of the singularity loci of a class of 6/6-Gough-Stewart manipulators in which the moving and base platforms are two similar semiregular hexagons. After constructing the Jacobian matrix of this class of 6/6-Gough-Stewart manipulators according to the theory of statical equilibrium, we derive a cubic polynomial expression in the moving platform position parameters, which represents the constant-orientation singularity locus of the manipulator. Graphical representations of the singularity locus of the manipulator for different orientations are quite various and complex. Further, we analyze the singularity locus of this class of 6/6-Gough-Stewart manipulators in the principal section, where the moving platform lies. This shows that singularity loci of this class of 6/6-Gough-Stewart manipulators in parallel principal sections are all quadratic expressions. We have also found that, for this class of 6/6-Gough-Stewart manipulators, there are also some special singularity cases in which six lines associated with the six extensible links of the manipulator can intersect one common line and the unwanted instantaneous motion of the manipulator is a pure rotation.
TL;DR: The proportional integral observer is proposed, which can render the error system stable with the noise in the output of the output, and can solve the synchronization problem of chaotic systems via observer.
TL;DR: A new method to measure the cutting forces in turning using inexpensive current sensors and the cutting force model is proposed and results demonstrate that the method proposed can measure tangential, axial, and radial cutting forces with an error of less than 10%, 5% and 25%, respectively.
Abstract: The importance of monitoring cutting forces in turning has been well recognized in machine tool communities. This paper proposes a new method to measure the cutting forces in turning using inexpensive current sensors and the cutting force model. First, the relationship between the various factors, which affect the performance of the spindle and feed drive systems, and the models of the spindle and feed drive systems are analyzed. Then, some reliable and inexpensive Hall-effect current transducers are employed to sense the current signals of the ac servomotor in a computer numeric control (CNC) turning center; the tangential (F/sub t/) and axial (F/sub a/) cutting forces in turning are estimated by applying a neuro-fuzzy technique. Finally, the normal cutting pressure (K/sub n/) and effective friction coefficient (K/sub f/) are calculated through the cutting mechanical model, so the axial cutting forces (F/sub r/) can also be estimated based on the model of cutting force. Experimental results demonstrate that the method proposed can measure tangential, axial, and radial cutting forces with an error of less than 10%, 5% and 25%, respectively.
TL;DR: The reducible correlation between the input and the output of 3-DOF translational mechanisms with decoupled motions is investigated and the definition of this topic is presented.
Abstract: Motion coupling is one of the typical characters of parallel robots. This makes it complicated to control the parallel robots. Therefore, the design of parallel mechanisms with decoupled motions is an important and challenging issue in the parallel robotic field. However, research in this field, including the definition and type synthesis theory, is weak or lacking. In this paper, the reducible correlation between the input and the output of 3-DOF translational mechanisms with decoupled motions is investigated and the definition of this topic is presented. A new parameter named Gf coordinate is propsed for the synthesis of 3-DOF reducible translational mechanisms. The type synthesis theory for this kind of mechanisms is obtained and some reducible mechanisms are synthesized.
TL;DR: A new chaotic secure communication scheme is constructed, and Unified chaotic system is used to encrypt the emitted signal and computer simulations show that the obtained theoretic results are feasible and efficient.
TL;DR: In this paper, a topology matrix-graph approach and a systematic linkage technique are proposed for type synthesis of a unified planar-spatial mechanism, and the formulas for calculating the number of DOF, the complexity, and acceptable associated linkage are derived.
TL;DR: A feed-forward neural network model based on the LM algorithm is established, which is established to realize real-time identification of material properties and friction coefficient for deep drawing of an axisymmetric workpiece.
TL;DR: In this paper, the effect of Ti additions on the phase composition, microstructure, thermal stability and the bonding strength of the HA/Ti composite coatings was studied, and a bone-like apatite layer formed on the coating surface after 7 days of soaking in simulated body fluid (SBF).
25 Oct 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the microstructure of 1Cr18Ni9Ti stainless steel subjected to compression deformation of 60% reduction at liquid-nitrogen temperature composes of two phases, deformation-induced martensite and austenite, with morphology of nanoscale laths ranging 20-80nm in width.
Abstract: This paper attempts to study the microstructures of 1Cr18Ni9Ti stainless steel subjected to compression deformation at liquid-nitrogen temperature and room temperature and subsequently annealing. The microstructure of 1Cr18Ni9Ti stainless steel subjected to compression deformation of 60% reduction at liquid-nitrogen temperature composes of two phases, deformation-induced martensite and austenite, with morphology of nanoscale laths ranging 20–80 nm in width. For the sample of room-temperature compression deformation in 60% reduction, the microstructure composes of mainly austenitic deformation twin with the average thickness of about 200 nm and a few amount of deformation-induced martensite and stacking faults. Nearly nanograined microstructures can be obtained in the two deformed samples by annealing at 580 °C for 30 min. Deformation at liquid-nitrogen temperature for the steel can have a positive effect on developing high-angle boundaries.
TL;DR: In this paper, a B3-spline finite strip method was employed to investigate the effects of forming parameters, such as the bend angle increment, the strip thickness, the material yield limit, the flange length, the web width, and the distance between two roll stations on the peak longitudinal edge membrane strain developed in the cold roll forming process of a channel section.
TL;DR: In this paper, the effect of toughness on the fatigue behavior of pipeline steels was investigated, including the fatigue crack propagation rate and low cycle fatigue test under the loading condition simulating the actual operation of pipelines.
TL;DR: In this paper, a forward/reverse kinematic analysis for lower-mobility (nf < 6) parallel mechanisms is proposed, where the number of single-degree-of-freedom pairs in each limb is fixed.
Abstract: In the family of lower-mobility (degrees of freedom Nf <6) parallel mechanisms, there is a class of mechanisms whose degrees of freedom equal the number of single-degree-of-freedom pairs in each limb. This paper proposes a novel forward/reverse kinematic analyses method for this class of mechanisms, which can build Nf ×Nf square Jacobian matrix and Nf ×Nf ×Nf cubic Hessian matrix. Thus both forward/reverse velocity and acceleration analyses for this class of mechanisms are derivable. In this method, the formulas for different parallel mechanisms have unified forms and consequently the method is convenient for programming. The more complicated the mechanism is (for instance, the mechanism has more kinematic pairs), the more effective the method is. In the rear part of the paper, a 5-DOF mechanism 3-RCRR is analyzed as an example.Copyright © 2005 by ASME
TL;DR: It has been elucidated why B 12N2 is metallic but B12N2Be is a semiconductor and this should open up new potential areas for predicting novel boron-rich compounds for industrial applications.
Abstract: Boron solids exhibit a fascinating geometric and electronic structure. The properties of α-rhombohedral boron can be significantly changed by the addition of other atomic constituents. It is found that Pauling's bond valence principle plays an important role in designing boron-rich semiconductors. We have designed the novel boron-rich phases B 1 2 N 2 X (X = Zn, Cd, Be) with the boron carbide type structure by combining Pauling's bond valence principle with first-principles techniques. Their energy gaps, bulk moduli, microhardnesses, and total energies have been calculated. The results show that they are new superhard materials and potential semiconductors. It has been elucidated why B 1 2 N 2 is metallic but B 1 2 N 2 Be is a semiconductor. This should open up new potential areas for predicting novel boron-rich compounds for industrial applications.